The generation of reactive oxygen species (ROS) and other free radicals (R) during metabolism is a necessary and normal process that ideally is compensated for by an elaborate endogenous antioxidant system. However, due to many environmental, lifestyle, and pathological situations, excess radicals can accumulate, resulting in oxidative stress. Oxidative stress has been related to cardiovascular disease, cancer, and other chronic diseases that account for a major portion of deaths today. Antioxidants are compounds that hinder the oxidative processes and thereby delay or prevent oxidative stress. This article examines the process of oxidative stress and the pathways by which it relates to many chronic diseases. We also discuss the role that endogenous and exogenous antioxidants may play in controlling oxidation and review the evidence of their roles in preventing disease.

Diet is believed to play a complex role in the development of cardiovascular disease, the leading cause of death in the Western world. Tomatoes, the second most produced and consumed vegetable nationwide, are a rich source of lycopene, beta-carotene, folate, potassium, vitamin C, flavonoids, and vitamin E. The processing of tomatoes may significantly affect the bioavailability of these nutrients. Homogenization, heat treatment, and the incorporation of oil in processed tomato products leads to increased lycopene bioavailability, while some of the same processes cause significant loss of other nutrients. Nutrient content is also affected by variety and maturity. Many of these nutrients may function individually, or in concert, to protect lipoproteins and vascular cells from oxidation, the most widely accepted theory for the genesis of atherosclerosis. This hypothesis has been supported by in vitro, limited in vivo, and many epidemiological studies that associate reduced cardiovascular risk with consumption of antioxidant-rich foods. Other cardioprotective functions provided by the nutrients in tomatoes may include the reduction of low-density lipoprotein (LDL) cholesterol, homocysteine, platelet aggregation, and blood pressure. Because tomatoes include several nutrients associated with theoretical or proven effects and are widely consumed year round, they may be considered a valuable component of a cardioprotective diet.

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The antioxidant activities of representative flavonoid classes (flavonols, flavones, flavanones, isoflavones and flavanols) relative to dl‐α‐tocopherol were evaluated using the Oxidative Stability Index (OSI) value. At 5 mM concentrations in tocopherol stripped corn oil (TSCO), antioxidant activity was determined as follows: (+) catechin > quercetin > (+,−) taxifolin > dl‐α‐tocopherol > THI (3′, 4′, 7‐trihydroxyisoflavone) > luteolin. Intra‐assay and inter‐assay coefficients of variation were 1.43% and 2.73%. Peroxide Induction (PI) values were utilizéd as a comparison method using compounds and conditions identical to those in OSI experiments. Relative values for OSI and PI of the flavonoids tested showed a 0.98 correlation. This method also revealed differences in antioxidant activity of catechins due to stereochemistry. The OSI offers a simple, reproducible method for the evaluation of flavonoid antioxidant activities in a lipid environment.