QUALH’Y OF .sorsmm muss AS magma av PRE - STORAGE TEMPERATURE AND composmaw GF smmeg ATMOSPHERE Thesis for the Degree of 932. S, 5‘:qu SW‘E UE‘SWERSEW EWRW GEL 296$ A‘- ggggg “WWW [’1 '0er gang! ABSTRACT QUALITY OF JONATHAN APPLES AS INFLUENCED BY PRE-STORAGE TEMPERATURE AND COMPOSITION OF STORAGE ATMOSPHERE By Efraim Gil‘ The storage life of fruit is presently extended by low temperature control and/or increased carbon dioxide and decreased oxygen content of storage atmosphere. This practice is known as controlled atmosphere (CA) storage, and apples are held at approximately 32°F in an atmosphere containing about 5% 002 and 3% 02. This study was conducted in two parts, each using Jonathan apples. First, apples were stored for 230 days in semi-commercial quantities (6O bu.) under three different conditions of temperatures and atmospheres as follows: 1) 20 bushels stored at 32°F in air, 2) 20 bushels stored at 32°F in an atmosphere containing 5% 002 and 3% 02, and 3) 20 bushels stored with a gradual decrease in tempera- ture to 32°F within four days in an atmosphere containing 5% CO2 and 3% 02 throughout storage. A second trial included 48 bushels of apples which were stored under different storage atmospheres, lengths of pre-storage treatment and temperatures. Atmos- pheres included 9% CO2 and 3% O2, 9% CO2 and 5% O2, 5% CO2 and 3% 02, and air. The three pre—storage treatments were for 3, 7 and 11 days and temperatures were 62°F during pre- storage, and 32°F during storage. Efraim Gil The apples were evaluated after 118, 182, and 225 days in storage, and after a 1A day post—storage holding time at 50°F. Each sample consisted of about 3/4 of a bushel, or about 85—120 apples. The apples were examined for two types of external damage, rot and lenticle spot. Rot is the soft watery spot or area showing typical deterioration, and lenticle spot is the superficial brown to black spot that is centered at the lenticle. The internal damage was evaluated as brown core, carbon dioxide injury or internal breakdown. Brown core is a premature browning of the flesh around the core area. Carbon dioxide injury is significant by the dry pithy areas around the core, and internal break- down is the browning of the flesh near the outside skin. The sum of the internal and external damage gave the total amount of loss and percentage of marketable fruit was cal- culated. The firmness of the tissue was measured by a penetrometer. When the storage temperature was gradually reduced to 32°F, apples in air maintained better quality (less deteri- oration and change) than when stored at 32°F in air, or at 32°F in an atmosphere containing 5% CO2 and 3% 02. When the apples were stored at 32°F in an atmos- phere containing 5% 002 and 3%(k3up to 11 days before storage, the quality after storage was superior to that of apples stored in air, in 9% CO2 and 3% 02 or in 9% C02 and 5% 02. QUALITY OF JONATHAN APPLES AS INFLUENCED BY PRE-STORAGE TEMPERATURE AND COMPOSITION OF STORAGE ATMOSPHERE By Efraim Gil A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Food Science 1968 “D“y“) \ ‘t‘fih": ACKNOWLEDGMENTS The author wishes to express his appreciation to his major professor, Dr. I. J. Pflug for his advice and help throughout this study. Grateful appreciate is extended particularly to Prof. L. E. Dawson and Prof. N. R. Thompson who served as members of the committee, reviewed the manuscript and made many constructive suggestions and comments. Thanks are expressed to the Whirlpool Corporation for their interest and support of this project including the graduate assistantship that made this study possible. To Dr. B. S. Schweigert, Chairman of the Food Science Department, I would like to express my appreciation for making available the graduate assistantship. Grateful acknowledgment is extended to Mr. K. Fox for his help in editing the manuscript. iii TABLE OF CONTENTS LIST OF TABLES .................... . ................... LIST OF FIGURES .............................. . ........ INTRODUCTION .. ................. . ............... . ...... REVIEW OF LITERATURE .................................. 3 Apple Storage Life .............................. Harvest and Storage Practice ........ ............ Picking date ..... . ......... .... ............ The post harvest temperature ...... . ........ Storage humidity ...... . .................... Atmospheric composition .................... Carbon dioxide composition in atmosphere ............ . ............... Oxygen composition in atmosphere ...... Ethylene and other volatiles in atmosphere ............................ Post harvest pre-storage temperature control EXPERIMENTAL PROCEDURE ................................ Experimental Apples . ................. . .......... Source ..................................... Preparation for storage .......... . ......... Storage Facilities .............................. Room construction .......................... Refrigeration .............................. iv Page vi vii NU'IU‘IUOU) ll 13 1A 15 l7 l7 l7 17 18 18 2O Gas source ................................. 20 Temperature control ........................ 2O Humidity control ........ ................... 22 Gas analysis ............................... 22 Sample Inspection ... ...... ....... ........... .... 22 RESULTS AND DISCUSSION ................................ 26 Experiment 1 .......... . ......................... 26 Experiment 2 .............. . ..................... 28 SUMMARY ............................................... AA CONCLUSIONS .... ...... .. .......... ............. ..... ... A5 BIBLIOGRAPHY .......................................... A7 Table Table Table Table Table Table Table Table Table Table Table LIST OF TABLES Page 1. Influence of pre—storage and storage condition on quality of apples stored 230 days at 32°F. . ............ ................ ....... 26 2. Influence of pre-storage delay and storage atmosphere on spoilage of apples stored 118 days at 32°F. ooooo .000...0 ooooooo 0.....00.0..0..0 ..... 29 3. Influence of pre- storage delay and storage atmosphere on firmness of apples stored 118 days at 32°F. ... ..... . . ..... ........ .... ...... 30 A. Influence of pre- storage delay and storage atmosphere on quality of apples stored 182 days at 32°F. 00.0.00... ....... O .....OOOOOOOOOOOOOO. 31 5. Influence of pre—storage delay and storage atmosphere on firmness of apples stored 182 days at 320F. 0.0.0.0..0..0.0 ........ 0000...... ....... . 32 6. Influence of pre-storage atmosphere on spoilage of apples stored 225 days at 32°F. ...... 