©1983 MARSHALL JAY ELLIOTT All Rights Reserved s-rumm on THE WRITE, POSTHARVEST PHYSIOLOGY AND CANNING or 'STALEEY' mums by Mershall Jay Elliott A.TEESIS Submitted to Michigan State university in partial fulfillment of the requirements for the degree 0: MASTER OF SCIENCE Department of Horticulture 1983 ABSTRACT STUDIES ON THE MATURITY} POSTHARVEST PHYSIOLOGY AND GANNING OF 'STANLEY' PLUIS by Marshall Jay Elliott Assosmment of 'Stanley' plum.(Prunus domestics, L9) fruit maturity indices showed flesh firmness, and soluble solids were reliable while titratable acidity, extractable pigments and ethylene evolution were not consistent. Maturity at harvest was a greater determinant of ripening than cold storage (00c), or conditioning period (20°c). Fruit weight often did not increase with.progressive harvest. Ethylene gassing (100 ppm) for 2 - 4 days enhanced fledh softening, pit removal and increased skin cracking, but had no significant effects on color, acidity, soluble solids or pitting losses and quality of the canned product. 602 production increased after 4 - 6 weeks at 0°C. Ethylene production increased after 2 weeks at 0°C but diminished with longer storages. Quality and pitting losses of processed plums were significantly affected by conditioning period and harvest date. A.predictive equation was developed based on gains in soluble solids and decreases in flesh firmness of the harvested fruit. DEDICATION ' to JUniper Li, who was plucked right on time and ‘ helped make this thesis a little Plumper and sweeter! 11 ACUOWLEDGMNTS I would like to acknowledge the assistance of all who supported me throughout my thesis research. Ebpecially helpful were the beneficiaries of this work; my wife, children, parents, major professor, committee members and sponsor, the Michigan Plum.Advisory Board. I would further like to recog- nize the encouraging support of those who may never benefit directly from.this thesis;:my fellow graduate students, visit- ing foreign scholars, the horticulture faculty and staff, and the many eager volunteers who assisted me in taste panel evaluations. Their service was born out of friendship and a love of knowledge. iii List of Tables TABLE OF CONTENTS L131: 0: Figures 0 e e e e e e e e e e I. INTRODUCTION TO THESIS . e . . . . II. REVIEW OF LITERATURE e e e . e . . A. Be C. D. E. .F. G. I. J. Introduction . . . . . . . . . Harvest Indices . . . . . . . variability . . . . . . . . . Temperature During Storage . . Weight Changes During Harvest Weight Losses During Storage Plum.Storage Disorders . . . l. Shriveling . . . . . 2. Internal Browning and Ethylene in Plum Ripening . . Soft Rots 3 0 m1 Sing 0 O C O O O O O O O O Exogenous Growth.Regulator's Effects htm ty 0 O O O O O O O O O O O 0 Research on Canned Plums . . . III. MEBIALANDHEPHODS....... A. Sampling and Design . . . . . B.HflJ‘VOCt31t68........ iv 0!! O O Page ix compass-H 13 14 14 14 15 16 16 19 22 22 23 TABLE OF CONTENTS-- Continued IV. I. RESUDTS AND DISCUSSION A. Harvesting unmatmtaeeeeeee Etaluation of laturity Ieasuring Ethylene and Carbon Dioxide Evaluation of Quality of Canned Product Etaluation of Quality of Fresh Plums lean Separation . . . . . . . . . . . . Section 1: Inturity Indices - Evaluating Parameters that Assess Optimum Harvest Date 1. Introduction 2. Rationale for Seasonal Analysis 3. Skin Color 4. Flesh.Firmness 5. Pit Removal Fbroe . . . 6. Soluble Solids 7. Acidity ..... Section 2: Postharvest Treatments 1. 2. 3. 4. 5. Introduction . . . Flesh Firmness . . Pit Removal Fbrce . Soluble Solids . . Acidity . . . . . . O O Naturity Indices - Effects of C O O O O O O O O O O O O Page 61 61 61 .4 67 73 TABLE OF CONTENTS-- Continued C. 6. 7. Skin calor O O O O O O O O O O O O O Conditioning and Storage - Overall . Section 3: Weight Changes . . . . . . . l. 2. 3. 1. 2. 3. Effect of Date of Harvest . . . . . EffoctofStorago......ee.. WeightChanges-Summary. .. . . . Section 4: Effects of Ethylene Gassing Ethylene Gassing Effects on Flesh Firmness Ethylene Gassing Effects on Pit Removal Page 73 78 80 86 86 89 92 Ethylene Gassing Effects on Other Parameters 92 Section 5: Ethylene and Carbon Dioxide mdnctj-MStudj-‘aeeeeeeeeeeeeee l. 2. 3. 4. 5. 6. 7. 8. 9. Intmduction O O O C O O O O O O O O .0 O Ethylene Production - Location Effects . . Ethylene Production - Harvest Date Effects Ethylene Production - Storage Effects Carbon Dioxide Production . . . . . . . Relationship betwaen 0234 and C02 PmdnCtian eeeeeeeeeeee Ethylene Evolution in Closed Systems - mu” “6 tion 0 O O O O O O O O O O O O 0 Comparison of Ethylene Evolution in Open andClOSodSyStm........... Effects of Harvest Date on Ethylene Evolution in Closed Systems . . . . vi 96 96 96 99 99 101, 104 108 108 115 TABLE OF CONTEETS--Continued F5 G. Section 6: Taste Panels on Fresh Market Fruit 1. Discussion of Statistical Bias . . . . . 2. Effects of Harvest Date, Conditioning and LocationonQuality . . . . . . . . . . . 3. Correlations Between Quality and Maturity Indices ................. 4. Correlations Between Factors Within the Tutepmaleeeeeeeeee Section '7: a Model for Timing of Harvest of FreshllarketPlums.............. 1. 2. 3. 4. 5. '7. Introduction ......... W1”. Eda: O O O O O O O O O O O O O O T086133 the ”ml-On. mdal " 1982 e e e 0 Effects of Chilling on C2H4 Evolution . . Modeling for Soluble Solids and Flesh Firmness - DeterminatiOn of Tolerances . . Utilizing Tolerances to Indicate Harvest ............ Testing the Soluble Solids-Flesh Model-1982.......... Section 8: Canning Studies . . . . 1. 2. 5. Pittlng Losses 0 e e e e e e e e Drained‘leights ..-...... Taste Panels on Canned Fruit . . vii Optimum Firmness Page . 116 . 116 . 119 . 124 . 127 . 127 . 127 . 130 . 138 . 144 . l4 8 . 151 ‘ . 157 . 157 . 1622 . 16'2 TABLE OF CONTENTS--Continued 4. Tolerances for Canned Fruit . . 5. 'Storage Effects on Canned V. DISCUSSION AND SCENARI A. laturation Indices B. Post Harvest Treatments . . C. weight Changes D. Ethylene Gassing EL Ethylene and 002 Production Pt Fresh Fruit Taste Panels 0 Fruit . G. lodeling for Ethylene, Soluble Solids Flesh Firmness E'CamlnsStuleS........ I. Conclusion Literature Cited viii and O O 0.. O O O O O O O O O O O Page 174 178 181 181 182 184 184 185 189‘ 189 191. 1953 194 LIST OF TABLES TABLE 1. 2. 3. 4. 5. 6. figction 6 Correlations of laturity Indicators with Quality “tings O O 0 O O O O O O O 0 O O O O O O O O O 0 Correlations of Taste Panel Components with mality..................... Section 7 Tolerances for Soluble Solids and Flesh Firmness as Determined by Taste Panel Quality Assessment. Reliability of Tolerances when Applied to Harvest and.Conditioning Treatments. . . . . . . . . . . Section 8 Canned Fruit Taste Panel Correlations - 1981 . . The Effects of Storage on the Results of Quality Assessment by Taste Panels - Canned Plums, 1980. ix 123 125 145 147 176 179 LIST OF FIGURES FIGURE . Page Section 1 1. Effects of the time of harvest and source of fruit on pigment content of skin of 'Stanley' p1um.at timofharvestin1980and1981.......... 37 2. Effects of time of harvest and source of fruit on pigment content of skin of 'Stanley' plum.in 1980 and 1981. Means pooled over conditioning and Stomgetmeoeoeeeeeeeeee.eeeeeee39 3. Effects of the time of harvest and source of the fruit on flesh firmness of 'Stanley' plum at time ofharveo‘tin19808nd1981............42 4. Effects of time of harvest and source of fruit on flesh firmness of 'Stanley' p1um.in 1980 and.1981. leans pooled over conditioning and storage time . . 44 5. Effects of the time of harvest and source of the fruit on pit removal force of 'Stanley' p1um.at time of harvest in 1980 and 1981. . . . . . . . . . 47 6. Effects of tame of harvest and source of fruit on it removal force of 'Stanley‘ plum.in 1980 and 981. leans pooled over conditioning and storage time O O O O O O O O 0 O O O O 0'. O O 0-. O O O O 49 7. Effects of time of harvest and source of fruit on soluble solids of 'Stanley' p1um.at time of harvest in19808nd1981..................52 8. Effects of time of harvest and source of fruit on .soluble solidsof fStanley‘ p1um.in 1980 and 1981. leans‘pooled over'conditioning and storage'time . . 54 9. Effects of the time of harvest and source of fruit on titratable acidity of 'Stanley' p1um.at time of harvest in 1980 and 1981. . . . . . . . . . . . . . 57 LIST OF FIGURES-~Continued FIGURE Page 10. Effects of time of harvest and source of fruit on titratable acidity of 'Stanley' plum in 1980 and 1981. Ileana pooled over storage and condi- tiOfliflgthOeeeeeeeeeeeeeeeeeee 59 get-ion 2 111. Erecta of conditioning and harvest date on flesh firmness of 'Stanley' plum in 1980 and 1981. Means pooled over storage and location . . . . . 63 118. Effects of storage and harvest date on flesh firmness of 'Stanley' plum in 1980 and 1981. leans pooled over storage and location . . . . . 65 12A. Effects ofconditioning and harvest date on pit removal force of 'Stanley' plum in 1980 and 1981. leans pooled over storage and location . . . . . 66 128. Effects of storage and harvest date on pit re- moval force of 'Stanley' plum in 1980 and 1981. leans pooled over conditioning and location . . . 66 131. Effects of conditioning and harvest date on soluble solids of 'Stanley.' plum in 1980 and 1981. leans pooled over conditioning and location . . . 69 138. Effects of storage and. harvest date on soluble solids of 'Stanley' plum in 1980 and 1981. leans pooled over conditioning and location . . . . . . 69 14a. Effects of conditioning and source of fruit on soluble solids of 'Stanley' plum in 1980 and 1981. . . loans are pooled over storage and location . . . 72 148. Effects of storage and source of fruit on soluble solids of 'Stanley' plum in 1980 and 1981. leans pooled over conditioning and harvest. . . . . . . '72 15a. Effects of conditioning and harvest date on ti- tratable acidity of 'Stanley' plum in 1980 and 1981. leans pooled over storage and location . . '75 158. Effects of storage and harvest date on titratable acidity of 'Stanley' plum in 1980 and 1981. Means pooled over conditioning and location . . . . . . 75 LIST OF FIGURES--Continued FIGURE 16A. 168. 17. 18. 19. 22. 23. Main effects of conditioning on skin color of 'Stanley' plum.in 1980 and 1981. leans pooled over storage, harvest and location . . . . . . . lain effects of storage on skin color of 'Stanley' plum.in 1980 and 1981. leans pooled over condi- tioning, harveat and location 0 e e e e e e e 0 Section 3 The effects of harvest date and location on the average weight of 'Stanleyf plums in 1980 and 1981eeeeee'eeeeeeeeeeeeeee The effects of harvest date and location on the average weight of 'Stanley‘ plums in 1980 and 1981 C O O O O O C O O C O O O O O O O O 0 O O The effects of storage on fruit weight of 'Stanley' plums in 1980. leans are pooled over harvest, conditioning and location . . . . Section 4 The effects of ethylene gassing at 100 ppm.on the flesh firmness of 'Stanley1 plums in 1980. Fruits of two harvests and two locations gassed contin- uously for 2 and 4 days . . . . .s. . . . . . . The effects of ethylene gassing at 100 ppmron the pit removal force of 'Stanley' plums in 1980. . Fruits of two harvests and two locations were gassed continuously for 2 and 4 days . . . . . . Section. 5 The effects of length of storage at 0°C, time.of harvest, length of conditioning and source of fruit on ethylene production on 'StanleyW plums in open mtmmlgmeeeeeeeeeeeeeeeo The effects of length of storage at 0°C, time of harvest, length of conditioning and source of fruit on ethylene production of 'Stanley' plums in open systemaln1980...............e Page ' 82 84 88 91 94 98 103 LIST OF FIGURES--Continued FIGURE 24. 26. 31. 32A. The relationship between ethylene and CO? production in 'Stanley' in 1980 as affected by length of storage, time of harvest, length of conditioning and source of fruit. . . . . . . . ' The effect of source of fruit, harvest date and length of time after harvest on ethylene pro- duction in 'Stanley“ plums in closed containers in 1981. Fruit from.Crand Rapids area orchards. The effect of source of fruit, harvest date, and length of time after harvest on ethylene pro- duction in 'Stanley' plums in closed containers in 1982. Fruit from.4 Grand Rapids area 0mm......'.............. The effect of source of fruit, harvest date, and length of time after harvest on ethylene pro- duction in 'Stanley' plums in closed containers in 1982. Fruit from 4 Southwest Michigan mmeoeeooooeeoeeeeeoeoe 22922.4 The effects of harvest date and source of fruit on the quality of 'Stanley'. plum in 1981 as de- tominodbya‘butopanel. e e e e e e e 0,. e The effect of harvest date and the length of conditioning time on the quality evaluations of 'Stanley‘ plum in 1981 as determined.by a taste panel. Means are pooled over location . . . . Section 7 Effects of the time of harvest and.the source of the fruit on ethylene evolution of 'Stanley' plums maintained in closed containers in 1981 . . . . Effects of the time of harvest, the source of fruit and the length of conditioning on ethylene evolution'in relation to taste panel quality ratings of 'Stanley' plums in closed containers, 1981 O O O O O O O O O O O O C O O O O O O O O The relationship of ethylene production rates of 'Stanley' plum.in closed containers to ideal harvest dates as determined by qualitative assessment. Four orchards from the Grand Rapidaaroa.................. xiii Page 106 110 112 114 118 121 129 132 135 LIST OF FIGURES--Continued FIGURE Page 328. The relationship of ethylene production rates - of 'Stanley' plum. in closed containers to ideal harvest dates as determined by qualitative as- sessment. Fbur orchards from the Southwest Michiganaroa................... 157 33. The effects of 48 hours of 0°C chilling on ethy- lene evolution (in closed containers) of 'Stanley' plums from.four Southwest Michigan orchards “1‘79:th AuguSt 26, 19820 e e e e e e e e e e e e 140 54. The effects of 3 hours of 5°C chilling on ethylene evolution (in closed_containers) of 'Stanley' plums from.four Grand Rapids area orchards harves- tedSept.6,1982................. 142 55. Effects of time of harvest, source of fruit, and length of conditioning on soluble solids readings and flesh softness index in relation to taste panel quality ratings for 'Stanley' plums, 1981. . . . . 150 36. The effects of time of harvest and length of condi- tioning time on soluble solids and flesh softness readings of four orchards (Grand Rapids area) of 'Stmloy. plum in 1982 O O 0 O O O O O O O O O O O 153 57. The effects of time of harvest and length of condi- tioning period on soluble solids and flesh softness readings of 4 orchards (Southwest lichigan area) of 'Stanley'plumin1982.............. 155 mm 38. A scatter diagram.and linear regression showing the effects of size (weight) of 'Stanley' plume on the weight losses resulting framwmechanical pitting in 1981 O O O O O O C C O O O O O O O O O O O O O O O 159 39. The effects of length of a 20°C conditioning period and the date of harvest on the percentage weight loss due to mechanical pitting of 'Stanley' plums in 1981. O O O O O O O O O O O O O O O O O O O O O 161 xiv LIST OF FlGURES--Continued FIGURE Page 40A. The effects of date of harvest and source of fruit on drained weights of 'Stanley' plums in 1981. . . 164 408. The effects of length.of'20°C conditioning period ' and.harvest date on the drained weights of 'Stanley' plm in 1981 O O O O O O O O O O O O O O O O O O O 164 41. A scatter diagram.and linear regression showing the relationship between drained weight and quality as getirmined by taste panels of 'Stanley' plum.in 98 O 0 O O O O O O O O O O O O O O O O O O O O O 167 42. The effects of time of harvest and length of 20°C conditioning period on the quality evaluation of canned pitted 'Stanley' plums as determined by a t88tep8n011n1981................ 170 43. The effects of time of harvest and length of 20°C conditioning period on the quality evaluation of canned pitted 'Stanley' plums as determined by a tastspanelin1981................ 172 X? THESIS INTRODUCTION The importance of 'Stanley' plums as a fruit crop in Michigan has increased in recent years. Total plum production has doubled in the last twenty years from 8 to 16 thousand tons. 