DEAR DR. BLONZ: You often discuss oxidation when dealing with health issues, and I wonder how this applies to foods when they’re exposed to air. Please explain more about how oxidation works. I also want to know if it is an issue with foods like carrot sticks and mushrooms, which now come cut and ready to use. -- R.W., Anderson, South Carolina
DEAR R.W.: Oxygen is essential for life; much of this comes from its ability to react with other substances. Something combining with oxygen undergoes “oxidation,” and when complete, it’s been “oxidized.”
“Antioxidants” are thought of as beneficial because oxidation is associated with bad things, but it’s important to understand that oxidation is integral to health. Our body gets most of its energy when fats are oxidized in a predetermined way inside a designated part of the cell, and oxidation is also a key player in our bodily defenses. Virtually everything we’re made of required oxidation at some point during the construction process.
Oxidation, therefore, should not be considered evil; it only becomes problematic when it takes place at the wrong time and place. We have systems set up to stop this using antioxidant substances; some are made by the body, while many come from our diet. Plant foods are the primary sources of dietary antioxidants. This makes sense, as they evolved systems that allowed them to flourish while exposed to the oxidizing rays of the sun. Curiously, antioxidants tend to work by being more attractive to oxygen: They take the oxygen “hit” first, to shield the substance they are designated to protect. From this, you may understand why having a diet that’s high in oxidizable fats while relatively low in antioxidant plant foods is a recipe for problems.
As to the other specifics of your question, fresh fruits and vegetables are living tissues, and they continue to breathe after harvest. There is no need to avoid ready-cut produce, but it pays to be a smart shopper. A couple of destructive processes are at play.
Plant cells contain enzymes that are tucked away until the plant food is sliced or peeled. At that point, the enzymes are liberated, and are free to act on the food. This is what causes apples and bananas to brown when cut -- a process called enzymatic browning.
Oxidation is another way that foods can break down. 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 changes in quality and some loss of nutrient value, but these will be minor due to the fact that vegetables (and fruits) are low in fat, and they contain their own antioxidants to help stave off damage. When damage is excessive, the food becomes unattractive and unpalatable.
Companies that do this type of minimal processing make use of 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 are more expensive, but the convenience can be worth the price, provided the product is wholesome and fresh. Be sure to observe freshness dating and let your eyes be your guide to ensure you are getting the best product.
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