Oxidation Reduced to Its Radical Essentials

Oct. 12, 2004
Antioxidants have a great reputation for staving off the ravages of time from the human body, but they are not well understood, even by many food industry pros. Read this to get up to speed.
By John K. Ashby, Contributing EditorOxidation kills, yet also enables life. Perhaps more precisely, insufficiently controlled oxidation kills, and sufficiently controlled oxidation is how we get our energy to live. And despite the fundamental importance of oxidation to how foods do their work, the concept is often poorly misunderstood by food industry professionals. The most simplistic definition of oxidation is the addition of oxygen to a given molecule, the combination of which liberates energy. Burning a piece of wood is a visible example of oxidation. When you burn a piece of wood you “oxidize” it. You are starting with the cellulose molecules of the wood that are mostly carbons and hydrogen (with some oxygen), and break these molecules apart by adding more oxygen molecules to them. The end result is water, carbon dioxide and a pile of ash—as well as heat and light generated along the way. The cellulose has been oxidized.A more precise physical chemistry explanation of oxidation is that you have oxidized the cellulose because you took away electrons from the cellulose. When an otherwise stable molecule has an electron taken away from it, it is not as stable anymore. This weakened (oxidized) molecule can then break, or might stay together until it “breaks” another molecule.Either way, oxidation causes molecules to change, and that induced change can be very bad. If the oxidizing damage is to DNA molecules in the cell, or to fat molecules holding cells together, or to proteins needed for structure or to fat cells lining the circulatory system, the result is damage.Good Oxidation?The controlled burning, or oxidation, of fuel that occurs in the mitochondria of our cells is the source of the energy we need to live. Our bodies (and every other living organism for that matter) continuously run a dangerous and precarious balancing act. The goal is to oxidize the right molecules in the right way at the right rate while minimizing the production of uncontrolled free radicals that can cause untended oxidation and physical damage. Even if mitochondria are running very smoothly, the process is not 100% efficient. Some small amount of this energy will not be perfectly funneled into creating the energetic molecules our mitochondria are designed to produce. The energy then goes into creating free radicals instead. And the more unbalanced the system is, the more free radicals are produced. If, in an extreme example, one of the enzymes used in the mitochondria energy production process is destroyed –- the reaction up to that point (leading up to that enzyme’s function) would continue. The energetic intermediate would continue to build up without the enzyme present to use it. This pool of energetic molecules is now available to diffuse away and oxidize any susceptible molecule it encounters. Not to mention that the end product that the mitochondria is attempting to make, that the cell needs, will not be made. It is clear, therefore, that our bodies produce damaging oxidizing chemicals as a natural by-product. Less when the engine is running efficiently, more when the engine is running inefficiently. Oxidants DefinedA free radical—or oxidant or oxidizer—is essentially a molecule with an unpaired electron. This unpaired electron is a dangerous thing because it wants to steal an electron from another molecule. When it does steal an electron from a target molecule, that target molecule is oxidized.Table I lists the basic hierarchy of primary metabolic oxidants—reactive oxygen species, or ROS, that if uncontrolled can produce significant physiological damage. Normal, atmospheric oxygen also is called “triplet” oxygen. If energy is added to this regular oxygen, one of the electrons can be forced into the opposite spin state. This elevated-energy form of oxygen is “singlet” oxygen, a much more reactive and dangerous form. Superoxide is formed when a regular oxygen molecule accepts an additional electron. Superoxide can either oxidize or reduce (donate an electron to) another molecule, and can create hydrogen peroxide. Hydrogen peroxide can be physiologically useful, but also can lead to extremely reactive hydroxyl radicals, which, in turn, can lead to peroxyl radicals. Peroxyl radicals can cause massive damage to DNA, proteins and to the lipids in cell walls—particularly the circulatory and nervous system.There are more radicals that our bodies have to deal with (reactive nitrogen species, for instance) but this is the basic set of destructive radicals that our body produces and we have to deal with.First Line of DefenseAnti-oxidants work by reacting with free radicals before they can damage important molecules (proteins, DNA, fatty acids, etc.). Anti-oxidants are the pawns sacrificed to protect Queen. There are three main mechanisms for this anti-oxidant activity: quenching, scavenging and supporting less inflammatory physiological changes.Quenching is frequently used in reference to singlet oxygen. Singlet oxygen has an electron that is in an energetic and therefore dangerously oxidizing state. A quenching involves accepting the energy from that energized molecule and returning the original molecule to its resting state. The anti-oxidant molecule now is energized; however, this is of physiological value if the energized anti-oxidant molecule is less dangerous--less reactive--than the original molecule.Carotenoids are a great example of this functionality. Carotenoids can be excited from their ground singlet state “S0,” to a higher energy singlet state “S1” by light absorption. They can also make this transition by taking the excess energy from singlet oxygen, for example. They can then harmlessly radiate this energy off as heat and do it all over again. This is exactly why they work so well as light