Moisture gain and loss in packaged foods
1982
Labuza, Theodore P.
Mathematical relationships and data concerning water activity (AW), rate of weight of water transport across the food (or food wrapping) film barrier, and shelf-life predictions are described and illustrated. In a 75% relative humidity (RH) atmosphere, a cracker will gain water while a slice of meat will lose water; they will both come to the same AW (albeit, different water contents). To employ useful packaging protection to minimize food moisture changes on storage, both the sorption isotherms (moisture content versus AW) of the food product, and the transport properties of the packaging film, must be known. Two basic principles of addressing the critical limits of AW (critical AW values) are discussed, along with 7 examples of food types as related to critical AW values. It is illustrated that, using laboratory data based upon some worst case situation, projecting the data to some common temperature and humidity (e.g., 73 degrees F, 50% RH) condition, and requiring a minor degree of overprotection to food moisture change, should satisfy both the US FDA's and industry's objectives concerning protection against food moisture changes. (wz)
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