33 7. Influence of pre-storage delay and storage atmosphere on firmness of apples stored 225 days at 32°F. ........ ........... ..... ............ 35 8. Influence on pre—storage delay on quality of apples stored in an atmosphere containing 5% CO2 and 3% CO2 at 32°F. ......o0000..0.00..0 ....... 36 9. Influence of pre-storage delay on quality of appleS stored in atmosphere containing 9% CO2 and 3% 02 at 32°F. ..................... ...... 37 10. Influence of pre—storage delay on quality of apples stored in air at 32°F. ............ ..... 38 ll. Influence of pre—storage delay on quality of apples stored in an atmosphere containing 9% CO2 and 5% 02 at 32°F. ........ ...... ......... . 39 vi LIST OF FIGURES Page Figure 1. Flow diagram for the three atmospheres supply system ...... . .......... .. ......... ....... 2l vii INTRODUCTION Horticultural products undergo many changes including wilting and rotting during maturation and storage. Fruit tissue is alive, at least in the first stages of storage, hence rotting is not due to the growth of micro- organisms in dead tissue but the spread of specific parasitic organisms in the living tissue. Fruits are also subject to certain undesirable physiological disorders. Through the use of suitable storage conditions some of these undesirable changes can be prevented, others only delayed. When optimum storage conditions are used, there is a stage when signs of deterioration and spoilage become apparent and beyond which further storage is not economically feasible. This is considered as the end of its storage life. After fruit has been stored commercially and removed from storage, it must remain in good condition for sufficient time to be marketed. This is known as the shelf life of the produce. During marketing the produce is usually not stored under optimum storage conditions at all times. Once an apple is detached from the parent tree the process of biological oxidation with both respiratory and fermentative features assumes a dominant role. In the glycolytic pathway, carbohydrates are broken down to pyruvic acid which is oxidized to carbon dioxide and water. This process of growing old or aging results in a decrease in vigor and a decrease in resistance of the organism to disease and adverse environmental conditions. The end product of aging is death. Apples are held under various types of storage conditions to provide a regulated supply of apples to the market throughout the winter and spring months. Controlled Atmosphere (CA) storage is the most advanced type of storage in use today. By this method we can retard the aging process and thereby lengthen the maximum marketing period of the fruit. With a clearer understanding and knowledge, gained through studies of the factors and mechanisms involved in aging process, it is hoped that optimum storage conditions can be established for quality apples. These apples should maintain their desirable quality without evidence of rotting or disease for a maximum period of time after picking. REVIEW OF LITERATURE Apple Storage Life‘ The storage life of different varieties of apples varies considerably (Smock, 1961; Spencer, 1965). The storage life of a particular sample of apples depends on several factors, such as: 1. environmental factors including light, water, mean temperatures, type of spring season, summer and fall temperatures, other climatic factors, soil (aeration) and fertility of the soil. Most of these factors cannot be controlled; 2. Cultural factors which can be controlled such as soil, fertilization, soil management, quantity of fruit per tree, pruning and spraying; 3. time of picking; and A. storage conditions. 7 The relationship between cultural conditions and shelf life is not easily explained, hence these factors are usually ignored in recommending storage conditions, since they are difficult to control in commercial practice. Several controllable factors affect the storage life of an apple. These factors are: l. picking date. 2. storage (environmental) temperature. 3. composition of storage atmosphere. A. relative humidity of storage atmosphere. In Controlled Atmosphere (CA) storage, an optimum combination of these factors is sought to produce the conditions leading to maximum storage and shelf life. 3. composition of storage atmosphere. A. relative humidity of storage atmosphere. In Controlled Atmosphere (CA) storage, an optimum combination of these factors is sought to produce the conditions leading to maximum storage and shelf life. Harvest and Storage Practice Picking date - The correct stage of maturity at which apple fruits should be harvested for maximum storage life has been reported by Ulrich (1958), Beever (1961), Biale (196A), and Spencer (1965). The relationship between respiration rate and development of the apple fruit during growth, maturation, and ripening has also been studied extensively (Smock and Neubert, 1950; Beever, 1961; Biale, 196A; Dilley, 1966). This relation- ship starts at the time of fruit fertilization and ends when the fruit is in an advanced stage of senescence which is beyond the stage of optimum storage quality (Platenius, 19A3; Hardenburg, 196“; Spencer, 1965). As the fruits develop on the tree, the respir— ation rate decreases gradually and reaches a minimum value, known as the climacteric minimum of respiration. The fruit is now considered to be physiologically mature. At this time, the fruits ripen properly, on or off the tree, and develop the characteristic flavor and aroma of the variety. After the climacteric minimum the respiration rate increases until it reaches a peak, then declines gradually. The rise in the respiration rate is called the climacteric rise, and the peak, the climacteric peak (Smock and Neubert, 1950; Spencer, 1965). When apples are declining in respiration rate following the peak, they are said to be in senescence (Dilley, 1966). While it is true that apples are normally picked after the respiratory rise has begun, they may be picked before this rise. Ideally the time of harvest will depend upon the end uses of the fruit. Practically, it may depend on weather and the availability of harvest labor. When the respiration rate reaches a peak value, it marks the end of the ripening process and the onset of aging of the tissue (Smock and Neubert, 1950; Kuhn, 1958; Pratt, 1961). Since fruit undergoes the climacteric more rapidly following harvest than it does on the tree (Dilley, 1966), it is usually recommended that the respiration rate be lowered as