energy antennae for the chlorophyll in plants. They can absorb and hold onto light energy, with no damage to themselves, until the chlorophyll is ready to use this energy.This is also why carotenoids can function as powerful nutritional anti-oxidants in our bodies. They can absorb the oxidizing energy that otherwise would have been used to oxidize some other molecule. They can then radiate this energy away harmlessly as heat--and do so repeatedly. Scavenging means that the anti-oxidant molecule lets itself be oxidized, giving an electron to the oxidizing molecule. Vitamin E is a great example of an anti-oxidant that scavenges free radicals. The d-alpha tocopherol lets itself be oxidized to the tocopherol-OH chemical form. The former free radical is now relaxed back to its ground state and is no longer highly reactive. This tocopherol-OH, much less reactive than the original free radical, can regenerate back to its original anti-oxidative form of d-alpha tocopherol by reacting with a vitamin C molecule. Now the vitamin E is good as new. But the ascorbic acid (vitamin C in its anti-oxidant ready form) is now oxidized to semidehydroascorbate, an even less reactive radical than the tocopherol form.Vitamin E is a very important vitamin--or at least we think so! Early this summer, the New York Academy of Sciences convened the first all vitamin E conference in the past 15 years with the following major conclusions:Virtually unanimous consent is that the current recommended daily amount is too little. We do not know how much to take, because we do not fully understand all of its nutritional functions.In addition, with respect to this current daily amount “remember that vitamin E is unique in that it is nearly impossible to get enough through a typical diet.” Supplementation is required! The USDA explicitly recognizes this. As part of the process in developing the new Food Pyramid, one of the three questions for comment was, basically, what do we do about our inability to construct meals with sufficient vitamin E?“The vitamin has now been shown to influence areas without acting as an anti-oxidant. For instance, it has been found to impact gene production.” Vitamin E, it’s not just an anti-oxidant anymore. d-alpha tocopherol has a protein that regulates its concentration in plasma! No one knows exactly why. Many point to this as evidence that there is a very important function for Vitamin E that we have not discovered yet.In addition to quenching and scavenging, anti-oxidants affect the inflammatory and consequently the oxidative state of our metabolisms. Fish oil is a great example here in that this is both a standard nutrient, and practically a drug in its ability to better balance our prostaglandin production. A Measured EffectOriginally developed a decade ago, oxygen radical absorbance capacity (ORAC) is becoming a standard measurement criterion for foods and for nutraceutical compounds marketed as anti-oxidants. The basic ORAC assay measures the ability of a given compound (or food) to scavenge the peroxyl radical. The result is a numerical score This “score” can be compared to the “scores” of other ingredients provided that the testing was done under comparable conditions, and that the units of the two scores are the same. There is a lot of fudging occurring here by not reporting the actual units, or conducting the tests under differing conditions (a fresh food versus a dehydrated extract, etc.). However, ORAC is a testing regimen that provides ways to compare radical quenching strengths among different foods and ingredients.Additional “ORAC” tests have been developed to measure the radical scavenging activity against the peroxynitrite (NORAC) and hydroxyl (HORAC) radicals, with plans to develop tests for activity against the superoxide, peroxide and singlet oxygen radicals.There are some obvious issues with these actual numbers which can be summarized by saying that a compound’s ORAC score only measures its effectiveness against one type of radical in a test tube. This number does not measure the compound’s effect in vivo against a soup of radicals. And, more importantly, the ORAC value does not necessarily directly express the healthful benefits to an organism when ingested.For example, two forms of vitamin E are d-alpha tocopherol (the naturally present isomer) and l-alpha tocopherol (present in artificially synthesized Vitamin E): each of these forms will have the same ORAC value. The scientific community, however, almost unanimously agrees that the artificial version is only half as effective as the naturally present isomer. This illustrates the principle that the goal is not necessarily to achieve the highest ORAC number for a supplement in order to maximize the healthful effect of the supplement. The ORAC number is one valuable tool for understanding oxidation/reduction issues in foods, supplements and nutrition, as long as the importance of the result is not over-emphasized.Entropy WinsPerhaps it is a bit ironic that our battle against oxidation is due to our dependence upon it. This battle is essentially our battle against entropy. Our bodies need a lot of energy to sustain ourselves and the ravages of time, oxidation and, yes, entropy ultimately take their toll. Eventually each of us will become a pile of dust as we finally run out of energy and our molecules decompose to their lowest energy state contributing our little part to the entropy of the cosmos. But in the meantime, through diet, lifestyle choices and appropriate supplementation we can win some of the battles against oxidation and perhaps buy a little more quality time.About the Author

Contributing Editor John K. Ashby is director of ingredient sales for California Natural Products, a pioneering manufacturer of aseptically packed rice and soy based drinks and rice ingredients for the food industry. He serves on the Manufacturing, Processing, Packaging and Labeling committee of the Organic Trade Association.

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