L32“ ll: 1,: A»! 1.."- . .! vzfgy . . 3.3.... :3. :71. ..t. Tact F)! :: HIGAN STATE llllilllllfLHllll Illlll WIUHIHMIWIIIHIIUW 293 01019 2049 This is to certify that the thesis entitled OPTIMIZATION OF PROCESSING PARAMETERS AND STUDY OF THE PHYSICAL- CHEMICAL CHARACTERISTICS OF PLUM JUICE presented by TUNG-SUN CHANG has been accepted towards fulfillment of the requirements for MASTER degreein FOOD SCIENCE MGM/4 JER Y N. CASH Major professor Date—SW. 1 9 9 3 0-7639 MS U is an Affirmative Action/Equal Opportunity Institution LIBRARY Michigan State University PLACE IN RETURN BOX to remove We checkout from your record. TO AVOID FINES return on or before one due. DATEDUE DATE DUE DATE DUE MSU Ie An Affirmative ActIoNEquel Opportunlty Institution cMma-m OPTIMIZATION OF PROCESSING PARAMETERS AND STUDY OF THE PHYSICAL-CHEMICAL CHARACTERISTICS OF PLUM JUICE By Tung-Sun Chang A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Food Science and Human Nutrition 1993 ABSTRACT OPTIMIZATION OF PROCESSING PARAMETERS AND STUDY OF THE PHYSICAL-CHEMICAL CHARACTERISTICS OF PLUM JUICE By Tung-Sun Chang Five commercial pectinase enzymes were used with Stanley plums to determine which gave optimum juice yield and quality. Among these five enzymes, Clarex L at 0.2% concentration produced the best overall plum juice. After the best pectinase enzyme was identified six new plum varieties (Prunus domestica L.) selected from the MSU variety trials were used in conjuction with Clarex L enzyme for the production of plum juice. Each of the six varieties were processed into press- juice, enzyme-treated juice, High Temperature-Short Time (HTST)—unfined juice, fined juice and HTST-fined juice. Physical and chemical characteristics such as yield, clarity, soluble solids, pH, titratable acidity, Hunter color values, pectin content, total anthocyanin content and total phenolics were determined. The analytical results were combined with sensory evaluation results to aid in the selection of plums for further juice processing and development. Dedicated to Shaw-Tsu Chang, memory of my father, and Lee Chu Cheng, my mother, to whom I stand in debt for my education and knowledge ACKNOWLEDGEMENT Sincere gratitude is extended to Dr. Jerry N. Cash for his guidance and support as major professor, and for his patience and understanding throughout the research program. Grateful appreciation is also proffered to Dr. Jack Giacin (Packaging), Dr. Robert C. Herner (Horticulture) and Dr. Mark A. Uebersax (Food Science and Human Nutrition) for serving as my graduate committee. My deepest appreciation is extended to Dr. Nirmal K. Sinha for his support, guidance and technical expertise with this research. Finally, I would like to thank my brother, relatives and friends, for their continual love and support through the highs and the lows. iv TABLE OF CONTENTS LIST OF TABLES ....................................... VIII LIST OF FIGURES ......................................... x INTRODUCTION ............................................. 1 REVIEW OF LITERATURE........ ........................ 3 I. Plum Production and Utilization .................. 3 II. Plum JuiceOOOOOOOOO OOOOOOOOOOOOOOOOOOOO O .......... 5 A. Liquefaction of Raw Plums ....................... 5 The pectic substances............... ...... .....6 The pectic enzymes ............................ 8 Commercial pectic enzyme (Pectinase) ..... .....13 B. Clarification of the plum juice ................ 16 Enzymes for Clarification. O O O O O O O O O O O O O I O I O O O O 19 Fining agents ................ ........ ......... 21 Gelatin... ................... . .............. 21 Bentonite. O O O O O O O O O O O O O O O O 0 O O O O O O O O O O O O O O O O O 23 Silica sol. ................................. 23 otherSOOOOOOOOOO0......0.0.0.00000000000000024 Filtration .................................... 24 Heat treatment ................................ 26 MATERIALSANDMETRODS.. ................ ..............27 I. Plum.Samples. ............. ..... ................... 27 II. Commercial Enzymes for Plum Juice Extraction ....................................... 27 III. Plum Juice ...................................... 27 IV. Plum Juice Processing Conditions . . . ..... . . . . . . . 28 V. Analysis ........................................... 31 H............................. ..... ...............31 Soluble solid...................' ....... ............31 Titratable acidity.................................31 Color................ ..... .... .............. .. ..... 31 Sugar analysis.....................................32 a. HPLC ...... ............ ............ ..........34 b. YSI.........................................35 Turbidity of juice..... ...... ......................35 Total anthocyanins.................................36 Total phenolics..... .............. .................36 Browning...........................................37 Pectins......... ................... ...............38 a. Versene—Pectinase extraction of pectin......38 b. Colorimetric determination of galacturonic aCidOOOOOOOOOOOOOOOOOOO00....0.00.00.00.000038 VI. Sensory Evaluation of Plum Juice ............... 39 VII. Statistical Analysis ..... 40 RESULTS AND DISCUSSIONS..UH....“”....HH.....“”...41 EFFECT OF COMMERCIAL PECTINASES ON PLUM JUICE EXTRACTION AND ITS QUALITY...............................................41 Juice yield (% by weight)................................42 Juice clarity............... ....... ......................45 Color....................................................46 Soluble solids (Brix)....................................53 % Titratable acid as malic acid (TA).....................53 pH.......................................................57 Brix/Acid ratio..........................................57 Sugar concentration....... ....... ........................57 Total anthocyanins (TACYs)...............................60 Total phenolics.... ............... .......................61 Summary..................................................65 PHYSICO-CHEMICAL AND SENSORY CHARACTERISTICS OF PLUM JUICE FROM SELECTED PLUMS GROWN IN MICHIGAN.....................67 % Plum juice yield.......................................67 Plum juice clarity.......................................69 Soluble solids, titratable acid and Brix/Acid ratio......71 Color....................................................77 Sugars.................. ........ .........................84 Pectins................... ................ ...............87 vi Total anthocyanins ..................................... ..90 Total phenolics...................... ..... . ..... .........93 Sensory evaluation..................... ..... . ..... .......97 SUMMARY AND CONCLUSIONS . ........... . .............. . . 103 BIBLIOGRAPHY. .......................................... 106 vii Table 1 . Table 2. Table 3. Table 4. Table 5. Table 6. Table 7. Table 8. Table 9. Table 10. LIST OF TABLES Enzyme preparation, composition and optimum processing states for extraction trials on Stanley plums (1992) ........ O ..... 00...... 000000000000 .0029 Analysis sugar contents of the plum juice by enzymes and combination of YSI and HPLC..........33 Effects of enzymes on juice yield from Stanley plumOOOOOOOOOOOOOOOOOOOO0.0.0.0000....0000000000044 Effects of enzymes on juice clarity from Stanley plum................................. ....... .....48 Effects of enzymes on CDM value of plum juice....49 Effects of enzymes on Brix, pH, titratable acid and BriX/ACid ratio Of plum juiceOOOOOOOOOOOOOOO00.0.55 Effects of enzymes on sugar contents of plum juiCQOO ......... O... ...... O ...... .0... ........... 59 The effect of Clarex L on juice yield in selected six plum varieties...............................68 Turbidity, pectin content, total phenolics and total anthocyanins of plum juice made from selected plumvarieties...0.00.00.00.00.COO...0.0.00.0000070 The correlation coefficients between %transmittance and pectin content of plum juice made from selected plum varieties...............72 viii Table Table Table Table Table Table Table 11. 12. 13. 14. 15. 16. 17. Soluble solids, %malic acid, pH and Brix/Acid ratio of plum juice made from selected p1ums....74 Colors (CDM values) of juice made from selected plumSOOOOOOOOOOOOOOOOO0.0.0.0.0000...0.00.00.00.78 Sugars content of juices made from selected DIMSeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeoeeee085 The correlation coefficients between pectin content and total phenolics, brix, glucose, fructose, sucrose, Hunter 'a' and Hunter 'b' of plum.juices.....................................89 The correlation coefficients between Hunter CDM values and anthocyanins in plum juices..........94 Means of sensory attributes for six varieties plum juiceOOOOOO..OOOOOOOOOOOOOOOOOOOOO...0......0.0.99 Correlation coefficients between overall acceptance and color, sweetness, astringency, tartness and flavor preference of plum juice...101 Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure 9. LIST OF FIGURES (a) Fragment of a pectin molecule and points of attack by pectic enzymes. (b) Splitting of glycosidic bonds in pectin by hydrolysis (polygalacturonase) and by B-elimination (pectate lyase and pectin lyase)........................1O Clarification processes and particle size in disperSionOOOOOOOOOOOOOO0......0.0.0.0000...0.018 Theoretical mechanism of clarification with and Without gelatiDOOOOOOOOOOOOOOOO0.00.00.00.0000020 Flow chart of plum juice processing....... ..... 