Ascorbyl palmitate radical

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). 

The antioxidants butylated hydroxyanisole (BHA), butylated hydroxytolu-ene (BHT), tm-butylhydroquinone (TBHQ), propyl gallate, ascorbyl palmitate and citric acid were evaluated for potential to reduce NOx emissions from a single cylinder, direct-injection, air-cooled, naturally aspirated Yanmar engine (Hess et al, 2005). BHA and BHT reduced NOx emissions by 4.4 and 2.9%, respectively, but the other antioxidants evaluated did not exhibit any beneficial effects (see Table 1.2). Antioxidants may impede NOx formation by inhibiting the formation of combustion-derived radicals. 

Figure 9-24 Prevention of Lipid Free Radical Formation by Ascorbyl Palmitate. Source From M.L. Liao and P.A. Seib, Selected Reactions of L-Ascorbic Acid Related to Foods, Food Tech-nol., Vol. 41, no. 11, pp. 104-107, 1987.

Jurkovic, P, Sentjurc, M., Gasperlin, M., Kristi, J., and Pecar, S. (2003), Skin protection against ultraviolet induced free radicals with ascorbyl palmitate in microemulsions, Ear. J. Pharm. Biopharm., 56(1), 59-66. 

Oxidative stability of 00-3 fatty acids can be increased using free radical scavengers. TBHQ (t-butyUiydroquinone) at a concentration of 0.02% has successfully slowed down the oxidation of menhaden oil for up to 40 days, compared with 3 days for the control group (83). a-Tocopherol and butylated hydroxytoluene (BHT) alone or in combination increased the oxidative stability of EPA and DHA (84). The most notable success in fish oil stabilization has been achieved with ternary antioxidant systems, which contain a- or y-tocopherol concentrates, ascorbic acid (or ascorbyl palmitate), and lecithin (85). 

By this synergistic mechanism, tocopherols and ascorbic acid can mutually reinforce one another by regenerating the oxidized form of the other. Radical exchange reactions among lipid radicals, tocopherols, and ascorbic acid are the basis of numerous approaches for stabilizing oil and foods with their mixtures. It is however important to note that vitamin C is not soluble in the lipid phase that is most susceptible to oxidation. This was the reason why L-ascorbic esters were developed, e.g., ascorbyl palmitate that has a lipid solubility superior to that of ascorbic acid. Mixtures of ascorbyl palmitate with tocopherols are well known for their synergistic activity. 

Vitamins (see Section 8.6), often added to cosmetic formulations, act as antioxidant preservatives due to their general antioxidant properties towards free radicals. Examples are retinol (vitamin A) and its precursor j5-carotene, tocopherol (vitamin E) and ascorbic acid (vitamin C). Moreover, vitamin derivatives, such as retinyl acetate, retinyl palmitate, ascorbyl palmitate, magnesium ascorbyl phosphate and tocopheryl acetate among others, are also employed as antioxidant agents. 

Colorless composites with good mechanical properties can be obtained with either -butyl perbenzoate, cumene- or -butyl hydroperoxide and ascorbic acid or ascorbyl palmitate systems (50). Mechanisms for the free radical formation are given in Fig. 4. Addition of trace amounts of transition metals in their higher oxidation state (Cu", Fe" ) to the perester component further speeds up the polymerization. On admixture with the ascorbic acid derivative the metal cation is reduced to its lower oxidation state which, because it is a potent one electron reductant and will rapidly activate the free radical decomposition of the perester, which it in turn is reoxidized to its higher oxidation state. Means for prevention of oxidation of ascorbic acid or its derivatives on prolonged storage must be developed for these formulations to be suitable for dental application. 

L-Ascorbyl-6-palmitate is a fat-soluble synthetic ester of ascorbic acid. It has been used extensively as an antioxidant in foods, pharmaceuticals and cosmetics, particularly as a preservative for various edible oils and waxes The inhibition of polymerisation of bovine serum albumin by HO radicals generated by the Fenton reaction indicated ascorbyi radical exerts a considerable protective effect against polymerisation by scavenging HO (Perri-CONE et al. 1999). L-Ascorbyl-6-palmitate was 1 order of magnitude faster in scavenging these radicals... 

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