Plant Products

MAP, in conjunction with proper temperature control, can be used to reduce spoilage and quality losses in fresh fruit and vegetables. The objectives of MAP of fresh produce are to:

• Inhibit microbiological spoilage, such as mold growth on product surface

• Reduce the respiratory activities of products, thereby delaying ripening and senescence

• Reduce enzymatic browning of plants

As a result of the biological nature of the stored products, the packaging of fruits and vegetables under MAP conditions is one of the most challenging problems facing the packaging industry. The major difference between plant products and other fresh foods is that plant products continue to respire after being harvested. This results in a depletion of 02 and a buildup of C02. However, when 02 supplies are too low or C02 levels too high, anaerobic respiration (fermentation) occurs, resulting in the production of alcohols, aldehydes, and ketones or other volatiles that impart undesirable off-odors and off-flavors to the product. To avoid oxygen starvation in MAP products, headspace oxygen generally should not fall below 2%. Some varieties of apples can withstand up to 10% C02, whereas strawberries can withstand 25% C02 for prolonged periods. Examples of gas mixtures for shelf-life extension of fruits and vegetables are shown in Table 5. Although carbon monoxide is not permitted in MAP of food, 4% by volume is permitted by the FDA in modified atmospheres to retard browning of lettuce cores. Currently, this is the only use of CO for food preservation permitted by regulatory authorities, although it is used rarely, if ever.

The key to successful MAP distribution of fresh and fresh-cut fruits and vegetables is to ensure the correct balance of gases within the package headspace. The challenge for the packaging industry in MAP of plant products is to develop package materials that allow the transfer of selected gases and moisture in a controlled fashion to reduce biochemical activity without a major reduction in head-space oxygen or a buildup of carbon dioxide. This is a very complex task, requiring the control of significantly more variables than with other products. Common films used are PE, PP, EVA, and styrene block copolymer. Microper-forated films (eg, P-Plus from Sidlaw), films diluted with minerals (eg, FreshHold), and films containing special polymers responsive to temperatures (eg, Landec) are all commercially available to control oxygen concentrations within packages of respiring foods. The use of PE bags with silicone rubber windows for controlled permeation of 02 and C02 have been used in France. These bags were capable of maintaining 3 to 5% 02 and C02 at 3°C.

Using MAP in conjunction with temperature control, shelf-life extensions of 15 to 30 days are possible for fruits, vegetables, and prepared salads. Excellent reviews on MAP of fruits and vegetables can be found in the text by Brody and the paper by Zagory and Kader (8).

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