quickly as possible following harvest (Eaves, 1934; Brooks, 1939; Platenius, 19A3; Smock and Blanpied, 1963; Hardenburg, 196A; Harvey, 1967). The fruit probably receives an anti-ripening hormone from the leaves or from the seeds which is responsible for the delay in ripening while the fruit is on the tree (Van Overbeck, 1966). The rise in respiration rate during climacteric provides a mean to measure the increase in energy neces- sary to carry out many chemical reactions involved in the ripening process (Dilley, 1966). Ripening can be slowed but it cannot be stopped or reversed (Burg, 1962; Biale, 196A). It can be slowed by lowering the temperature of the fruit tissue and further slowed by altering the atmosphere surrounding the fruit (Thornton, 1930; Thornton, 1931; Eaves, 1936; Claypool and Allen, 19A7; Dewey, 196A; Eaves, 196A; Olsen and Schomer, 196A). The importance of the climacteric is that the respiratory behavior may be utilized as a guide for estimating the storage potential of fruits. The storage potential becomes progressively shorter as the fruit advances into the climacteric rise; maximum storage potential is achieved by harvesting at the climacteric minimum. By the time the fruit has reached climacteric peak of respiration there is little storage potential remaining (Briggs and Robertson, 1957; Biale, 196A; Spencer, 1965; Varner, 1965). The post-harvest temperature - Since fruit is usually mature when harvested, physiological and chemical changes take place during its senescence. Temperature affects the rate of all physiological changes which fruit undergo (Van Doren, 1939; Smock and Neubert, 1950; Tomkins, 1959; Padfield and Mandeno, 1963; Hardenburg, 196“; Spencer, 1965). The respiration rate is often considered the best criterion of the physiological activity of the fruit (Beever, 1961). The rate of respiration is directly related to the temperature; at the freezing point, the living tissue does not respire since it stops functioning in controlled metabolism (Wright _t _1, 195“; Spencer, 1965). The rate of respiration is relatively low at a temperature just above the freezing point of the tissue, and it increases 2 to 3 fold for every 10°C rise in the temperature (Kidd and West, 1936; Smock and Neubert, 1950). The reason for this is that the energy of activation for respiration and enzymatic reactions is lowered as the temperature increases (Davis 33 a1, 1964). However, if the temperature is raised beyond a certain limit, depending upon the variety of fruit, the tissue may be damaged due to denaturation of its protein fraction. Then the rate of respiration decreases (Stiles and Leach, 1932, Beever, 1961). During storage, the initial rate of respira— tion and the respiration over long periods of time are important. Therefore, respiration can be regarded as proportional to the temperature (except for some tempera- tures between 23°F—32°F). If storage life were inversely proportional to respiration, the life in days at any temperature t1 multiplied by tl - t0 (the difference between t1 and the minimum temperature, to) should be constant and the storage life could be expressed in storage terms of "degree-day". This concept of degree-day, often used in determining the rate of growth of plants, can also be applied to storage problems to calculate the effect of different conditions (Tomkins, 1959). The germination of microorganism spores can be considered a timing device which ensures that growth occurs when conditions are most favorable. These environmental conditions, whose margin line affects the germination, are moisture, temperature, light and nutrient supply, (Smock, 1961; Sussman and Halvorson, 1966). Among these factors, temperature is the easiest to control in storage. As temperature decreases the time for germination of microorganism spores is increased and the rate of mycelium growth is reduced. Some fungi which cause rot in apples can grow at 30°F, and therefore will spread slowly at storage temperatures of 32°F. Other fungi which cause rot can be controlled by reducing the temperature below their minimum growth temperature (Smock, 1961). Although reducing the temperature may be beneficial, apples are damaged when they are stored too long below a certain minimum temperature (Smock and Neubert, 1950; Lyones £2.2l: 196“). Low temperature injury in apples may appear as a browning of the flesh with normal appearing skin or it may appear as skin disorder. Common disorders are: soft scald, soggy breakdown, and core browning (Brooks and Harley, 193A; Eaves, 1936; Plagge, 19A2; Smock and Neubert, 1950; Smock, 1961). The relationship between storage temperature and low temperature injury have been investigated (Smock 10 and Neubert, 1950; Smith, 1962). They distinguished between what they called "Primary susceptibility" which occurs in the apple at the time of storage, and "secondary susceptibility" which results from changes in the apple after cooling. The secondary susceptibility increases with time of storage. It is important to distinguish between these two forms of two temperature injury since the control measures for each are different. For example, Smith (1962) showed that it might be possible to reduce secondary cold injury due to continuous exposure to low temperatures by exposure to high temper— atures for short periods. Susceptibility to low temperature breakdown in any form is an important factor to be considered in determining the conditions of storage for a variety of apples since this determines the temperature which gives the maximum storage life. Early stages of scald or of low temperature injury which might be slight or unseen when fruit is removed from storage, may become more obvious when the fruit is held at increased temperatures (Smock, 1961). Therefore, it is desired in storage experi- ments to record the wastage on removal from the storage and again after a period of time at increased temperatures. Storage humidity - The storage life and the degree of defects in apples is influenced by water loss, and it is recommended that the humidity of the storage be kept 11 within certain limits, i.e. 90—95% R.H. (Smock and Van Doren, 19A1; Smock, 1961). Humidity in this range promotes the growth of microorganisms, however, the low temperature and the modified atmosphere in the storage inhibits most of their growth (Smock and Neubert, 1950). Atmospheric Composition Carbon dioxide composition of atmosphere - When fruits are held in an unventilated container they produce, through respiration, changes in the