Microsoft Word - 3 Journal nr 4 2010 din 8 noiembrie_44-50.doc Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel Mare University – Suceava Year IX, No. 4 - 2010 48 THE INFLUENCE OF COLD CONVENTIONAL STORAGE ON FRUITS QUALITY Oana – Viorela NISTOR1, Mihai ŢÂMPĂU1, Elisabeta BOTEZ1 1Bioingineering Department, Food Science and Engineering Faculty, „Dunarea de Jos” University, 111 Domneasca Street, 800201, Galati, Phone/Fax +40 236 460165, Oana.Nistor@ugal.ro Abstract: To determine the most suitable method of cold fruits preservation, we used three types of fruits: pome fruits (apples, pears and quinces), citrus (oranges) and exotic fruits (kiwi and bananas). The fruits were stored, using a household refrigerator, operating at refrigeration temperature (5˚C) and freezing temperature (-10˚C). The storage was made in two variants: bulk and packed fruits (using LDPE bags) for a total period of 14 days. Temperature measurements were made with a two day frequency, inside the storage space and in the fruits’ core. To determine the water losses during evaporation, the fruits were weighted, before and after the storage. During the refrigeration of the bulk fruits, the quince, the orange and the banana registered a constant evolution, while the behaviour of the same packed fruits was irregular. The evolution of bulk fruits represented by quince, orange and banana, during freezing period, was regular while for the packed ones such as banana, apple and orange we registered the best results. The results lead to the conclusion that the refrigeration storage of the bulk pome fruits had a lower quantity of moisture losses (2.5-4.1%) comparing to the exotic fruits (6.5-21.3%). In packed fruits case the lowest quantities of moisture losses were registered in the pome fruits (0.6-1.1 %). To draw a final conclusion, orange and apple presents the best evolution during the conventional cold preservation, while the behaviour of banana and kiwi is not proper for this kind of storage. Key words: fruits preservation, refrigeration, freezing, pome fruits, bulk, packed, LDPE bags 1. Introduction Deterioration of fruits and vegetables during storage depends largely on temperature. One way to slow down this change and so increase the length of time fruits and vegetables can be stored, is by lowering the temperature to an appropriate level. It must be remembered that if the temperature is too low the produce will be damaged and also that as soon as the produce leaves the cold store, deterioration starts again and often at a faster rate [1]. All fruits and vegetables have a “critical temperature” below which undesirable and irreversible reactions or “chill damage”' takes place. The storage temperature always has to be above this critical temperature. One has to be careful that even though the thermostat is set at a temperature above the critical temperature, the thermostatic oscillation in temperature does not result in storage temperature falling below the critical temperature. Even 0.5°C below the critical temperature can result in chill damage. Table 1 gives the critical temperatures for various fruits and vegetables. [1] Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel Mare University – Suceava Year IX, No. 4 - 2010 49 Table 1. The critical temperatures for various fruits ([2]) Fruit type Temperature, °C Relative humidity, % Maximum storage time recommended Apple 0-4 90-95 2-6 month Orange 0-4 85-90 3-4 month Pear 0 90-95 2-5 month The biological factors involved in postharvest deterioration of fruits are: respiration, ethylene production, transpiration or water loss, physiological disorders physical damage, pathological breakdown. [2-4] Ethylene production rates, which depend on the fruit (Table 2), generally increase with maturity at harvest, physical injuries, disease incidence, increased temperatures up to 30°C, and water stress. On the other hand, ethylene production rates by fresh fruits are reduced by storage at low temperature and by reduced O2 (less than 8%) and elevated CO2 (above 1%) levels in the storage environment around the commodity. Table 2. Classification of Fruits According to Their Ethylene Production ([2-4]) Ethylene production rate Fruits Very low Cherry, citrus fruits, grape, jujube, strawberry, pomegranate Low Blueberry, cranberry, olive, persimmon, pineapple, raspberry, tamarillo Moderate Banana, fig, guava, mango, plantain High Apple, apricot, avocado (ripe), nectarine, papaya, peach, pear, plum Very high Cherimoya, passion fruit Temperature is the most important environmental factor that influences the deterioration rate of harvested fruits. For each increase of 10°C (18°F) above the optimum temperature, the rate of deterioration increases by two- or threefold. Exposure to undesirable temperatures results in many physiological disorders as mentioned above. Temperature also influences how ethylene, reduced oxygen, and elevated carbon dioxide levels affect the commodity. The growth rate of pathogens is greatly influenced by temperature and some pathogens, such as Rhizopus rot, are sensitive to low temperatures. Thus, cooling