30 Effect of enzymes on juice yield from Stanley plumSOOOOO...OOOOOOOOOOOOOOOOOO0.00.00.00.0000043 Percent transmittance of juice treated with enzymeSOOOOOOOOOOOOOOOOOOIOOOOO0.0.0.... ....... 47 Relationship between juice clarity and Hunter 'L' value for Clarex L treated juice...... ..... ....51 Effects on color hue of plum juice.............52 Effect of enzymes on Brix of plum juice ........ 54 10. Effect of enzymes on titratable acid of plum jUiceOOOOOOOOOOOOOOOOOOOOOOOOO0.0000000000000056 Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure Figure 11. 12. 13. 15. 16. 17. 18. 19. 20. 21. 22. 23. Effect of enzyme concentration on Brix/Acid ratio 0f plum jUice.............. Total anthocyanins of juice treated with enzymes.................... ........ ... ......... 62 Effect of enzyme concentration on browning of plum jUice........ ..... . ............ . ......... 63 Relationship between browning and anthocyanins for Rapidase Press treated juice...............64 Effect of enzyme on total phenolics of plum juiceOOOOOOOOOOOOOOOOOO. 000000000000 00.0.0.0...66 Effect of Clarex L on soluble solids contents of plum juice.......OOOOOOOOOOOOOOOOOO0.0.0.0.0...75 Changes on Hunter L of plum juice .............. 79 Change of Hunter 'a' value in plum juice.......81 Effect on Hunter 'b' of juice made from selected PlumOOOOOOOO... ..... ......OOOOOOOOO0.00.0.0000082 Change in hue angle of juice made from selected Cultivars..............OOOOOOOO0.0.0.000000000083 Effect of processing conditions on total anthocyanins content of plum juice.............91 Changes in total phenolics content of plum jaiceOOOOOOOOI ....... 00...... ..... .... ......... 96 The suitable Brix/Acid ratio on plum juice for sensory evaluation. ......................0....98 INTRODUCT I ON Plums are grown in several areas of the United States and are considered to be a major fruit crop in some of these growing locations. The production of plums in Michigan is not as extensive as in some states, nevertheless, plums are important to the fruit industry in the state. Economically they represent a modest income for the growers and processors at a time in the harvest schedule when other crops are not available (i.e. after cherries and before apples). Also, 'with the active plum variety program presently underway at the MSU Northwest Horticulture Research Station there are very good possibilities for new cultivar introductions that 'will further enhance the viability of the plum industry. Presently, one of the major needs within the plum industry is development of new processed products, such as juices, paste, 'wine and jelly to utilize plums. The purpose of this study was to 8 a) investigate the effect of commercially available cell wall degrading enzymes such as Clarex L, Clarex ML, Rapidase Press, Rapidase C80L and Klerzyme L200, on yield and quality of plum juice. b) optimize processing conditions for plum juice production. 2 c) analyze plum juice made from plum cultivars grown in Michigan for physical, chemical and sensory chanmfimmistflxL REVIEW OF LITERATURE I. Plum Production and Utilization The term."pluml includes several species of Prunus. The most commonly grown species are P; domestica L; (the European plum) and P; salicina Lindl. (the Japanese plum). Most research on plums deal with these two species. Of minor importance as a source of edible fruits: P. maritima (beach plum), used for jelly and jam, is grown on the coast from Virginia to Canada; P. americana (De Soto and Hawkeye), grown in Connecticut , Montana, Colorado, Texas , and Florida; the wild goose plums (P. hortulana and P. mnnsoniana), also used for jams and jellies, are found in the Mississippi valley; and the Pacific or western plum, P. subcordata, native to California and Oregon (Childers, 1973; Magness, 1951 and Seelig, 1969), are grown in all states except.Alaska (weinberger, 1975). Michigan was the 3rd largest producer of plums in the nation in 1991 (Michigan Agricultural Statistics, 1992). The leading varieties grown in Michigan are the Italian purple plums, Blufre and Stanley. Stanley, which was used as the control in this study, is a large, partially freestone plum that has firm greenish-yellowish flesh with a dark blue-black outer skin. As indicated earlier, a number of varieties and selections of plums are 4 being tested in Michigan and several of these were used in this:naxwuoh. Plums are mainly used for fresh consumption at harvest but storability at refrigerated temperature is poor because of the soft texture and high moisture content. In Michigan, about 4,000 to 5,000 tons go for the fresh market, while the remainder of the crop (ranging from 2,000 to about 7,500 tons) is processed. The plum growers have a need for and a genuine interest in alternate outlets for new products. One such outlet may be the beverage industry. Since the mddel9803, packaged soft drink consumers have increasingly picked up on new, upscale or good-for—you beverages. Some of the most significant representatives include "New Age" drinks such as, Clearly Canadian, sports drink king, Gatorade, and the entire spectrum of fruit juices and drinks. The big winner in the New Age fountain has been juice, with juice consumption increasing approximately 10 percent in the last two years alone. A number of companies are beginning to gear up expressly for the juice business. Because of the popularity of Clearly Canadian, the trend in beverage flavors has begun to shift to more northern fruit flavors such as plum and raspberry (Kortbech-Olesen, 1991, Prince, 1992 and Sfiligoj, 1992a, 1992b, 1993a and 1993b). It looks like juices with plum flavor or plum juices may have a very bright future . II. Plum.Juice Previous research on plum juice production has examined various methods of extracting and clarifying the juice (Ismail et al., 1981; Ichas et al., 1976; Cejkova, 1977, Grinberg and Kolesnich-enko, 1979; Komiyama et al., 1977; Samsonova et al., 1982; Flaumenbaum.et al., 1986; Lion and WU, 1986 and Wani et al., 1990a and 1990b). As with many other juice products, the most promising process methods seem to involve the use of pectinases and clarifying agents. However, additional research is needed on the effectiveness of other enzymes in addition to pectinases on yield, turbidity and filterability of plum juice. This work is intended as an investigation of the effect of commercial pectinases effect on the qualities of plum juice, and processing conditions affecting the quality of plum juice. A. Liquefaction of raw plums Most plums contain very little free run juice so simple extraction procedures (i.e.. maceration and cold pressing) are not effective in producing good yields of high quality juice. A number of operations must be carried out, including heating of macerated pulp to inactive polyphenoloxidase (PPO) enzyme responsible for color loss of plum juice (Arnold, 1992 and Siddiq, 1993) and liquefaction of the heated macerate with pectinase enzyme. The Pectic Substances Pectic substances have been investigated from several points of view, and work has been done to define their relation to the metabolic changes which take place in fruits and vegetables during maturation and senescence, their relation to plant diseases, their use in the setting of jams and jellies, their use as emulsifiers and their importance in clarification or retention of "cloud" of juices. Pectin is the intracellular cement of cell-wall tissue occurring in fruits and succulent vegetables (Bailey, 1938). It is a polymer whose major building blocks are units of galacturonic acid linked by alpha-1,4 glycosidic linkages. The water-insoluble pectic material is usually referred to as protopectin. When the solubilized material retains most of its methyllgnmqmsandzflmmmsgelstuxknrcerUEUICKEMUtions,.it is commonly referred to as pectin. If all of the methyl groups are removed, the remaining polymer of galacturonic acid units is called pectic acid (Kertesz, 1951 and 1959, and Deuel and Stutz, 1958). The pectins extracted from most fruits under mild conditions usually have the degree of esterification (DE, % of galacturonic acid monomers which are methyl-esterified) of over 70 (Doesburg, 1965). The molecular weight of the soluble pectin and the extent of methylation of the -COOH 7 group are subject to large variation. Commercial pectins form colloidal solutions and usually 2/3-3/4 of the -COOH groups are methylated. Molecular weights of 50,000-250,000 have been reported for pectin, so that the polymer may contain several hundred units. However, it is not a homopolymer and has been found'o3thermnmods of Krop et al. (1974) for citrus juice and Ough et al. (1975) for red grape wine. At specified time, the juice sample was 36 shaken and 10 ml portions of samples were centrifuged for 10 minutes at 360 x g to remove pulp and coarse cloud particles. Percent transmittance was determined at 660 nm on a Milton Roy Spectronic-70 spectrophotometer (820 Linden Avenue, Rochester, NY 14625) with distilled water as blank. The percent transmittance was considered a measure for the cloudiness and duplicate runs were made for each sample. Total Anthocyanins Total ACY in the plum juice was measured spectrotometrically at 535 nm. A 5 ml sample of juice was mixed with 45 ml acidified ethanol (15 ml, 1.5N HCl+ 85 ml, 95% ethanol) left for 5 min. and filtered though a No. 2 Buchner funnel. The pH of the solvent was adjusted as required to obtain a final pH of 1.0 in the plum extract. The diluted extract was stored in the dark for two hours before absorbance measurement on the spectrophotometer (Milton Roy Spectronic-70, Rochester, NY). The total anthocyanin content was calculated with the aid of the appropriate volume, dilution factors and E(=98.2) values (Fuleki, T. et al. 1968a, 1968b; wrolstad, 1976; Francis, 1982). Total Phenolics The tannic acid concentration of each plum juice sample was determined by the method of Singleton and Rossi (1964). Tannic acid was used to assay the total phenolics. For the 37 preparation of the calibration curve, 0, 1, 2, 3, 5, and 10 mi aliquots of tannic acid stock solution (0.59 of dry tannic acid dissolved in 10 ml of ethanol and diluted to 100 ml volume with water) were pipetted into 100 m1 volumetric flasks, and diluted to volume with water. The tannic acid concentrations of these solutions were 0, 50, 100, 150, 250, and 500 mg/L. Analysis consisted of mixing 1 ml sample (or standard) with at least 60 ml of water in a 100 ml volumetric flask. Folin-Ciocalteu reagent, 5 Ed, was added and mixed. .After about 30 seconds 3 g of anhydrous NazCO3 in aqueous solution.