composition of the atmosphere. The concentration of the oxygen will decrease and the carbon dioxide will increase in almost equal proportions (Smock, 1958; Eaves, 1960). The effect of this change in the composition of the atmosphere on the retardation of ripening of apples was first reported by Kidd and West (1920). They also demonstrated that when the ven— tilation was excessively restricted, the fruit was damaged. At first Kidd and West (1920) thought that restricted ventilation in storage might be an alternative to cold storage, but after their first commercial trials (Kidd and Wesg 1932) they found that, for successful storage, it was necessary to control the temperature and the composition of the atmosphere. Furthermore, they reported that optimum conditions required lower carbon dioxide and oxygen than could be obtained by simple restricted l2 ventilation. Later they combined restricted ventilation with carbon dioxide removal by using lime or caustic soda scrubbers (Kidd and West, 1932; Claypool and Allen, 19u7; Pflug, £2 3;, 1956; Eaves, 196M; Dewey, 1964). Apples stored under CA conditions show slow ripening as judged by the rate of yellowing of the skin and softening of the flesh, delayed rotting, and de- creased dessication of the apple (Plagge, 19A2; Spencer, 1965). Since these three processes accompany aging, their effects on retarding ripening and rotting are almost directly proportional to the first 3—A% rise in the concentration of carbon dioxide (Caldwell, 1956). A further rise in carbon dioxide during storage beyond a certain limit (depending on the variety) may be harmful (Plagge, 19u2) since it increases the development of brown core (Thornton, 1930; Tomkins, 1965; Spencer, 1965). Carbon dioxide damage increases with the concentration of carbon dioxide during early stages of storage but not noticeably with time (Smock, 1961; Fidler and North, 1963). The conditions which, together with suitable concentrations of carbon dioxide, produce brown core are not fully known (Fidler and North, 1963; Spencer, 1965). But even if brown core is not produced, there may be other undesirable effects during storage in moderate con- centrations of carbon dioxide. For example, apples may have the taste of alcohols or aldehydes (Samisch, 1936; 13 Harvey, 1967). The effect of CA storage in delaying rotting is believed to be due to the retarding effect of carbon dioxide on ripening of the apples, and not to a direct effect of carbon dioxide on the fungi. The presence of carbon dioxide can affect the rate of production of enzymes in certain rot producing fungi. However, when the concentration of carbon dioxide is increased, rotting may be increased (Davis 33 al, 196“). Oxygen composition in atmosphere - Lowering the concen- tration of oxygen to 10% (from the normal 21% in air) retards ripening only slightly, and reducing it to 2.5-3% has a more significant effect (Kidd and West, 1936; Smock and Van Doren, 19A1; Blanpied and Dewey, 1960; Dewey, 1962; Mattus, 1963; Hardenburg, 1964; Parsons, 196A). Absence of oxygen results in anaerobic respira- tion which is accompanied by alcoholic flavors and eventually, death of the tissue (Eaves, 193A; Claypool and Allen, 19A7; Van der Meer, 1962). Lowering the oxygen concentration to 5% delays rotting by retarding ripening (Dewey, 1962, 196M; Dilley, 1966). Lowering the concentration below 5% may also have a direct effect by reducing the growth of fungi and hence further reducing rotting (Smock, 1958). l4 Kidd and West (1937) stored apples under low oxygen (2.5-3.5%) with zero carbon dioxide, and found that low concentrations of oxygen were more effec- tive with higher concentrations of carbon dioxide (5—10%). Since 1940 it has become clear that successful CA storage of most varieties of apples requires control of the concentration of both oxygen and carbon dioxide (Martin and Cerny, 1956; Caldwell, 1956; Smock, 1958; Blanpied and Dewey, 1960; Fidler and North, 1961; Padfield and Mendeno, 1963; Dewey and Pflug, 1963; Lord and Zaharadnik, 1964). Ethylene and other volatiles in atmosphere — Advances in CA storage have also come from investigations into the effects of ethylene (C2H2) and other volatiles which accumulate under restricted ventilation (Fidler, 1948; Pratt, 1961; Burg, 1962). Traces on ethylene cause acceleration in respiration and ripening. It has been suggested that accumulation of volatiles may be the cause of scald and therefore CA storage would enhance this disorder (Brooks and Harley, 1934). Different methods have been suggested for removing ethylene and the other volatiles from storage but these methods have not generally been accepted and there is evidence now that ethylene does not enhance ripening when the storage temperature is below 40°F and the carbon dioxide concen- trations are high, i.e., 5% (Fidler, 1960; Spencer, 1965). l5 Post-harvest pre-storage temperature control - Pre—storage treatments at high temperatures have been found to in— crease the storage life of apples, by decreasing brown core (Smock and Neubert, 1950), scald and soggy breakdown (Brooks and Harley, 1934), and internal breakdown (Schreven, 1961, 1962, 1963, 1964). Delayed storage de- creased softening rate (Brooks, 1939). Gurevitz and Pflug (1966) found a marked decrease in total wastage of Jonathan apples subjected to a delay in storage compared with regular CA storage. The objectives of this study were: A. To determine the benefit of a three day delay in storage and a slow temperature pull down with different atmospheres on Jonathan apples in semi-commercial quantities. B. To evaluate the effect of several storage conditions with different delay periods on the storage life of Jonathan apples. The overall project consisted of a number of tests where apples were subjected to different storage conditions for different periods of time. The effect of these storage conditions was evaluated by the final physiological condition of the fruit using disorders l6 and spoilage as the evaluation criterion. In addition, pressure tests were conducted and fruit flavor was evaluated. EXPERIMENTAL PROCEDURE Experimental Apples Source - Jonathan apples were obtained from two different orchards. For Experiment 1, apples were obtained from Ebers Orchard, Sparta, Michigan on October 17, 1966, and for Experiment 2, they were obtained from the Braman Orchard, Belmont, Michigan on October 12, 1966. Preparation for storage — All apples were placed in bushel sized field crates after picking. Those used in Experiment 1 were