'Stanley' is the major variety and comprises over 86% of the total volume. In recent years the plum crop has ranged between 2 and 3 million dollars in total value. Besides its production figures, 'Stanley' plum is vital to Michigan for two major reasons: 1) timing of harvest falls between that of two main fruit crops, cherry and apple, thus Optimizing available labor and equipment; 2) culture of 'Stanley' plums is especially suited to Iichigan's climate. The develop- ment of strong markets for Michigan plums is essential for the state's fruit growers as it is one of their most important minor crops. -. Michigan plums have two major outlets, fresh market and processed, which are primarily canned. In the last ten years the fresh market has increased from 39% to 47% of the total plum tonnage. Since both markets currently hold about 50% of the volume, marketing high quality fruits through both channels is vital to the industry. The lack of definitive research on 'Stanley' plum maturity coupled with pressures in the marketing channels often force fruit of low quality into both markets. To 1 promote the availability of high quality fruit, research was conchlcted with three distinct objectives: 1) determine the optimum maturity for harvest of plums for both fresh and processing markets; 2) evaluate parameters which can be used to assess optimum maturity; 5) develop postharvest treatments to maximize quality of both fresh and processed fruit. Recent advances at Inchigan State University on mechan- ical pitting of 'Stanley' plums has encouraged development of a canned pitted product. Currently Michigan processors do not pit and halve;p1ums, while Oregon processors, who are strong competitors, handle about 50% of their total. canned volume in this manner using 'Italian' purple plums. There- fore, regarding processed plums, the target of this thesis research has been to develop a high. quality pitted product with the hopes of implementation and market expansion in Michigan. At present the maturity of 'Stanley' plums is comonly determined by color change for the fresh pack and sugar ‘ content for the canned market, although in some cases determination is totally. qualitative. Knowledge of when fruits in the orchard are approaching optimal maturity could be a cornerstone of sound marketing, ultimate demand and profit to the grower. To insure a consistent supply of high quality plums and eliminate human errors in harvest determination, growers have voiced a priority for improvements in maturity indicators. As a result this thesis research was funded through an organisation supported and.organized by growers, the Michigan Plum Advisory Board. In common usage "plum? indicates a fresh market product, while ”prune” indicates a dried product. However, the word prune is commonly used for many cultivars (e.g. Italian prune, French prune, Stanley prune) regardless of the treatment of the crop. Throughout this thesis, the word prune is used synomously with plum and is not an indicator of a dried product unless specifically stated. ham or W - lama—E The following literature review focuses on varieties of Elropesn plmn (M domestiu): however, references to oriental plums (Pi-anus M.) have been included because of their similar physiology. Research on°p1mss utilised for a dried product are also included in this review since they involve the use of similar harvest indicators. While many varieties are discussed, the cultivar 'Stanley' is the only onsevalnstedinthe thesis sndisofEIropesnorigin. 5 Harvest Indices . Harvest indices have been evaluated for over sixty years: however, only one major stuw is known which deals with 'Stanlsy' plum in nobigan (16). This review presents research on other varieties of m domestics, but different. powing conditions and marketing situations limit the drect application to nchigsn's 'Stsnley' crop. A wide variety of indices has been employed in plus maturity including; soluble solids, fineness, acidity, soluble solids to acid ratio, flesh color, specific gravity, separation of the pit and taste. Harman (13), lurking with 'Italisn' prunes in Oregon, observed marked increases in sugar content and size together 4 with decreases in firmness and acidity as plums matured. - Using a now obsolete firmness tester he concluded that finances was the most reliable maturity guide. Similar findings on 'Italian' prunes in Idaho were reported by Vincent. 'et al. (52 i and Verner ( 51) using the modified lurneek pressure tester. Vincent et al. ( 52) and Tucker et al. ( 43) determined that sugar readings via a hydrometer were cumbersome and too susceptible to error to be practical as a harvest indicator. likewise, acid changes were too small to be reliable. Their recommendations, based on a 5/16" diameter firmness tester, were 12 - 8.5 pounds for immediate ' shipment and 11.5 - 9 poundsfar. storage. La. Rosa (18) concluded that flesh firmness was the most satisfactory single index of maturity for lichigan 'Stanley' plums. It was superior to soluble solids because of decreased seasonal variation; however, he recommended no workable tolerances for harvest. In a concurrent study Xenworthy (16) recomended 15-20 pounds firmness for fresh market Michigan 'Stanley' plums. Fisher (9 ) concluded that the firmness test for 'Italian' prunes in British Columbia was inadequate because of seasonal variability in firmness from prunes harvested at a constant soluble solids level of 17%. He therefore recomended that fresh market plums be harvested only after attaining a soluble solids level of'l'li. Gerhardt, English and Smith. (10) echoed similar conslusions working with 'Italian' prunes in Washington. They suggested that soluble solids levels of 14 - 16% and a soluble solids to acid ratio between 12 and 15 were optimal for fresh market plums for distant markets. They - also integrated qualitative visual skin color changes in their harvest strategy. Gerhardt et al. (11), after a follow-up stuw a few years later, decided that soluble solids alone was an unworkable parameter. They restated a soluble solids-acid ratio of 13 - 15, and further recom- mended that flesh color changes to dark amber also be in- corporated into harvest decisions for long distance shipping. Robinson and Holgate (33 ) have studied the two primary parameters, soluble solids and flesh firmness, for four varieties of Earopean plums in New York State, where climatic and cultural conditions are similar to those in Michigan. Their findings were that soluble solids ranged from 10 - 14% in the least sweet to 15 - 25K in the sweetest variety, suggesting that optimal soluble solids was dependent on the variety. They suggested that firmess changes were more indicative of ripening changes than were soluble solids. Using the Ballauf firmness tester with a 7/16" plunger, they recommended that 10 pounds firmness was the maximum for harvest finances. They found that freshly harvested fruit firmer than 10 pounds may be better suited for long distance shipment in some cases, but such fruit may not fully ripen. Tucker (4? ) studied the relationship between soluble solids, firmness and taste in 'Italian' prunes. He found that both flavor and firmness, and flavor and sugar content had strong correlations. However, a correlation between sugar content and firmness was insignificant. When either factor was held constant, the other factor affected the flavor. nevertheless, because of large variabilities in both orchard and season, when firmness was constant, quality and soluble- solids varied considerably. Sibbett et a1. (38 ), working with California 'French' prunes for drying, found that accum- ulation of solids proceeded until fruit reached three to four pounds flesh firmness. Beyond this, apparent increases in soluble solids were due simply to water loss. The research team stressed that refractometer readings alone didn't measure maturity but had to be combined with a fleshfirmness reading in order to determine potential fruit quality. Ryall (34 ) reported that sugar content of .VItalian' prunes did not increase after harvest as they are a non-starchy fruit. chean et a1. (.23) also worked with soluble solids as an indicator.in the maturity of 'D'Agen' plums in Australia. By developing a specific gravity hydrometer that was practi- cal for field use, he used specific gravity in concert with soluble solids readings to pinpoint harvest date. The mean regression of soluble solids with specific gravity was util- ed to predict the time it would take a crop to reach optimal soluble solids levels. Saleem et al. (35) reported that brix, reducing sugars, total carbohydrates, and nitrogen content increased as fruit maturity advanced; however, .vitamin C- content of the plums did.-not exhibit any specific trend. Iestwood ( 55) reports that for many years litalian' prune maturity in the Villsmette Valley in Oregon has been estimated by the change of flesh color from yellow-green to golden-yellow (amber), and is the present maturity index in the voluntary grades and standards adopted by the Northwest Canners and Freezers. G. Plum Variability Plum ripening variability is a major problem in the resolution of fixed indicators. Vincent et al. ( 52) state -that the irregularity of ripening of the fruit oz. individual trees constitutes by far the greatest obstacle to successful storage 'of theprunes. La Rosa ( 18) made an identical observation with Michigan 'Stanley' prunes, finding variability between fruits on the same tree greater than between orchards. Wiley ( 56) found that there was significant variation between trees in fineness but not - s in soluble solids, acidity or flesh color. Tucker and Werner ( 48) noted that season and orchard variations were also striking with season having the stronger effect. Hartman (13 ), Gerhardt and English (10 ) and Sibbett et a1. ( 38) had similar findings. 11W Early research by Ramsey (31) indicated that cold storage lengthened the time prunes would- keep and that re- 5...; from storage led to rapid deterioration. Furthemore, ' he showed that precooling of plums before iced shipment could greatly reuse decay during and after transport. Harman (13) determined that when 12 days storage at 45°! (7.2%) with 3-4 days after-ripening was used as a postharvest temperature regime, later harvested fruit were of a better dessert quality than earlier halved fruit. Vincent et al. (52) found that storage periods of about one week did not appreciably affect the physical condition and edibility of plum fruits. it higher tempera- tures there was more rapid ripening. Shriveling was. by far the largest postharvest problem, followed by soft rots. Cracking and internal browning were relatively minor problems. Longer storage at 32°? (0%) prorated increased deterioration due to soft rots. Tucker and Verner ( 48) "ported rapid decreases in flesh firmness of prunes stored at room temperature compared to those stored at 32°? (0°C). While they found prune storage to be limited by shriveling, decay and internal browning, shriveling was usually the limiting factor. Nevertheless, the increase in shrivelling was not paralleled by a decline in flavor. The “authors found that firm fruit held up better than soft so that firm fruit with a high sugar content was 10 recommended for storages. They recommended "limited" periods of storage at 32-35°F (O-l.7°C) for 'Italian' prunes. Fisher (9) reported that Italian prunes held in 32°F (0°C) storage for four weeks attained satisfactory quality. The fruit, which had reached soluble solids levels of 18%, developed into good quality dessert plums and maintained mar- ket quality with 5-7 days at room temperatures of 65°? (18.3°C). Ryall'( 34.). showed that three weeks in cold storage caused plums to have a characteristic browning of the pit upon ripening at 65°? (18.3%). a. attributed this to normal deterioration in storage. Pentzer and Allen (27 ) studied transit temperature regimes extensively in both European and Japanese varieties of plm and concluded that 32°F (0°c) for 12 dqs was the best temperature to retard ripening. Tempera- tures of 40°F (4.4°C) permitted small amounts of ripening while 45-5501" (7.2-12.8°C) resulted in considerable softening and coloring of the fruit. They also recomended a ripening temperature of 55°F (12.3%) rather than 65°? (18.3°C) for both improved color end texture. 80°F (26.7°C) was found to have a retarding affect on ripening. 'President,' a European plum variety, was held in good condition at temperatures of 32, 35, 40 and 45°F (0, 1.7, 4.4 and 7.200) for :50 days. Gerhardt, English and Smith (11) found that 'Italian' prunes held at 31-36%" («0.6 - 2.2°C) for 10 days would not ripen normally when moved to room temperatures of 65°F (18. 3°C). 11 However, fruit held at 45°F (7.2°C) for 10 or 20 days produced a prune that ripened normally. Gerhardt and English ( 10) reported a low temperature injury which resulted from ined- iate storage at 31°F (-o.c°c). They indicated that the dis- order could be remedied by partial ripening of the fruit prior to storage at 31°F (-O.6°C) or by holding it at temperatures of 40-450? (4.4-7.2°c). Verner et al. (51) studied the effects of delaying cold storage placement after harvest. However, they found that this didn't prevent development of internal browning, one of the major postharvest problems in Ehropesn plums. . Proebsting and Hills (30 ) discovered a cold requirement for the ripening of 'Early Italian' prunes. Bsed mainly on sheer press values, they showed that when prunes were subjected to a two week 35°? (1.7%) cold treatment prior to 70°F (21.1°c) ripening, softening was significantly advanced. Proebsting et a1. ( 28) did further work and showed an improved ripening response in. firmness, color and acidity using the previous cold treatment. No soluble solids changes occured. Taste panels indicated that the canned juice of cold treated plus was sweeter, more flavorful and less astringent than that of non-treated controls. La Ross (13) also concluded that a 32°? (0°c) cold storage for one or two weeks appeared to be essential for the development of nulxinmm quality of 'Stanley' and 'Bluefree' var- ities of an early harvest. This treatment, however, benefited fruit harvested at any stage of maturity. w. H. Smith (44 ) determined 34°F (1.1%) to be an ideal storage temperature for 'Victcria' and 'llonarch' plums in England. Both jellying and internal browning were lower at this tewerature. He found that internal browning could be further checked by interrupting a 35 day cold storage period midway with four days of 65°F (13.3%) temperatures. Smith also showed that a combination of low 02 atmospheres with 34°F (l.l°C) temperatures could lengthen the storage and maintain the quality of 'Victcria' plume. Considerable research has been done on Jhpanese plum.varieties involving controlled atmospheres and yielding similar results (a, 4.0, 41). Sibbett et al.’ (38 ) studied the effects of storage temperature on the keeping quality of California's 'Frenchfi prunes. These fruit were harvested when quite ripe due to their use as a dried mit. Nevertheless both at 3251? (0%) and 41°F (5°C), internal breakdown symptoms were delayed for considerable time by storage for six.weeks at 41°F (5°C) and for five weeks at 32°F (0°C). Since softening was more rapid at 41°F (5°C), 32°C (0°C) was the preferred temperature. Iitdhell, layer and Beede ( 24) studied the effects of temperature on flesh softening in 17 varieties of plums including European and Jhpanese varieties. After 3 weeks of storage, flesh firmness had dropped 8% at 32°F (0°C) vs. 32% at 41°F (5°C). When held at 32° (0°C), firmness in all varieties remained relatively stable for 5 - 6 weeks. 15 3. Weight Changes Qgring EEEIQQE Enlargement during the final swell accompanying maturity is significant in Elropean plum varieties. Vincent et a1. (52) reported an average daily volume increase of 0.5% from August 31st until Sept. 16th. Gerhardt, English and Smith ( 11) witnessed a daily average of 1.1% per day wiring a similar 3 week harvest period, and therefore discouraged premature harvests because of losses in tonnage. Fisher ( 9 ) noted a 1-2% daily increase in one week. Westwood (56) sumarized that prunes grow at a rate of 0.5 to 1% during the pro-harvest period and can gain 20-25% in weight from the first picking until they are tree ripe. La Rosa (13) found considerable variation in weight gains with 'Stanley' plums. Depending on location, his data indicates weight increases ranging from 0-25% within one week's time. Claypool and Kilbuck ( 6 ) found that 'French’prune weight increased greatly after the disappearance of chlorophyll from the flesh. Color change was thus rejected as being a good maturity index. because of large sacrifices that might be made in yields. None of these researchers recommended weight change as a harvest index, yet, all stress it as a major harvest consideration. F. Weight Losses in Storage There is less research about weight loss during storage. Couey ( 8 ) working with an oriental variety *El Dorado', observed considerable weight loss during a six week storage period. Plums in sealed and vented liners averaged less than 14 0.5% weight loss while those in open containers averaged 4. 6% loss. Mitchell, layer and Beede ( 24) studied the effect of waxing on both oriental and Elropean plums. Overall, waxing resulted in a 16% redaction in water loss from the combined 17 varieties. Waxing treatments were particularly effective in preventing water losses in 'President' plums, a European variety. G. Plum Storage Disorders There are several postharvest disorders in plums. Verner et al. (51) cites 3W MW to be the main problems in 'Italian' prunes. Lutz and Hardenburg . (20) state that the three major plum problems; 4933‘, m1, meterga}_jmm all become apparent after three days removal from storage, but are often not visable during the storage period. This makes the identification of these dis- orders very deceiving. 1‘.. Shriveling Tucker and Verner (48 ) reported that shriveling is usually the limiting storage factor for western 'Italian' prunes and that riper and softer fruit shrivel sooner than imature ones. 'Rate of flavor loss, however, does not run parallel with shriveling for prunes picked at different stages of maturity. Hulme (14 ) reports that control of relative humidityjcan reduce shrivel problems. Atmospheres of near saturation result in abnormal skin splitting, while dry atmos- pheres lead to shrivel. Lutz and Hardenburg (20 ) recommended relative humidities of 90-95% for plums. 