(e.g. 15 ml of 20% solution) was added, and the contents of the flask made to volume. The absorbance was determined after 2 hours at 249C, using a 1 cm cell with the spectrophotometer set (Milton Roy, Rochester, NY) at a wavelength of 765 nm. The blank used for zero absorbance was water . Browning Tristimulus reflectance calorimetry (usually the measurement of Rd or Hunter values) has been used to follow the extent of enzymatic browning in juice (Smith and Cline, 1984) and apple slices (Ponting et al., 1972). For this study, the method and the time selected was according to Sapers et al. (1987). Juice samples were poured into a glass cylinder, and the "L" value was measured with a Hunter Color Difference meter (Model D25 DP-9000). The degree of 38 browning was expressed as the L value differences at times 0 and 60 min. .All analyses were carried out in duplicate. Pectins The procedure for extraction and colorimetric analyses of pectic substance followed was a combination of Mc Cready et al. (1952 a 1970) and Kintner et al. (1982). An versemedmctinaselbnuactioncifIkntin 10 mas of juice were mixed in a beaker for 5 minutes with 150 nu.95% ethanol. The sample was filtered and the ethanol containing the sugars was discarded. The pulp was washed twice with 75% ethanol then transferred to a 250 ml beaker. Cations were sequestered and the pectin deesterified with 100 ml of a 0.5% Versene solution at pH 11.5 (adjusted with 1N NaOH) for 30 min. The mixture was acidified to pH 5 with acetic acid and 0.19 of pectinase was added, stirred for one hour, diluted to 200 m1 and filtered. The first few milliliters of filtrate were discarded before collecting 2 mls of sample for analysis. B. (kflorflmnrictruermfluuiontnfGalmmwromszcid A 1 ml sample containing pectin was pipetted into a 15x180 mm Pyrex test tube and placed in ice-water bath for 5 minutes. Subsequently 6 ml H2804/ tetraborate solution (0.0125M solution of sodium tetraborate was prepared in concentrated sulfuric acid) was added to each tube in the ice 39 water and the tube was shaken carefully on vortex mixer. The mixture was heated in a 1009C water bath for precisely 5 min. and immediately placed in an ice-water bath to cool. Duplicate samples were developed by adding 0.1 ml 0.15% m- hydroxydiphenyl solution (in 0.5% sodium hydroxide) mixing and allowing to stand for at least 20 min. at room temperature to allow bubbles to dissipate (absorption values were stable for up to 1 hour). A.sample blank was prepared by replacing mrhydroxydiphenyl with 0.1 ml 0.5% NaOH, keeping all other additions and treatments similar. The sample blank absorbance was later subtracted from.the total absorbance to obtain the absorbance due to mrhydroxydiphenyl. Absorption measurements were taken at 520 nm using a Milton Roy Spectronic-70 spectrophotometer. A reagent blank containing 1 ml distilled water, 6 m1 Sulfuric acid/ tetraborate solution and 0.1 mi of 0.5% Sodium hydroxide was used to zero all instruments. VI. Sensory Evaluation Preliminary sensory trials were done with a limited number of panelist (8-10) from our lab to determine the optimum level of Brix for each of the juice samples. Then each of the samples was adjusted by sucrose, based on the preliminary trials, and samples were tested by a larger panel for, tartness, bitterness, color, flavor preference and acceptability using an unstructured 10 cm hedonic scale. Judges were asked to mark the horizontal scale at the point 40 that most closely corresponded to their judgment of the intensity of each attribute. These points were then measured in cm and translated into numerical values for statistical analysis. Each panel consisted of 40-45 panelists from the faculty, staff and students in the Food Science and Human Nutrition department. Panelists ranged in age from 18-55 years old. All tests were conducted in the sensory evaluation laboratory of the Department of Food Science and Human Nutrition, Michigan State University, under cool white fluorescent lighting. All samples were evaluated twice and the data were analyzed by the Analysis of Variance using Super ANOVA (1989-1991, Abacus Concepts, Inc., 1984 Bonita Aye., Berkeley, CA.), with LSD at 5% level used to separate varflmqrneans. VII. Statistical Analysis In this study, the experiment was designed as a three factor (replication x enzyme x concentration) a (replication x varieties x processes) randomized model with balanced data. All determination values were made in duplicate, except for the value for color, which was determined in triplicate. Mean, standard errors, mean square errors, one factor ANOVA (analysis of variance), two factor ANOVA, correlation and interaction of main effects were done using the SuperANOVA software (Berkeley, CA). Mean separations were performed using LSD with the mean square error term at the 5% level of probability. RESULTS AND DISCUSSIONS Effect of Commercial Pectinases on Plum Juice Extraction and its quality Fivetxxmmnxfial gnmkegxmtinaseenmymesrmmx:used mntflfis study to extract juice from Stanley plums. These were (a) Clarex L, obtained from.Asp§rgillus niger, which hydrolyzes both colloidal and soluble pectins, and has been used on apple, pear and grape to clarify and increase juice yield; (b) Clarex ML, derived from selected strains of Aspgrgillus pigg; and Trichoderma reesei, this enzyme system having pectinase, hemicellulase, and cellulase activity, is usually applied in fruit juice extractflmrtflmn employs maceration or liquefaction of fruits. The role of this enzyme is to increase overall juice volume, and decrease mash viscosity. (c) Rapidase Press, extracted from Aspergillus niger is designed to increase juice yield and aid in press efficiency. (d) Rapidase C80L, this enzyme is used primarily by the wine and juice industry to improve clarification and extraction, increase rate of pressing and prevent the formation of pectin gels. It possesses a range of enzymatic (pectin esterase, polygalacturonase , pectin lyase , arabanase , etc .) activities and is especially adapted for depectinization of apple juice. (e) Klerzyme L200, derived from Aspergillus niger, the 41 42 functions of this enzyme are for the rapid depectinization and clarification of fruit juices, and the extraction of juice fromwonmfluxifruits. Investigations into use of these commercially available enzymes on plum juice yield, clarity and quality were made. The purpose of this work was to identify the enzyme which gave maximum yield and quality of plum juice. The enzyme which gave the best results in these preliminary studies was then used for the extraction of the various plum.cultivars used in later efforts. Juice Yield (% by weight) When the enzymes listed above were added to macerated plum in concentrations ranging fran 0.05% to 0.6% (w enzyme/w plums), yields of juice increased with increasing concentration of enzyme (Fig. 5). Juice yield of the untreated controls was approximately 38% (weight of juice /weight of plum fruits) as compared to yields that ranged from 60-73% in the enzyme treated samples. The juice yields ShOW’the different results that are dependent on the enzymes and use level (Table 3). Clarex L, Clarex ML and Rapidase C80L showed highest yield (about 70%), while the Klerzyme L200, treated samples gave yields of only 56%. The 0.2% to 0.6% Clarex L on Stanley showed the highest juice yield whereas Rapidase Press gave the highest yield at 0.1% levels. The Clarex ML, Rapidase C80L and Klerzyme L200 at 0.4% and 0.6% use levels gave the best yield. Arnold (1992) I 100 g fruits) Juice Yield juice (9 Fig. 5 Effect of enzymes on juice yield from Stanley plums 80 70 - 60 - .l 50 - Clarex L —0— Clarex ML 40 " -—-I— Rapidase Press —°— Rapidase CBOL —I— Klerzyme L200 30 I ' I ' l ' T ' I T I Control 0.05 0.1 0.2 0.4 0.6 Concentration of Enzyme (96) .8835 c8333 comrades Beam 8: meet 038 if. .eoccocEwa ..c 6.6. exam 3 898:6 353.:ch so: as mace Seduce: E 3:2 088 2: £5 mes—Sr Eons—.588 253:0 :853 8a mccmtcaEcU N as: w SEEP; are: a 83m 2.3m mean see. same. Sam 83 Sassoon Soc. 38:. 