sized at the Belding Fruit Company, Belding, Michigan in their hydro-handling system. The apples under 2.5 in. diameter were discarded. The sized apples were transported to Food Science Laboratory, East Lansing, Michigan and sorted; all externally damaged apples were discarded. A random sampling technique was used to select apples for each treatment; two sized and sorted apples, randomly selected, were alternately placed in each treatment. The apples for Experiment 2 were selected in a similar manner and hand sized and sorted in the Food Science Laboratory. The sampling procedure was the same as described for Experiment 1. Each crate containing sized, sorted and sampled apples was identified by a label giving the following 17 18 information: Date, experimental treatment, gas concen- tration and temperatures. Storage Facilities Room construction - The Metal room was a wood frame structure insulated on the inside with polystyrene, and the outside covered with galvanized sheet metal which acted as a gas seal. This room had an opening at the rear for the thermo— couples and gas sampling tubes. A side opening served as the gas inlet, and the power cord for the evaporator passed through the rear. This room had double doors. The outside metal covered door was locked with bars and had a rubber gasket. The inner door was made of galvanized steel and served as the gas seal. The inside room dimensions were 6.0 x 3.25 x 5.0 ft. (97.5 cu. ft.). The Haskolite room was constructed with Haskolite panels of prefabricated polystyrene foam type material assembled with epoxy type resins. This room had an opening at the rear for gas sampling tubes, thermocouples and power cord for the evaporator. The inside dimensions were 6.5 x 3.3 x 5.0 ft. (107.25 cu. ft.). The Haskolite material from which the room was constructed was gas tight. The Tile room was a double tile wall structure insulated with palco wool. The inside was covered with a mylar-aluminum-mylar foil laminate which served as a gas seal. This room had an access tube on the right side that served as an inlet for gas. An opening on the left side l9 permitted the sampling tubes, thermocouples, and power cord to pass into the room. The tile room was equipped with double doors: the inner door served as the gas seal and fitted into a vaseline filled groove Whereas the outside door was the thermal insulation door which was bolted in place on the outside of the room. The inside dimensions of the room were 6.0 x 5.0 x 3.5 ft. (105.0 cu. ft.). The Panel rooms installation consisted of five small CA chambers, inside an overall facility, that included a work room and a 40°F storage area. The panel room unit was made of a Dow Styrofoam insulator sandwich, consisting of 4 in. of flame retardant expanded polystyrene insulation, with 1/4 in. Douglas fir plywood faces. The corners were sealed by galvanized sheet metal angles, installed over a layer of architectural calking compound. Each small chamber was equipped with its own evaporator and had pipes for gas inlet, sampling inlet, thermocouples, and power service for thexoom. The inside dimensions of the indi- vidual CA chambers were 4.0 x 5.0 x 7.3 ft. (146.0 cu. ft.). The Hermetic room (Pflug et a1, 1956)was constructed of thick (0.134 in.) steel plate. The room dimensions were 6.5 x 3.3 x 5.0 ft. (107.25 cu. ft.) and it was insulated with 4 in. of board form styrofoam. This room had an opening at the rear for gas sampling tubes, thermocouples and a power cord for the evaporator. This room was designed to be hermetic. 2O Refrigeration — Each room contained an evaporator fan. The metal, tile and Haskolite rooms contained evaporators with a larger surface area than the panel rooms. The evaporator system for each room was designed to maintain a high humidity. Suction line pressure control valves were used with liquid line and suction line solenoids to completely isolate the rooms during the off cycle. The evaporators in the panel and hermetic rooms were of the electric defrost type. Gas source — The CA gas for the experiments was provided by two Tectrol gas generators (Lannert, 1963) operated on natural gas. The natural gas was burned in the generator and the evolved high carbon dioxide and low oxygen gas was supplied to the storage rooms by a compressor. In the two experiments, three different gas con- centrations were evaluated: 9% CO2 and 3% C02; 9% CO2 and 5% 02; 5% C02 3% 02- In order to produce these three different atmospheres from the two generators, they were adjusted to produce 5% CO2 and 3% 02 and 9.7% C02 and 2% 02. By mixing the 9.7% C02 and 2.0% 02 with different amounts of air (20.8% 02 and 0.03% CO2) and the carbon dioxide evolved by the produce respiration, two atmospheres of 9% C02 and 3% 02 and 9% CO2 and 5% 02 were produced. The scheme is pre- sented in Figure 1. Temperature control - Each of the panel rooms and the hermetic room was controlled by a thermistor sensing element connected to a transistorized amplifier control relay. In the other 21 wa MUSE". a i Cogmmow meombmm woo: Haw? - em comb mm om 38:. Ken, meowbmw woo: [AL wfioo Wmflo, N.» m >9 .2. - EH mega.” woox T _i mm no e mm o Hoaxes HE. mm 8» e um on m m ENE... H. 3.0: 9:525 wow. $5 $5.3 09:83.03 26%”? 34.95? 22 rooms the temperatures were controlled by a filled thermal system with a bellows element activating a mercury switch. The temperatures were checked and recorded every day. Humidity control - The humidity in the storage room was maintained between 90-100% for the storage period. Since the rooms were tightly closed, each resembled a closed system in that water evaporated from pools maintained on the floor would remain in equilibrium with the storage room atmosphere, thus giving a humidity near saturation. Moreover, the temperature in the room was about 32°F during storage, and little water was required for saturation of the atmosphere. Gas analysis - The gas levels in each room were analyzed and recorded each day with an Orsat gas analyzer. For two days, immediately following storage of apples, the gas levels were checked every 3-4 hours, and adjustments of the genera- tors and air pumps were made. When the atmosphere in a storage room was altered by generator defect, stoppage of electrical power or opening the room for sampling, it took between 2—7 hours to reestablish the required atmosphere. This length of time depended on the void volume, the location of the gas distribution system and the room construction. Sample Inspection Apples in Experiment 1 were evaluated after 230 days in storage, and after a 14 day post storage period at 50°F, and after 118, 182 and 230 days in Experiment 2. 