The shelf life of fresh citrus juices (orange and grapefruit) packaged in polyethylene bottles is dependent primarily on storage temperature (Fellers, J. Food Sci. 53, 1699, 1988): 1.1.degree. C., 16-22 days; 4.4.degree. C., 10-16 days; and 7.8.degree. C. 5-8 days. Kopelman and Rauchwerger (J. Food Proc. Preserv. 8; 241, 1985) reported the following shelf life values for Shamouki orange juice: 2.0.degree. C., 16 days; 2.7.degree. C., 14 days; 5.7.degree. C., 10 days; 7.4.degree. C., 9 days; 9.6.degree. C., 4 days. The pH values of various orange juices range from 3.0 to 4.0. The pH for grapefruit juice is about 3.4. At these pH values, molds and yeast organisms can proliferate.
During the storage of citrus juices, ascorbic acid decomposes, the rate depending on the amount of oxygen, the pH and the storage temperature of the juice. Orange juice (pH 4.06) held for 16 days at 5.degree. C. lost 70% of the original amount of ascorbic acid (Alli and Kermasha, J. Food Sci. 54, 674, 1989).
Fresh citrus juices, tropical fruit juices and citrus-tropical juice blends, fruit juices and fruit juice blends are popular with consumers since they possess ripe fruit quality attributes such as fresh fruit flavour, an appealing colour and turbidity (cloud). The addition of tropical fruit juices such as papaya, mango and pineapple to citrus juices has gained a niche in the marketplace. Blends of citrus juices with up to about 20% tropical fruit juices have pleasant flavour profiles.
The shelf life of fruit juices can be prolonged by heat treatment to inactivate enzymes and microorganisms (J. J. Jen, Quality Factors of Fruits and Vegetables. 1989. American Chemical Society, Washington, D.C.). However, with pasteurization of juices, the fresh fruit flavour changes to a heat-processed flavour. In the case of orange juice, pasteurization brings about the formation of secondary aroma compounds such as oxidation products of limonene and of Maillard reaction products (P. Schrier, In Quality in Stored and Processed Vegetables and Fruit, 1981. Goodenough, P. W. and Atkin, R. K. Eds. Academic Press, New York).
Modified atmosphere packaging (MAP) is a term used to denote the process of gasifying the headspace around a commodity such as a fruit or vegetable in a container prior to hermetically sealing the container. The gas mixture introduced into the headspace is commonly made up of oxygen, carbon dioxide, nitrogen and sometimes noble gases. The composition of the gas mixture is dependent on the type of fruit or vegetable, the cultivar and the required storage time. The container generally has specific gas permeability characteristics, the values being dependent on the rate of respiration of the fruit or vegetable involved and the desired ultimate gas composition. At some point during storage of a fruit or vegetable under MAP, an equilibrium gas mixture in the headspace of the container will evolve whereupon the contents of oxygen, carbon dioxide, nitrogen and other gases in the headspace gas mixture are constant. Under these circumstances, the amount of oxygen utilized per unit time in the respiration of a fruit or vegetable is equal to the amount of oxygen transported through the walls of the container. Further, the amount of carbon dioxide generated per unit time in the fruit respiration is equal to the loss of carbon dioxide per unit time from the headspace by transport through the walls of a container to the outside air.
References relating to modified atmosphere packaging (MAP) of fruit and patents granted for such a technique have conventionally focused on whole, uncut commodities. In general, MAP technology is concerned with the maintenance of a suitable oxygen-containing microatmosphere around whole fruits in oxygen permeable containers. MAP technology for whole fruits requires that aerobic conditions be maintained in the microatmosphere enveloping the whole fruit in order to prevent the development of anaerobic or fermentation "off-flavour" in the fruit. Yet at the same time, the atmosphere must contain a sufficient amount of carbon dioxide to inhibit the rates of fruit respiration, ripening and microbial growth. Certain patents disclose the removal of some of the ethylene and carbon dioxide in the surrounding atmosphere by the inclusion of a packet of chemicals in the container prior to sealing.
In a general sense, the development of modified atmosphere packaging (MAP) of fruit is in its infancy. Studies have focused on the O.sub.2 /CO.sub.2 gas flushing of packages containing whole strawberries. It has been determined that with such a process, the storage life of the strawberries can be lengthened by up to 8 days. It has also been discovered that when apples are packaged in Cryovac.TM. bags with a modified atmosphere, the shelf life of the whole apples is extended from one week to four to six weeks (LaBell, Food Processing, January, 152, 1985).
A wide variety of plastic films with different permeabilities to gases are commercially available for the modified atmosphere storage of fruits. Saguy and Mannheim (Cooling and Ripening of Fruits in Relation to Quality, Refrigeration Science and Technology, 149, 1973, Int. Inst. Refrig.) have shown that selected plastic films with various O.sub.2 permeabilities can prolong the shelf life of strawberries. Marcellin (Rev. Gen. Froid 64:217, 1974) discusses the use of a polyethylene and a silicone membrane for the modified atmosphere storage of several fruits. It has been noted that O.sub.2 transport through the plastic films ensured aerobic respiration of the fruits, yet contributed to the proliferation of aerobic microorganisms such as molds.
The following patents relate directly or indirectly to whole or fruit segment preservation:
______________________________________ Inventor Issue Date ______________________________________ U.S. Pat. No. 3,111,412 Mouk Nov. 19, 1963 4,001,443 Anantray Jan. 4, 1977 4,006,257 Kolk Feb. 1, 1977 4,055,931 Myers Nov. 1, 1977 4,079,152 Bedrosian et al. Mar. 14, 1978 4,235,750 Cazalet Nov. 25, 1980 4,331,693 Gozdziewicz et al. May 25, 1982 4,337,276 Nakamura et al. June 29, 1982 4,411,921 Woodruff Oct. 25, 1983 4,423,080 Bedrosian et al. Dec. 27, 1983 4,515,266 Myers May 7, 1985 4,895,729 Powrie et al. Jan 23, 1990 West German Patent Number 2,922,145 Kurz Mar. 20, 1980 3,136,622 Chekalov et al. May 30, 1984 Austrian Patent Number 225,346 Fetkenheue Jul. 31, 1985 ______________________________________
Modified atmosphere packaging technology for the preservation of freshly extracted fruit juices and juice blends has not been reported. Modified atmosphere packaging technology has been applied to fruits and vegetables where the cells remain intact and continue to respire. Modified atmosphere packaging technology also usually employs gases with low to moderate levels of carbon dioxide, or none at all.
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