256% same .58 83... some sesame 3.5 .39 Home 2.3.8 ease exam .8... 8.28m an...» 82.? also ease s28 Newman e2 536 an: Esme Seat .33 Samoa rams... a sec . ed to cor 3, mod assoc museum 3:303 >2 may eE>Em Co 296..— E=E .8?ch Sea 22> 022. cc 3635. Lo macetm m 033. 45 reported that use of 0.25% pectinase on Stanley plums (1990) resulted in juice yield increases of 59%. The different results from.this study and the one by Arnold may be due to harvest and maturity differences. The increased juice yield by addition of enzymes is due to their action on the plant tissue. A combination of various exo- and endopectinases (which hydrolyze the pectic substances through the alpha-1-4-glycosidic bond), and hemicellulases and cellulase liberate the pectin through hydrolysis of polysaccharides, resulting in free expulsion of juice (Bielig et al., 1971; Ough et al., 1973). Meischak (1971) and Samsonova et al. (1982) reported that plum.juice could not be satisfactorily expressed without the use of cell vallcmxnmdingemunmee butxdmxltOOImKflIemzymeifimsused,'Uma release of total phenolics made the juice bitter. In this study, higher levels of all five commercial enzymes (beyond 0.2%) tended to make the juice slightly bitter according the the sensory tests. Therefore, the addition of 0.2% enzyme to the macerated plum.pulp was considered to be optimal. Even at this enzyme level juice increases were high and quality <flunmmmswene1mUfinmm. Juice Clarity The percent transmittance (% T) was taken as a measure of clarity. Juice with 60% transmittance was considered as Clarified (Amar-uz-Zaman, 1985). The enzyme treated juice was free from sediments and had clear consistency as indicated by 46 significantly higher % T compared to the control juice. Fig. 6 shows the effect of varying concentrations of the different pectinases on plum juice clarity. Beyond 0.1% enzyme concentration, no significant effect on juice clarity (64% T) was obtained for Clarex L and Rapidase C80L (Table 4). Klerzyme L200 showed the highest transmittance values, whereas Rapidase Press treated juice had the lowest txanannzmcewnflnes. Addithnofixxximmnenotcx y bummed the viscosity but also caused cloud particles to aggregate to larger units which were easily roneved by centrifugation and filtration. In grapes these enzymes increased the average juice clarity fourfold and filterability by 100% (Ough and Berg, 1974; Brown and Ough, 1981). Color Hunter CUM color values and hue angle are shown in table 5. Color value (L, a, b) of enzyme treated plum.juice was significantly different from control juice. Hunter L value represents the lightness and darkness with higher L being lighter and lower L being darker, '+a' is redness, '-a' is greenness, '+b' is yellowness and '-b' is blueness. Addition of enzymes resulted in decreases in all values in this study and varying the concentrations of enzyme had little significant effect on these values. Rapidase C80L treated juice had somewhat higher 'L' and 'a' values as enzyme level increased, resulting in a redder juice than other enzyme- treated samples. Conversely, Clarex L gave the lowest color Percent transmittance (at 660nm) Fig. 6 Percent transmittance of juice treated with enzymes 70 r 60 - 50 - 40 - Clarex L Clarex ML 30 q Rapidase Press Rapidase C80L Klerzyme L200 20 l ' l ' I ' I ' I ' l Control 0.05 0.1 0.2 0.4 0.6 Concentration of enzyme (96 by weight) .8835 503.2. :omtaoEoo >65. .0: 80¢ 6.98 we... .oocoocEwa ..o .96. new E :8st 3:8:in so: 8a 958 328:2. E .28. 2:9. 2.. 5.3 825» gong—688 6:558 :823 2a macaw—8:80 N 8:62.8me as m. 35 . 836 83% 63m 2.3% 82m 3on 83 canto. 8mg 83% 80$ $3.0 .526 .83 .58 caeaam 836 88am 2.8% 38.3. swam £de .8... 8.8.3. $66 88.3 3518 2.8% 83m mafia 1:2 .350 can: .86 08.8 .38 down 1.8.8 4536 . no so do ..o mod .828 Siam 35.63 .5 as. BEE—m. .0 £96.. Es... 3.53m Soc 5.6.0 8.3. no mofixuom ..o Sootm— v 0.3... Table 5 Effects of Enzymes on CDM Value of Plum Juice Levels of Enzyme (% lfiweight) CDM Control 0.05 O. l 0.2 0.4 0.6 9mm. L 7.15a2 3.25b 2.62c 2.59d 2.57d 2.34e a 21.78a 9.71b 7.33c 7.13d 6.73e 6. 15f b 6.11a 2.24b 1.70b 1.70b 1.68b 1.54b Color I-Iue1 1.30a 1.34b 1.34b 1.34b 1.33b 1.33b Clarex ML L 7.16a 2.68b 2.60c 2.18d 1.85: 2.441' a 21.783 7.73b 8.00: 6.0% 4.80e 6.85f b 6.12a 1.76b 1.82b 1.30b 1.021: 1.6% Color Huel 1.30a 1.35b 1.35b 1.36b 1.36b 1.34b Rapidase Press L 6. 12a 2.85b 2.88c 2.82d 2.57e 2.57c a 19.83a 6.82b 8.90s 9.20d 7.49e 7.96f b 5.42a 1.50b 1.96b 2.09b 1.64b 1.7% Color Hue1 1.30a 1.35b 1.35b 1.35b 1.36b 1.35b Rapidase C80L . L 6.33a 2.98b 2.92c 2.87d 3.36e 2.89d a 19.08a 8.39b 8.25c 7.74d 10.30c 8.301“ b 5.513 1.84b 1.83b 1.90b 2.29b 1.70b Color Huel 1.29a 1.36b 1.35b 1.33b 1.35b 1.36b Klerzyme L200 L 6.13a 2.84b 2.76c 2.74c 2.66d 2.55:: a 19.83a 9.06b 8.25c 8.21c 8.08d 7.70e b 5.42:: 1.97b 1.77]: 1.88b 1.88b 1.87b Color I-Iuel 1.30a 1.36b 1.36b 1.35b 1.34b 1.33b 1 calculated as the angle whose tangent equals a/b 2 Comparisons are between enzyme concentrations. Values with the same letter in horizontal rows are not significantly different at 5% level of significance. This table does not show comparison between enzymes. 50 values of any of the samples and the result was a darker, purple colored juice. Fig. 7 shows the relationship between juice clarity and Hunter 'L' value. In this study, Clarex L, Clarex ML, Rapidase Press, and Rapidase C80L revealed a declining linear relationship between % transmittance and Color 'L' (R2 for Clarex L, Clarex ML, Rapidase Press, and Rapidase C80L was 0.978, 0.938, 0.927, and 0.974, respectively). This is probably due to release of ACYs with enzyme added because the hunter L value significantly (r=0.342, p<0.05) related to the amount of ACYs in the samples from this study. The correlation shows that the higher the level of ACYs, the darker the juice. Little (1975) defined the hunter hue angle as tan-1 a/b. A.negative tan"1 a/b indicates greenness and a positive tan-1 a/b shows redness in samples. Ough et al. (1975) found that enzyme treated red grape juice was darker than the untreated control, and was more red as judged by hunter hue. In this study, hue angle of enzyme treated juice was not influenced by enzyme concentration (Fig.8) but hue angles of control juice were smaller than that of enzyme-treated. This indicated that juices became more blue-green (but still red because angle was positive) than untreated juice. The hue angle was significantLylmxfinfixedy'correlated to the hunter L value of Stanley juice through an increase of hue angle and a decrease of 'L' value. All these results indicate that Stanley juice became darker amdrmnxapurple when enzymes were added. Hunter 'L' 51 Fig. 7 Relationship between juice clarity and hunter 'L' value for Clarex L treated juice 8 y = 10.472 - 0.12640x IN = 0.977 7 - 6 ... 4 5 .. 4- .l El 3 . 4 El 2 I ' T r I r 1 ' 20 30 40 so 60 70 Percent transmittance (at 660nm) Color hue of juice Fig. 8 Effects on color hue of plum juice 1.38 1.36 - 1.34 - 1.32 - Clarex L —e—— Clarex ML 1.30 - —l— Rapidase Press —°— Rapidase C80L —I— Klerzyme L200 1.28 1 . T ' I ' I ' I ' T Control 0.05 0.1 0.2 0.4 0.6 Concentration of enzyme (96) Soluble Solids (Brix) While the average soluble solids content of the enzyme- treated plum.juice ranged from 14.5 to 16.79 Brix, untreated Stanley plum juice had soluble solids content of 14.49 Brix (Fig. 9). Clarex ML, Rapidase C80L and Klerzyme L200 did not show significant effect on Brix value of plum juice but Brix values (Table 6) increased significantly as Clarex L and Rapidase Press were added. The greater degree of tissue breakdown released more components which contribute to soluble solids, so higher Brix levels were obtained in these enzyme treated juices. This has also been shown in apple, pears, apricots and carrots (Pilnik et al., 1975 ; Mclellen et al., 1985). % Titratable Acid as Malic Acid (TA) Enzyme-treated juice had higher titratable acid than untreated control (Fig. 10). This may be due to enzymatic de-esterification and degradation of pectin resulting in increase of total acid. Enzyme concentration significantly (p<0.05) influenced titratable acid, and as enzyme concentrations increased so did TA values for Rapidase C80L- treated and Clarex ML-treated juice, as compared to other enzymes. An increase.flnrmfljc:acid has been reported during enzyme liquefaction of Guava (Aurora et al., 1990). Fig. 9 Effect of enzymes on Brix of plum juice arex ML Rapidase Press R arex L apidase C80L Klerzyme L200 IIIED 20 AXan 5° OOLBOUV ‘m—Ow Uni-=0” 0.05 0.1 0.2 0.4 0.6 Control Concentration of enzymes Table 6 Effects of Enzymes on Brix, pH, Titratable Acid and Brix/ Acid of Plum Juice Levels of Enzvme (% by weight) Control 0.05 0. 