23 The fruit was evaluated at several time intervals during the storage season and after a 14 day post-storage hold at 50°F. Time between opening and closing of the chambers was held to a minimum during each sampling time. During inspection, six crates of apples from Experiment 1 and one crate from Experiment 2 were evaluated. Each crate contained 85-120 apples which were examined for two types of external damage: rot and lenticle spot. Rot is the soft watery spot or area showing typical deterioration and degradation of the general structure. Lenticle spot is the superficial brown to black spot that is centered at the lenticle. Spoilage was recorded and the percentage of the total sample calculated. Fifty of the evaluated apples were selected randomly and cut into four equatorial slices to determine interior damage. The internal damage was evaluated as brown core, carbon dioxide injury or internal breakdown. Brown core is a premature browning of the flesh around the core area. Brown core can exist as a trace in which the brown is barely visible, to severe brown core where this core area is almost black: the flesh is normally firm with the only change being the change in color. Carbon dioxide injury is characterized by dry pithy areas normally near the core of the fruit. Holes may develop in the tissue where large numbers of cells have collapsed. The pithy void area is normally brown in color. Internal breakdown is the brown- ing and degradation of the flesh of the fruit normally near 24 the outside skin rather than near the center of the fruit. Each type of disorder was evaluated, recorded and percent— age of total calculated. Total wastage was calculated by adding the number of apples with rot, lenticle spot and internal damage, and calculating the percentage. The percentage damaged was used as one measure of overall quality. A panel of ten men evaluated the flavor of the apples in Experiment 1. Ten apples were then selected randomly and subjected to a pressure test in the following manner: 0.5 infzof skin on each of three sides of the apple was removed. A penetrometer with a 5/16 in. diameter plunger was forced 3/8 in. into the apple tissue as a measure of flesh firmness or texture and moisture loss. The Magness-Taylor pressure was used and the measurement was taken in pounds. The remainder of the sample was held for two weeks at 509F in an air atmosphere, and then checked again in the same manner. RESULTS AND DISCUSSION Experiment 1 Apples were evaluated after 230 days storage in different atmospheres, and after two additional weeks at 50°F in air. The percentage of apples showing internal and external spoilage, rot and flesh firmness are reported in Table 1. Since CO2 and O2 percentages in atmosphere were major treatment variable, they will be referred to as ratios in the following discussion (%CO2:%02). Total apple damage was twice as much for the apples held three days in a 5:3 atmosphere as those stored immediately. The apples held three days in air had a very marked increase in total wastage compared to those held in atmosphere of 5:3. The apples held three days in an atmos— phere of 5:3 had significantly higher flavor scores than those held in air. These results varied from those reported by Gurevitz and Pflug (1966). This variance might be due to an unknown orchard growth or climate factor. A metabolic factor may have been affected differently by the storage temperature during the first three days. Another reason for this difference could have been the lack of a positive defrost system in the storage room. The lack of the posi— tive defrost system could imply higher mean temperatures, 25 26 Table 1. Influence of pre-storage and storage condition on quality of apples stored 230 days at 32°F. Quality 1 Storage Agmosphere 3 Measurement 5:3 5:3 Air Spoilage (%) Internal 2.5 6.5 0.9 External 0 O 1.2 Rot 1.9 2.7 41.8 Total 4.4 9.2 43.9 Firmness (lbs.) 7.2 7.2 5.5 1 - 5% C02 and 3% 02; No pre-storage holding (average of 4 samples) 2 - 5% CO and 3% O Held 3 days for gradual decline in 5 2 2 temperature (average of 4 samples) 3 - Held 3 days for gradual decline in temperature (average of 7 samples) 27 which may have accelerated the metabolic processes and decreased the storage life. Texture or firmness of the apples was the same for those stored in an atmosphere of 5:3 following 0 and 3 days pre-storage treatments (Table 1). However, the apples stored in air with three days pre—storage treatment were less firm than those stored in a controlled atmosphere (5:3). After two weeks post—storage at 50°F in air, no damage was incurred. 28 Experiment 2 The influence on quality of pre—storage delay (up to 11 days) and storage atmosphere for apples stored 118 days is shown in Table 2. Less spoilage occurred in apples held in a 5:3 atmosphere than in air. A higher percentage of apples held in a 5:3 atmosphere spoiled after pre—storage delays of 7 and 11 days, than after delays of 0 or 3 days. A lower percentage of apples spoiled (when held in air) in those lots held 3 or 7 days than in those held 0 or 11 days. The reasons for these differences are not known. Apples stored in 5:3 atmospheres and in 9:3 atmospheres were more firm than those held in air or in 9:5 atmospheres (Table 3). Table 4 shows the effects of apples stored 182 days in different atmospheres following pre—storage delays. Total spoilage was higher in apples held 0 or 11 days before refrigeration than in apples held 3 or 7 days. Lowest spoilage occurred in apples held 3 or 7 days in 5:3 atmosphere prior to storage. In general, the apples held 0 or 11 days before refrigeration had the highest degree of spoilage. Apples held in air were less firm (Table 5) than those held in all controlled atmosphere con— ditions. Table 6 shows the effects of apples stored 225 days in different atmospheres following pre-storage delays of 0, 3, 7 and 11 days. 29 Table 2. Influence of pre-storage delay and storage atmosphere on spoilage of apples stored 118 days at 32°F. Storage . Pre-storage Delay,(days) Atmosphere Spoilage Factor 0 - 3 7 11 % CO2 : % 02 % of apples 5:3 Internal 0 0 0 2.0 External 0 0.8 1.8 0.7 Rot 1.7 0 1.6 0.7 Total Waste 1.7 0.8 3.4 3.4 9:3 Internal 0 0 0 0 External 0 0 0 0 Rot 0 0 0 0.6 Tbtal waSte O O 0 0.6 9:5 Internal 0 0 0 0 External 0 0 0 0 Rot 0 0 0 0 Total waste 0 0 0 0 Air Internal 6.0 0 0 2.0 External 2.8 1.8 1.3 5.2 Rot O 0 0.6 0 Total Waste 8.8 1.8 1.9 7.2 30 Table 3. Influence of pre-storage delay and storage atmosphere on firmness of apples stored 118 days at 32°F. _. 