2. Internal .BrowninLaind Soft Rots Verner et a1. ( .51) noted that while internal breakdown is associated with ripening, its predisposing cause resides in the orchard. There was a high positive correlation between fruit firmness and resistance to browning. Smith (44 ) and Gerhardt et a1. (11 ) both indicated low temperature storage under 34°F ( l.1°C) to be a factor in the development of internal breakdown. is cited before, both reports recomended some warmer temperature treatment to circumvent this disorder. Conversely, llitchell et a1. ( 24) studied four varieties of Japanese plan along with several varieties of peach and nectarine. They noted that browning and mealiness was most severe following storage between 36°F (2.2°C) and 41°F (5°C), and least severe at or near 32°F (0°C). However, these researchers also indicated that exposure of fruit to temperatures over 68°F (20°C ) delays the onset of breakdown. ‘ Cargill et a1. ( 4 ) have noted that-broil rot and penicillium rots are prominent problems with 'Stanley' plums. Jones et- al. ( 15) have found that fungicide sprays and dips did not significantly reduce postharvest decay in plums. However, a hot water dip of 51.5°C for three minutes did an excellent job in controlling postharvest diseases. Cargill. et a1. ( 4 ) reported that a three day. treatment of 100 ppm of ethylene gas eliminated any noticible fruit rot on 'Stanley.’ l6 3. Bruising Bruising, while not a postharvest disorder, is also a major problem in plum handling and storage as its occur- rence increases the incidence of other disorders. Ramsey (:51), though working during a time of primitive refrigeration, clearly showed that the careful handling of plums reduces the incidence of decay at distant markets. Ceponis and Friedman ( 5 ) discovered a positive correlation between the amount of bruising and the percentage decay of fresh market Idaho grown 'Italian' prunes. Furthermore, temperatures of 70°F (21.10C) for 3 to 5 days greatly accelerated the bruise induced decay, whereas holding fruit at 35°F (1.7°C) for two weeks markedly curbed the decay development. Mitchell, layer and Beede (24) determined that waxing could reduce the bruise scores of plums, peaches and nectarines. K. Ethylene in Plum Ripening There is a limited amount of research dealing with ethylene production and action in the ripening of plums. According to Abeles (l ), the plum, like all members of the stone fruit family, is climacteric. However, all plum var- ieties do not produce or respond to ettwlene in a cindlar fashion. Vote (49 ) has reported a correlation between the ability of a fruit to evolve ethylene and the speed at which it ripens. Working only with Japanese varieties of plums, Uota showed that cultivars which ripened normally at 90°F (32.2°C) produced 1'7 measurable amounts of ethylene gas at that temperature but production was supressed in varieties that did not ripen properly at 90°F (32.2°C) without added ettqlene gas. kitchell et al. (24') also studied varietal responses of plane to ethylene. 'Santa Rosa, ' a late variety, ripened nominally, only after two days of ethylene exposure and was also unaffected by a two week 32°? (0%) treatment. an the other hand, 'Wickson,’ an earlier variety, ripened well without added ethylene and developed accelerated ripening after the two week's cold treatment. Uota ( 49) also studied the effects of ethylene gassing on Japanese plums. In general, fruits gassed with 2000-5000 ppm of ethylene at temperatures of 70°? (21.1%) and 90°F (32.2%) increased their rates of respiration and ethylene evolution. There was a similar but greatly reduced respiratory response with ettn'lene gassing at 55°F (12.8°C) and no response at 35°F (1.7°C). Volatiles, including ethylene, seemed to be involved in ripening; however, volatiles other than ethylene did not significantly change with applied ethylene. This was determined by absorbing volitles on a sulmric acid tower and oxidizing them with a sulfate-«rate solution at high temperature and pressure. Smith‘ (44 ) found that 002 evolution from 'Victoria' plums exhibited a climacteric about 10 days after harvest without added ethylene. In Uota's report untreated plums reached a respiratory peak in 4 - 6 days at 70°F (2l.l°C). 18 Plums treated with ethylene gas reached their peaks about one day in advance of these controls. In a preliminary stumv Cargill et a1. ( 4 ) found that ettwlme gassing for 3 days at 100 ppm had a positive effect on the ease of pitting of 'Stanley' plums. After treatment, plum pits did not cling to the flesh during pitting and the percentage of halves with pit fragments had decreased. Smith (43 ) reported a maturity advancement in the mropean variety, 'llonarch, ' following a 10,000 ppm acet- ylene gassing for one day. Treated fruits (probably of an early harvest) showed improvements in color, odor, and matur- ity as judged by subjective analysis. After storage at 31°F (-O.6°C) for l, 2 or 3 weeks, plums were gassed with various high concentrations (2000 ppm and over) of acetylene or. ethy- lene for one to two days. The general trend was a narrowing of the ripening differences between gassed and control fruits as the storage period pragressed. Treated fruit was most notably different from non-treated in having: 1) stronger plum odors; 2) more. uniform ripening; 3) 'a smaller percentage of cling- stones; and 4) a higher percentage of rot. Similar but weaker ripening effects were noted with two other treatments: 1) fruit which had been treated with the air that had been passed over already ripened plums; 2) fruit which had been confined to an atmosphere with limited ventilation. However, a one day ethylene or acetylene gassing of fruits while in storage at the 8th, 13th or 18th day after harvest had only a slight effect. While 19 the author suggested that longer gassing during storage might be effective, it appeared that gassing effects were greatest under room temperature conditions. .I_.__§k_ogenous Growth Regulators ' Effects on Maturity There are a few reports on the effects of ethephon sprays to plums which further implicate a role for ethylene in plum ripening. Paunovic et al. (26 ) observed a 8 - 10 day advancement in maturity with the 'Pozegada' cultivar, while Savic et a1. (36 ) noted a ten day advancement in both 'Pozegada' and 'Stanley' plums. Proebsting and Mills (29 ) obtained a two week advancement in color and soluble solids combined with a one week advancement in softening following ethephon treatment of 'Early Italian' prunes. Responses were greatest at 80 ppm but lower rates down to 10 ppm produced lesser effects. All of these above reports were on Ehropean varieties. Similarly the maturation enhancement with ethephon has been reported on Japanese plums by some researchers. Guelfat-Reich and Ben Airs (12 ) noticed the promotion of coloring, fruit softening, ethylene and C02 evolution with a one minute dip in 250-500 ppm of ethephon. Soluble solids and acidity were not affected. Bloomaert et a1. ( 2 ) also witnessed an earlier and more uniform ripening of the 'Santa Rosa' variety as judged by the advancement of color. Succinic acid 2,2, dimethylhydrazide (Alar) has also been used in an attempt to enhance plum ripening (l9 ). Yeager et al. 20 (57) found that Alar advanced the maturity of California's 'Fronch' prunes by eight days, while La Rosa (18) found that the ripening of 'Stanley' and (Blush-ea! was not affected using several concentrations of Alar. - J. Research on Canned Plumg. Hartman (13) reported that cold-treated 'Italian' prunes of earlier harvests develOped a high quality canned product, provided they were picked within a desirable picking range and allowed to become ripe before canning. After cold treatments, p1um.color development was so enhanced that treated fruit had an appearance similar to tree ripe fruit. Proebsting et al. (30 ) found that a cold treatment enhanced ripening. Coldstreated 'Italian' prunes yielded juice that was preferred to non-treated, being judged as less acid and astringent and having more plum.flavor. The appearance of the canned plume was also influenced by cold treatment. Less mature fruit that received a cold treatment tended to split in cooking and the flesh darkened. Some cold treated, canned fruit was downgraded by industry inspectors because of soft flesh» La Rosa (18) found that cold treatment did not improve color in canned 'Stanley' and !Bluefree' plums. Conditioning the fruit, however, whether it recieved a cold treatment or not, improved the color rating of the canned product. He also witnessed lower texture ratings as the fruit matured and the conditioning period lengthened, but again, no effects due to 2]. cold treatment were observed. There were no significant differences in the flavor ratings for 'Stanley' and 'Bluefree' plums. In paired tests for preference cold storage had no effect on improving the quality of the canned plum. Working specifically with maturity parameters for a canned plum, Wiley (56) discovered good correlations between quality of the canned product and the following indices: flesh firmness, percent soluble solids, percent acidity, soluble solids to acid ratio and flesh color as measured by the Hunter A scale. Westwood (55) states that the Oregon State University Food Science bepartment has determined that the ss/acid ratio is the best criterion for canning maturity. Kenworthy et al. (17) considered the separation of the pit from the flesh to be the . most workable guide for determining the readiness of a 'Stanley' crop destined for canning. IlIERIAL AND NEIHODS a. gggpling and Desigg Data were gathered in three harvest seasons, 1980, 1981 and 1982. The techniques varied slightly for the three years but the experimental designs were similar. A.major sampling difference existed.in monitoring of maturity for the two harvest seasons. In 1980 one sample of ten individual plume was chosen per treatment; data were recorded for each fruit. After an evaluation.ofzthe-variation.within.the treatments,- anew sampling scheme was designed for 1981. Three samples of ten plums each were used, and the mean of each.sample was used for statistical analysis. During 1982, these three samples were reduced to 8 plums each.to facilitate the broad testing of a harvest model developed during the first two years research. In 1980 and 1981 a four way factorial was utilized with variables of: 1) orchard location; 2) harvest date; 3) duration of 0°C storage and 4) duration of 20°C conditioning. In 1980 only, a fifth factor of ethylene treatment was added. In 1982 only, the factors of location, harvest date and conditioning time were studied. ‘ 22 23 B. Harvest Sites ‘5‘ a In 1980 two orchards were employed, the Michigan State university Ebrticulture Research Center in Ehst Lansing and the Graham.Ekperiment Station near Grand Rapids. In 1981 the research was expanded to four orchards: three commercial orchards from the Grand Rapids area of Michigan (Rasch, Thoma and Reister) and the Graham.E:periment Station. Different blocks were used at the Graham.Station in 1980 and 1981 which had different sites and tree age. In 1982 8 orchards were researched. The 4 identical blocks (and trees) from.the 1981 study were used in 1982 in the Grand Rapids area. Fhur other orchards were harvested in Southwest Michigan (Biaers, Berry- brook, Buskirk a and Buskirk B). A code used throughout the thesis is listed below: {Orchard Code, Orchard Code 1980 ‘ i 1982 #1 e Horticulture Research Center A, B, C, D - same as 1981 .#2 - Graham Experiment Station E - Buskirk's A Orchard 1981 ' F - Buskirk's B Orchard a - Rasch's Orchard ’G - Berrybrook Farms .8.- Thome's Orchard H - Biaers' Orchard 0 - Reister's Orchard D - Graham Experiment Station 24 .C. Harvesting Random.samples of about 50 lbs. of fruit were picked at weekly intervals from.each of four trees sectioned into quadrants. A new quadrant was used for each harvest. The first sample was taken before normal commercial harvest (final stages of skin chlorophyll degradation) and the last at least one week after commercial harvest when the fruits were approaching an overripe condition for fresh market. The number of fruits in each sample was recorded and fruits from each tree were weighed in order to determine the change in average fruit size. -The harvest dates were as follows: 1980 - Sept. 2, 9, l6 and 23: 1981 - Aug. 27, Sept. 3, lo and 17: 1982 (southwest area) - Aug. 19, 26 and Sept. 3; 1982 (Grand Rapids area) - Aug. 30, Sept. 6 and 13. Fruit of the last harvest in 1980 was not used for’maturity experiments as it was overripe; however, weight measurements were taken. ‘ D. lain Treatments Readings for’harvest.maturity were obtained as soon as the fruit was transferred to the laboratory. Fruit for storage treatment was immediately placed in refrigerated storage at 0°C and.90% relative humidity. Times of storage were 0, 2, 4 and 6 weeks in 1980. This was reduced to O, 2 and 4 weeks in 1981 as the majority of the ripening transformations had occurred within four weeks. In 1982 storage treatments were not performed. 25 At harvest and after storage, samples of fruits were conditioned for various lengths of time at 20°C (room.temper- store) to assess shelf-life of the fruit during retailing. Times were 0, 2 and 4 days in 1980: O, 2,'4 and 6 days in 1981 and 1, 3, 5 and.7 days in 1982. Throughout the thesis this treatment will be referred to as conditioning. In 1980, samples of fruits were gassed with 100 ppm ethylene during the postharvest and.poststorage conditioning treatments.‘ Utilizing flow boards and capillary tubes, 120 fruit from each orchardhharvest-storage combination were placed in 10 liter desiccators and 100 ppm of ethylene in air was administrated _ at a flow rate of about 100 md/min. non-treated controls were mintained in desiccainra in flowing air, scrubbed free of ethylene. Fruits were examined every other day according to conditioning times to assess the effect of ethylene treatment at harvest and after storage. I ‘ . W In 1980 the following parameters were used to measure maturity: 1) skin color, 2) soluble solids, 3) percent titrat- able acidity, 4) flesh firmness, 5) soluble solids:acid ratio, 6) pit removal force and.7) weight. In 1981 all but the last two parameters were used, while in 1982 only soluble solids and firmness were used. In all 3 years ethylene measurements were made and will be discussed in the next section. 26 Skin color was measured objectively by extraction of slain pigments. Small discs of skin tissue were obtained from the larger cheek of plums by cutting the skin with a 1.27 cm diametercorkbererandremovingthe disc andathinlayerof - flesh with a razor. Then discs were placed in a test tube . and.anthocywnin extracted with 10% oxalic acid over a period of three days at 3°C. Absorbance at 313 nm was read with a spectophot'ometer and expressed as units O.D. In 1980 one disc per fruit was extracted with 10 ml of oxalic acid solution. In 1981, ten discs (one from each of lo fruits) were extracted with 10 ml of acid. The pigmented solution was then diluted with his. velumes of ms oxalic acid to be similar in absorbence to the 19% readings. Three reps of ten discs were read in 1981. In m..