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Moisture effects on enzymatic activity |
L. N. BELL, Dept. of Nutrition & Food Science, Auburn Univ., 328 Spidle Hall, Auburn, AL 36849 Enzymatic activity is responsible for a variety of food quality losses, including discoloration, off-flavor formation, and textural modification. Moisture is a critical factor that influences enzymatic reactions, and as such, its control can be used as a simple method for limiting these undesirable changes in foods. One way that water in foods can influence enzyme activity is by serving as a reactant (e.g., hydrolysis reactions). Dehydration processes or humectant addition can reduce the amount of water available for the reaction and consequently reduce its rate. In addition, water can act as a solvent, solubilizing reactants and co-factors, which would influence enzyme activity. Dehydrated model systems containing sucrose and invertase demonstrated this effect; inversion was faster above a critical water activity due to greater sucrose dissolution. Water also influences the mobility of reactants within a food by its plasticization ability. Reactants must diffuse into the active site of the enzyme, which itself must be in the appropriate configuration for the reaction to occur. Steps to increase the glass transition temperature of the food, such as reducing the moisture content, can restrict the mobility of the enzyme and substrate and possibly lower enzyme activity. Water also influences enzyme stability. Enzymes are more susceptible to denaturation and inactivation at higher moisture contents. For example, the thermal denaturation of lysozyme occurred at progressively lower temperatures as moisture content increased. Enzyme inactivation would greatly reduce the quality changes associated with the enzymatic reactions. Therefore, understanding the various roles of water with respect to enzyme stability and activity can help control enzymatic reactions and the subsequent deterioration of food quality.
Session 3, Control of endogenous enzymes in foods: A practical approach
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