DEAR DR. BLONZ: If oxidation starts when air hits the cut surfaces of foods, then shouldn’t one avoid all the produce items that come cut and ready to use? Such as pre-chopped celery, carrot sticks and sliced mushrooms? -- P.M., Pima, Arizona
DEAR P.M.: Consumers are demanding more fresh, natural and convenient foods, but it is important to consider that fresh fruits and vegetables are living tissues that continue to “breathe” and metabolize after harvest. While this does not imply a need to avoid ready-cut produce, we should have some basic understanding of the process so that we can be smart shoppers.
Plant cells contain many enzymes, some of which are tucked away in special locations in the cell, walled off from the rest of the cellular contents. They remain there “on assignment,” so to speak -- the plant relies on these enzymes to metabolize (break down) what gets brought in. The products of these enzymatic actions get released for use by the rest of the cells, and the plant in general. The housing of powerful breakdown enzymes in special sub-cellular locations keeps them from acting on the plant’s vital components.
When a plant food is sliced or peeled, or if the plant has aged and dehydrated, there can be a break in the protective subcellular membranes insulating the cellular contents from their own breakdown enzymes. The liberated enzymes can begin to act and initiate breakdown on whatever cellular contents they come in contact with. This causes an apple or banana to brown when cut or peeled.
Oxidation is another way that foods can break down, this often coming from a reaction with oxygen. Cutting or slicing does expose cut surfaces to air and oxygen, but the effects can vary according to the type of food and the way in which the food is cut, packaged and stored.
There can be slight changes in quality and nutrient losses, but these tend to be minor. Vegetables and fruits tend to contain their own antioxidants that can help stave off damage. It will be obvious if the damage is significant, as the food will be unattractive and unpalatable. Color and flavor components are vulnerable to the attacks.
Companies that make use of minimal types of processing often rely on low temperatures, special washes and oxygen-scavenging systems to slow breakdown. There is even “active packaging” and controlled atmospheres that can safely maintain product freshness.
Ready-to-eat products tend to be more expensive, but in exchange, you should get a wholesome, convenient food. Be sure to observe freshness dating, and let your eyes and nose be your guides to assure you are getting the best product.
Send questions to: “On Nutrition,” Ed Blonz, c/o Andrews McMeel Syndication, 1130 Walnut St., Kansas City, MO, 64106. Send email inquiries to firstname.lastname@example.org. Due to the volume of mail, personal replies cannot be provided.