Phenolic compounds and their role in oxidative processes in fruits

Antioxidant activity has been assessed in many ways. The limitation of many newer methods is the frequent lack of an actual substrate in the procedure. The combination of all approaches with the many test methods available explains the large variety of ways in which results of antioxidant testing are reported. The measurement of antioxidant activities, especially of antioxidants that are mixtures, multifunctional or are acting in complex multiphase systems, cannot be evaluated satisfactorily by a simple antioxidant test without due regard to the many variables influencing the results. Several test procedures may be required to evaluate such antioxidant activities. A general method of reporting antioxidant activity independent of the test procedure is proposed.

http://ucce.ucdavis.edu/files/datastore/608-46.pdf

Methods for testing antioxidant activity

Role of reactive oxygen species in male infertility.

Improved analysis of malondialdehyde in human body fluids.

As a consequence of aerobic life, an organism must deal with the continuous generation of reactive oxygen species (O2-, H202, OH) as byproducts of metabolism and defend itself against the harm that these can do to cellular macromolecules Organisms protect themselves from such damage with both enzymatic and nonenzymatic antioxidant defenses However, the reperfusion injuries noted after ischemic insult in mammalian organs and ascribed to a burst of reactive oxygen species produced when oxygenated blood is reintroduced demonstrate that the antioxidant defenses of many organisms can be overwhelmed, Although unusual among most mammals, many organisms routinely experience wide variation in oxygen availability to their tissues due to factors such as environmental oxygen lack, breath-hold diving, extracellular freezing, or apnoeic breathing patterns in arrested metabolic states In recent studies using various animal models (anoxia-tolerant turtles, freeze-tolerant snakes and frogs, estivating snails) our laboratory has explored the adaptations of antioxidant defenses that allow such organisms to deal with rapid changes in tissue oxygenation with little or no accumulation of damage products The key to successful transitions in several systems is the induction, during the oxygen-limited state, of elevated activities of antioxidant and associated enzymes, such as catalase, superoxide dismutase, glutathione-S-transferase, and glutathione peroxidase, so that damage during the reintroduction of oxygen (such as lipid peroxidation) is minimized However, animals that are excellent facultative anaerobes, such as freshwater turtles, appear to deal with potential of oxidative stress during the anoxic-aerobic transition by maintaining constitutively high antioxidant defenses (eg enzyme activities similar to those of mammals and much higher than those of anoxia-intolerant lower vertebrates) that can readily accommodate the burst of reactive oxygen species generation when breathing is renewed

Oxidative stress: animal adaptations in nature

Publisher Summary Lipid peroxidation is a complex process whereby unsaturated lipid material undergoes reaction with molecular oxygen to yield lipid hydroperoxides; in most situations involving biological samples, the lipid hydroperoxides are degraded to a variety of products, including aikanals, alkenals, hydroxyalkenals, ketones, and alkanes. Although attack by singlet oxygen on unsaturated lipid has been shown to give lipid hydroperoxide by a nonradical, nonchain process, the vast majority of situations involving lipid peroxidation proceed through a free radical-mediated chain reaction initiated by the abstraction of a hydrogen atom from the unsaturated lipid by a reactive free radical, followed by a complex sequence of propagative reactions. The peroxidation of polyunsaturated fatty acids (PUFAs) can proceed through nonenzymic autoxidative pathways or through processes that are enzymically catalyzed. The importance of autoxidation in the deterioration of foods, and in the oil industry, has long been recognized, and authoritative reviews are available for such aspects. A relatively new growth point for studies on lipid peroxidation has been the realization that many toxic agents can be metabolically activated within cells to free-radical intermediates that can initiate lipid peroxidation and result in cell injury. A very large number of such studies on lipid peroxidation in biological systems have demonstrated the degradation of membrane PUFAs, with a subsequent disorganization of membrane structure and disturbance of membrane function. This chapter discusses the methods used for studying lipid peroxidation concentrates on such aspects of lipid peroxidation in relation to biomembrane disturbance.

Slater Tf

Papers

Overview of methods used for detecting lipid peroxidation.