of commodities below 5°C immediately after harvest can greatly reduce Rhizopus rot incidence. [2-5]. Table 3. Classification of fruits according to their optimum storage temperatures and potential storage life Optimum storage temperatures Potential storage life (weeks) 0-2°C 3-5°C 12-14°C <2 Apricot, bush berries, strawberry, fig Cantaloupe, ripe avocado Cherimoya, guava, pineapple 2-4 Cherry, nectarine, peach, plum Tangerine and mandarin, carambola Avocado, banana, mango 4-6 Grape, tamarillo Orange, pomegranate, kumqut Grapefruit, lime, pummelo >6 Apple (nonchilling sensitive cultivars), pear, cranberry, kiwifruit Apple (chilling sensitive cultivars) Lemon Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel Mare University – Suceava Year IX, No. 4 - 2010 50 Relative humidity - the rate of water loss from fruits depends upon the vapor pressure deficit between the commodity and the surrounding ambient air, which is influenced by temperature and relative humidity. Air circulation rate and velocity can influence the uniformity of temperature and relative humidity in a given environment and consequently rate of the water loss from the commodity [2- 5]. Produce is usually cooled to its long- term storage temperature in special facilities designed to rapidly remove produce heat. Forced-air cooling is the most widely adaptable method and is commonly used for many fruits, fruit-type vegetables and cut flowers [6-10]. Hydro- cooling uses water as the cooling medium and is less widely used than forced-air cooling because some products do not tolerate water contact, and it requires the use of water-resistant packaging. It is commonly used for root, stem and flower- type vegetables, melons and some tree fruits [6-10]. Vacuum- and water spray vacuum-cooling are usually reserved for crops, such as leafy vegetables, that release water vapor rapidly allowing them to be quickly cooled. Cooling times are at least 24 h and can be much longer if produce is not packaged correctly or no provision is made to allow airflow past boxes. It is used for a few commodities, such as citrus and CA-stored apples that can have acceptable, although not optimal, quality without use of rapid cooling. Fruit are commonly classified by growing region as follows: temperate-zone (pome fruits: apple, Asian pear (nashi), European pear, quince, stone fruits: apricot, cherry, nectarine, peach, plum, small fruits and berries: grape (European and American types), strawberry, raspberry, blueberry, blackberry, cranberry), subtropical (citrus fruits: grapefruit, lemon, lime, orange, pummelo, tangerine, and mandarin, noncitrus fruits: avocado, cherimoya, fig, kiwifruit, olive, pomegranate), and tropical (major tropical fruits: banana, mango, papaya, pineapple, minor tropical fruits: carambola, cashew apple, durian, guava, longan, lychee, mangosteen, passion fruit, rambutan, sapota, tamarind). Growing region and environmental conditions specific to each region significantly affect fruit quality. [2-5] The aim of the study was the chosen of the most suitable method of cold fruits preservation for three types of fruits: pome fruits (apples, pears and quinces), citrus (oranges) and exotic fruits (kiwi and bananas). The fruits were stored, using a home refrigerator, at refrigeration (5˚C) and freezing temperature (-10˚C). The storage was made in two variants: bulk and packed fruits (using LDPE bags) for a total period of 14 days. 2. Materials and methods 2.1. Raw materials: fruits (pome fruits - apples, pears and quinces, citrus - oranges and exotic fruits - kiwis and bananas), LDPE (Low Density Polyethylene) bags. 2.2. Apparatus/equipments: mercury thermometer, core product thermometer type AMPROBE TPP1-C1, refrigerator ZANUSSI A enery class, scale Owa Laborator. 2.3. Methods The fruits were stored, using a home refrigerator, at refrigeration (5˚C) and freezing temperature (-10˚C). The storage was made in two variants: bulk and packed fruits (using LDPE bags) for a total period of 14 days. As main analyses we studied: the temperature in fruits’core, the cooling rate, water losses and the final aspect of the fruits. The temperature measurements were made with a two day frequency, inside the storage space and in the fruits’ core. To determine the water losses during evaporation, the fruits were weighted, before and after the storage. Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel Mare University – Suceava Year IX, No. 4 - 2010 51 The water evaporation was calculated as a difference between the initial fruit’s weight and the final one. mw = mif - mff where, mw – water mass; mif - initial mass of the fruit; mff – final mass of the fruit. Also it was determined the cooling rate for the refrigeration storage with a 3 hours frequency in a 15 hours interval. To express the cooling rate it was used the Newton's Law of Cooling states that the rate of change of the temperature of an object is proportional to the difference between its own temperature and the ambient temperature. This equation is of interest for either positive or negative values of the constant r. In fact r=k, and another case in which r=-k. This is a differential equation which describes cooling slope. 