a. Caused by Sugars. Nonenzymatic browning is a process in which foods darken without the catalytic effect of enzymes. It differs markedly from the darkening of fresh fruits and vegetables due to enzymatic degradation. The food constituents responsible are certain simple sugars which react with proteins, amino acids, or other substances normally present in the foods.
b. Flavor Change in Some Foods. Although the darkening in color of the food may be undesirable, the more notable changes are often those of flavor.
(1) The rate of browning reactions increases with temperature, and these chemical changes may contribute to desirable flavor development on cooking.
(2) Maple syrup gets its characteristic flavor from the chemical process as the maple sap is concentrated by boiling.
(3) A similar reaction causes the caramelized flavor in canned evaporated milk, which many people find much less acceptable than the taste of fresh milk. But the same flavors of evaporated milk are characteristic of the desirable flavors of caramel candy and certain other foods.
c. Limiting Factor for Dehydrated Foods. Nonenzymatic browning may occur in dehydrated foods (such as meat, eggs, and some fruits and vegetables) after storage for a time. This browning reaction makes dehydrated items objectionable, so much so that this otherwise promising method of food preservation is extremely limited in its practical uses.
d. Problem in Long-Term Storage. Nonenzymatic browning is most troublesome in foods, even canned sterilized foods stored for long periods of time at relatively high temperatures. Consequently, food deterioration due to nonenzymatic browning is a great problem in military and survival rations, which are often stored at relatively high temperatures. Although, in a few instances, the browning reaction can be delayed by certain food ingredients, the best way to diminish nonenzymatic browning is proper food processing and storage conditions.
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