Fruit and Dry Product Irradiation Processes

13 Fruit and Dry Product Irradiation Processes R. A . D E N N I S O N

Downloaded by CORNELL UNIV on May 22, 2017 | http://pubs.acs.org Publication Date: January 1, 1967 | doi: 10.1021/ba-1967-0065.ch013

University of Florida, Gainesville, F l a .

The tolerance limitation of fruit for irradiation establishes the maximum acceptable dose. If this dose controls decay organisms, the use of irradiation for a particular fruit may appear promising. Response to irradiation may be influenced by fruit maturity, variety, pre- and postharvest temperatures, handling, and extent of fungus growth. Climacteric fruits irradiated prior to the normal rapid increase in respiration usually show an immediate increase in respiration and the production of ethylene. These fruits are frequently retarded in ripening.

pproximately 30 billion pounds of fruit are sold each year i n the United States, and about half is consumed fresh. There are various estimates of spoilage losses resulting from decay i n marketing fresh fruits. A fair estimate for strawberry losses appears to be 15%, even with improved han dling practices. M a n y investigators are seeking further improvements i n the handling of fresh produce. Among methods receiving much attention are the use of postharvest chemicals, retardants of senescence, thermal treatment, con trolled atmospheres, new packaging techniques, better temperature control in storage and transit, and irradiation. One method may work well w i t h one fruit or a particular variety of fruit but not with another fruit. A reduction i n the amount of fruit spoilage during marketing is urgent, but treatments designed to reduce spoilage must not unduly alter the nat ural quality of the fresh fruit. The use of ionizing radiation is one method of reducing spoilage. H i g h doses of irradiation will completely sterilize or k i l l microorganisms, but flavor, texture, and appearance of the fruit w i l l be atypical. Therefore, low dose pasteurization levels must be used if gross changes within the fruit are to be avoided. Several summary reports and reviews on fruit irradiation are available (1,2, 8, 4, 6, 6, 7,8). 152 Josephson and Frankfort; Radiation Preservation of Foods Advances in Chemistry; American Chemical Society: Washington, DC, 1967.

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Factors Influencing


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Fruit and Dry Products Fruit Response to

Irradiation

A n y statement with regard to the response of fruit to irradiation needs to include the condition of the fruit prior to irradiation. The physiological status and disease condition will have a marked influence on this response. Species and Fruit Maturity. Great differences exist among fruit spe cies. I n general, fruit can be classified as exhibiting or not exhibiting a climacteric increase i n the rate of respiration and ethylene production as they ripen. Peaches, pears, mangoes, and tomatoes are typical fruits i n the climacteric class. If they are irradiated before climacteric, the normal physiological development is modified. Usually there is an immediate i n crease i n respiration and the production of ethylene, and ripening is fre quently retarded. If the fruits are irradiated during the climacteric, there is little change from the normal respiratory response. Citrus fruits are representative of the nonclimacteric class. Follow ing harvest, the rate of respiration of citrus slowly declines. Irradiation does not noticeably influence ripening changes in these fruits. Variety. Frequently extreme differences are found i n the response of species or varieties to irradiation. Irradiated Southland peaches tend to become somewhat mealy following irradiation, but the Loring and Dixieland varieties do not. Valencia oranges show considerable peel injury from i r radiation but not Pineapple oranges. However, this could be more of a seasonal response than a varietal difference. Temperature of Fruit. Several conditions will cause physiological stress i n fruit. E a c h fruit species varies as to the minimum temperature it can tolerate. Fruits exposed to a temperature below the minimum t o l erance prior to or after harvest will show symptoms of chilling injury. Irradiation also creates physiological stresses, which are often cumulative, so that symptoms may become evident at a higher minimum temperature. For example, untreated grapefruit can be stored at 55°F. without any ap parent chilling injury as observed on the peel, but after 200-krad irradiation or storage at 55°F., typical symptoms of chilling injury appear. Fruit Handling. The methods of handling fruit following harvest will influence the response to irradiation. M a n y fruits are highly perishable. They are easily damaged by rough handling, undergo rapid physiological changes and deterioration, and if contaminated with decay organisms may spoil i n a short time. Fruits should be precooled soon after harvest and irradiated as quickly as possible. Fungus Growth. Surface contamination of fruits is usually controlled by fungicidal materials as well as ionizing radiations. The greatest prob lem of spoilage control is experienced when spores have contaminated cuts and wounds and the fungus has grown within the tissues. Ionizing radia tions penetrate deeply and exert an effect within fruit tissues, where chem icals cannot go. However, the more extensive the growth of the fungus

Josephson and Frankfort; Radiation Preservation of Foods Advances in Chemistry; American Chemical Society: Washington, DC, 1967.