3. Results and discussion To determine the rate of cooling is directly related to the temperature difference between the cooling medium and the product. So the medium temperature was 5°C and the time interval was 15 hours fragmented into 3 hours sections. In the Figure 1. is represented the cooling rate of the studied fruits at refrigeration temperature. First, when the temperature of the fruit is the same with the room temperature, the temperatures drops rapidly, after the point of cooling shock (registered after 9 hours of refrigeration 4.5°C, an almost similar temperature for all the fruits being under the medium temperature 5°C). 3 5 7 9 3 5 7 9 11 13 15 Time, hours Te m pe ra tu re , 0 C Quince Apple Pear Kiwi Orange Banana Figure 1. The cooling rate of the bulk fruits at refrigeration For the core temperature determinations there were obtained the variation of each fruit variety as a particularity depending on the chemical composition and anatomical structure [11-15]. The core temperature variation of each studied fruit is presented in Figure 2. 2 3 4 5 2 4 6 8 10 12 14 Time, days Te m pe ra tu re , 0 C Apple Pear Quince Orange Banana Kiwi Figure 2. The variation of bulk fruits’ core temperature at refrigeration From this graphic it can be drawn that the orange, the quince and the banana had a constant variation, even if their anatomical structure is not similar. This can be explained as a relation between the peel presence for the citric and for the exotic fruit. Referring to quince structure, the core temperature variation can be constant as an influence of the rich fiber structure, pectic substances and sugar (8,5%) against the water natural contain which is the main responsible for the temperature variation. The bigger temperature variation was observed for the apple (decreasing temperature reaching 2.9°C) and kiwi (increasing after reaching the 3.0°C). Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel Mare University – Suceava Year IX, No. 4 - 2010 52 The water losses variation during the refrigeration storage of the bulk fruits were centralized in the following graphic. 0 100 200 300 Apple Pear Quince Orange Banana Kiwi Fr u its Weight, g Final weight Initial weight Figure 3. The water losses variation during refrigeration of bulk fruits The water losses produced by the storage at refrigeration temperature preservation are lower for the pome fruits (2.5-4.1%) than for the citric and exotics (6.5-21.3%). Correlating these technological aspects with the final aspect of the products, the exotic fruits represented by kiwi and banana had become unfit for consumption. The lowest quantity of moisture which was lost by the pome fruits can be justified by the homogeneous structure of these fruits. In Figure 4 is presented the core temperature variation of the packed fruits in LDPE bags. It had been chose the LDPE bags because the material is considered an excellent barrier for steam and water, but not so good for gases. Also because is a very used material in food industry and also for economic criteria being cheaper comparing to other types of packages. The allure of the temperatures curves is more similar than the other from the bulk fruits, but it can be seemed that during the refrigeration of the bulk fruits, the quince, the orange and the banana registered a constant evolution, while the behavior of the same packed fruits was irregular. 2 3 4 5 6 2 4 6 8 10 12 14 Time, days T em pe ra tu re , 0 C Apple Pear Quince Orange Banana Kiwi Figure 4. The variation of packed fruits’ core temperature at refrigeration In comparison with the bulk fruit the packed fruits as banana, apple and orange were registered the best results; this is a positive indicator in use of the LDPE bags. In the following graphic is presented the water losses variation during refrigeration of packed fruits. 0 50 100 150 200 250 Apple Pear Quince Orange Banana Kiw i F ru it We ight,g Final w eight Initial w eight Figure 5. The water losses variation during refrigeration of packed fruits The LDPE package is a very good protection for the water elimination, as it can be seemed all kinds of fruits presented a lower quantity of moisture content than the bulk fruits. The significant losses were diminishing since 10% for kiwi, 9% for orange and 17% for banana. For the freezing storage preservation of the bulk and packed fruits there were lead the same analyses as for refrigeration. The storage temperature was -10°C for 14 days. Besides the refrigeration process, at freezing there were made two kinds of weight determination, before the thawing Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel Mare University – Suceava Year IX, No. 4 - 2010 53 and after it. The thawing temperature is the room temperature (21°C). In Figure 6 is represented the core temperature variation of the freeze fruits. -14 -12 -10 -8 -6 -4 -2 0 2 4 6 8 10 12 14 Tim e, days T em pe ra tu re , 0 C Apple Pear Quince Orange Banana Kiwi Figure 6 The core temperature variation of freeze bulk fruits From the graphic it can be seemed that the biggest variation of the core temperature at freezing temperature is assigned to apple. Kiwi and orange had a constant variation during the freezing period. The following graphic is presenting the water losses during the storage process at freezing temperatures for the bulk fruits. 