Enzymes
Enzymes are complex proteins that catalyze or accelerate the chemical changes that occur in the cells of organic substances. They are naturally present in all plant and animal tissue cells produced in all living cells, to help carry on the various life-sustaining activities. Enzymes also play an important role in the germination of seeds, the reproduction and growth of animals and plants, fruits ripen, and digestive processes animals. There are many different kinds of enzymes, each producing a specific chemical reactions. In General, they are defined as substances that they have or are the result of their catalytic action. For example, die enzyme lactase is known because it affects lactose (milk sugar)to convert it into lactic acid. This process is mainly responsible for "souring" milk.
Enzymes are also naturally present in the dead cells in the tissue, aiding in its decomposition and decay. They have the primary responsibility for the decomposition and decay of organic materials. Therefore, they almost always are destructive for perishable products.
And enzymes act arrange the meat, fish, fruit and vegetables, fetid products are created. These odors are a good indication that die food becomes unfit for human consumption. Except in a few special cases, when the fermentation is the desired outcome for the food procedures enzyme action should be either cancelled or seriously inhibited if the food should be stored in edible state.
Fortunately, enzymatic activity, is sensitive to the temperature of food products, providing practical means of control activities. Most of the enzymes are destroyed completely when exposed to temperatures of more than 170 F (77C). Therefore, correctly cooking destroys the enzymes contained in its cells. In addition, cooked food can more experience enzymatic decomposition. Unfortunately, enzymes are very resistant to low temperatures. Although their rate of a chemical reaction decreases as the temperature decreases, reactive enzyme activity continues, albeit at a slower pace. Therefore, although the enzymes are not destroyed, their activity is significantly reduced at low temperatures, especially those below the freezing point (32 F, 0C)...
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Food refrigeration and freezing