How should food products be wrapped to prevent oxidation and other problems?

By Susan Brewer, Ph.D.

University of Illinois, Department of Food Science and Human Nutrition

Fatty foods, especially fatty foods that have been cooked, should be wrapped in oxygen-impermeable materials (such as aluminum foil or Saran Wrap) to prevent oxidation,. Examples include fried chicken, left-over roast beef, cut salami, and macaroni salad containing mayonnaise.

Foods that should be wrapped in oxygen-impermeable materials to prevent discoloration include fresh red meat (steaks, etc.) and fruits which suffer from “oxidative browning” if exposed to air, such as cut or mashed bananas, apples, or peaches.

Vegetables such as carrots, turnips, potatoes, onions, and bean sprouts should be wrapped loosely so that air can circulate around them. This will prevent Clostridium botulinum from growing and producing botulism toxin.

Unlike vegetables, fruits can be wrapped tightly in plastic wrap (with no holes) even if the packaging is airtight. Because fruits are very acidic, Clostridium botulinum can’t grow on them.

However, for other reasons, some fruits should be only loosely wrapped. Fruits that “transpire” (give off) a lot of moisture (berries especially) are commonly store-wrapped in a manner that allows the moisture to escape. If fruits transpire moisture into an airtight atmosphere, bacteria (ones that don’t cause disease) will grow and make the fruit slimy. Also, some fruits produce large amounts of ethylene gas, which stimulates ripening. Allowing this gas to escape from the package slows the ripening process.

Packaging fruits in environments that don’t contain oxygen has an additional advantages. Mold requires oxygen to grow, so air-tight packaging prevents that. Sometimes fruits are packaged in modified atmosphere packaging in which the air has been replaced with carbon dioxide and/or nitrogen, thereby eliminating the oxygen. This is often what you are looking at when you see 4 or 5 pieces of fruit on a styrofoam tray that is overwrapped with plastic film. Fresh-cut fruits should either have the cut surface covered in an airtight manner (with plastic film) or be placed cut surface down into a plastic container or on a plate. This will prevent dehydration (melons), discoloration (apples and peaches) and mold growth (most fruits).

Source(s):

Susan Brewer, Ph.D., University of Illinois, Department of Food Science and Human Nutrition