Chemical Changes in Food

Chemical Changes in Food

Chemical changes, or reactions, can also contribute to the deterioration of foods. Enzymes play a significant role in catalyzing these reactions and can be categorized depending on the substance they act on (substrate) or their mode of action. Proteases, also called proteolytic enzymes, split proteins into smaller compounds. Fish have many more active proteases than meats, which is one of the reasons they deteriorate so quickly. Lobsters are also prone to proteolytic breakdown, which begins to occur the minute they expire, unless lobsters are kept alive to the very last second. The proteases cause the lower abdomen to partially liquefy and the tail meat to become crumbly when cooked.

Lipids are broken down by enzymes called lipases, which degrade the triglycerides of fat into glycerol and fatty acids. Further degradation leads to rancidity, or off-odors and tastes. Enzymes that decompose carbohydrates are carbohydrases, each named after the particular sugar on which it acts. For example, sucrase breaks sucrose down into glucose and frutose. Yet another group of enzymes serves to oxidize compounds. Some of the more common oxidases include ascorbic acid oxidase, peroxidase, tyrosinase, and polyphenolase. The latter two enzymes are involved in enzymatic browning, which leads to unappetizing brown discoloration in some fruits and vegetables. Hydrolysis may also contribute to the deterioration of foods.