Problems And Concerns Associated With Map Of Freshcut Produce

Considerable care must be taken in designing MAP for fresh-cut produce. Polymeric packaging materials having appropriate permeabilities for oxygen and carbon dioxide must be carefully selected to prevent the development of an anaerobic atmosphere within the package after filling and sealing. When the in-package atmospheric oxygen concentration declines to a low level (usually somewhere between <1 and 3%), the tissue aerobic respiration rate reaches a minimum termed the extinction point. If the oxygen level falls below the extinction point, anoxia ensues and the tissue begins anaerobic respiration, which is fermentative in nature. This event triggers the rapid destruction of the tissue's like-fresh sensory quality, generating off-flavors and negatively impacting texture and appearance; in short, the product becomes unmarketable.

The optimum atmosphere within the modified atmosphere (MA) package, with respect to oxygen and carbon dioxide concentration, depends on the variety of produce, the extent of tissue damage sustained during processing, and the product temperature. Maximum quality retention is achieved when product temperature is maintained either just above its freezing point or, for some items, just above the chill-injury temperature. Lowering produce temperature reduces respiration by a factor of two- to threefold for each 10°C decline (Q10 = 2-3), and use of an appropriate MA package can result in an additional fourfold reduction in respiration rate (6).

When the temperature is sufficiently cool and an appropriate MA package results in an in-package oxygen concentration slightly above the extinction point, aerobic microbial growth also is slowed, further retarding tissue decay. However, if the package is temperature abused or improperly designed or filled, causing the oxygen concentration to fall below the extinction point, the anoxic atmosphere can encourage the growth of anaerobic and/or facultative anaerobic, psychotrophic microorganisms (2), some of which are pathogenic. This potential for pathogenic microorganisms to develop within MA-packaged fresh-cut products is of considerable concern to food science professionals and regulatory authorities.

In many cases the steady-state (equilibrium) oxygen content in fresh-cut MA packages is 2 to 5%, and there is a potential that carbon dioxide will increase to as high as 16 to 19% (7). Maximum tolerable carbon dioxide concentrations for many fresh-cut or intact items, including cauliflower, lettuce, celery, kiwifruit, cabbage, radish, sweet pepper, banana, and carrot, are in the 2 to 5% range, and physiological damage can occur at levels in excess of 2 to 6% (5). Thus, the polymeric materials selected for use in MAP need to be four to six times more permeable to carbon dioxide than to oxygen. Sometimes it is necessary to use package parameters for fresh-cut produce that provide a compromise, with the equilibrium atmosphere somewhat higher in oxygen concentration than ideal, in order to avoid excessive accumulation of carbon dioxide. The package material selected also should have a moderate to high permeability to moisture vapor in order to minimize the chance of moisture condensation on the inside surface of the package due to minor temperature fluctuations during storage and distribution.

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