Enzyme Action - The activity of enzymes naturally present in foods results in changes in appearance, texture and flavor, and loss of vitamins. For example, apples, lettuce and bananas all darken when cut due the present of the enzyme, polyphenoloxidase. When the cells of the fruit or leaf are ruptured, the enzyme is able to come in contract with colorless compounds (polyphenols) that it changes into brown or reddish compounds. Similarly, enzymes reduce the vitamin C content of freshly harvested green beans by about 1/3 in 24 hours, if the beans are held at 68°F. In the first 6 hours after harvest, sweet peas will lose about 40 percent of their sugar content due to enzyme action, if not cooled right away. Development of flavor changes, sometimes described as hay-like, bitter, oxidized, or simply old, also occur as a result of enzyme action. Bruising or crushing of raw foods increases enzyme activity and quickens the loss of quality.

Enzymes are easily inactivated by quickly heating raw food to temperatures of 170°F to 190°F in boiling water, in steam, or with a microwave oven. This is the purpose of blanching vegetables before freezing or drying.

Oxygen -The presence of oxygen causes oxidation, which causes many color and flavor changes, including rancidity of fats. Oxygen can also increase activity of many chemical substances in food.

Good airtight packaging, careful wrapping of food to exclude oxygen and vacuum packaging machines are all good ways to exclude oxygen and improve the shelf life of stored food.

Insects in Food -Some unavoidable insect eggs are contained in freshly harvested grain, vegetable seeds, herbs, tree nuts, and some fruits. If they are not controlled, the eggs will hatch and become larvae that will burrow through these foods to eat. Proper preservation steps will prevent hatching of these eggs.

To avoid stored food pests, use good sanitation. Clean up spilled foods. Store dry foods in covered containers. Glass, food-grade plastic, or metal containers are more insect-proof than cardboard or plastic bags. Buy food staples in quantities that can be used within the time periods listed in Storing Foods at Home , EB1205.

If insects are found in food:

• Locate all infested foods and discard them.
• Clean storage areas thoroughly.
• Chemical control is not usually recommended. If problem is severe and widespread, assistance may be obtained from a reputable pest control operator.

Controlling Stored Food Pests in the Home , CIS 850 offers additional information.