1 -— 1LtJ Storage Atmosphere Pre-storage Delay (days) Z CO 2 Z O 0 3 7 11 2 2 . ‘lbs. force 5:3 10.0 9.9 9.9 10.0 9:3 10.5 10.7 9.9 9.7 9:5 901 808 808 809 Air 9.3 8.7 8.9 8.8 31 Table 4. Influence of pre-storage delay and storage atmosphere on quality of apples stored 182 days at 32°F. Storage Atmosphere Pre-Storage Delay Ldays) % C02:% 02 Spoilage Factor 0 3 7 11 % of apples 5:3 Internal 0 2.0 0(2)* 0 External 4.8 2.0 1.9 7.8 Rot 2.0 0 0 6.0 Total Waste 6.8 4.0 1.9 13.8 9:3 Internal 4(4)* 4.0 12(2)* 14(2)* External 2.2 1.9 5.4 6.5 Rot 2 2 * 2.0 2.0 2§22* Total Waste 8.2 7.9 19.4 22.5 9:5 Internal 10.9 0 0 8. 5(6. 6)* External 0.6 0.4 1.9 1.2 Rot 3.6 4.0 0 7.1 Total waste 15.1 4.4 1.9 16.8 Air Internal 10.0 2.0 2.0 2.0 External 6.9 5.0 6.1 7.7 Rot 4.0 2:9. 2.0 0 Total Waste 20.9 9.0 10.1 9.7 ( )* Means data obtained after 14 days at 50°F. All other data shows no damage was incurred. 32 Table 5. Influence of pre-storage delay and storage atmosphere on firmness of apples stored 182 days at 32°F. Storage Atmosphere Pre-Storag§:delay (days) 7 co :1 o o 3 7 11 2 2 lbs. force 5:3 10.5: 8.9 9.17 8.5 8.5 9.5 9.7 $8.6 9:3 8.8% 10.8 9.7 10.1 9.7 8.9 9.5 88.5 9:5 7.31 8.9 8.9 8.0 8032 803 704 901 Air 6.21 6.9 6.7 7.6 7.82 7.1 6.7 .9 l/Firmness after storage 2/Firmness after 14 days at 50°F following storage. 33 Table 6. Influence of pre-storage atmosphere on spoilage of apples stored 225 days at 32°F. Storage Atmosphere Pre-storage Delay (days) Z CO2 : 02 Spoilage Factor 0 3 7 11 Z of apples 5:3 Internal 2.0 1.4 0 0.6 External 0 0 0 0 Rot 0.7 l * 0 1.2 0.6 Total Waste 2.7 1.4 1.2 1.2 9:3 Internal 8.0 8.0 10(11)* 2.0 External 0 0 0 0 Rot 0 1.2 0.831)*0.8 Total waste 8.0 9. 10.8 2.8 9:5 Internal 2(1)*. 0(1)* 0 0 External 0 0 0 0 Rot 0 0.5 .4 0.8 Total Waste 2.0 0.5 .4 0.8 Air Internal 0 0 0 0 External 0 1.2 1.2 2.9(4)* Rot 0 0 2.0 0.6 Total Waste 0 1.2 3.2 3. ( )* Means data obtained after 2 weeks at 50°F in air. All other data shows no damage was incurred. 34 Total spoilage was high in apples held in a 9:3 atmosphere compared to that in apples stored in other atmospheres. Here in general, a large percentage of apples held 0 or 11 days before storage were spoiled when held in 5:3 and in 9:5 atmospheres. In the other atmospheres the difference in apple spoilage was not significant. Firmness of apples varied slightly among treatments (Table 7). Table 8 summarizes the spoilage data for apples held for different periods of delay in a 5:3 atmosphere. It is very clear that the amount of spoilage in apples held for 9 to 11 days delay was much higher than in those with 3 or 7 days delay. Apples stored without delay were firmer than those subjected to a delay before storage. Table 9 shows the influence of the pre-storage delay on apples held in a 9:3 atmosphere. Spoilage increased as the pre—storage delay period increased. Firmness did not vary significantly among the different pre-storage periods, although minor differences were found. Tables 10 and 11 show the increased amount of spoilage in apples held 0 or 11 days pre-storage in either air or a 9:5 atmosphere. However, no significant difference in firmness was detected. The apples for this experiment were small: about 2.5 inches in diameter, due to some unknown orchard or climatic factors. This may have reduced the amount of spoilage compared to the results obtained by Gurevitz and Pflug (1966). 35 Table 7. Influence of pre-storage delay and storage atmosphere on firmness of apples stored 225 days at 32°F. Storage Pre-storage Delay fidays) Atmosphere 0 , 3 7 ll lbs. force 5:3 6.1% 6.4 6.3 6.0 6.4 6.3 6.0 6.0 9:3 7.6% 7.1 6.4 7.3 7 4 7.0 6.5 6.4 9:5 6.31 7.7 8.2 8.3 6.52 7.5 8.0 8.0 Air 6.11 6.1 6.4 6.1 5.92 6.0 6.2 6.0 l/Firmness after storage 2/Firmness after 14 days at 50? following storage. 36 Table 8. Influence of pre-storage delay on quality of apples stored in an atmosphere containing 5% 002 and 3% 02 at 32°F. Days in Quality Pre-stOrage Delay (days)_ Storage Attribute 0 3 7 11 118 Total waste (Z) 1.7 0.8 2.4 3.4 Firmness (lbs.) 10.0 9.9 9.9 10.0 182 Total waste (Z) 6.8 4.0 1.9 13.8 Firmness (lbs.) 10.5 8.9 9.1 8.5 225 Total waste (Z) 2.7 1.4 1.2 1.2 Firmness (lbs.) 7.5 6.4 6.3 6.0 Average Total Waste (Z) 3.7 2.1 1.8 6.1 37 Table 9. Influence of pre-storage delay on quality of apples stored in atmosphere containing 9% C02 and 3% 02 at 32°F. Days in Quality Pre-storage Delay fidays)_ Storage Attribute 0 3 7 11 118 Total waSte (Z) 0 0 0 0.6 Firmness (lbs.) 10.5 10.7 10.0 ’927 182 Total Waste (1) 8.2 7.9 19.4 22.5 Firmness (lbs.) 8.8 10.8 9.6 10 1 225 Total Waste (1) 8.0 9.2 10.8 288 Firmness (lbs.) 7.6 7.1 6.4 7.3 Average Total Waste (X) 8.1 8.5 15.1 12.6 38 Table 10. Influence of pre-storage delay on quality of apples stored in air at 32°F. 1L M ‘- Days in Quality Pre-storage_Delay(days)_ Storage Attribute 0 3 7 11 118 Total Waste (Z) 8.8 1.8 1.9 7.2 Firmness (lbs.) 9.3 8.7 8.9 8.8 182 Total waste (Z) 20.9 9.0 10.1 9.7 Firmness (lbs.) 6.2 6.9 6.7 7.6 225 Total waste (Z) 0 1.2 3.2 3.5 Firmness (lbs.) 6.1 6L1 6.4 6.1 Average Total waste (Z) 9.9 4.0 5.1 6.8 39 Table 11. Influence of pre~storage delay on quality of apples stored in an atmosphere containing 9Z C02 and SZ 02 at 32°F. Days in Quality Pre-storage Delay (days) Storage Attribute 0 3 7 11 118 Total waste (Z) 0 0 0 0 Firmness (lbs.) 9.1 8.8 8.8 8.9 182 Total Waste (Z) 15.1 4.4 139 16.3 Firmness (lbs.) 7.3 8.9 8.9 8.0 225 Total waste (Z) 2.0 0.5 0.4 0.8 Firmness (lbs.) 6.3 7.7 8.3 8.3 Average Total waste (Z) 8.5 2.5 1.2 8.5 90 The reason for the gradual increase in spoilage from first to second storage time and the decrease from second to third storage time (common for all the treatments) is not known. This may have been caused by the location of the crates in the stack, or by a lack of uniformity in sampling the product. The fact that these apples in air were very wilted is not shown in any one of the tables. The shriveling may have been due to a lack of a positive defrost system in this storage room. The shriveling process began at the very beginning of storage and may have influenced the low percentage of disorders in apples in air since the desiccation of the tissue has a primary role and adversely affects the appearance of the disorders and apple firmness. It was shown in all treatments and after each storage period that the apples held 3 days before storage had a lower degree of wastage. Moreover, the lower