Lipid oxidation ascorbic acid, activity

Ascorbic acid, found in milk at a concentration of 10-20 mg/1, is also apparently linked with the development of oxidized flavors in milk. Milk treated to remove ascorbic acid is more resistant to copper-catalysed lipid oxidation. The catalytic activity of copper is enhanced in the presence of ascorbic acid. However, when ascorbic acid is present in milk at sufficiently high concentrations (50-200 mg/1), it inhibits effectively the development of oxidized flavors. Combinations of ascorbate and copper have either prooxidant... 

Antioxidant capacities of common individual curcuminoids were determined in vitro by phosphomolybdenum and linoleic acid peroxidation methods. Antioxidant capacities expressed as ascorbic acid equivalents (pmol/g) were 3099 for curcumin, 2833 for demethoxycurcumin, and 2677 for bisdemethoxycurcumin at concentrations of 50 ppm. The same order of antioxidant activity (curcumin > demethoxycurcumin > bisdemethoxycurcumin) was observed when compared with BHT (buty-lated hydroxyl toluene) in linoleic peroxidation tests. The antioxidant activity of curcumin in the presence of ethyl linoleate was demonstrated and six reaction products were identified and structurally characterized. The mechanism proposed for this activity consisted of an oxidative coupling reaction at the 3 position of the curcumin with the lipid and a subsequent intramolecular Diels-Alder reaction. ... 

Since ascorbate reduces photooxidation of lipid emulsions and multivitamin preparations (see Figure 4) [19], Lavoie et al. [34] studied the formation of oxidative by-products of vitamin C in multivitamins exposed to light. They found that the loss of ascorbic acid in photoexposed multivitamin preparations was associated with the generation of products other than dehydroascorbate and 2,3-diketogulonic acid, which are the usual products of vitamin C oxidation. The authors showed that hydrogen peroxide at concentrations found in TPN solutions induced the transformation of dehydroascorbate into new, biologically active compounds that had the potential to affect lipid metabolism. They believe that these species have peroxide and aldehyde functions [35]. 

Several workers have shown that a high concentration of ascorbic acid added to liquid milk inhibits oxidation. Chilson (1935) suggested that added ascorbic acid acts as a reducing agent, which is oxidized more readily than milk fat. Bell et al. (1962) suggested that addition of L-ascorbic acid to cream produced a medium less conducive to oxidation by lowering the oxidation-reduction potential. Addition of an adequate level of surface-active ascorbyl palmitate to milk products may retard lipid oxidation by orientation at the lipid-aqueous interface where it intercepts free radicals (Badings and Neeter, 1980). 

Vitamin C is also able to protect the hypothalamus from oxidative stress induced in rats by an environmental toxicant (Muthuvel et al., 2006). Ascorbic acid confers protection from increased free-radical activity in the brain of spontaneously hypertensive rats by improving total antioxidant and superoxide dismutase status, thus preventing high blood pressure and its complications (Newaz et al., 2005). Also, intravenous cerebroprotective doses of citrate/sorbitol-stabilized DHA are correlated with increased brain ascorbate levels and a suppression of excessive lipid peroxidation (Mack et al., 2006). 

Iron being a redox-active metal, it most hkely exerts its toxic effects through the generation of hydroxyl radical or by generation of ferryl ion. In iron loaded condition, there is generation of radical species leading to hpid peroxidation. Lipid peroxidation of cellular membrane would have deleterious effects on their function and hence on the function of the cell. There is also irreversible oxidation of ascorbic acid. Deficiency of ascorbic acid can lead to a reduction in the amount of iron available for erythropoiesis. 

Several proteins that exist in food (e.g., lactoferrin, ferritin, transferritin, heme protein) possess strong binding sites for iron. Reducing agents (ascorbate, cysteine, superoxide anion) to low pH causes release of iron from proteins and accelerates lipid oxidation (34). Some amino acids and peptides found in muscle foods (e.g., carnosine) are capable of chelating metal ions and inhibit their prooxidant activity (35, 36). 

All natural antioxidants under special conditions possess pro-oxidant activity. It was primarily noted for ascorbic acid by describing the initiation of lipid peroxidation by pair Fe - ascorbic acid because vitamin C easily reduces Fe " into Fe " supporting its ability to regenerate SAR from molecular oxygen. Ascorbate itself is transformed into oxidized state ... 

The concentration of ascorbate in the human plasma is 25 pM and above. Cells take up ascorbate by a Na -coupled uptake mechanism against a concentration gradient. A marked stereo-selectivity for L-ascorbic acid relative to D-isoascorbic acid in their cellular transport has been shown by Franceschi et al. [12]. The same transport is also important in the intestine. The nutritional supply of ascorbic acid is the only source for this vitamin in humans, primates, and guinea pigs. Other mammals are able to produce ascorbic acid. There exists sufficient evidence for an active role of ascorbate as an antioxidant in vivo. Decreased ascorbic acid will increase lipid peroxidation and decrease vitamin E and is connected with oxidative DNA damage. The supply of ascorbate in some cases will reduce the amount of oxidative damage in diseases that... 

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