- to determine the adherence of the pit to the flesh as affected by maturity, a system was devised for meas- uring the pit remval force. Plans were cut transversely, approx- imately 1 cm from the stem and near the point where the pit tapers. The skin was then cut at the distal end to facilitatepit ex- cision and the fruit positioned longitudinally in a rubber on. A 7/16 inch plunger with a concave surface was installed on an Effegi firmess tester and used to measure the force required to eqel the pit from the opening at the base of the fruit. The force required to remove the pit was recorded in pounds and is termed the pit removal force. This measurement was done in 1930 but not repeated in 1931 or 1982. This index 1: similar 27 to flesh firmness in that it is measured with the same instrument and is a rough indicator of the cell wall changes a plum is undergoing. It does perhaps give a closer picture of the internal plum ripening as the flesh firmness measures only the enter 1 cm of the flesh. . Soluble solids were measured with a Bausch and Lamb ASHE-3L refractometer. After the firmness test was completed, 1-3 drops of juice from each fruit were transferred to the prism of the refractometer. Individual plums were used in 1980, while in 1981 and 1982, 2 drOps of juice were collected from each plum in the 10 or 8 plum sample and pooled as one replication. Titratable acidity was determined by titrating to pH 8.1 with 0.1 N sodium.hydroxide and is expressed as malic acid equivalents. Because of time limitations, fruits were frozen at -20°C and acidity measurements were made several weeks after harvest. Pitted.plums were removed from.the freezer, weighed, boiled in 100 ml of distilled water and blended for two minutes in a Ihring blendorlat high.speed. Titration was done after cooling and acidity computed as grams of acid per 100 grams of f1esh.weight. In 1980 data were recorded for'individual plume while in 1981 a l/lOth slice was taken from.each.of ten plums and the pooled sample was used as one replication. In 1980, in order to determine the weight losses due to storage, conditioning or ethylene treatments, 10 plums were 28 weighed after their respective treatments and the mean used for statistical analysis. WW Ethylene and carbon dioxide evolution was measured in 1980 by holding individual plain in one pint jars equipped with inlet and outlet ports. Ten plum were used per treatment. Half of the fruits in each treatment were exposed to air streams containing 100 ppm ethylene (plus or minus 3 ppm) at 10 ml per minute, and half of then exposed to ethylene-free air at the same rate. Flow boards and capillary tubes were utilized to obtain the proper gas mixture. Ethylene and C02 production were unitored by gas chromatograpw in 1 ml gas susples at one to two day intervals and the rates were expressed. as ul/kg/hr and ml/kg/hr for ethylene and C02, respectively. . In 1981 and 1982, samles of ten plums were placed at 20°C in nearly air tight 2.6 liter plastic containers equipped with a serum stopper for gas sampling with a syringe. A 30 gram paper envelope of dry hydrated lime was placed in each container to absorb 002. This closed' system allowed ethylene to acclunulate and in the absence of C02 (an inhibitor of ethylene action) so that autocatalytic ethylene production could be induced. Oxygen was partially depleted in the containers but? did not fall below 14% cm, to oat-moving through. the‘seal'a- CO2 levels were checked periodically but did not rise above 2$due to Ca(OH)2 scrubbing. There was an undeterminable leakage of ethylene out so that readings could not reflect real production rates but only 29 relative changes in this semi-closed systan. Gas samples of one ml were taken daily and analyzed for ethylene and 002 by gas chromatography. In 1981 a four container sample for each harvest x location treatment was used. This was in- creased to six containers in 1982. Upon observation that short chilling treatments advanced ethylene production in closed containers, several auxillary experiments were perfolmed in 1982. Plums were given treat- ments at 0 or 5°C for various lengths of time, from 3 to 70 hours, before being placed in containers. Ethylene production was measured as above. G. aluatio of of Canned Product In the first two years of the study (1980 and 1981) fruits of the same lots used for ripening measurements were hot pack processed in No. 303 cans for future taste panel evaluation. In 1980, fruit from each harvest and orchard combination received storage treatmmts in addition to a gassing treatment with ethylene. Because of time and logistical limitations, all 1980 fruits were held for six days at room temperature prior to processing. In 1981, a similar scheme was utilized, but room tenperature conditioning periods of 0, 2, 4 and 6 days were used as treat- ments prior to canning. Due to time limitations, only fruit of two weeks storage was evaluated in 1981. After conditioning, plums were halved and pitted using a manual pitter with cups 30 and blades from a German Earhart p1um.pitter. Plums were pitted singly and the pit and waste flesh and juice collected and weighed. Fitting loss as a percentage of original weight was calculated for each treatment. Three hundred grams of plums were placed in each #303 can and filled with a boiling sugar syrup. In 1980 a 30% brix was used but this was dropped to 20% brix in 1981 to eliminate potential masking effects of heavy syrups on flavor. Cans were heated in a water bath to 90°C to exhaust gas. After sealing, the cans were processed in a boiling water bath for ten minutes and immediately cooled in cold tap water for about 13 minutes. Three cans per treatment were processed. In 1980 only, prior to canning, p1um.halves were analyzed on the Hunter color meter. The color values of’plums were compared to a standard red.plate on all 3 scales of the meter: L, dark to light value; A, green to red value; B, yellow to blue value. Approximately 6 to 10 plum halves were.placed in the reading cup with the skin side exposed to the light source. Plums were rotated and 3 replications were made per treatment. In both years drained weights were recorded for the canned fruits about 6 months after processing. Each can of'plume was drained for two minutes on a U. 8. Standard Seive Series screen, 0.093? inch opening. The drained weights were not replicated and were recorded in grams. 31 Canned fruit of both harvest years and on fresh fruit of the 1981 season was evaluated at the taste panel labs of Michigan State university's Food Science Department. Ten panelists per treatment were selected from students, faculty and staff of [80's Horticulture and Food Science Departments. Panelists were given a random selection of‘ six treatments to evaluate. Different panelists scored each group of six so that no panelist was used for tasting and comparing all treatments. In 1981 the following parameters were rated: 1) texture, 2) flavor, 3) acidity, 4) color,“ 5) sweetness, and. 6) overall quality. All scales except the last had a plus and minus range, e. g., texture ranged from too soft to too firm. The judgements of each panelist were translated into quantitative scores and the mean of the ten panelists was used as the treatment score. There was no replication. 3. Evaluation of Quality of Fresh Plums In 1981 a second taste panel similar to l980's'evaluated the fresh product. In order to compare different harvest dates at the same sitting, fruits were kept in cold storage until the last harvest. Then fruits of all four harvests were compared with each other. hits from earlier harvests were therefore stored longer than those from later harvests. This design handicap will be considered when weighing the results. Taste panels evaluated fresh plums from 12 treatments; four harvest dates and three conditioning times (0, 3 and 6 days). Storage treatments were excluded due to the design 32 problems as indicated above. Data for'each orchard were analyzed separately. I. lean Separation lost or the 1980 data and some of the 1931 data were not replicated; therefore the mean square error consisted of four and five way interactions of major treatments. Least significant difference (LSD) and honestly significant difference (BSD) are expressed with bars in each figure at the 3% level. Discussion of significant differences refer to the LSD's. In all cases the LSD and the BSD apply to all means (points visible in the graph), and are not limited to separation of one main effect. RESULTS AND DISCUSSION A. Section I: Maturi Indices-.Evaluat arameters t Assess Op est Da e 1. Introduction In order to harvest plums for optimum quality and storagability, maturity in'dices must be selected with the following criteria: 1) effectiveness and reliability; 2) broad applicability over varying locations and seasons; 3) economical; 4) accessible to growers; 3) quick and 6) in line with physiological changes in the plums. Five primary maturity indices were observed throughout harvests in 1980 and 1981. These include; color, firmness, soluble solids, acidity and ease of pit rennval. The data of this section is organized in paired graphs to illustrate two aspects of harvest date effects. The first graph of each pair shows the direct effects of harvest date only. The second graph of each pair shows the main effects of harvest date (as pooled over postharvest treatments of conditioning and storage). Data for each season is presented in an indi- vidual graph. 2. Rationale for Seasonal Analysis Before examining the data for each index, an important generality can be drawn about data from Orchard #1 in 1980: 33 34 with regard to all parameters, fruits of Orchard #1 were . considerably advanced in comparison with those from Orchard #2 and all four orchards of 1981. This is particularly true with.respect to color>and soluble solids. This orchard was the only one atypical of a commercial operation: poor weed, in- sect and disease control were evident along with declining vigor. The advanced age of the orchard coupled with these stresses in- duced early ripening of the fruit and limits the applicability of the data in comparison with other orchards. Thus, the data for the two years was not pooled, but is presented separately' to avoid a bias in evaluating seasonal variation. It should be further pointed out that maturation occured about one week later in 1980 than in 1981; for example, the 3rd harvest of 1980 would most closely approximate the 4th harvest of 1981 in physiological maturity. 3. Skin Color Color changes were generally gradual and OD values climbed nearly consistently with progressive harvests throughout both harvest seasons (Figures 1 and 2). An exception to this was a drop in color in the 4th harvest of 1980 (Figure l). A possible explanantion for such a dip could be the dropping of more advanced fruit leaving the least mature ones attached. As mentioned earlier, color advancement was much more rapid in Orchard #1 than in the other orchards. Color increased with progressive harvest in most orchards. This was not the case, however, with the Graham Station fruit (orchards #2 and D) for either 1980 or 1981 (Figure l). 35 By casual observation there was no correlation bottleen the timing or a visible purple overcoloring and a notable increase in anthocyanin pigmentation. This visual skin color change preceeded commercial harvest by at least one week and occurred between the first and second harvest for most orchards. Looking at' only three comercial orchards (A, B and C) in 1981, absorbance values approaching 1.00 roughly corresponded with comercia'l harvests (Figure 1). Color (both visable and extractable pigments) changes with conditioning and storage (to be discussed later), so that color levels of fruit ined- iately after picking are not critical in deciding the optimal timing of harvest. In addition, couplicated instrumentaion, location and seasonal variation, along with very gradual changes over time, limits the use or a color index as a worthwhile har- vest indicator. 56 .aoan one coca nu veepnen . cam a no 053 no Soda .hedneum. no age no announce a: a . . e oennu no flan no e952. one accrue: no 3.3 on» no a . a ensmg 37 H can—mg mhm<1 hwxa opsm oxa nwxo a: re. o 22.206 p o . . c 22206 e E...2o-e —. CG r < 22.20 .4 QNB .. mzm m\m Nxm 00.0 omd 8.9 omé CYP 00.— i. .. 8.. pm... on. . e 32.20 - D 8.N COG P p 32.30- I smote: 3 302m. .025 amaz<=o :38 2% (0'0) BONVSHOSSV 58 .esdu cmsnoae one mnancaadonoo ne>o deacon undo: .HmaH one omaa nd anan heanenm. no naxu no anesnoo anoamda no adsnn no cannon ens aeopnsn no can» no uncenhm .m ensmym 39 . :3 0—3 03 Nana 0.3 GB - N3 8 COO) sowvaaosav O V. p O 22.20 I c 22.20 0 I 93395 ‘ n. w <. o .820 4 - 1.2.30 I g a 22.5 D me; 3955 one ascoEocoo. ao>o maootw amaze: mmwzmo eeaoon «one: .33 e5. 83 5 5.3 L353? no amassed.“ nsenn no udsnn n0 cannon and use>nsn no can» no eaoennm .« ennmnm 44. hzm. 93 «3.. e enough . h «so mike. hmm>m<2 .( once mna an. 'o 0 s '0 .2 a 2220 .e 0 22.20 -0 m odesoacu‘ < 22.20 -4 swap 1.: 05.... 03.05 was. ascozficoo .05 202E 6020: q _ : as: a». . . a 22.20 .. u — nan-.050 o I comp mp mm62<20 mmMZEm—E fawn—n. (‘SS'D SSSNWBH H8313 45 5. Pit Removal Force Pit removal force generally paralleled the flesh fimess readings (compare Figures 3 with 5, and 4 with 6). Responses were basically linear with values 4-8 lbs. greater than the corresponding flesh finances readings. An interesting exception to this decreasing slope was witnessed in the 2nd orchard beheen the 1st and 2nd harvests (Figure 5). Here the reading increased slightly followed by a rapid decrease by the next harvest period. From all physical parameters and additional subjective taste evaluations, the pit removal force decrease corresponded with the completion of maturation of the plums from this 2nd orchard, whereas these changes had occurred in the 1st orchard somewhat earlier. There was basically no separation of orchards with the LSD. There were significant differences with respect to harvest date (Figure 5). The rapid decreases in pit removal force (Figure 5: Orchard 1 - 1st and 2nd harvest; Orchard 2 - 2ndharvest) appears. to correspond with accelerated saturation of the internal flesh of the fruit and provides a good indicator of ripening. The pooled data show that the main effects of harvest date also significantly decreased with each progressive harvest (Figure 6). Here, however, the orchard differences were larger than those of the direct harvest data, reflecting the general advanced condition of Orchard #1. Figure 5. Effects of the time of harvest and source of the fruit on pit removal force of 'Stanley' plum at time of harvest in 1930 and 1931. PIT REMOVAL FORCE (LBS) 22 2.0 18 16 '14 12 1O 47 PIT REMOVAL FORCE - 1980 Direct Effects of Harvest U _ ls.d h‘sd n . F r I J- D\ I D l-Orchard1 . D-Orchardz 9/2 9/9 9/16 9,23‘ ' HARVEST DATE Figure 5 48 Figure 6. Effects of time of harvest and source of fruit on pit removal force of 'Stanley' plum in 1980 and 1981. leans pooled over conditioning and storage time. PIT REMOVAL FORCE (LBS) _49 PIT REMOVAL FORCE - 1980 ' Harvest Effects over Conditioning and Storage Time a I -Orchard 1 \ fl' ‘Orchard 2 s . U :[ hsd .lsd 9/2 9/9 9/16 HARVEST DATE Figure 6 50 Despite the potential of this indicator, it was. dis- continued in 1981 since it gave similar results to flesh firmness and was more involved and time consuming. However, it is clearly as workable as flesh firmness and is a good indicator of cell wall changes within the flesh. Wills—Salli: Soluble solids levels also displayed rapid changes as the season progressed. In both data sets, with successive harvests, soluble solids increased during the two seasons except in one orchard at the 4th harvest of 1980. This may have been (me to ripe fruit dropping in the more advanced Orchard #1. Utilizing the LSD's in the direct harvest data or 1961 (Figure 7), all locations showed a significant increase in soluble solids with later harvests while in most cases this was not evident with each progressive harvest. Using mean separation in 1980, there was little significance with respect to harvest due to the large variation between individual plums. Also, there was little separation in the orchard means. .In contrast there was strong harvest separation in the pooled data in 1980 and 1981 (Figure 8), with strong orchard sep- aration in 198) but not 1961. as indicated earlier, Orchard #1 (1980) was greatly ad- vanced over the others in soluble solidsldevelopment. Excluding Orchard #1'8 data, the comercial'harvests of the other 5 orchards (1930-31), comenced when soluble solids readings approached the 51 .aoen ecu owed on causes: no «can a. aaac.aon:ecm. no seduce canswoe no pannn no eonsou one aee>nen no can» no eeoennm . a. 95mg 52 :La a. shaman m._.mm<1 ozc 03 sane H I .4 - J ‘ 0 e 4 0 022.20 . 4 02.20 so. 02.. d. (22.20 ramp. \« H . e.oo.s.2o. el 0:0 03 4.3 L neon-=20 I . 22.20 Oman 0...: 090.05 2.0 05520.30. .26 0.005. .0020... 002.05,. 09.00. 0.0300 . Z. N. 2 2 D— 0.. h— (96) SONGS 3180108 55 12-13% range. This parameter is applicable for harvest date determination for the following reasons: 1) it rises steadily throughout the harvest period; 2) it reflects significant differences in harvest date; 3) it utilizes a rapid and simple technique; 4) it is economical. 7. Acidity In both 1980 and 1981 titratable acidity dropped as harvest progressed, with linear-tendencies similar to the other parameters (Figures 9 and 10). The exception to this trend occurred in the immediate harvest effects (Figure 9) at the 4th harvest - 1980, where there was a considerable increase in acidity. Again, the probable cause for this unexpected rise could have been the drop of ripe fruit leaving a less ripe, more acid sample on the tree for harvest. For both sets of data (Figures 9 and 10) 1980's fruit was much lower in acidity than 1981's, demonstrating substantial seasonal variation. In the pooled data (Figure 10) there was a large variation befieen the-two orchards of 1980 with Orchard #1 being again far advanced. . In 1981 acidity decreased significantly at each succeeding harvest. However, in 1980 the only significance-occurs between the 2nd and 3rd harvest in Orchard #1. In the main effects of harvest date (Figure 10), there was nearly complete sep- aration of means with respect to harvest in both years. The acidity levels which corresponded to the comencement of commercial harvesting ranged from 0.80 - 0.95%. 56 .HmmH ons coma n« .322. no 2.3 no and. .223... no .333. .3323» no ansnn n0 cannon one pecans: no one» one no euoennm .m ennmun 57 a enema... . .020 .0032 2.0 o. .0 0.0 3.0 . 00.... . 0.3 0.0 0.0 3.0 \o 00.0 .. / 00.0 o/H/ 05.0 . a 00.6 o . D . .. 00.0 60.9 a oosgoeo-I ._. OP .9 0,3...p-OnO-o ”W: B”. mum; UQ— - D 9.2.050-‘ . 5.89.0- < 22.20-4 P mm P ”H.220.” OQQ P ON-p .0020... .0 0.00.5 .00.... ">299. (pm; 4° 5 COL/5) AJJGIOV 58 .05.» w:«:o«udv:oo and omahoan n¢>o deacon «can: 48. v5. 83 5 :33 L353. no 33.8 £92.23. :0 push. no 00950» can ano>h¢£ no 024. no oaoouhm .OH oh:Mfim 59 2” 926.3 . WEE 5m>m._._0_0< (14m; 40 5 COL/6) AJJCROV Acidity does show striking seasonal variation and sub- stantial orchard variation. As with the other parameters, changes are gradual and there is no clear demarcation to separate mature from ripening fruit. The relative diffi- culties involved in making this index field accessible makes it of limited value for formulating grower recommendations. it best, acidity along with color might be used as backup information for the other parameters. When eoluhle solids to. acid ratios were reviewed, they showed abnormal variations which did not correspond with plum quality changes. There- fore this index was omitted. M no effects of the two major postharvest treatnmts, storage and room taweratnre conditioning are presented togeth- er' and are arranged according to ' the. five ripening parameters. In all cases the data represents main effects involving means pooled over 2 or 3 cf the remaining treatments. Each harvest season's data is plotted separately in» the graphs. . 