1 0.2 0.4 0.6 M. Soluble Solid(°Brix) 14.40al 14.73a 14.87a 15.28a 15.17a 14.553 pH 3.35a 3.28a0 3.250 3.250 3.260 3.210 Titratable Acid (% as Malic Acid) 1.10a 1.230 1.26bc 1.33c 1.300c 1.34c SS/Acid 13.09a 11.99ab 11.76ab 11.51ab 11.66a0 10.900 Clarex ML Soluble Solid(°Brix) 14.423 15.820 15.200 15.850 16.020 15.510 pH 3.31a 3.23a0 3.170c 3.14c 3.12c 3.12c Titratable Acid (% as Malic Acid) 1.1 la 1.260 1.29bc 1.37c 1.34c 1.35c SS/Acid 12.992: 12.59:: 11.78a l 1.54:: 11.98a 11.45a Rapidase Press Soluble Solid (degree of bn'x) 14.50a 15.55abc 15.21a0 16.40bc 16.73c 16.110c pH 3.35a 3.28a0 3.260 3.240 3.270 3.250 Titratable Acid (% as Malic Acid) 1.09a 1.190 1.21bc 1.29c 1.230c 1.250c SS/Acid 13.30a 13.09a 12.55a 12.74a 13.63a 12.87a Rapidase C80L Soluble Solid(°Brix) 14.50a 14.55a 14.88a 15.08a 14.92a 14.93a pH 3.353 3.230 3.250 3.220 3.200 3.200 Titratable Acid (% as Malic Acid) 108:: 1.280 1.31bc 1.35bc 1.360c 1.37c SS/Acid 13.43a 11.410 11.370 11.140 10.970 10.920 Klerzyme L200 Soluble Solid(°Brix) 14.52a 15.55a 15.70a 15.8la 15.82a 15.97a pH 3.33a0 3.39a 3.37ab 3.34ab 3.32a0 3.300 Titratable Acid (% as Malic Acid) 1.09a 1.13a 1.13a 1.220 1.240c 1.31c SS/Acid 13.32a 13.75a 13.92:: 12.96a0 12.78:: 12.190 1 Comparisons are between enzyme concentrations. Values with the same letter in horizontal rows are not significantly different at 5% level of significance. This table does not show comparison between enzymes. Titratable acid (8) of juice 1.4 1.0 Fig. 10 , . Control 0.05 Concentration of enzymes (96) l 0.1 0.2 0.4 0.6 Clarex L Clarex ML Rapidase Press Rapidase C80L Klerzyme L200 Effect of enzymes on titratable acid of plum juice pH The pH of plum.juice ranged from 3.12 to 3.35 and pH was lowered by addition of enzyme. The higher the concentration of enzyme the lower the pH values (Table 6). The pH of juice made by adding 0.1% Clarex L, Clarex ML and Rapidase Press was significantly different than the control juice. Rapidase C80L lowered pH significantly. The Klerzyme L200 did not effect pH at the lower concentration but did show an effect at the 0.6% level. Brix/Acid Ratio The Brix/acid ratio is the major analytical measurement for quality in citrus and several other juices. The higher the ratio the better the flavor of the juice (Fellers, 1991 a 1988) . With plum juice the Brix/acid ratio was significantly influenced (p<0.01) by addition of Clarex L, Rapidase C80L and Klerzyme L200 (Table 6). The higher the concentration of enzymes the lower Brix/acid ratio (Fig. 11). Unlike these three enzymes, the use of Clarex ML and Rapidase Press showed no significant effect on the ratio. Sugar Concentration In this research, glucose, fructose, sucrose and sorbitol were analyzed by combination of HPLC and YSI analyzer. The effect of added enzymes on sugar content was apparent. Glucose, sorbitol and fructose increased significantly as the enzyme concentration (below 0.4%) was raised (Table 7). The Soluble solid! titratable acid ratio Fig. 11 Effect of enzyme concentration on Brix/ acid ratio of plum juice 14 13 - 12 a —El-— Clarex L . —0— Clarex ML —I—- Rapidase Press 11 -—°— Rapidase C80L —l— Klerzyme L200 10 T ' l ' I ' l ‘ l T l Control 0.05 0.1 0.2 0.4 0.6 Concentration of enzymes (96 by weight) Table 7 Effects of Enzymes on Sugar Contents of Plum Juice Sugar Content Levels of Enzyme (% by weight) . (g/ 100ml juice) Control 0.05 0. 1 0.2 0.4 0.6 $111.. Glucose 3.17:3:l 3.75c 4.12d 5.32: 4.14d 3.570 Fructose 1.52:: 1.900 1.930 3.06d 2.22c 1.74210 Sorbitol 0.648 0.81a 0.71a 1.550 1.630 0.72a Sucrose 3.22a 3.83a 3.78a 5.27c 5.26c 3.240 Clarex ML Glucose 3. 17a 4.610 4. 16¢ 5.22d 4.33e 4.630 Fructose 1.52a 2.68 2. 150 3.00d 2.71c 2.82cd Sorbitol 0.64a 1.490c 0.95a0 1.69c 1.57c 1.300c Sucrose 3.22a 4.970 4.35c 6.20d 3.33e 3.58e Rapidase Press Glucose 3.64a 3.76a 4.670 4.88c 4.96c 5.26d Fructose 1.87a 1.96a 2.530 2.650 3.04c 3.14c Sorbitol 0.50a 1.06ab 1.05ab 1. 150 1.360 1.240 Sucrose 3.87a 4.050 3. 12a 3.09a 2.95a 2. 16¢ Rapidase C80L Glucose 3.23a 3.930 4.63c 4.7% 6.06: 5. 151‘ Fructose 1.50a 2.210 2.60c 2.61c 3.60d 3.16e Sorbitol 0.36a 0.86a0 1.050 0.94ab 1.320 1.180 Sucrose 3.15a 3.07a0 3.1421 2.570 1.81c 1.13d Klerzme L200 Glucose 3.644: 4.020 5.01c 5.51d 4.65e 5.03c Fructose 1.87a 1.89ab 2.23m 2. 160c 2.47de 2.59e Sorbitol 0.50a 0.50a 0.522: 1.200 0.61a0 0.46a Sucrose 3.87a0 3.55c 5.06d 4.88d 3.320c 2.67a 1 Comparisons are between enzyme concentrations. Values with the same letter in horizontal rows are not significantly different at 5% level of significance. This table does not show comparison between enzymes. 60 greatest concentrations of simple sugars were provided by addition of Rapidase C80L. The concentration of glucose, fructose and sorbitol ranged from.3.23 to 6.06, 1.5 to 3.6, and 0.36 to 1.32 g/lOOmd plum.juice, respectively. Robertson et al. (1991) reported Au-Rubrum plums contained glucose, fructose and sorbitol but had no sucrose. However, Vangdal (1982), in an investigation of the sugar contents of 11 plum cultivars, revealed that the major sugar in ripe plums was sucrose which accounted for 65% of the total sugar. wrolstad and Shallenberger (1981) showed that not only varietal differences can change the amount of sucrose but also processing can make sucrose disappear. All these difference are most likely due to invertases in the juice (wrolstad et al., 1981 and Gorsel et al., 1992). The content of sucrose in Stanley plum juice went up with addition of enzymes but after a period of time the sucrose level dropped (Table 7). This is most likely due to enhanced invertase activity during processing resulting in sucrose hydrolysis. Levels of invertase activity in Stanley plums during ripening, processing and storage is worthy of investigation because of the changes in the physical and chemical properties brought about by sucrose hydrolysis. Total Anthocyanins (TACYs) The ACYs located within the flesh and skin of plums are responsible for desirable purple color of Stanley plums. Pectinase enzymes have been reported to aid in release of 61 pigments from plant cell (Reed, 1975). In this study the effect of various commercial enzyme on TACY release is apparent (Fig. 12). The increase in TACY content is about two-fold by addition of Klerzyme L200, which was in contrast to Rapidase C80L which had little effect on ACY release. Rommel et al. (1992) indicated preferential release of ACYs from blackberries into the liquid phase by pectinases. Arnold (1992) reported TACY content of 0.18 absorbance unit by treating Stanley plums with 0.25 pectinase as compared to the 0.165 units from control juice. In this study, enzyme treatment gave better release of ACYs (6% increase) from Stanley plum.then Arnold's results (1.5%) in 1992. The mean ACY content of enzyme treated juice is 0.26 units in Stanley plum juice as compared to the 0.2 units of control juice. Browning results are shown in Fig. 13. The correlation between ACYs and browning index is detected significantly (r=0.368, p<0.05) through all data. The higher browning level in the juice the higher degradation of the ACYs (Fig. 14). Total Phenolics Total phenolics as tannic acid in plum juice were determined colorimetrically in this study. Pectic enzymes extract not only the pigments but also other phenolic compounds, such as tannic acid which gives a bitter flavor in the fruit juice. In this study, the total phenolics in enzyme treated plum juice ranged from 88 to 142 mg/lOOml f Juice (Absorbance at 535nm) Total anthocu anins o 0.4 0.3 - 0.2 ‘ 0.1 Fig. 1 Z I ' I ' I ‘ 1 ' I ' Control 0.05 0.1 0.2 0.4 0.6 Concentration of enzymes (96) Clarex L Clarex ML Rapidase Press Rapidase C80L Klerzyme L200 Total anthocyanins of juice treated with enzymes Browning index (a L) of plum juice 13 0.3 Clarex L Clarex ML Rapidase Press Rapidase C80L 0.2 - Klerzyme L200 0.1 - 0.0 u Control 0.05 0.1 0.2 0.4 0.6 Concentration of enzyme (96) Effect of enzyme concentration on browning of plum juice Browning Index (A L) Fig. 14 Relationship between browning and anthocyanins for Rapidase Press treated juice 0.4 0.3 - 0.2 - 0.1 ‘ y = 1.0143 - 3.3265x RAZ = 0.817 0.0 0.20 T 0.22 I ' I ' I ' 0.24 0.26 0.28 0.30 Total anthocyanins (at 535nm) 65 (Fig. 15) as compared to a total phenolic content in the control of 70 mg/lOOml. Brown (1981) and Ough (1979) indicated that pectinases influence on the amounts of total phenolics released in grape juice was related to grape varieties, enzyme types and concentration of enzymes. George et al. (1990) reported on the comparison of total phenolics determined by HPLC and colorimetrically. They found that colorimetric analysis resulted in a 10-fold higher level of total phenolics than the HPLC determinations. Gorsel et al.(1992) measured the phenolics in plum.using HPLC. There was an 8 to 12 fold difference between their results (11 mg/lOOml plum juice) and the data from this study. Interference of intermediates and final browning products may explain the discrepancy in the total colorimetric quantitation (Van Buren et al., 1976; Spanos et al., 1990a and 1990b). In addition, HPLC is a specific method for quantitation of individual phenolic compounds while the colorimetric procedure is a general assessment of the levels of phenolics. This may explain some of the variation in txnaljpmaxflioscflnzdned:UIthis:nmdy. Summary Among the five enzymes investigated Clarex L at 0.2% concentration produced the best overall plum juice. It gave optimum juice yield (compared to Klerzyme 200L), a more stable color (compared to Clarex ML and Rapidase Press), higher ACY content , better flavor , lower phenolics (compared 1 60 ’2 .2 140 ‘ s .H ‘ I- A . s; v e 8 120 ' - \ a a I". \ f E ‘5 v . In 3 ° ’ .3 e 100 7 I- Q 1 o S 'L' z a . ~ —9— Clarex L :95 // ——0-- Clarex ML 0 V 80 - - a; —I— Rapidase Press '- --0— Rapidase C80L —I— Klerzyme L200 60 I ' I ' I ' I ' I 1 f Control 0.05 0.1 0.2 0.4 0.6 Concentration of juice Fig. 15 Effect of enzyme on total phenolics of plum juice 67 to Rapidase C80L) and a sediment free, clear juice (compared to Rapidase Press). Enzyme concentrations above 0.2% resulted in bitter flavor which were not acceptable though they gave very high yields . Physico-Chemical and Sensory Characteristics of Plum Juice from Selected Plums Grown in Michigan Plum juice was extracted and processed from six selected Michigan plum cultivars, Au Red, Abundance, Pobeda, Shiro, Peach Plum and Early Golden. Enzyme Clarex L (0.2% w/w of plums) which produced optimum quality plum juice in phase I of this research (Selection of Enzymes) was used to extract plum juice from these cultivars . This section describes the physico-chemical and sensory quality of plum juice made from the above plum samples. % Plum Juice Yield As a result of Clarex L addition, a 26-54% increase in juice yield was obtained in plum samples (Table 8). Highest yield was obtained in Au Red sample (54%) followed by Peach Plum (50%) and Shiro (45%), and the yield of plum juice in these varieties was higher than Stanley plum (32%) . In a study by Wani and Saini (1990), plum juice (extracted from Santa-Rosa, Satsuma and Alubukhara plum varieties) yields of 17% and 23% were reported through the .8:8_.