spoilage in apples stored in a 5:3 atmosphere was somehow extended to include those held 7 days before storage. The reason for this phenomenon might be the deterioration and rapid aging reactions during the prolonged high temperature holding period of 7 and 11 days. Apples stored in the 9:3 atmosphere (Table 9) showed the highest percentage of total wastage due to the high percent carbon dioxide, which caused carbon dioxide injury. However, these apples were more firm than apples stored in air. Al The atmosphere containing carbon dioxide and relatively high oxygen, 9:5 (Table 11) may have compen- sating effects. Apples stored in this atmosphere had a lower percentage of waste, but were more firm than those stored in air. The quality of apples stored in the 5:3 atmosphere (Table 8) again show the advantage caused by a delay at high temperature. The apples held 3 days had less spoilage than those without delay. The 7 days delay was also found to be beneficial. The apples subjected to delayed storage were less firm than those stored immediately. No visible spoilage occurred in apples held for two weeks in air upon removal from storage after 118 days (Table 2). However, apples evaluated after longer storage periods and held two weeks in air, had similar or lower losses than those evaluated immediately after storage (Table A and 6). i The beneficial effect of 3 days high temperature treatment before storage together with high concentration of carbon dioxide and low concentration of oxygen may be explained by the kinetic theory in which molecules of matter are in motion, and heat is a manifestation of this motion (Barrow, 1961). The contact between the cells of the fruit and the gaseous environment of the fruit is indirect, through the intercellular spaces. The spaces occupy almost 30% of the total fruit volume and are very important in assisting gas diffusion in the bulky tissue of the fruit. A2 The gas circulation also occurs through the len- ticles, the skin or superficial wounds. By increasing the temperature, the velocity of carbon dioxide molecules in the higher carbon dioxide atmosphere increases, and there- fore diffusion is also increased. It is important that the increased carbon dioxide diffusion is in the early storage period becuase of two reasons: (1) Aging has an effect on the gas diffusion through the air. The perme- ability of apples to air decreases during ripening due to wax formation, and due to other factors during senescence (Spencer, 1965). (2) The application of carbon dioxide in the early stages of storage will decrease the OXygen in the intracellular spaces and the respiration inside the tissue. The increased temperatures during the first period of storage also increased the amount of carbon dioxide evolved. This carbon dioxide was added to the air spaces and decreased the relative oxygen level. The 02 level also decreased by the increased respiration. Hence, a delay occurred in the onset of climacteric, and a depression occurred in the climacteric rise. Thus it appears that the atmosphere within an apple changes with both the external atmosphere and with metabolic activities of the fruit cell. Later, after the internal atmosphere has been changed, the low temperature (32°F) adds its retarding ‘43 effect by reducing the respiration. However, if the apples reach low temperature too late (after 7 to 11 days) the prolonged high temperature decreases the storage life of the apples. SUMMARY Controlled atmosphere storage is the most ad- vanced type of storage for apples. Lowering the temperature and the oxygen will, in combination with elevated carbon dioxide, slow down the metabolic processes in the apple. Pre-storage and storage factors affecting the spoilage of Jonathan apples were evaluated. Apples were held from 0 to 11 days in air or controlled atmosphere before storage, and in air or controlled atmospheres at 32°F for periods up to 225 days. Spoilage was recorded as internal, external or rot; and flesh firmness was also measured. Controlled atmOSpheres used were, in percentage of C02 and 02, 5:3, 9:3 and 9:5. These were used in both pre-storage holding when temperature was gradually reduced to 32°F, and in storage at 32°F. When apples were subjected to a gradual decrease in temperature to 32’F in air after harvest, their quality was superior to those immediately stored at 32°F in air, or in atmosphere of 5:3. The quality of apples held before storage and during storage in 5:3 atmosphere was superior to that of apples subjected to air, or 9:3 and 9:5 atmos- pheres. 44 CONCLUSIONS On the basis of these results the following conclusions and recommendations are offered: 1. The atmosphere containing 5% C02 and 3% 02 was found to be best for storage of Jonathan apples, and better than that containing 9% C02 and 3% 02 since the high carbon dioxide content increased the carbon dioxide damage. This atmosphere was also better than that containing 9% C02 and 5% 02 and air due to high oxygen levels. 2. Delayed pre—storage holding, while temperature was gradually reduced during a 3-5 day period, was beneficial for Jonathan apples (Gurevitz and Pflug, 1966). However, different apple varieties and other orchard growth and climate factors might require a different combination of delay periods, atmospheres and storage temperatures. 3. It was shown by Gurevitz and Pflug (1966) that delayed storage in CA (5% 002 and 3% 02) at 62°F decreases the total wastage compared to CA storage without delay. Since the results of this experiment do not agree with these previous results, it is recommended that addi- tional research be conducted to determine the reasons for such differences. 4. Since there is some evidence that acceleration in changing the internal atmosphere of the apple toward 45 46 high percentage of carbon dioxide and low percentage of oxygen has a beneficial effect on its storage life, the following experiments are suggested: 8.. Increase the percentage of carbon dioxide produced by the generator in the pre—storage high temperature period above 9% in order to modify the atmos- phere as fast as possible. Introduce an atmosphere free of oxygen from the generator during the pre- storage period. Introduce some extra carbon dioxide during the initial pre-storage period. BIBLIOGRAPHY BIBLIOGRAPHY. Barrow, G. M. 1961. Physical chemistry, McGraw-Hill Book Company Inc., N.Y., N.Y. Beever, H. 1961. Respiration metabolism in plants. Ron Paterson, N.Y., N.Y. Biale, J. B. 196“. 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