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within the tissues, the higher the radiation dose required for inactivation. If spoilage control requires a large dose, the tolerance of the fruit may be exceeded.


Radiation and Physiological Effects on Fruits The tolerance limitation of fruit for irradiation establishes the max imum acceptable dose. If this dose is sufficient to control decay organisms, the use of irradiation for the particular fruit may appear promising. Irradiation has a serious effect on softening and texture changes of many fruits. The level required for disease control in grapes is too high to avoid extreme softening of the tissues. Therefore, irradiation does not ap pear possible for grapes. Off-flavors and atypical odors have been developed in some fruits, par ticularly tangerines and limes. Increased development of red color i n the flesh of peaches and nec tarines has been noted by a number of workers, but color development has been delayed in tomatoes, pears, and mangoes. Fruits Showing Promise for Radiation Whether it will be economically feasible to irradiate particular fruits will depend upon a number of factors. A most essential point is that the fruit must not undergo appreciable quality change with irradiation levels necessary for destruction of the disease-causing organisms. Strawberries appear to be most promising for commercial radiation. There is little change in texture, flavor, color, and odor after a 200-krad dose, and the treated fruits have stood up well i n test shipments. Berries are produced i n large quantities i n concentrated areas for several months. Peaches are quite susceptible to brown rot, caused by the fungus Monilinia fructicola (Wint.) Honey. If the infection is not too severe, it can be controlled at about 200 krads. There appears to be a marked varia tion i n varietal response. Some varieties retain relatively good quality while others show gross changes, particularly i n texture. The anthocyanin pigment content i n the flesh increases as a result of irradiation. Nectarines show a response to irradiation similar to that of peaches. The ripening process in pears is inhibited by irradiation. This should be advantageous since overripening of pears is frequently a problem. Oranges have shown variable results between locations. When grown in the more arid regions, no peel injury of irradiated fruit was observed. However, Valencia oranges produced i n Florida, under humid conditions, showed considerable peel injury with treatment. W i t h 200 krads or lower treatment, the flavor of the juice was as acceptable as that from untreated fruit. A t this irradiation level, decay in Valencia oranges was significantly reduced.


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Irradiation of Dry Products


Irradiation appears to hold some promise for treatment of dry prod ucts. Insects and their larvae can be controlled i n dried fruits, such as figs and apricots. Dehydrated irradiated vegetables will absorb water much more rapidly than the nonirradiated product. This process may have great promise for use i n manufactured products, such as dried soups, where rapid reconstitu tion is highly desirable. Consumers must be educated to accept irradiated produce. Irradi ators adapted to rapid fruit treatment must be designed. Costs will largely depend upon the volume of commodities treated. Literature

Cited

(1) Droge, J. H., "Radiation-Pasteurizing Fresh Strawberries and Other Fresh Fruits and Vegetables, Estimates of Costs and Benefits," Report prepared for U . S. Atomic Energy Commission, TID 21628/Isotopes-Industrial Technology/TID 4500. (2) Green, R. J., "Relation of Environment to Disease Development in Storage and Transit," 16th National Conference on Handling Perishable Agricultural C o m modities, 1962. (3) Maxie, E. C., Sommer, N . F . , "Irradiation of Fruits and Vegetables," Natl. Acad. Sci.-Natl. Res. Council, "Radiation Preservation of Foods," Publ. 1273, 39-52 (1965). (4) Maxie, E. C., Sommer, N. F . , Brown, D . S., "Radiation Technology in Conjunction with Postharvest Procedures as a Means of Extending the Shelf Life of Fruits and Vegetables," U . S. Atomic Energy Commission, Research and Development Rept. UCD-34P80-2 (1964). (5) Schroeder, C . W., Beltran, E. G . , "Effect of Irradiation on Cooking Time of Dehydrated Vegetables," Institute of Food Technologists, Annual Meeting, 1964. (6) Sommer, N . F . , Maxie, E. C., Fortlage, R. J., Radiation Botany 4, 309-16 (1964). (7) U . S. Atomic Energy Commission, "Radiation Pasteurization of Foods. Summaries of Accomplishment 1963," Conf-Isotopes-Industrial Technology, T I D 4500, 37th ed., 1963. (8) Ibid., Conf-641002, Isotopes-Industrial Technology, RECEIVED November 9,

1964.

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Fruit and Dry Product Irradiation Processes

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