==w_m do .32 ten 8 .58...in Lo: 2a 52o. 2:8 05 .23 8:73 swam 38.0w oohmm 5200 33m 8.0m webdw £06m 82m 58m 85» covwgw £Nom 82m 5% 85% Beam «88¢ mom Fog oewwn 8565?. m: .em owvdn momma 8% :< GE 38.3655 .8250 8865 £820; 85.. 33 22> 83.. 83c; museum.» 82m em 8628 E 22» 88.. :o A gem—U ..o Looto on... w 29¢. 69 use of pectinase. Compared to this, yields of plum juice using Clarex L, are much higher. Although the increase in juice yield is cultivar specific, Clarex L enzyme system ‘which combines the properties of pectic, hemicellulose and cellulose enzymes obviously enhances liquefaction of plums resulting in higher juice yield, which is very important from economic standpoint . Plum Juice Clarity Percentage transmittance (%T) of plum juice made from different plum cultivars was used as an indicator of juice clarity (Table 9). As can be seen the %T of Clarex L extracted juice samples was higher than the control in all cases, indicating that the Clarex L enzyme system was effective in the different cultivars in removing constituents ‘which affect juice clarity. A higher %T represents less finely dispersed matter in juice. Meischak (1971) reported separation of plum juice treated with cell wall degrading enzyme into two distinct layers of partially clarified juice and settled precipitates. Combination of fining and clarification can remove the precipitated matter. Juice -treated with fining agents in addition to enzymes are usually more clear than juices treated only with enzymes. Hsu et al. (1989) showed that enzyme extraction and fining reduced the concentration of total protein resulting in clearer juices . frable 9 shows the degree of clarity (%T) of plum.juice which had added enzymes, pasteurized (HTST-unfined juice), Table 9 Turbidity, Pectin Content, Total Phenolics and Total Anthocyanins of Plum Juice Made From Selected Plum Varieties Varieties Au Red Abundance Pobeda Shiro Peach Early Plum Golden Turbidity (%) Control 25.3.11 55.8721 59.9521 36.21a 34.6la 53.80a A 27.00b 87.55b 75.40c 87.90b 84.90d 94.20c B 22.70a 86.85b 68.75b 92.85c 78.30b 91 .93b C 38.15d 95.50c 83.85:: 96.25d 81.40c 96.00c D 35.60c 94.70c 81.00d 95.80d 82.65:: 95.80c Pectin (gllOOml) Control 0.44d 0. 20d 0. 15d 0.26d 0.22d 0.35c A 0.25c 0.07b 0.08b 0.1 lb 0.09c 0. 16b B 0.14a 0.091: 0.11c 0.14c 0.05b 0.16b C 0.16a 0.03a 0.03a 0.0421 0.01a 0. 13a D 0. 18b 0.01a 0.02a 0.03a 0.02:: 0. 16b Total Phenolics (mg/100ml) Control 123.711 116.0a 205.921 26.76a 67.09a 43.82a A 350. 1d 330.0d 429.2e 156.3d 96.55d 143. 1d B 298. 2c 330.7d 417.6d 150.1c 77.94b 128.3c C 255.5b 282.7c 345.5c 126.8b 94.23d 113.6b D 259.4b 274.9b 332.3b 122. lb 88.02c 109.7b Total Anthocyanins (mgz 100ml) Control 16.53a 3.00b 22.64b 0.33a 0.42a 0.40a A 58.66d 4.30c 32.18d 0.39a 3.31b 0.93a B 51.11c 4.05c 30.76c 0. 15a 3.18b 0.87:: C 31.07b 0.9la 12. 10a 0.07a 0.97a 0.2821 D 30.64b 1.06a 1 1.67a 0.07a 0.9311 0.293 Values with the same letter in the column are not significant at 5% level of significance. Juices were treated by A. Clarex 1.. B. I-lTST of unfined juices C. Fined juices D. HTST of fined juices Control juice without treatment 71 clarified using gelatin and bentonite (fined juice), and juice which was fined and pasteurized (HTST-fined juice). The clarity of fined juices was highest in all plum.samples. This was followed by samples which were fined and pasteurized. The high temperature short time heat treatment of juice always decreased % transmittance for all varieties. Heat induced dissociation of protein-phenolic complex of fruit cell walls during pasteurization has been shown to influence clarity of fruit juices (Hsu et a1, 1989). In this study, Early Golden plum.juice had the highest %T values followed by Shiro, Abundance and Peach Plum. Plum juice from An Red had the least clarity with only 2% transmittance and 10% increase due to enzyme and processing. Clarex L, gelatin and bentonite had little influence in this variety. The correlatnxitemween %rauxlrxxmin ammumnzis shown in Table 10. As expected, pectin content negatively correlated *with %T for all cultivars. The higher the pectin content of juice, the lower was their %T, indicating that clarity of the plum.juice was in direct proportion to the degree of pectin lnxfifldknnity'the Clarexlgeuuqmmesystem. Soluble Solids, Titratable Acid and Brix/Acid ratio Sd®hsdfi(fihhtfimfiflemm(%mhcmfi)md brix/acid ratio are some of the major indicators of fruit quality. Soluble solids are used as a factor in determining maturity of fruit, to establish various grades of quality, 623. wear—cocoa one can: .1— 535 H m 85.. .328: a 536 sac “ < 85:89 Eoocoa Foe R ER: be: 8 8:8E:w_m 3. 3961*me ooccocfiwa * 3.. 8.0 **ww.o 3.8.0 «*mod 33.0 3.9 m 3.306 ......wood 33de 3.006 380.0 384 < 5200 EBA cocoa a. H be :5 58a 8:5 «ounce 85:3... 8m .2 ..o eeaaeoo 85.5; SEQ taco—om EC: 288 83. 82a .8 88:8 swoon one 353ng be 5933 856508 coca—oboe 2:. 9 058. T3 and as a pricing index under some conditions. The brix/acid ratio is also used as an index of maturity of fruit (McAllister, 1980). In the fruit and juice industry, brix/acid ratio indicates the relative tartness or sweetness of juice. In this study, the brix values of juice from six plum cultivars analyzed ranged from 9.85 to 18.45 (Table 11). Au Red had the highest soluble solid content (18.45 QBrix) followed by Early Golden (12.98 QBrix) and Peach Plum (12.709 Brix). Abundance had the lowest brix reading (9.859 Brix). The recent analysis of 160 plum cultivars (Gur, 1986) in 0.3. showed soluble solids of this fairly large sampling of plums ranged fruit 7 to 249 brix. Addition of Clarex L for plum.juice extraction increased the soluble solid of all plums by 2.20% to 20.80% (Fig. 16). Commercial pectinase has been shown to release about 80% polysaccharides from apple cell wall, in addition to degrading the pectic material, thus increasing the soluble solids content (Pilnik and VOragen, 1991). Plum juice has been characterized as having a predominance of malic acid (Meredith, 1992). The % acidity «of plume used for juice extraction in this study ranged from. 1.10 (Shiro variety) to 1.83 (Pobeda variety). There were no significant effects on acidity from.processing. Addition of lenzyme for juice extraction increased the acidity of plums by an average of about 24%. These data are in agreement with 1the work of Jenniskens et al.(1990) who reported 24.2% acid 74 Table 11 Soluble Solids, % Malic Acid, pH and Brix/Acid Ratio of Plum Juice Made from Selected Plums Vaflfies Au Red Abundance Pobeda Shiro Peach Early Plum Golden . Bria Control 18.45a 9.85a 1 1.12a 12.86a 12.7a 12.98a A 18.85b 11.90c 12.31c 14.28b 14.40b 15.03b B 18.95b 11.77bc 11.83b 14.15b 14.38b 14.98b C 18.38a 11.60bc 12.05bc 14.03b 14.08b 14.84b D 18.50a 11.53b 12.22c 14.20b 14. 15b 14.80b Malic Acid (%) Control 1.22a 1.22a 1.83a 1. 10a 1. 13b 1.52a A 1.33a 1.59b 2.18b 1.55b 1.17a 2.00b B 1.37a 1.59b 2.17b 1.57b 1.19ab 1.96b C 1.33a 1.59b 2.18b 1.55b 1. 17a 2.00b D 1.25a 1.50b 1.96ab 1.44b 1.11a 1.66a Brix/ Acid Ratio Control 15.18a 8.09b 6.09a 11.67b l 1.23a 8.53a A 14.163 7.49ab 5.66a 9.24a 12.31b 7.51a B 13.85a 7.44ab 5.45a 9.01a 12.08b 7.63a C 13.81a 7.30ab 5.54a 9.09a 12.01b 7.42a D 14.86a 7.68a 6.24a 9.84ab 12.77b 8.92a pfl Control 3.37a 3.19a 3.01a 3.24ab 3.37a 3.17a 3.37a 3.23a 3.07b 3.23ab 3.39ab 3.28b 3.45b 3.22a 3.13c 3.29b 3.41ab 3.30b 3.40ab 3.21a 3.11bc 3.23a 3.45b 3.32b 3.40ab 3.20a 3.09bc 3.23ab 3.53b 3.27b Values with the same letter in the column are not significant at 5% level of significance. Juices were treated by A. Clarex L B. HTST of unfined juices C. Fined juices D. HTST of fined juices Control = juice without treatment. Soluble Solid (SBrix) on plum juice 75 Fig. 16 Effect of Clarex L on Soluble Solids Contents of Plum Juice 20 [:1 Control a enzyme 10 ‘ o -— AuRal Mm Rink Shin PeadileEaldeden Plum Cultivar 76 increase in apple juice, and Rommel, et al. (1992) who found a 22.9% acid increase in blackberry juice. These results are likely due to enzymatic de-esterification and degradation of pectin resulting in increase of total acid (VOragen et al. 1985). The brix/acid ratios of plum.juice samples in this study were not significantly different among enzyme-added, fining agent-added and pasteurized juice (Table 11) . Among the plum varieties, Au Red had the highest ratio (15.18) while Pobeda plums gave the lowest values (6.09). This tends to indicate that Pobeda may not be suitable for fresh use in spite of its desirable red color, but it can be processed into acceptable quality juice (or juice drink) by modifying its brix/acid ratio through the addition of sugar or sugar syrup. The same situation occurred in grapefruit juice where a large consumer study (USDA, 1958) showed that tart on sour are directly related to the ratio of the juice. The higher the tartness factors the lower the consumers preference. Adjustment of the Brix/acid ratio (usually by the addition of other fruit juices) was the key to improving this juice. Barros et al.