0 100 200 300 Ap ple Pe ar Qu inc e Or an ge Ba na na Kiw i Fruits W ei g h t, g Initial w eight Weight bef ore thaw ing Weight af ter thaw ing Figure 7. The water losses variation during freezing of bulk fruits It can be observed that the evolution of the quantity of moisture lost from the product is very similar for apple and pear in all three phases (freeze, before thawing and after thawing). The quince had hard texture and for this consideration it retained a big quantity of water (~20%) after thawing, by hydrating the fibers and the pectin. Even the banana had a big content of starch (29.6%) or sugars (glucose – 4.7%, fructose – 8.6% and sucrose – 13.7%) after the thawing it didn’t received a proportional quantity of water, this fact may be put on the protective thick peel which didn’t allow the mass transfer. Banana is the only fruit which is registering a water loss after thawing. Figure 8 presents the core temperature variation of freeze packed fruits. -14 -12 -10 -8 -6 -4 -2 0 2 4 6 8 10 12 14 Time, days T em pe ra tu re , 0 C A pple Pear Quince Orange Banana Kiw i Figure 8. The core temperature variation of freeze packed fruits The allure of the temperature curves is constant, almost similar for the pome fruits. The minimum temperature inflexion is detected after 10 days of storage for the majority of the studied fruits. -50 50 150 250 350 Ap ple Pe ar Qu inc e Or an ge Ba na na Ki wi Fruits W ei g ht , g Initial w eight Weight before thaw ing Weight after thaw ing Figure 9. The water losses variation during freezing of packed fruits The water losses variation is lower than in the bulk fruits; almost the weight Food and Environment Safety - Journal of Faculty of Food Engineering, Ştefan cel Mare University – Suceava Year IX, No. 4 - 2010 54 increasing is minimal (~3 g) for all the fruits. These aspects can be justified by the LDPE bags protection. 4. Conclusions As a final conclusion apples and oranges are both suitable to refrigeration and freezing storage both in bulk as in packed state. Due to the natural wax protection layer the apple complies with this kind of preservation methods. The exotic fruits represented by banana and kiwi did not comply with this kind of cold preservation, being improper for later consumption. After refrigeration the exotic fruits had been dehydrated, while after thawing the tissue structure was soaked. For the cooling rate the product is considered ‘half cool’ when its temperature drops to half the difference between its initial temperature and the cooling medium temperature. After another half-cooling period the product is ‘three-quarters’ cool. The product is usually finished at ‘seven-eighths’ or ‘fifteen-sixteenths’ cool. The cooling time predictions can be made by equations presented by Thompson et al. (1998) or a graphical method by Sargent et al. (1988). 5. References 1. FAO (Food and Agriculture Organization of the United Nations Fruit and Vegetable Processing), FAO Agricultural Services Bulletin 119,1995 2. A.A., KADER, Fruit maturity, ripening, and quality relationships, Acta Hortic:485, 1999, 203– 208 3. A.A., KADER, Postharvest Technology of Horticultural Crop, 3rd ed. University of California, Division of Agriculture and Natural Resources, Publication No. 3311, 2002 4. A.A., KADER, A summary of CA requirements and recommendation for fruits other than pome fruits, Acta Hortic. 600, 2003, 737–740 5. A.A., KADER, D., ZAGORY, E.L., KERBEL, Modified atmosphere packaging of fruits and vegetables. CRC, Crit. Rev. Food Sci. Nutr. 28(1), 1989, 1–30 6. C.A., DAVIS, Pre-cooling and Storage, Facilities James F. Thompson, Department of Biological & Agricultural Engineering University of California, 2004 7. ASHRAE (American Society of Heating, Refrigerating and Air-Conditioning Engineers), Handbook Series, Atlanta GA, 1999 8. G.S.V., Raghavan, C., VIGNEAULT, Y., GARIÉPY, N.R., MARKARIAN, P. ALVO, Refrigerated and Controlled/Modified Atmosphere Storage, 2006 9. F.B., ABELES, P.W., MORGAN, M.E., SALTVEIT Jr., Ethylene in Plant Biology. 2nd ed. Academic Press, San Diego, 1992 10. B.R., CHAMP, E., HIGHLEY, G.I., JOHNSON, Postharvest handling of tropical fruits. International Conference Proceeding, The Australian Centre for International Agricultural Research, Canberra, Australia, 1994 11. http://postharvest.ucdavis.edu: University of California Postharvest Research and Information Center 12. http://www.uckac.edu/postharv: University of California Kearney Agricultural Center 13. http://postharvest.ifas.ufl.edu: University of Florida Postharvest Group. 14. http://www.nutrition.gov: Gateway to U.S. government information on human nutrition and nutritive value of foods. 15.http://www.nal.usda.gov/fnic/foodcomp: Composition of foods