2. Flesh Rimes In both years flesh times was significantly reduced by room temperature conditioning (Figure Ila). Biwever, .1. longer conditioning periods (4 m: 1930. 5 days 1931) there was a leveling in the finaness decreases and here some means were not significantly lower than the preceding condi- tioning treat-ant. The effect of conditioning 'on fruit texture (flesh firmness and pit. removal) is one of the met pronounced of all post harvest treatments. ' The effect of increasing cold storage periods on flesh firmness is less dramatic and exhibits a less parallel response (Figure 115). Particularly in regard to seasonal changes, the two years'results are dissimilar. In 1981 there was a ripening trend for the fruit of the earlier harvests with additional 61 62 Figure 11A. Effects of conditioning and harvest date on flesh firmness of 'Stanleyi plum in 1980 and 1981. Means pooled over storage and location. Figure 113. Effects of storage and harvest date on flesh firmness of 'Stanley'plum in 1980 and 1981. Means pooled over conditioning and location. A. 63 FLESH FIRMNESS CHANGES Conditiorhg Effects over Storage and Lomflcn 14 _ 1980 FK1981 1 2 - . - '- _ 1st - g 1 O " " \Q \ E " 1“ had ' ‘ g 8 _ ‘ _. lsdhsd E nd I _ rd I I 6 .. II. I. \ — \|\A\. 3rd ‘ . ' .‘. 4 \ \. _ \R' l 4. I l l 1 O 2 4 2 4 8 DAYS commons!) AT 20‘ C e1 -912 , _ e1-8127 l3-9/1O .2-9/9 '3‘9’13 '. ' A2-9/s 04-9117 '8 Storage Effects over Condflorhg and Location 14 _ 1980 led hsd _ ‘ 1981 lsdhsd 12 ' I . ' \13t I I a - — \ _. g 10. - 3 .° 1st 0" _ g ‘ / . I; 8I" n .. 2nd‘ 0:) - A - \. A g 6 - 37d - w. ‘0 '_"\-‘_ ‘- . 4th ' ‘9 4 .. l l L l l l 0 2 2 4 4 a 0 WEEKS IN STORAGE 0° c Figures 11A and 118 ‘64 storage. In 1980, however, this trend ‘8 only apparent from zero to two weeks storage. Thereafter, the firmness either in.“ or actually increased ‘(in the case of the first uni-new. In general there sea a clear decrease in the flesh firmness of fruits from the two earlier harvests (both years) at two-weeks. duration. . 3 t e Pit ramval force data were collected in the 1980 season only. Pit runoval force data parallel flesh firmness with respect to both storage and conditioning effects. Conditioning, in particular,ebrought on stew decreases in the pit removal foree.. These rednctions are most evident after two days, .- followed by a leveling at four days conditioning (Figure 123). The effects of storage on pit Ir-soval force- resulted in both significant decreases and increases (Figure 121). The major trend is for a drop or plateauing at two weeks storage, followed by a steacb' increase at four and six weeks. This was similar to ease of the flesh firmness data discussed above, reinforcing the observation that there is afirming effect when .fruits are stored for “extended periods (4 - 6 weeks). While not visible from the graphs, there’ was an interaction. of storage with conditioning. The high values at four and six weeks conditioning were not the result of the pit becoming more tightly bound to the flesh wiring storage, but rather due ' t0 the failure of the fruit to undergo non'n'al flesh softening when long storage periods (4 - 6 weeks) were followed by 65 .nodasoon one mndnoaaacnoo he>o deacon acne: .amo. on. omen o..as.c .hofleaum. do canoe deposen can no cusp auo>asn one omsnopu no uuoeuufl .mmfi onsmfim .noaasooa use omshoau hope eoaood asap: .Hmo. use one. a. sand .honcuam. do coped Hs>oaea add no cusp amo>hss one madnodudpnoo.uo aaocuum, .dma shaman 66 mm. as. «a. 25m... O eon h< 0m20_._..0200 m><0 0 so m0<¢0hm z mxmm; c w o m w. m o . . n . - o O. 0 m ..\m . e 1 wpxm n m a N e\e e/ I a. as a a < ./_. . .\. N N\0 I P e , F \l/ l v— mba Swizz . _ /a 1 . I\ I o— 3”: U0- - a”; U“— §§J g 8.8a” .33 Cash.“ is m . §§J in. go 3,0 0.8:“ gazaw <. one. I mecca ._<>o_2mm E ('881) 3080:! 'IVAOWBH .le 67 conditioning for two to four days. When short storage was followed by conditioning, softening and smooth pit removal _ was enhanced. However, following long storage. conditioning treatments didn't change softening and pit removal. A possible hypothesis for such a phenomenon could be the loss of scmle of the enzyme systems involved in pectic changes during the prolonged storage periods. Since membranes can incur degenerative damages with prolonged cold storage (21), the activity of membrane bound enzymes could be reduced at long storages (4 and 6 weeks). Thus flesh softening would be retarded and prevent the smoth removal of the pit. The reduction of softening following prolonged storage reinforces the practice of holding plums for about a maximum of four weeksin standard cold storage and utilizing CA if longer storage life is desired. This firming trend? (or reduction in softenirg) was also witnessed during the pitting process for canned plums, and will. be discussed later. 4. Solublegligg The storage and conditioning effects were the least domina- ting on the variable of soluble solids when compared to the other 4 indices. This was particularly true of conditioning. In all harvests except the last (both 1980 and 1981 data) there was no significant difference between the soluble solids treatment means after various conditioning periods (Figure 13A). Storage, 68 Figure 13.. Effects of conditioning and harvest date on soluble solids of 'Stanley' plum in 1980 and 1981. Means pooled over storage and location. Figure 138. Effects of storage and harvest date on soluble solids of 'Stanley plum in 1980 and 1981. Means pooled over conditioning and location. SOLUBLE SOLIDS (96) 17 15 15 14 _ b L 69 . . SOLUBLE SOLIDS A Condition'mg Effects over Storage and Location %' 1980 ./ /T’ ...[ r... 1* 1981 2 4 5 0 DAYS CONDITIONED AT 20‘ C e1-912 a2-9/9 l 3 -9/1d " Az-sls o 439/17 B Storage Effects over Conditioning and Location 1980 [ 17 15 I-—— \':\/<: 15" 14-\ .. 1 ° 13 \./ \. 12 - 11- IsdI had I 10 in 1 l _L-L O 2 4 6 1981 { WEEKS IN STORAGE 0° C Figures 15A and 13B 70 also, had minor effects (Figure 133). There was no change in soluble solids in 1980, but in 1981 soluble solids in- creased slightly during four weeks storage. Since the effects of location had greater influence than either storage or conditioning, a second set of graphs has been added, breaking down conditioning and harvest treatments by location in order to illustrate postharvest treatment effects. In Figure 14, each line represents a different orchard. The data for 1981 again produced clearer trends than 1980, showing soluble solids increasing with days at room temperature (Figure 14A). Equally evident were some significant differences between orchnds. The data of 1980 possibly suffers from sampling problems caused by pulpy fruit. The storage data reflect similar trends with 1981's data showing a slight soluble solids increase with extended storage (Figure 148). In 1980, fruits from.the second orchard signif- icantly increased.in soluble solids while those from.the first orchard continuously dropped, perhaps due to its highly advanced maturity compared to the other locations. These data suggest that desirable soluble solids levels are best achieved by selection or proper harvest date at a given location. 71 Figure 14A. Effects of conditioning and source of fruit on soluble solids of 'Stanley' plum in 1980 and 1981. loans are pooled over storage and location. Figure 143. Effects of storage and source of fruit on soluble solids of 'Stanley' plum in 1980 and 1981. leans pooled over conditioning and harvest. soweus some (96) 72 SOLUBLE SOLIDS READINGS A Conditionho Effects over Storage and Harvest _ 17 1980 1931 16" ...:/\ .- _lsd had o ‘2' l l I o 2 4 o z 4 e DAYSCOIOH'IONEDATW c ownm1 I ,4 mamas. o~mnc:o B Storage Effects over Conditioning and Harvest 17 1980 1981 16 b .\. _. \ 15-)“ has .- “-II I'll/A 0 ‘ A 1 o 2 4 e o 2 4 wssxs {N aromas o- o Figures 14A and 148 73 5, Acidity Acidity was decreased by storage and conditioning treatments (Figures 15; and 158). The effect of conditioning on acidity was significant and acidity consistantly decreased in 1981 while it leveled at long conditioning periods in 1980 (Figure 15A). The effect of storage on acidity was also significant (Figure 158). In 1981 there were consistent significant decreases with.progressive harvests. In 1980 there were significant decreases only at 6 weeks storage as fruit acidity stayed relatively level up to 4 weeks storage. Ehrvest date had equal or greater effects than either postharvest treatment in regulating acid levels. There were consistent significant decreases in acidity with.progressive harvest 1:: 1991 with admin:- trends in 1960. 6; Skin Color Skin color (extractable pigments), like flesh.firmness. is a variable affected by the conditioning period. The data in Figure 161 are simply presented with conditioning main effects without the harvest lines plotted. In 1980 the increases are immediate; however, in 1981 the fruit did not advance until after the second day of conditioning. The general riper condition of the 1980 fruit might have been responsible in part for this. Outside of’the changes in texture, skin color was the only parameter where conditioning 74 Figure 15A. Effects of conditioning and harvest date on titratable acidity of 'Stanlsy' plum in 1960 and 1981. leans pooled over storage and location. Figure 158. Effects of storage and.harvest date on titrat- acidity of 'Stanley' plum in 1980 and 1981. leans pooled over conditioning and location. ACDITY (9/ 100 g of fruit) A CmditioMg Effects over Storage and Location 1.00 75 AC'IDITY 03¢ .oso-I:;\\\§ ‘ 1950 O 2 4 hsdlsd Lt 1981 _ L 2 DAYS CONDITIONED AT 20‘ C 01-9,: ‘_2..9fi’ '13-9Vfll .1-e/27 ee-sno Az-s/s o 4-9/17 B Storage Effects over Conditioning and Location :1 0.00 b 1980- 0.5C Wmmssusnruoso-c Figures 15A and 158 76 Figure l6A.’ lain effects of conditioning on skin color of 'Stanley' plum in 1980 and 1981. Means pooled over storage, harvest and location. Figure 168. lain effects of storage on skin color of 'Stanley‘ plum in 1980 and 1981. leans pooled over conditioning, harvest and location. 7’7 SKIN COLOR CHANGES A WEflectsoverStorage Harvest andLocetion "7° 1 980 l l 1.” I- I I, In. / :- MO " [3d hsd ' III l L 1981 led. hsd Ii/° .\ b 1 ‘ O 2 . 4 cars m" 2o- c \ 1980 1981 led hsd _ I . fsd hsd . .I I .\e .\ b b 1 ' . ./ ‘2 i i 3 Q i wears N STORAGE 0' C Figures 16A and 168 78 had an equal or greater effect than the harvest date. Consequently, fruit of a given harvest could be advanced considerably by conditioning. The change in extractable pigments was not reflected in visible color. The effect of storage was to decrease the extractable pigments. Pigments may have migrated from.the skin tissue to the flesh as storage duration increased. Since these two postharvest treatments act in different directions, this precludes a.more detailed breakdown of the data. 7. Conditioning and Storage - Overall In summarizing the postharvest treatments, the following generalizations can be made. All postharvest treatments tend to advance ripening. Conditioning markedly reduces flesh firmness and pit removal and increases skin pigmentation. Storage decreases pit removal force and.may promote pigment migration from the skin to the flesh. Storage also decreases the acidity levels while having relatively minor effects on the soluble solids levels. . In the majority of the graphs of this section the harvest date effects predominate over the postharvest effects, as evidenced by comparing the separation between lines (harvest date effects) with the slope of’the lines (postharvest effects). This trend of the overriding influence of harvest date can be further illustrated by observing the graphs of Section 1. When comparing the direct effects of harvest date with the 79 pooled effects of harvest date (Figures 1 to 2, 3 to-4, 5 to 6, 7 to 8, and 9 to 10), values were slightly altered by the pooled postharvest effects, but the direction of the slapes and the rates of change remained similar to.the data of directly harvested fruit. While Section 2 indicates that both condi- tioning and storage significantly affect the ripening indices, these variations were on the whole dwarfed by harvest date effects. 3 C. Section 3: Weight Changes 1. fleet of Date of Harvest There was a striking difference between‘the 3 seasons with respect to harvest effects on weight changes. In 1980 there were clear increases with advancing harvest during the beginning of the season (Figure 17). In 1981 (Figure 17) and in 1982 (Figure 18) in the four orchards from the Grand Rapids area, there were small weight differences between harvest dates. Finally in the four orchards from Southwest Iichigan in 1982 (Figure 18) there were steah weight increases in all orchards as the harvest sea- son progressed. Iarge differences between orchards were appar- ' ent in both years (Figures 17 and 18). In 1980 fruits from both locations decreased in weight at the latter harvests (Figure 17), possibly because of sampling error from fruit drop. In Orchard #1, which was the most ad- vanced, fruit drop was observed earlier than in Orchard #2, where a substantial drop did not occur until the last harvest. Since the most advanced fruit tend to drop first, and also tend to be heavier, this would bias the remaining sample to be underweight; however, it would not reflect any actual weight loss of the in- dividual fruits. In 1980 fruit from Orchard #2 increased 13.9% in two weeks, while fruit from Orchard #1 increased 9.6% in one week, so 81 {33 e5 .83 5 8.3a L353. oo .232. omuhobe on» no soapsooa pas cued aaephsn no auoohue one .ra oaswuh 82 5 953% . mhma on» no noaaaooa was e adv aae>h¢n no a aoeuue one .ma ossmam 84 N3 S 3&3 mpg Ema/5: . . . 83 EB . 23 ca 83 - a Eageoe o 9.2.95.0 m paesoao.‘ < 9.2.20-4 «m2 mmoz—l-——h—-l—l——/'Hl 7- ‘ we - m" 6- '- 5r- F’ 44r- ' 3.- . 2t - I 1:4—‘J too zoo still as: one - 8120 912 8/19 ' 8128 912 Harvest Date and Total Hours Figure {52B 138 have conformed to the model. The use of endogenous ethylene prochtction as a harvest indicator was successful in selecting optimal harvest dates ' in at best 9 of the 12 orchards in the two year study; however, ethylene levels were unable to signal the ideal harvest in three orchards during the second season of testing. This limits the applicability of ethylene as the key indi- cator of maturity. This does not preclude its use with other indicators, but emphasises that ethylene readings must be interpreted with caution. Additional auxiliary experiments perfomed in 1982, however, present some praise of the use of ethylene as a more reliable index of maturity. 4. Effects of Chilling on 9%, Evolution Various periods of chilling at various temperatures were found to affect the level of ethylene evolution in the closed containers. The results of two such treatments are presented in Figures 33 and 34. hits of the second harvest from the four orchards in Southwest Michigan were chilled at 0°C for 48 hours before being placed in containers (Figure 33). In 3 of the 4 orchards the ethwlene production was greatly advanced over the control fruits (no chill treatment). The other orchard, F, as discussed earlier, was infected with 139 Figure 33. The effects of 48 hours of 0°C chilling on ethylene evolution (in closed containers) of 'Stanley' plums from.four Southwest Michigan orchards harvested Ausust 26, 1982. ETHYLENE PRODUCTION ult’kglhr 9 . Orchard E I - Orchard F a ' ‘ ’ 7 _ ' V .. U " " 5 ' ' r. .. 3 ' ' z- I: - «seen-.- 140 EFFECTS OF CHILLING ON ETHYLENE PRODUCTION Orchard 6 HOURS AFT ER HARVEST Chilled '°" Non-Chilled —e— Figure 33 141 Figure 34. The effects of :5 hours of 5°C chilling on. ethylene evolution (in closed containers) of 'Stanley' plums from four Grand Rapids area orchards harvested September 6, 1982. ETHYLEhE (mks/hr) aromas-o" 142 ,EFFECTS OF CHILLING ON‘ ETHYLENE" PRODUCTION orchard c I an...“ o ”ahaafl Orchard A ' Orchard 3 i g . LLLLLILILLLLII lllllllllLll Chll'Od-O- Non-Chlllsd -e-— I Figure 34 143 brown rot and therefore had an inflated peak in the control. It is likely that the chilling treatment of 48. hours curbed the spread of infection on the tissue and resulted in the more re- duced and delayed ethylene curve in Orchard F. Fruits from orchards in the Grand Rapids area were chilled for an even shorter duration at the second harvest producing similar results (Figure :54). After a 5°C chilling treatment for merely 3 hours, fruits were placed in containers and responded with advanced levels of ethylene_production in all four orchards. In :5 of the 4 orchards etwlene production was substantially increased. Only in Orchard C were the ethylene production levels similar to the control. The fruit of this orchard failed to respond to any of the chilling or stress treatments. While these chilling treatments only advanced ethylene evolution in 6 of the 8 orchards, further experimentation may reveal that specific chilling treatments can be valuble tools in determining Optimum harvest dates. The treatments appear to artifically advance the climax of ethylene production. Since during the period of plum maturation fruits are often exposed to night temperatures between 0 and I 5°C for various lengths of time, there is a likelihood that chilling in storage may intensify a natural mechanism in plum ripening. Furthermore, if fruit only respond to this treatment 144 in a short period before becoming mature, this advanced ethylene production may serve as an early signal in pre- dicting the best ‘harvest date. 5, maligg for Soluble Solids and Flesh Firmness: Determinat on o Tolerang_e_s_ Tolerances for soluble solids and flesh finnness were determined by utilizing data from the taste panels. Table 3 presents the weighted means of flesh firmness and soluble solids which were calculated for each specific orchard from the taste panel ratings of all treatments. These means were calculated by taking the sum of the products of the taste panel quality rating and the maturity index reading, and dividing by the sum of the quality readings. A simplified hypothetical example my clarify this: Harvest Soluble Solids Quality Ratim Product '. I 10 _ 5w 2 - ll 50 550 3 12 50 600 4 15 SO 1040 35-236" W Weighted seen -.