(1984) found brix/acid ratio to be significantly correlated (p<0.01) with flavor in grapes (n=1039). Fellers et al. (1988) reported that lower brix/acid ratios of 7.0 in grape juice they tested had the lower score in consumer preference than juice with higher Brix/acid ratios in the range of 11.1. Color A bright natural color in food products is essential to the enjoyment of eating. The importance of color is a psychological, as well as a physical fact that has been well established. The Hunter L, a, b and color hue angle are measurements which are for estimating visual color. Determination of color hue angle (tan'1 a/b) was proposed by Little (1975). The function of a/b was described as a hand sweeping counterclockwise on a dial, starting at Our (red), to nr/2 (yellow), to nr (green), to 3nr/2 (blue) and at 2nr back to red. The concept follows conventional trigonometric nomenclature, with the yellow-red quadrant (+a, +b) as positive and the yellowbgreen quadrant (-a, +b) as negative. The measurement of hunter 'L', 'a', 'b' and color hue angle for all plum.juice samples are shown in Table 12. As expected, the L value varied with varieties and processing (Fig. 17). The dark red colored varieties, Au Red and Pobeda, produced juice with lower L values while the yellow Shiro variety gave the lightest juice. Enzyme treatment decreased hunter L value (30%) of juices because more pignent was released from the cells (Pilnik and Voragen, 1991). Shiro color wasn't significantly effected by enzyme due to lack of ACY pigments. However, Shiro was effected by heating, which caused browning in the juice. Browning was also indicated by a decrease in the L value in the unfined juice from Shiro which was heated by HTST. Nonenzymatic browning due to heating may not have been as extensive as Table 12 Colors (CDM Values) of juice made from selected plums Varieties Au Red Abundance Pobeda Shiro Peach Early Plum Golden . Hunter L Control 1.93a 20.44a 5.51a 23.94a 14.89a 10.72a A 1.46b 12.40b 2.69b 24.26b 5.02b 9.68b B 1.28c 13.09c 2.40c 14.16c 4.30c 7.26c C 0.80d 2.66d 0.99d 5.64d 5.48d 2.83d D 0.99e 3.08e 1.04e 4.65s 6.27e 3.45e Hunter 'a' Control 3.46a 28.55a 20.28a -1.04a 3.1 1a 2.79a A 2.46b 23.45b 8.36b -3.44b 9.43b 6. 67b B 1.81c 23.94c 4.74c -l.36c 7.63c 5.56c C 0.42d 1.69d 1.45d —1.04d 3.22d 0.54d D 0.34e 1.9% 1.716 -0.18e 3.63e 0.70e Hunter 'b' Control 0.5221 22.43a 5.56a 13.72a 12.53a 3.76a A 0.35b 10.91b 1.97b 7.90b 2.68b 2.10b B 0.45c 12.00c 1.08c 2.23c 2.02c 1.78c C 0.00d 0.62d 0.28d 5.64d 1.57d 0.85d D 0.02e 0.81e 0.21e 0.68e 6.27e 0.76e Color Hue Angle Control 1.43a 0.91a 1.30a -0.08a 0.24a 0.649. A 1.43a 1.14a 1.34a -0.41a 1.29a 1.27a B 1.33a 1.11a 1.35a -0.55a 1.31a 1.26a C 0.00a 1.22a 1.38a -0. 18a 1.12a 0.57a D 1.51a 1.18a 1.45a -0.29a 0.53a 0.74a Values with the same letter are not significant at 5% level of significance. Juices were treated by A. 0. 2% Clarex L B. HTST on unfined juices C. fined the juices D. HTST on fined juices Control means the juice without treatment. Hunter '1' Fig. 17 Changes on Hunter L of Plum Juice 30 ——El— Au Red —-0— Abundance i F #‘ —II— Pobeda —°— Shiro 20 _ —I— Peach Plum —o—- Early Golden 10 " . I 0 I ' I ' I ' I ' I Could Enzyme-Treated HTST-mined Fliig HTST-fried Processing Condition 80 browning from PPO enzyme which was inactivated by heating (Sapers, 1992; Siddiq, 1993). The Hunter L, a and b value was decreased by fining agent. The color value changed less by HTST-fined because fining agent removed the browning factors in the juice. Sapers (1992) reported that the capacity of raw apple, grape and pear juices to undergo browning was associated with particulate fractions that could be removed by filtration with bentonite and diatomaceous earth. Plum.juices from Abundance and Pobeda had higher '+a' values, indicating more redness while Shiro gave '-a' values (Fig. 18). The higher the Hunter 'a', the redder the juice tflrnreeltheikwmm"a'xmuue,'Unanoreqpmem.the;hdce. tnfice from.Shiro was located in the yellowbgreen quadrant so it had a slight green tint, although this was not so readily visible to the eye. Abundance juice had the highest 'b' value in control juice while the Hunter 'b' value of Au Red and Early Golden were only 0.52 & 3.76 respectively (Fig. 19). The ‘more blue the juice the lower the ’b' value. The Au Red and Early Golden gave the lowest 'b' value while the Abundance, Shiro and Peach Plum.showed the higher 'b' value. The juice was more blue and less yellow when enzyme and fining agents were added to the plum juices. The analysis of variance (ANOVA) of color hue angle indicated that there were no significant differences (p>0.05) between juices from the different varieties or from.processing. Figure 20 shows the change in hue angle for each of the plum varieties. All .91 i” . Hunter 'a ' 81 Fig. 18 Change of Hunter 'a' Value in Plum mm 30 20‘ 10- Au Red Abundance Pobeda Shiro Peach Plum Early Golden [BIDS-II -10 . . . . (mud €1me HTST-mm Flip HIST-flied Processing Condition Hunter 'b ' Fig. 19 Effect on Hunter 'b' of juice made from selected plums Au Red Abundance Pobeda Shiro Peach Plum Early Golden 20- IDS-II 10" \\\\\‘%\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ \\.\\\\\\\\\\\\\\\\\\\ ' R\\\\\\\\\\\\N 3” a i . o _ 3’1;- l I WWW Processing Condition Fig. 20 Change in Hue Angle of Juice Made from Selected Cultivars Shiro E Early Golden I Au Red I Abundance I] Peach Plum I Pobeda 3% Camd Emyn'eatthd HTST-mfned Flilg HTST-flied ...—9.5. on: .330 Processing Conditions 84 color value for Au Red are lower than expected. These results are probably due to the lower transmittance (lower clarity) of light in Au Red juice. Sugars Plum fruit contains both non reducing (sucrose) and reducing (fructose and glucose) sugars and sorbitol, a sugar alcohol. Plums contain moderate amounts of sucrose and the presence of large quantities of sucrose in plum juice has been used as an indicator of adulteration (Flynn, 1970) which is similar to the situation with apple juice (Fitelson, 1970). In this study, juice from Au Red had the most glucose, fructose and sorbitol of any cultivar but was lowest in sucrose content (Table 13). Plum juice from.Abundance was lowest in glucose and sucrose, while juice from Early Golden plum had little sorbitol . The variety , geographic , seasonal , maturity, postharvest condition and processing can all affect sugar compositions. The sugar content of plums have been reported by Richmond et a1. (1981), Gur (1986), wrolstad et a1. (1981), and Robertson et al. (1991). The range of fructose was from 0.72 to 4.93 g/lOOg plums, glucose ranged from 1.26 to 5.22 g/IOOg fresh plums, sucrose content was from.0.02 to 5.68 g/lOOg fresh fruit and sorbitol content was from 0'to 2.7 g/100g plums. All varieties but Abundance have glucose to fructose ratios (g/f ratio) over 1. Usually, pear and apple contain Table 13 Sugars Content of Juices Made from Selected Plums 85 Varieties Au Red Abundance Pobeda Shiro Peach Early Plum Golden . Glucose Control 6.03a 1.84a 1. 90a 2.70a 2.15a 3.18a A 6. 57b 3.17b 3. 42b 5.13b 3.73b 4.05b B 6.130 3. 31c 3.970 5.230 4.03d 4.220 C 6. 64d 3. 270 3. 99c 5. 17b 3.990 4.42d D 6. 426 3.310 4. 09d 5. 55d 3. 79b 4.56e Fructose Control 5.9la 2. 50a 1.21a 1.64a 1.29a 2. 67a A 5. 71b 3. 75b 2.73b 4. 08b 2.83b 3. 55b B 5.300 3.870 3.180 4.17c 3.09e 3.750 C 5. 72b 3. 84c 3.180 4.140 3. 03d 3.89d D 5.56d 3. 89c 3. 31d 4.41d 2. 91c 4.070 Sucrose Control 0. 10a 2.410 3.730 4.73d 7.45s 3.80b A 0.22a 0.65ab 0. 69b 1.22b 4.09d 1.99a B 0.42b 0. 57a 0. 75b 1.450 3.48a 1.99a C 0.53b 0. 77b 0.48a 0.59a 3.880 1.86a D 0.880 0. 57a 0.46a 0.59a 3.70b 1.82a Sorbitol Control 1.61a 0. 05a 0. 053 0. 43a 0.04a 0.01a A 1.53b 0. 05a 0. 34d 0. 50b 0.140 0.01a B 1.580 0. 07a 0.310 0. 50b 0.130 0.01a C 1. 39d 0. 14b 0. 21b 0. 43a 0.120 0.02a D 1.37c 0.14b 0.20b 0.41a 0.11b 0.01a Total Sugar Control 13.65a 6.8a 6.89a 9.5a 10.950d 9.66a A 14.03b 7.62b 7.18b 10.930 10.79bc 9.60a B 14.280 7.830 8.21d 11.35d 10.73b 9. 97b C 14.28d 8.02d 7.860 10.33b 11.02d 10. 190 D 14.23d 7.9lcd 8.06d 10.690 10.51a 10. 46d Values with the same letter in the column are not significant at 5% level of significance. Juices were treated by A. 0. 