One can hardly avoid hearing about how important antioxidants are. Ads for diet supplements and skin lotions stress the usefulness of antioxidants in preventing disease and even postponing the inevitable aging process. Although common sense suggests that these guardians of good health should come from eating plenty of fresh fruits and vegetables, in some cases cooking them may make them even better for us. Studies comparing the tumor-fighting abilities of cooked and fresh tomatoes have yielded surprising results. While it is true that the high temperatures exceeding 190 °F that are needed to safely preserve tomatoes results in lower values for vitamin C, the total antioxidant benefits in cooked tomatoes are actually higher than in the fresh variety (Dewanto and others 2002).
The term oxidation describes the damage done to our cells by light, oxygen, and certain metals, often referred to as “free radicals.” These disruptive thieves steal a speck of hydrogen and start a domino effect of damage. Much like that last card on a house of cards, this action causes the whole structure to fall down. This collapse undermines the way our immune system works. Our body's natural defenses against diseases such as cancer no longer work. Antioxidants work in one of the 2 ways: some slow the chain reaction, while others donate hydrogen and stop the damage before it starts.
Studies of lycopene, an antioxidant that occurs naturally in red or orange plant foods, from Cornell Univ., Taiwan, and Germany, have found that lycopene content is much greater in the tomatoes that have been cooked. Lycopene works by pairing with single oxygen atoms, which are unstable alone and usually occur in pairs, and therefore can stop the oxidation process. Lycopene is recognized as a valuable fat-soluble component that supports the immune system and slows the damage caused by free radicals. The higher concentrations of tomato pulp in such products as tomato paste in relation to fresh tomatoes give one possible explanation for the increase in lycopene. However, the data support that the process of cooking the tomatoes releases the normally tightly bound lycopene from the plant cell walls, making it easier for our bodies to use. Studies have also shown that other chemical compounds in tomatoes called phenolics help to protect and work with the lycopene to make the antioxidant effects even stronger (Shen and others 2007).
Many of the possible chemical reactions in our bodies do not hurt us because they happen much too slowly. Sometimes catalysts, called enzymes, help these reactions along. Scientists have identified an enzyme referred to as COX-2, which causes tumors to form when cells are exposed to cancer-causing compounds. The antioxidant cocktail provided by processed tomatoes has been shown to suppress this enzyme and to help prevent the growth of cancerous tumors in laboratory experiments (Shen and others 2008). Results show much greater antioxidant and tumor suppression ability in the heat-treated tomatoes. It is believed that the heat process releases these antioxidants from the plant tissue and makes them more available for us to use.
This is good news for gardeners who, faced with more tomatoes than they can possibly eat, resort to making and freezing sauce as well as canning their tomatoes. The cooking process may actually improve the overall nutritive value by releasing the lycopene from the plant's cell walls. This information also bodes well for people who do not like fresh tomatoes. When ketchup first arrived on the scene, dietitians, who feared that it would provide empty calories, eyed it suspiciously. Although ketchup also contains a fair amount of sugar, it does contain concentrated processed tomatoes, so it may have some antioxidant effect. Many people who may not want to eat a fresh tomato do enjoy eating pizza. Pizza sauce would also contain a significant amount of concentrated tomatoes as well. Fresh fruits and vegetables undoubtedly provide us with the best Mother Nature has to offer, but it is good to know that the process used to preserve these beauties may actually enhance their nutritive value.