- 2690/230 a 11.69% s. 3. If however, the panelists had' rated the sweeter fruit higher, the result would be: 1 10 00 000 2 ll lo 110 3 12 70 840 4 1:5 95 1235 Z = 175‘ x-2T_ss Weighted lean 2 2185/175 g 12.48% S. S. This provides a balanced measure of what specific, index- readings were collectively associated with high quality fruit via the evaluations of all the panelists. The table indicates 145 TABLE 3 Tole ances for luble Solids and ash F'irmess as Determined by Taste Panel gngigz Assessment Orchard Flesh Firmness Soluble Solids A 7. 2 13. 4 B 5.8 12.9 c 7.5 12.6 D 6.5 13.4 leans: 6.75 13.07 Table 3 presents tolerances for soluble solids and flesh firnmess to be used in determining optimal harvest ' date. Each index reading for the various treatments (each harvest x orchard x conditioning treatment) was multiplied by its. quality rating. Then the sum of the products for each index was divided by the sum of the quality ratings. 146 that a maximum flesh fineness of about 7 lbs. and a minimum soluble solids reading of about 13% are the closest integers that relate to these two parameters. When these two tolerances are applied to selecting the ideal fruit in each of the 16 (harvest x orchard) treatments, the results are shown in Table 4. As fruits from.the various locations were conditioned after their respective harvests, the conditioning period brought on decreased flesh firmness (approaching 7 lbs.) while solbule solids levels remained equal to or slightly above the level at harvest. When the fruit attained the ~ two tolerances (13$ soluble solids and 7 lbs. firmness) with conditioning, the taste panel quality score was recorded at that point. Of the 16 orchard x harvest combinations observed - only 9 had advanced their indices sufficiently to have attained the two tolerances. The remainder were still too immature regardless of the maximum six days conditioning treatment. 147 . TABLE 4 Reliability of Tolerances When Applied to Harvest and Conditio Treatments Orchard Harvest Condition- . Flesh ‘ Soluble Quality ing (days) Firmness Solids 2 6 4.4 13.4 51.8 A '5 5 5.1 14.2 55.1 4 O 6.8 14.6 41.5 3 O 4.2 14.0 48.7 B 4 O 6.2 13.1 41.4 C 3 3 5.2 13.3 42.2 4 3 4.9 14.4 47.6 a ' 5 5.8 12.7 63.7 D 4 O 6.3 16.6 45.9 Table 4 presents the quality ratings of the taste panel for fruits of treatments which satisfied the 13% soluble solids and 7 lb. firmness tolerances. For each orchard, at each harvest, the earliest conditioning treatment that brought the plums within the tolerances is recorded. orchard x harvest combinations only 9 treatments came within these levels. Of the 16 148 6. Utilizing Tolerances to Indicate @timal Harvest As mentioned previously though, conditioning is not a controllable variable within fresh market ctnnnels. With this in mind, Figure .35 has‘ be en presented to show the reliability of soluble solids and‘flesh firmness tolerances in predicting the optimal harvest date. In the graphs, flesh firmness had been converted to flesh softness with the simple equation: softness a 20 lbs. minus flesh firmness reading. Since ideal soluble solids readings are 13 and ideal flesh firmness readings are 7, ideal softness readings will also convert to 13 (20 lbs. - 7 lbs.). The dotted line on the four orchards'graphs represents this 13 unit level comon to the parameters of soluble solids and flesh firmness. Individual short lines represent the development of fruit picked from the tree at harvest and then conditioned for 2, 4 and 6 days. From. earlier data on conditioning effects, it is clear that flesh firmness rapidly changed with increased conditioning while soluble solids changed slowly. Thus the convergence of the flesh firmness reading upon the slower changing soluble solids reading, at or near 13 units, focuses upon the best time to harvest fruits for mafimm quality within an orchard. Thereafter, the date. of convergence of these two lines is related to the quality reading above, which is the quality 149 A.uue>aen_aou eeodaodou Henna neenuhoe .nna nu on» use eodaoe cannaoe find ceaeewmse on» senescence coda conned one .eaoeaaeeap moanoaaacooe ae>o ceased one needs: haaasaav .Hmma dd cacao rheandom. sou emodueh hudaeso Hosea eons» on noaasaen ad wound announce needy one nmndoeea sudden eHAsaoe do mnanodpnonoo no mama—ea one one aaasau mo season on» .oee>aem no saw» one no message .8 enemas 150 an 9532 bags: E 0>535 35.... do 4:30:53 XBONI AJDVI'IO I .8 I v 690108 enemas om xsou ssaulsos° 151 . average of all conditioning treatments for each harvest. In Orchards a.and.B these tolerances indicated.maximal quality. In Orchard D it indicated a climbing, but still high quality plum. In Orchard C the model was ineffective in pinpointing 'optimal quality. Therefore an overall precision score for the model utilizing only soluble solids and flesh firmness is 75% in the four orchards tested. is discussed earlier, there is a likelihood that quality scores at the earlier harvests were inflated upward due to longer storage treatments. 7. gestigg the Soluble Solids - F1esh.Firmness ModelI 1982 In the 1982 season the soluble solids - softness tolerances were field tested in the same 8 locations that the ethylene model was tested. Though conditioning was obtained at l, 3, 5 and 7 days rather than 0, 2, 4 and 6 days of 1981, the trends are similar to the 1981 results. Soluble solids generally rose gradually with each successive harvest (Figures 36 and 37). While soluble solids increased with lengthened conditioning in some cases, in many instances it decreased. The "softness index” generally increased greatly with longer conditioning treatments and also increased sub- stantially with successive harvests. In all of the 8 locations the convergence of’soluble solids and softness at the suggested 13 tolerance corresponded with a period of high quality of the fruit. Black arrows indicate the suggested time of harvest based on the qualitative assessment of our research team. 152 Figure 35. The effects of time of harvest, and length of conditioning on soluble solids and flesh softness readings of four orchards (Grand Rapids area) of 'Stanley' plum in 1982. (Dashed line represents ideal tolerance levels, 13%‘solub1e solids and 13 lbs. softness, for harvest. Black arrows indicate optimal time of harvest and dashed arrows represent actual 1982 harvest.) e—————~‘ sauwBSdusamISMMHmshuax c————e '4 153 um: “0 “"3 um: HARVESTandDAYSCXNINDONIEI Figure 36' Figure 37. 154 The effects of time of harvest and length of conditioning period on soluble solids and flesh softness readings of 4. orchards (Southwest Michigan area) of 'Stanley' plum in 1932. (Dashed line represents ideal tolerance levels for harvest, 13% soluble solids and 13 lbs. soft- ness. Black arrows indicate optimul time of harvest and dashed arrows represent actual 1982 harvest.) e—--O Sohblo Bolda and Sonnets hdex o——o 155 SOLUBLE SOLIDS AND FLESH SOFTENNG - 1982 M I O I lllpllllll l 35713571357135713571357 ° N20 N2 ens size 912 HARVEST and DAYS CONDITIONNG Figure 37 156 The dashed arrows indicate the actual time the grower harvested. In one orchard (H) from.the Southwest area and in three orchards (a, s and c) from the Grand Rapids area, growers harvested before plums reached these tolerances and likely sacrificed quality for earliness, filling the market with hard, astringent and unsweet fruit. In a fifth.participating orchard from the Grand Rapids area (data not shown) the grower picked early also, but because be harvested tagged research trees, data are not available. However, he did harvest when soluble solids were under 12%, firmness was higher than 11 lbs. (softness index under 9 lbs.), and fruit were extremely underripe. Orchard D. was an agri- ‘ cultural experiment station and the management was not under the same market pressure for earliness as a commercial orchard. This site was harvested slightly after attaining optimal maturity as the fruit went to a late speciality mar- ket at a local roadside operation. This decision on harvest timing is not generally reflective of commercial marketing. The model indicates that at least half of the cooperating growers in 1982 harvested.somewhat early. In 11 of the 12 cases (1981-1982) this model seems to have been operational for Inchigan 'Stanley' plums in selecting an optimal harvest date (Figures 35, 37 and 37). H. Section 8; Canning Studies 1. Fitting Losses Figures 38 and 39 diagram the pitting losses of halved plums during 1981. There were 3 major controlling factors, size, conditioning period and harvest date. The first graph (Figure 38) illustrates the size (weight) effects. Since size was not a predetermined variable, a correlation was used in this analysis. It was discovered that medium.sized plums were most suitable for clean pit separation due largely to their tailored fit in the standard cups equipped on the pitter. When a line was fitted to the pit-loss data of the 16 orchard~ harvest combinations, 52 grams in weight was projected as the ideal plum.size. When plums' weights were above or below this ideal size, pitting losses increased in a linear fashion. The correlation has an r value of 0.73 and is highly significant. The majority of poor performing plums were in the heavier ranges, which was advantageous as most orchards producing large plums (ever 40 grams) would be more economically suited to the fresh market. Harvest and conditioning treatments regulated pitting losses to a greater degree than sizing. These treatments are represented in Figure 39 where the means are pooled over 157 Figure 38. 158 A scatter diagram and linear regression showing the effects of size (weight) of 'Stanley' plums on the weight losses resulting. from mechanical pitting in 1981. (Points are weight differences from.32 grams and the line is fitted to the 16 points, each representing an orchard x harvest combination. The r value is a correlation coefficient significant at a 1% alpha level.) WEIGHT DIFFERENCE FROM 32 g. A N I .5 uni 9 c-l 0.03 NI ms: to.“ I; 159 STANLEY PLUM DATA - 1981 EEEECT OF SIZE ON PTI'TING- LOSS ,/ // ./ / e/ / / e a '/ 0 / / O / e { e / e /e 1 1 l l 1 I 1o - 11 12 13 14 ’ 96 FITTING LOSS Figure 38 15 160 Figure 39. The effects of length of a 20°C conditioning period and the date of harvest on the percentage weight loss chae to mechanical pitting of 'Stanley' plums in 1981. s PITTNG L088 -PLUM HALVESJ *17 16 15 14 13 12 10 161 STANLEY ELuMEn‘nNo LOSSES - 1931 U HARVESTS O-1-m27 ' O-2I-SEPT.3 s-a-SEP‘I'.10.'_ _ no4-SEPT.17 i 162 storage and location. Regardless of harvest, plums which were conditioned less than two days were subject to minimal pitting losses of less than 10.5iL While there was no significant increase in pitting losses for up to two days of conditioning, beyond two days of conditioning, pitting loss increased significantly. Later harvests tanded to have more pitting debri at the later conditioning treatments. After four days conditioning, the last two harvests were significantly higher in pitting loss than the first two. Thus, pitting losses were minimized by periods of up to four days for the earlier harvests, but for only two days for the later harvests. Since fruit were more advanced in maturity at the later harvests, this would allow for high quality fruit to be canned without increasing the conditioning treatment. With less mature fruits however, this benefitial conditioning treatment could be stretched up to four days without a heavy loss in tonnage resulting from large pitting debris. warm The effect of various treatmmnts on drained weights is presented in Figure 40. As with pitting loss, the major influencing factors were harvest and conditioning period. The harvest data is illustrated in the first graph (Figure 40-A). The four orchards were nearly parallel with respect to conditioning and the data are pooled over storage and location. With.few exceptions increasing conditioning time lowered the drained weight values. Fbr all orchards the SiX‘ 163 .Hmma :4 nsoflo .heaosom. no magmas; oeoaaoo on» so coco uue>aen on: ocaaeo woaooaaaoooo Doom no numoea no mucouue one .83 5 mafia Leases? oo «anode: 3598 23 so mason no season one pme>od£ no coco Ho noochme one once easwfim .doo enough 164 moo cos <3 menowrm 0 ea“ ._.< owzghazoo m>¢<2 o v a o the 93 To an; . . . . . q . can a 1 / UO- ‘0‘ . .eete: so a _ .. 4 3. o. g .. 1 1 one \ a o C :25: 1a . 1 _ 4 ie 1 co... e/e a e . :25: 1 VA L 4 1 con 4 a . c SESOe e a a 3 .9 o 2233 Opxa 1. o l a Yea-sORYQ 1 Op 0 a; 1‘ \ < 93.3.94 thQ .0 ”Basis: m e < om... 3023 9.265260 ass gets: 302E «acts: (5) .LHoIaM aamvsa 5o. 1 3.3.. 8225 .._o carom; 322mm 165 day conditioning treatment was significantly different than the O and 2 day treatment. Advances in ripening brought on by later harvest and increased conditioning reduced drained weights. High drained weights are usually indicative of firmer, more compact fruits, often with better'appearance. Low drained weight fruits are often softer and more ragged. Decreased drained weights occurred with increasing maturity due to the cell wall breakdown accompanying ripening. The added solubility of pectic substances could permit their movement into- the juice and result in lower drained weights. When the flesh is soft there could also be an added physical separation of small parts of the solid fraction into the liquid. Finally, the os- motic pressure of the syrup, which is more concentrated than cell solute, creates an osmotic gradient which draws plum cell solute out, also reducing weight. a correlation coefficient was determined for drained weight vs. overall quality, as judged by taste panels testing the canned.product. Means of the 16 harvest-conditioning combinations were compared, however due to an overripening response in the extrame conditioning treatment of the last harvest, only the first 15 were run. Drained weight was found to negatively correlate with the overall quality rating by the taste panels of the canned product. A line fitted to the points is presented in Figure 41. The correlation coefficient was highly significant. Accordingly, the panelists have Figure 41. 166 A scatter diagram and linear regression showing the relationship between drained weight and quality as determined by taste panels of 'Stanley' plum.in 1981. (The line is fitted to 16 points, each representing a harvest x conditioning treatment pooled over location.) 167 Correlation of Drained Weight with Quality ' 320 ' 310 m . \ . 3 '\ El ‘ \\ r a -0.657 \ 8- '\ z . \ . ' 3 300 \\ u. \' o \ . . \ '5 ‘ ' Q \\ m C 290 ‘\ z \ Lu . \ \ z 2 \ m \ c: . \ . \ 280 . 270 . '30 4o 50 so QUAUTYINDEX Figure 41 168 displayed an appreciation for improvaments in fruit quality with ripening despite the textural integrity and appearance improvement which accompanied high drained weight fruits. This should present a dilemma to canners. Higher drained weights are considered to be a favorable factor in canning economics because fruit that can maintain a minimum legal drained weight requires a smaller initial canning weight. Fruit that have low drained weights have lost weight in the can and must be packed at higher volumes to insure that they remain above the legal standards. Since high drained weights correspond to lower quality, there is'a clear trade off to be made in the economic benefit of maintaining initial canning weight and the economic drawback of selling less than optimal quality fruit. 3. Taste Panels on Canned Fruit Figures 42 and 43 display the results of the canned product taste panels. The data in the two graphs are the same but arranged differently for ease of interpretation. Figure 42 clearly illustrates quality changes as time pro- gresses through the succeeding harvests and conditioning periods. The early harvests (1st and 2nd) show general increases in quality with more conditioning. The last har- vest shows a decline with more conditioning probably due to overripening. The 3rd harvest is a compromise trend between Figure 42. The effects of time of harvest and length of 20°C conditioning period on the quality evalu- ation of canned, pitted 'Stanley' plums as determined by a taste panel in 1981. 170 ' CANNED PLUM TASTE PANELS - 1981 Harvest and Conditioning Effects . Quality Index 65!— G O P (I (I 8 o 01 T I I .5 o . I 35" 301 1 / Isd hsd L 0" 4L .. I l lAII l l___ll I. l4. l 02 46024602460246 2 3 4 Harvest and Days After Harvest Figure 42. 