2% Clarex L B. HI” ST on unfined juices C. Fined juices D. HT ST on fined juices Control = juice without treatment. Unit is g/ 100ml juice 86 much more fructose than glucose, while peach and plum have more glucose than fructose (wrolstad et al., 1981). The g/f ratio of Abundance was around 0.85 which is similar to the ratio found in pears or apples. This plum.cultivar has some rather distinctive flavor characteristics which may be due in part to its sugar composition. Addition of enzymes had some effects on sugar contents of plum. Enzyme extracted plum juice was higher in total sugar content compared to control sample due to release of soluble solids from the cell wall (Cheetham, 1985). The glucose and fructose content of juice were higher and the sucrose content was lower with addition of enzyme but invertase may be a prime factor in sucrose decrease and simple sugar increase. Probably, invertase hydrolyzed the sucrose with addition of enzyme and then it was stopped by the high temperature short time heating process. Gorsel et a1. (1992) reported that fresh plum.juice was always higher in sucrose. In contrast, either no sucrose or low levels were found in prunes and processed plum.products (wrolstad et al., 1981; Flynn and Windt, 1970; Gorsel et al., 1992) due to the existence of invertase that caused the reducing sugars to be slightly more dominant. In this study, the juice from Au Red was an exception because it had low concentrations of sucrose even in control juice. The sugar composition of Au Red changed very little (p>0.05) during processing but its total sugar was increased slightly by enzymes. Pectins Pectin is one of the major cellular structural components. It exists both in the primary cell wall and in the middle lamella, the intercellular cement between cells. In this capacity it contributes significantly to structural integrity of fruits and vegetable (Gur, 1986). As a soluble component of juice and an insoluble component of juice particulate material, pectin affects many facets of juice quality, such as viscosity, gelling ability, and ability to precipitate as pectates, so determination of pectin contents cnfpflums is nmxnxamt. Pectin contents of control plum juice made from An Red, Abundance, Pobeda, Shiro, Peach Plum and Early Golden plum were 0.44, 0.20, 0.15, 0.26, 0.22 and 0.35 g galacturonic acid/100 ml fresh plum.juice respectively (Table 9). Other studies on plum (Hardinge et al., 1965; Krause and Bock, 1973; Vidal-Valverde, 1982; Southgate, 1991) have reported pectin content of plum to range from 0.23 to 1.00 g/100g fresh plums using similar methods as those employed in this work. Enzyme extracted juice had an average 54% lower pectin than control sample. This could be due to enzyme break down of the pectin into simpler compounds, such as galactose, xylose, monomers, and oilgomers of galacturonic acid (Ryu, 1980). Fining process further reduced the pectin content by almost the smmeckxnxmeas enzyme'tnmmmmnnn This is probably due to the fact that the fining process removed particles 88 larger than 150mw (Fig. 2). In the enzyme extracted, fined and pasteurized plum juice, the pectin content ranged from 0.01 to 0.18 g/100 ml juice. Only Early Golden and Au Red had higher pectin (0.16-0.18 g/100 ml). Other processed juice pectin content was very low (0.1-0.3 g/100 ml). Pectin content of plums correlated with total phenolics, brix, sugar content and color values (Table 14). Total phenolics, brix, glucose and sucrose had a negative correlation with pectin while sucrose, hunter 'a' and hunter 'b' positivekyrmmnxflated‘U31fluapeotin.content. The higher the value 'a' and 'b' the higher the pectin contents for Abundance and Pobeda. Sugar content of samples had a direct bearing on the measurement of pectins because sugars tend to interfere with the analytical procedure. The method used to measure pectic substances is subject to interference from the nonuronide carbohydrates associated ‘with pectin samples but removal of these compounds entails considerable manipulation (Selvendran, 1975). This caused difficulty in obtaining reliable uronide measurements from samples containing high levels of sugar substances. .Although Blumenkrantz and Asboe-Hansen (1973) found mehydroxydiphenyl reagent was the more specific for uronic acids and less sensitive to extraneous carbohydrate interference, Kintner and van Buren (1982) reported that when high levels of sugar are present, the interference was increased. Carbonell et al. (1989) concluded that using mrhydroxydiphenyl as .22 em a 8.8888 . “wood .88 .88 .88 .88 88 b. .25: 88 28 E8 .88 .88 .88 .... beam .88 .88 .88 .888 .58 .88 0.888 .88 .88 .88 .88 .88 .F8 .885 .88 .88 .88 .88 .88 88 8820 .88 .88 .88 .88 .88 88 Em .88 .88 .88 88 .88 .88 8:828 38. cow—CO EEK ram :88 228 888 8:858... 88 3. 80:8. 828 ..o 8888 cocoa 58 b. 5:5: use .8. 5:51 .8888 .8225 .882» .55 82—05%— .QQ new. 8:08:08 8:88 88389 $820580 cons—oboe BE. 3 28¢. 90 chromogenic reagent with previously extracted and purified samples was the most effective method for determination of pectin in plum jams (0.9%o_ 8m 85 L8 328:6 3858:in 88 8.588. 888:6 5? 8828 E 2882 so... .88. 2.2 8 88. 888.8 .8... 5200 ram 3%....” Emmw 388% amps. ambd find. 82m 58?. n8mm.v gamma. £8on 8mm._ 8888 8w: aim 8w.m 3.0.0 2120 Exam 8808 8mm? 883m Eomw wa.m 9.800% £56 8858 flaw 88823.8. 385.8. 8854. 8o©.v 88d .508 88.54. com 8.8. 3:58:38... 88288.8 885826 1200 .85chme 80588.8 83:50 .855 to>8E 88:9 .53. domwom 83a. 82m manor—g 58 5.. 8235.8 .0588 ..o 8:82 9 838.8 100 judges' perception of astringency, with less astringency being related to a better flavor. Although it is difficult to assign a reason for this correlation it may be due to, or associated with , the fact that higher concentrations of phenolics which contribute to astringency may mask aroma vohnfiles. Correlation coefficients among the sensory attributes and overall acceptability was determined (Table 17). The overall acceptability showed significant correlation for all juices ‘with flavor preference of judges calculated across groups. From table 16, Pobeda had the highest score for flavor preference, with Peach Plum.and.Abundance also showing high flavor preference by judges and the overall acceptability of these three juices was high. Sweetness significantly (p<0.05) correlated with acceptance for Au Red, Abundance and Early Golden. The higher the sweetness the higher acceptability. This result agrees with LaBelle et al. (1960) who reported positive effects of sweetness and brix/acid ratio on flavor and acceptability of apple sauce. The color, astringency and tartness of Peach Plum had significant correlation (p<0.05) with overall acceptability. The astringency of Au Red and Abundance highly correlated with acceptance of these two juices. The juices from Pobeda, Peach Plum.and Abundance gave the highest score for overall acceptability (Table 16). In summary, the laboratory evaluation of acceptable plum juices indicated that these juices could be characterized by 101 62: 83.0 88 8980:me .3. 89,2 888 .8 8:88.888 . 888 828 588 .388 :88 528 3:8 .80». .0 .80m .0 ..8m .0 m0N.0 ...an0 ESE 5880 02.0 82.0 05.0 VON.0 150.0 9:50 mm0.0 000.0 30.0 0NN.0 10m 8.0 86300 N000 mom .0 .08 .0 tum m .0 ..03.0 88:80:39.. wm _ .0 .8000 me .0 .00m .0 ..mvnd pom a< .530 888588... $585.52 885895 co>8E mobot8> 83.. 820 00 88.8080 .880 98 888.88 $385.88 885338 .828 688 8830888 =8.8>o 582580 858588 soufiohou S 858,—. 102 sweetness, tartness, color and astringent sensations but the preference rating for plum juice could be adequately predicted by flavor preference (r=0.75, p<0.01) under the condition that brix/acid ratio was suitable. SUMMARY AND CONCLUSIONS In this study, five commercial pectinases were used in plum juice processing. They all had some ability to improve the yield, color (release of anthocyanins) and clarity of juice but at concentration higher than 0.2% they tended to cause a bitter flavor in the juice. Among five pectinases, 0.2% Clarex L was identified as the best enzyme for plum juice yield and quality so it was used with six new plum \nujemdes being‘ewihnnxx11km'juiaelmxneesing. Of these six varieties, Au Red had the highest content of pectin while Pobeda showed the lowest value for pectin. Press juice from Au Red gave the least juice yield and % transmittance but it was the sweetest of all varieties. Pobeda and Au Red were red colored varieties so they had the highest content of.ACYs. Shiro was a yellow'plum.and had the lowest ACY content. Pobeda was the most acidic variety and had the highest phenolic content . The juice from Abundance showed the lowest amount of total sugar. The use of 0.2% Clarex L enzyme with the new varieties increased juice yield, clarity (i.e.. percent transmittances) soluble solids, titratable acidity, content of total ACY and total phenolics, but caused decreases in the pectin contents in most instances. The color and pectin content of juice from An Red variety was least affected by enzyme treatment of KB 104 any of the varieties. Fining agents removed pectin, ACYs and phenolics but increased the % transmittance of juice. This almost sediment-free, clear juice was considered to be more like an artificial juice by consumers because the loss of natural color and brilliant clarity made it seem somewhat unnatural in appearance. The fined juice are more stable than unfined juice. tflxatxuifififity, total phenolics and total ACYs of unfined juice were decreased by heat but heat didn't significant effect fined juice characteristics. All cultivars included in this study produced highly acceptable juices. The Brix/Acid adjustment had the biggest impact on sensory ratings, causing greater acceptance of juice from all cultivars. The juice from Abundance, Pobeda and Peach Plum showed the highest flavor preference and amquxxnfijity by