The Rationale For Modified Atmosphere Packaging Of Freshcut Produce

Damaged plant tissue usually demonstrates marked increases in aerobic respiration and catabolic metabolism and is accompanied by increased moisture loss and a decline in sensory and nutritional quality. Two primary means that are used to delay postprocessing quality degradation are refrigerated storage/distribution and alteration of the atmosphere surrounding the fresh-cut produce. Modified atmosphere packaging (MAP) of fresh-cut pro duce results in a reduced oxygen concentration and an increased carbon dioxide concentration surrounding the product.

Living plant tissue takes up oxygen and liberates carbon dioxide during aerobic respiration. When this tissue is hermetically sealed inside a package that is selectively permeable to oxygen and carbon dioxide, the initial rate of oxygen uptake by the tissue exceeds the rate at which oxygen permeates by diffusion into the package from the surrounding air. When the oxygen concentration inside the package falls to around 12%, the respiration rate of the tissue begins to slow (5). At an 8% oxygen concentration, metabolic activity such as ripening of fruit tissue declines significantly Aerobic respiration, and the rate of oxygen uptake by the tissue, reach a minimum when the in-package oxygen concentration attains a 1 to 5% level. If the package material is appropriately permeable, the minimum oxygen concentration is maintained at a steady state; that is, the rate of oxygen uptake by the tissue equals the rate of oxygen permeation into the package from surrounding air. At this minimum respiration rate, tissue quality loss due to catabolic metabolism is minimized and the onset of senescence is delayed.

Since the plant tissue also liberates carbon dioxide during respiration, the carbon dioxide concentration inside the package rises simultaneously as the oxygen level declines. Therefore, the MAP material must be sufficiently permeable to carbon dioxide to prevent excessively high levels from accumulating inside the package, which would injure the plant tissue. After the package is sealed, the interior relative humidity rapidly increases to nearly 100%. The package material is a good barrier to water vapor, so the rate of moisture vapor transmission through the package is much less than the rate at which moisture vapor accumulates inside the package via évapotranspiration from the plant tissue. Thus, shortly after the produce is sealed inside the package the moisture vapor pressure deficit between the tissue and the in-package atmosphere attains zero and further tissue moisture loss is arrested.

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