171 Figure 43. The effects of time of harvest and length of 20°C conditioning period on the quality eval- .uation of canned, pitted 'Stanley' plums as determined by a taste panel in 1981. Quality Index 1'72 CANNED PLUM TASTE PANELS '- 1961 Harvest and Conditioning Effects 65 60 55 00 O A Of .5 O (a) Cl 03. .o. 173 the first and last harvests. While there were no signif- icant differences with extended conditioning periods, maximum.quality was obtained at a midprange conditioning treatment (4 days). These trends are similar in nature to those of the fresh market panels as illustrated in Figure 28. LSD mean separation provides at least one major quality difference between the highest and lowest rated fruit within each harvest, except for the third harvest. . The interaction between harvest and conditioning is so in- fluential that a discussion about harvest effects in themselves is incomplete. Given any harvest, quality can be modified to a high rating by altering the conditioning time. A look at Figure 43 gives a clearer idea of the mean separation as all points are within the same time frame. At the first and second harvest, the six day conditioning treatment is signif- icantly greater than the three other conditioning treatments. By the 3rd harvest, while four and six days conditioning still had produced superior fruit, the ripening on the tree brought up the quality rating of the shorter conditioned fruit (0 and 2 days) to values high enough that added conditioning could not significantly improve quality. By final harvest the situation had reversed from.the earlier harvests, and tree ripe fruit were superior to all conditioned treatments. The non-condi- tioned fruits (0 days) were significantly greater than six or two days, but not four days. 174 The relationship between conditioning and.maturity at harvest is much.more useful in the canned product than in the fresh. Because the conditioning period necessary for development of'optimal fruit quality attributes can be controlled by the fruit handler, it use as a ripening regulator is important. This scenario presents another dilemma to canners. If the fruits are harvested early and conditioning is nedessary for full ripening, there will be considerable gain in the pit loss percentages as shown in Figure 39. Thus weight loss will be sacrificed for quality. If later harvested fruits are used, there is a less clear cut distinction as to the ideal condition- ing time. From.Figure 45 it appears that tree ripe fruit at 4th harvest and minimal conditioning performed the best of the later harvested fruit. Furthermore, this fruit would.have had very low pit losses from.Figure 39. This then suggests that fruit ripened well on the tree and immediately pitted has a small qualitative and quantitative advantage over all other treatments. 4. Tolerances for Canned Fruit The setting of tolerances for canned fruit is more dif- ficult than with the fresh market product, for two simple reasons: 1) processing alters the nature of the fruit from its original condition (forced sweetening and softening); 2) there are rapid changes in quality with conditioning that -175 cannot be easily predicted from the orchard condition. Nevertheless, it was found that quality of the canned . product showed important correlations with two main parame- ters, color and sweetness (Table 5). There was a highly significant correlation to quality with color scores within the panel and with absorbance readings from.the color index. Fruit with CD readings ran- ging from 0.86 to 1.43 had quality ratings 13%?higher than the mean of all quality ratings, and 30.4% higher than any fruit whose OD readings were outside that range. The observation that quality improvements correlate well with color absorbance in the canned.product but not in the fresh plum seems contradictory; however, closer examination reveals sound reasons for this occurance. In the fresh fruit taste panel, skin color is similar in most treatments. (The exception was fruits from.the earliest harvests and conditioning treatments which still had an observable green tinge.) During canning, the cooking of the fruit gives a purple-red tone to the flesh and syrup from.the diffusion of the anthocyanin pigment out of the skin. Thus the intense pigmentation which is a deep purple in the skin of the fresh product becomes "thinned out" in canning and differences became apparent so that quality ratings of the canned product correlated positively with both; 1) the color rating of the same taste panels, and 2) the absorbance of the TABLE 5 -176 Canned Taste Panel Correlations -1981 Correlation r Value Slgnifl- No. Of cance 1 Means QUALITY/coma .762 * 4* 16 (Panel Ratings) QUALITY/COLOR .557 it 31(- 15 (Absorbance) QUALITY ISWEETNESS .786 _ 6? ¥ 16 (Panel Ratings) QUALITY/SOLUBLE SOLIDS .462 ns 15 The above correlations were determined from the base of 16 harvest-conditioning treatments pooled over location. Since harvest and conditioning were the most influencing variables, this s‘cheme was chosen. were accompanied by a low quality score, so in the case of quality/absorbance and quality/soluble solids correlations, only 15 of the 16 means were utilized in order to maximize the linearity of the reaponses. 1. us 3 Significant at 1% level 3 Not significant ns Advances in final indices 177 fresh product. likewise there was a highly significant correlation of. quality with sweetness values but not with soluble solids readings. This later correlation was only realized at an alpha level of 8.7% rather than the 5% necessary for significance. Nevertheless, the quality to sweetness correlation does show a significant relation to the perception of sweetness and the ultimate quality. Since it has been shown that drained weights and accompanying cell solute concentrations change with conditioning and harvest treat- ments, perhaps an explanation exists here for the correlative significance between quality and sweetness, but non-signif- icance between quality and soluble solids. If fruits of the earlier harvests absorbed some of the 20% glucose syrup, they were likely to be judged sweeter and consequently of higher quality, reinforcing the quality- sweetness correlation. However, since those same fruits that were artifically sweetened had low soluble solids levels, the quality-soluble solids correlation would have a looser fit. The relative importance of both color and sweetness both tend to further the recommendation that optimal quality can be best obtained with advanced ripening on the tree. Since both of these parameters increase with fruits on the tree, the selection of a later harvest date would be more - 178 advantageous than dealing with somewhat uncertain changes to be regulated with conditioning. Therefore recommenda- tions for optimal fruit for canning would be along the following lines: 1) Color (O.D.) values 0.85 - 1.40; 2) Soluble solids readings l3 - 14% or higher. 5. Storagg §£fects Evaluated on Canned Fruit - 1980 In 1980 storage tests were evaluated with canned fruit. The samples were conditioned for 6 days, unforunately eliminating any avaluation of conditioning or storage- conditioning interactions. Another deficiency in the experi- mental design was a lack of an "overall quality” rating within the panel evaluation. nevertheless, despite these two limiting factors, some interesting trends due to storage can be extracted from.the data. The results of the panel are presented in Tablo 6. The trends were the following: 1) texture became firmer with extended storage; 2) flavor strength and off flavor dropped; 3) tartness and color were fairly stable throughout the various storage periods. The general trend was for no quality improvements with storage, unless one could arbitrarly consider firmer fruit to be of higher quality. However, no such correlation existed in the 1981 data with canned fruit. What is impressive about the panel data however, is that it parallels some of the trends of the indices. Firmness in both panel and index dropped at the second storage period 179 Table 6 The Effects of Storage on the Results of gality usgssgnt by Taste Panels - gagged Elm. 12m Taste Component . Length of Storage Period 0 Weeks 2 looks 4 Weeks 1% 1. Texture 30.1" 1 29°1a 59.51, 76‘5c 2. Flavor Strength 54-0. ‘ 51.8.. 52.5at 44.6.0 :5. Off Flavor 40.2‘ 43. 2‘}, 50.01, 34. 4a 4. Tartness ' 3.5.0,L . 33.4, 36.4,EL 30.4‘ 5. Flavor Acceptability 55.71, 50.91, 40.43 56.8b 6. Color 59.3; 32.4‘ 55.3" 51.0. The effects of storage time on individual components of the taste panel evaluations for canned, pitted 'Stanley' plums in 19%. All values are the storage effects pooled over location, harvest and ethylene treatments. Conditioning was six days for all treatments before canning. Least significant differences (LSD's) indicated by different letters following the values. Calculated at the 5% level .180 and climbed at four and six weeks (Figure llB,:mean of the 1980 graph). This complimented an overall.firmirg trend _that was observable in longer stored fruit. The strongest drop in panel tartness ratings also accompanied the major drop in the acidity index at the sixth week (Figure 15). Color showed dropping trends in both panel and absorbance index (Figure 168). 6. Tests with the Hunter Color meter In 1980 all the skin side of halved plums were analyzed on the Hunter Color Meter. There were no significant dif- ferences with respect to harvest, storage or ethylene treat- ment on the three scales, L, A and B. W h Iaturation Indic es Selection of a proper harvest date was by far the most important factor in this research that influenced ultimate plum.quality for the fresh.market or processing. It was found that from.a handful of traditional harvest indicators, the standbys of flesh firmness and soluble solids proved to be the most revealing of changes in plum.maturation. Debate surfaces in the literature as to the one most desirable.index. lhile some researchers opt for flesh firmness (IS, 17, 18, 51, 52), others stress some level of soluble solids should be incorporated into quality assessment (9, lo, 47). Since-both of these indicators are accessable and useful to growers in assessing maturity, a compromise of both parameters should be used for Michigan's 'Stanley' plum crop. The use of either color or acidity presents problems to fresh market quality assessment. Skin color changes (extractable pigments) are an ineffective tool. While rapid changes in OD readings might mildly correspond with changes in plum.quality, the bulk of the 0D readings do not reflect any qualitative color change porceptablo by the consumer. 181 182 Color changes visible to the eye can only distinguish very immature fruit from.slightly immature. The visual change of flesh color from yellow green to amber has been discussed in two reports (10, 65) and appears applicable to 'Stanloy' fruit but awaits development of a reliable physical measure or color chart for research and implementation. Acidity, an index rarely prescribed in the literature, was found to be unapplicable to 'Stanley‘ plums, largely because of seasonal variation and a low correlation with quality. While soluble solid - acid ratios are suggested as a potential index in one report (10), the use of this ratio with 'Stanloy' was less effective than soluble solids readings alone. This supports the view of La Rosa (18) that it is of limited value. Both color and acid readings also suffer from.the use of complicated and time consuming instrumentation. I A high degree of seasonal variability in maturation and ripening was witnessed.in this three year study, and is sup- portive of previous reports (10, 18, 38, 48, 55). variations due to location were also pronounced. 8. Post Harvest Treatments The use of two postharvest treatments, 0°C storage (2, 4 and 6 weeks) and room temperature conditioning at 20°C (2, 4 and 6 days) advanced all maturity indicators (color, texture, pit removal, soluble solids and acidity). 183 The only exception to this was a drop in color readings (extractable pigments) with extended storage and.this may reflect pigment migration from the skin to the flesh. The most notable changes due to a postharvest treatment were: 1) flesh firmness decreases and color (anthocyanin pigment) increases with progressing conditioning periods. 2) acidity decreases with storage and conditioning, and color (anthocyanin pigment) decreases with storage. 3) small and largely non-significant soluble solids increases with both storage and conditioning. The increases in flesh firmness and stability of soluble solids readings with conditioning are in agreement with other research (18, 34, 48) concerning the postharvest changes in these parameters. The relatively stable levels in flesh firmness despite long storage as presented in Figures 11, 13 and 14 have also been reported previously (24). Despite significant changes with postharvest troammonts, har- vest date selection had considerably more influence in reg- ulating the degree of ripening. The general maintainenco of quality in plums at 0°C reported here coincides with the bulk of the literature (9, 18, 27, 44, 48) as plums retained quality 2 - 4 weeks in cold storage with a small incidence of internal browning occurring at six weeks storage. The abnormal ripening at 32°F (0%) as reported by Gerhardt et a1 (10) was not 184- witnessed in this report. While shrivelling problems are cited.in some of the literature (48, 52), this was not visible until the sixth week of storage. Four weeks storage had little damaging effect on fruit quality even in the later harvested 'Stanley' fruit. C. weight Changes _ weight improvements with.maturation were evident at the later harvests but were often erratic and unpredictable. Sampling indicated that weight losses could also occur and might be tied to environmental or physiological changes. In the majority of orchards, plum seemed to gain the greatest weight in the last week of fruit development prior to drop. In this time frame, increases of 1% per day were observed and echo the findings. of other reports (9, 11, 13, 52). However, the lack of any steady weight gains in several locations suggests that harvesting for optimal quality is Just as critical as harvesting for maximum.tonnage. The less of weight during storage agrees with Couey's research (8) where losses of about 5% were obtained with open storage. In 'Stanley' all of the weight loss was observed after the first storage period (2 weeks), and at extended storages (4-6 weeks) plum.weight losses stabilized. D. Ethylene Gassing Gassing of fruits with ethylene has produced signif- icant advancements in only two textural parameters, flesh 185 firmness and pit removal, both in the first two harvests (Figures 19 and 20). a trend toward increased.absorbance readings was witnessed but was not significant. Smith reported similar advances on another European variety, 'Monuch,’ with ethylene and acetylene gassing (43). Further- more, the use of ethephon, an ethylene generator, has also hastened flesh firmness loss and color gain in 'Early Italian! plums as observed by Proebsting et a1. (29), while other researchers have reported similar effects of ethephon on oriental plums (2, 12). Gassing increased the incidence of skin cracking in 'Stanley' plums. In addition gassing treatments had no effect on the quality of the canned product or on the pitting losses of halved plums. Gassing is not recommended for either the ripening of fresh market fruit or for the pro-treatment of processed fruit. E. Ethylene and 092 Production Emhylene production of plums at harvest was a function of harvest date. This was observed in 3 years with two ethylene monitoring systems. There appeared to be a clear ethylene climacteric of the fruits in the open system and while this was paralleled in the closed system, it was confounded by the accumulation of ethylene. a respiratory climacteric followed this burst of ethylene production in the non-stored fruits. This supports Abeles classification of the plum as a 186 climacteric fruit-(1). Short storage (2 weeks) enhanced or sustained ethylene production while longer storages (4-6 weeks) diminished it. It was suggested that this data supported a mechaniem of ethylene physiology as hypothized by Wing (54) with cucumber fruits. The elevated ethylene production in fruits of omm “:31 I: short storage may be the result of increased capacity of chilled tissues to make ACC, while the depressed ethylene production'ny fruits after lpng storage may be due.to the damaging of the ethylene generating system with.extended chilling temperatures (54). Increased production of ethylene was observed in closed.systems when fruits were subject to short chilling exposures (3 hours and 3 days). Ethylene production following chilling appeared to be dependent on both the chilling treatment and the level of fruit maturation. This advance in ethylene production in treated.plums further supports the hypothesis that ACC levels increase.with chilling. Such a hypothesis could also interpret findings of La Rosa (18) and Probesting et al. (28, 30) who witnessed ripening advances in fruits subject to cold storage treat- ments of one and two weeks. These advances could be tied to the accumulation of ACC during storage that was sufficient to generate enough _poststorage ethylene to initiate climacteric 18"] ripening responses. Smith (43) found that although ethylene gassing improved ripening of fruits after storage for '7 or 14 days, a higher proportion of ungassed fruit ripened after 14 days compared to 7. If ACC accus- ulatod consistantly .under this limited chilling, then this could explain a more complete ripening response in the ungassed fruit chilled for a longer period. Furthermore when Smith (43) gassed fruit with high concentrations of ethylene while in 31°F (-O.4°C) storage there were no effects. Chilling temperatures have stimulated ethylene evolu- tion in grapefruit, sweet oranges and avocados (7). Research on 'Boss' 'poars has indicated that chilling periods of sov-‘ oral days at 5°C promote earlier and greater ethylene production than at room temperature (37). In addition 'Bartlett' pears have been shown to ripen prematurely with artifically con- trolled warm days and chilling night temperatures (53). Both ' ethylene and 002 evolution occurred; earlier in chilled samples than in non-chilled controls (53). The increased ethylene production in plum suggests that the system may be similar to peers and part of a natural ripening mechanism. 602 production in plums after cold storage- appeared to be influenced by: 1) normal respiratory climacteric; 2) catabolism of respiratory intermediates that have accum- ulated during storage. it extended storage there was a downward trend in C02 production with no recovery suggesting 188 a build up of intermediates had occured along with a' depletion of substrate. however, .in some cases with short storages the fall in C0 production was followed by a re- 2 covery, suggesting normal respiration occurred after the catabolism of built up intermediates.) These trends appear to fit a pattern of respiration as hypothesized by Lyons (21) who're respiratory intermediates are built up due to increased energies of activation in membrane bound enzyme system. Furthermore, plums respond favorably to intermittent warming treatments (42, 45) indicating that a period of active metabol- ism may have the effect of reducing the buildup of toxic in- termediates and thus ameliorating chilling injury. While other hypotheses for a chilling response exist, the Lyons (21) hypothesis seems most applicable to the data. These patterns tend to compliment the work of Uota (49) (working with Japanese plums) who was unable to obtain strong respiratory increases with high levels of ethylene and cool temperatures (35-55°F, 1.7-12.s°c). Total ethylene and respiratory increases with high levels of ethylene and cool tomoraturos, and chilling temperatures inhibit respiratory action oven in the presence of ethylene (49). Uota was able to obtain respiratory increases in plum after ethylene gassing at high concentrations and warm temperatures (70 and 90°F, 21.1 and 32.2°C), and was also able to hasten the initiation of the respiratory climacteric by about one day (49). 189 F. Fresh Fruit Taste Pan_o_l_s_ Fresh fruit taste panels revealed strong interactions between harvest and conditioning and harvest and location. it a given location fruits must be harvested at the proper time for maximal quality. Using this framework, correlations were drawn betwoen quality as determined by taste panels . and various indices. Flesh, fineness, soluble solids, and a modified log function of ethylene evolution were most significantly linked. G. Iodoling for Ethylene, Soluble Solids and Flesh Firmnesg The use of closed systems for measuring ethylene showed promise forfestimating the optimal harvest date in its initial year of testing. The rates of evolution had strong variations between both harvest dates and locations. Favor- able results have been attained using such monitoring system with apples (Dilley, D. 3., personal communication) and pears (Iitchell', F. 6., personal communication). Considering the results of the taste panels and ethylene ' involvement in ripening, a harvest model was designed using two traditional parameters, soluble solids and firmness, along with ethylene. Tolerances were established utilizing changes in harvested fruit as indicators of when to harvest the fruit on the tree. Lovels of 131 soluble solids, 7 lbs. flesh firmness and 2 ul/kg/hr of ethylene were set as those- harvest indicators in the conditioned fruit._ ' 190 The soluble solids and f1esh.firmness tolerances were different from.recommendations of other research. The sweetness levels were somewhat lower than those recommended for western plans (9, l0). Lower light levels and shorter growing seasons in the East are often responsible for this divergence in the soluble solids of many fruit crops. Firmness levels were lower than the 15-20 lbs. previously recommended for Michigan 'Stanleys' (17), but considering the different techniques in determing flesh firmness, this was difficult to compare. Flesh firmness and soluble solids showed considerable seasonal differences along with orchard variation as evidenced by the results of this report and others (9, 18, 47). . Upon testing in 1982, the model gave reliable assessments of optimal harvest dates with respect to the soluble solids and firmness tolerances. The ethylene tolerance though, failed to be workable in a few locations. Nevertheless, auxillary experiments indicate that exposing fruits to some chilling treatment may not only facilitate the use of the ethylene index but also enable growers to get an earlier warning of when their crop will ripen. Continuing research on this matter is recommended. 191 mamas: Results of the canning studies produced several variables to consider in determing harvest and postharvest treatments of plums; drained weights, pitting losses and taste panel evaluations. Fitting losses were modulated by size, harvest and conditioning. Conditioning was the most dominant factor followed by harvest and size. The sizing relationship, though minor, was previously suggested by Cargill et al. (4). The selection of medium sized plums however, was instrumental fer proper alignment of the pit in the cup, and considerably roduced the fracture of pits which leaves undesirable fragilents in the can. Drained ‘ weights were found to be “negatively correlated with taste panel quality. Extended storage appeared to have no benefit on the quality of the canned product and coincides with the conclusions of La Rosa (18), while diverging somewhat from the storage-induced quality improvements reported by ‘Proebsting et al. (28, 30). Rather than being influenced by storage, quality of the canned product was most strongly tied to the conditioning treatments, and particularly interwoven with the harvest- conditioning combination. By properly conditioning fruits of any given harvest, fruit can be brought up to a high quality level. This added conditioning however, produces an 192 increase in pit losses-so the canning of fruits from later harvests directly after picking presents the optimal tradeoff between these two factors. However, when market, or processor pressures force the canning of less mature fruit, the proper conditioning period is mandatory for high quality. Tolerances for canning are as r6110": 1) minimum of 13%soluble solids; 2) minimum.of 0.85 O.D. units when anthocyanin extractions (1.3 cm2 skin tissue/lo ml of 10$ oxalic acid solution) are read at 515 nm on a spectophotometer. These two indices were recommended as they showed a correlation to canned.plum quality._ The basic problems with pitting of 'Stanley' plums are engineering difficulties regarding proper sizing and alignment of the plum.into the cup to minimize pit fragments. If these problems can be solved, proper postharvest treatment will ensure a minimum.pitting weight loss to the processor. I. Conclusion Determination of the best harvest date and the ideal postharvest treatments for Michigan 'Stanley' plums is a complex.issue that frequently stretches beyond the borders of postharvest physiology. Iany factors face the grower from the cultural, environmental and managerial problems in the orchard to the logistical and economic pressures of the marketplace. when these factors are interwoven to the results of this thesis, they can modify the application of the conclusions and recommendations. The findings of this 3 year study are thought to be representative of the mainstream of 193 the lichigan plum industry, but their interpretation falls within a wide variety of specific cultural-marketing situ- ations, each demanding its own particular application. The success in implementing the recomendations of this research lies ultimately in the search for higher quality by our plum producers. LITERATURE CITED 1. Abeles, F. B. 1973. Rt lens in Plant Biology. Academic Press p. 6 — - 2. Blemmaert, L, Theron, T. and Steenkamp, J. 1975 Earlier and more uniform ripening of 'Santa Rosa' plums using ethephon. The Deciduous Fruit Grower. 25(10): 267-271. 3° 311.8, Se Pa and 311.8, Es As 1965e Ethylene action and the ripening of fruits. Science. 148: 1190-1196. 4. Cargill, B. F., Barton, 0. 1..., Cash, J’. N. and Burns H. H. 1980. Mechanical pitting and post-harvest treatments of 'Stanley' plums. Transactions of the American Soceity of Agricultural mgineers. 23(5): 1101-1104. 5e 0090318, “0 Jo “d MOM, Be A; 1957s 3:.ct of ' ' Bruising injury and storage temperature upon decay and discoloration of fresh, Idaho-grown Italian prunes en the New York City market. U. S. Agr. Res. Serv. Plant Disease Reporter. 41: 491-492. 6. Claypool, L. 1. and Kilbuck, J. 1958. The influence of maturity of interior valley French prunes on the yield and quality of the dried product. Proce more SOCe Harte Sci. 68: 77-85e 7e COOP", W. Ce, mm.aang Ge Keg Waldon, 8e 3e 1969e Ethylene evolution stimulated by chilling in citrus and Persea Sp. Plant Physiology. 44: 1194-1196. 8. Couey, H. II. 1960. mfects of temperature and modified atmosphere on the storage life, ripening behavior, and dessert quality of Eldorado plums. Proc. Amer. SOCe Harte Sol. 75: 207-215. 9.. Fisher, D. V. 1940. A threeyear study of maturity indices for harvesting Italian prunes. Proc. Amer. SOC. Harte Sci. 37: 183-186. 10. Gerhardt, F. and mglish, H. 1945. Ripening of the Italian prune as related to maturity and storage. Proc. Amer. Sec. Hort. Sci. 62: 205-209. ‘ 194 ll. 12. 513. 14. 15. 16. 17. 18. 19. 195 G'I'h‘rdt, Fe, Mgllah, He ‘m Smith. 3. 1942s Th. influence of maturity and storage temperature on the ripening behavior and dessert quality of the Italian prune. Proc. Amer. Soc. Hort. Sci. 42: 247-257. Guelfat-Reich, S. and Ben-Airs, R. 1975. A comparison of the ripening effects of ethephon on Japanese plums and apricots. Colloques Internationaux du Centre National de la Recherche Scientifique. Me 238‘ 105-108s Hartman, R. 1926. Studies relating to the harvesting of Italian prunes for canning and fresh fruit shipment. Ore. Agr. Exp. Sta. Cir. 75. Hulme, A. C. 1970. The Biochemist of Fruits and their Products. Academic Press. V51. 17 p.545. Jones, A. L. and Burton, C. 1973. Heat and Fungicide treatments to control postharvest brown rot of stone fruits. Plant Disease Reporter. 57: 62-66. Kenworthy, A. L. 1972. Studies on prune maturity indices. Report for the Michigan Processors Raw Products Conference. Horticulture Department, lichigan State university. Kenworthy, As Le, L‘ 808‘, Jo As md B‘drord, Ce Le 1971. Maturity indices of Stanley and Bluefre plums for fresh market and conning. Mdmeographed Report, Horticulture and Fbod Science Departments, Michigan State University. La Rosa, J; 1972. laturity, conditioning and canning studies on Hichigan grown plums. Iaster's Thesis, lichigan State university. Looney, N. 3., HoGlasson, W. B. and Coombe, B. G. 1974 Control of fruit ripening in peach, frunus Eersica: Action of succinic acid-2,2-dimethylhydrazi e an (2-chloroethyl) phosphonic acid. Aust. Jour. Plant Phys. 1:' 77-86. Lutz, J. M. and Hardenburg, R. E. 1977. The Commercial Storage of Fruits, Vegetables and Florist and nursery Stocks. USDA Agr. Handbook No. 66, pp. 36-37. 21s 22. . 23. 24.1 . 25-. 27.. 28. 29. 196 Lyons, J. I. 1973.. Chilling Injury in Plants. Annual Review of Plant Physiology. 24: 445-466. Matteo, A. K., Baker, J. E., Chalutz, EL and Lieberman, H. 1977. Effect of temperature on the ethylene synthesizing systems in apple, tomato and enicil- lium.di itatum. Plant and Cell Physiology. : HOBO“. De I., outh‘Cd, Re Log Jomaon, As As md COOtO, G. G. 1969. The prediction of maturity in plums for prune production. Aust. Jour. of Ex. Ag. and mm Husbmdrys 9 : 648-654s Mitchell, F. 0., Mayor, Gtand Bsede, R. H. 1976. Postharvest performance of shipping stone fruits. university of California Cooperative Extension Industry Report. utOhOIJ.’ Fe Ge, “’01., Ge, M99 Es Cs “6. CO‘tOS, . I. I. 1974. Cold storage effects on fresh market peaches, nectarines and.p1ums: using low temper- atures to delay internal breakdown. California Agriculture. 28(10): 13-14. Paunovic, S. A., Jankovic, R. and Ogasanovic, D. 1978 Effect of Ethephon on the flower and fruit abscissicn of Prunus domestics E. Cv. Pozegaca. Acta Horti- culture. (Growth regulators in fruit production) 80: 291-295 Pentzer, W. T. and Allen, F.‘I. 1944. Ripening and breakdown of“plums as influenced by storage temperature. Proc. Amer. Soc. Hort. Sci. 44: 148-156. Proebsting, E; L., Jr., Carter, 0. H..and Mills, H. H. 1974. Interaction of low temperature storage and maturity on quality of 'Early Italian' prunes. Journal Amer. Soc. Hort. Sci. 99(2): 117-121. Proebsting. EB In, Jr. and Mills, 8. H. 1969. Effects of 2-ch1orethane phosphonic acid and its interaction with gibberellic acid on quality of 'Early Italian' prunes. Jour. Amer. Soc. Hort. Sci. 94: 443-446. 31. 32. 33. 34. 35. 38. 39. 197 Proebsting, EL L., Jr. and Mills, EL H. 1971 Ripening of 'Ehrly Italian' prunes improved by low temper- ature exposure. HortSoience. 6(4):.410-411 . Ramsey, R. J; 1916.‘ The handling and shipping of fresh cherries and.prunes from the Willamette valley. U. S. D. A. Bulletin Nb. 331. Roberts, K. 0. 1964. laturity of French prunes in relation to time of harvest. Ore. St. University I. S. Thesis. Robinson, I. B..and Holgate, K. C. 1949. How ripe is a plums new York State, Geneva Experiment Station FIrm.Research Reports. July 1949, p. 7. Ryall, A. L. 1935. Certain physiological effects of carbon dioxide treatment of plums. Proc. Am. 800. Harts 361s 32: 164.169e Saleem, I. T., Rehman, R. and Hearst, R. R. 1970. Biochemical changes in p1um.fruit during develop- ment and ripening. Punjab Fruit Journal. 32(110/111): 23-29. Savic, s. and Stankovic, D. 1975. The effect of Ethrel on abscission layer formation in Pozegaca and Stanley plums. Jugoslovensko. 8(31/32): 133-138. srm0tm3, Be Me and Dillay, De Rs 1974e Induction of ethylene production in 'Bosc' pears by post- harvest cold stress. RbrtScience. 9(4): 336-338. gibtht, Sop ntChsll, Go and “701‘, Gs 1980s 0016. storing French prunes: a way to an Optimum harvest. (Results of twe'studies,'#l)' Ddamond/Sunsweet Rows. - Jun/Jul 1980, 16: 41-45. ' “ Sibbett, S., litchell, G. and Mayer, G. 1980. Cold storing French prunes: a way to an optimum.harvest. (Results of two studies, #2). Diamond/Sunsweet Hews. Jun/Jul 1980, 16: 46-48. Sive, A. and Reznitsky, D. 1972. The effect of control- led ahmosphere storage on 'Sagiv' Italian prune plums. Report of the Isreal Fruit Growers Associ- ation Cold Storage Research Laboratory. 41. 42. ‘ 43. 44. 450 46- 47s 43. 49.. 52. 198 Sive, A. and Resnizky, D. 1978. Extension of the storage life of 'Red Rosa' plums with controlled atmosphere storage. IV International Congress of Refrigeration Report. Smith, J. l. 1950. A Dual temperature method for the refrigerated carriage of plans. Journal of Hort. Science. 25: 132-144. Smith, 1.13. 1938. The artificial ripening of Monarch plums. Great Britian Food Investigation Board Report, 1938. pp. 165-169. Smith, V. BL 1940. Further observations on physiologi- cal breakdown in stored plums. Journal of Pomology. 18: 74-87. Smith, W. R. 1947. Control of low temperature injury in the Victoria plum. nature. 159: 541-542. Smith, I. H. 1967. The refrigerated storage of Victoria plums in low oxygen atmospheres. Jour. Hort. Sci. 42: 223-230. Tucker, L. R. 1931. Orchard variability in the maturing Italian prune. Proc. Amer. Soc. Rort. Sci. 28: 578-582. Tucker, L. R. and verner, L. 1933. Prune maturity and storage. Idaho Agr. Exp. Sta. Bul. 196. Uota, n. 1955. Effect of temperature and ethylene on evolution of carbon dioxide, ethylene, and other exidizable volatiles from three varieties of plmm. Proc. Amer. Soc. Hort. Sci. 65: 231-243. van der Plank, J. EL, and Davies, R. 1937. Temperature - cold injury curves of fruit. Journal of Pomology and Horticultural Science. 15: 226-247. . VOHCI" Ls, Kocm, We Jog Laney, Cs, “91.0, Do C. “d- Khmal, A. L. 1962. Internal browning of fresh Italian prunes. U. of Idaho Ag. Ezpt. Sta. Res. Bul. 56. Vincent , Ce Cs 3 Vomor, Ls md Blodgott , Es Cs 1929e Progress report of prune storage and maturity studies. Idaho Agr. EXp. Sta. Bul. no. 252. 55. 56. 57. 199 Rang, C. 2., Hellenthin, W; M. and Hansen, E. 1971. Effect of temperature on development of premature ripening in 'Bartlett' peans. Jour. Amer. Soc.~ Harte Sci. 96(1): 122-125e Rang, C. I; and.Adams, D. 0. 1980. Ethylene production by chilled‘cucumbers (Cucumis sativus Er)- Plant Physiology. 66: 841-843. westwood, H. N. 1970. Prune maturity. Mdmeographed Report, Oregon State University Horticulture Department. Wiley, R. C. 1953. Relation of fresh fruit quality factors to the canning quality of the Italian prune. th Th Thesis, Oregon State University. YCaSOr, Jo To, Fitch, Ls Be, Sibett, Gs Se, Tylar, R. H., Roncoroni, E. J. and Ramos, D. E. 1973. Prune maturity advancement with growth regulators. California Agriculture, Dec. 1973, p. 13. GENERAL REFERENCES Cruess, w. V. 1938. Commercial Fruit and Ve etable Pzgducts. MoGraw-EIII. Lopez, A. 1969. A Complete Course in Canning. The Canning Trade. 7111111711111)In“