Synergist, antioxidative effect

This leads to a synergistic antioxidant effect in the presence of both... 

Zhou, B., Jia, Z.S., Chen, Z.H., Yang, L., Wu, L.M. Liu, Z.L. (2000). Synergistic antioxidant effect of green tea pofyphenols with a-tocopherol on fiee radical initiated peroxidation of linoleic acid in micelles. Journal of the Chemical Society, Perkin Transactions 2,785 791. 

Ascorbic acid also forms soluble chelate complexes with iron (142—145). It seems ascorbic acid has no effect on high iron levels found in people with iron overload (146). It is well known, in fact, that ascorbic acid in the presence of iron can exhibit either prooxidant or antioxidant effects, depending on the concentration used (147). The combination of citric acid and ascorbic acid may enhance the iron load in aging populations. Iron overload may be the most important common etiologic factor in the development of heart disease, cancer, diabetes, osteoporosis, arthritis, and possibly other disorders. The synergistic combination of citric acid and ascorbic acid needs further study, particularly because the iron overload produced may be correctable (147). 

There has been some evidence of a higher antioxidant effect when both flavonoids and a-tocopherol are present in systems like LDL, low-density lipoproteins (Jia et al., 1998 Zhu et al, 1999). LDL will incorporate a-tocopherol, while flavonoids will be present on the outside in the aqueous surroundings. A similar distribution is to be expected for oil-in-water emulsion type foods. In the aqueous environment, the rate of the inhibition reaction for the flavonoid is low due to hydrogen bonding and the flavonoid will not behave as a chain-breaking antioxidant. Likewise, in beer, none of the polyphenols present in barley showed any protective effect on radical processes involved in beer staling, which is an oxidative process (Andersen et al, 2000). The polyphenols have, however, been found to act synergistically... 

BisHov s J, MASUOKA Y and KAPSALis J G (1977) Antioxidant effect of spices, herbs and protein Hydrolyzates in freeze-dried model systems Synergistic action with synthetic phenolic antioxidants, J Foot/ Processing Preservation, 1, 153-66. 

This mechanism is now considered to be of importance for the protection of LDL against oxidation stress, Chapter 25.) The antioxidant effect of ubiquinones on lipid peroxidation was first shown in 1980 [237]. In 1987 Solaini et al. [238] showed that the depletion of beef heart mitochondria from ubiquinone enhanced the iron adriamycin-initiated lipid peroxidation whereas the reincorporation of ubiquinone in mitochondria depressed lipid peroxidation. It was concluded that ubiquinone is able to protect mitochondria against the prooxidant effect of adriamycin. Inhibition of in vitro and in vivo liposomal, microsomal, and mitochondrial lipid peroxidation has also been shown in studies by Beyer [239] and Frei et al. [240]. Later on, it was suggested that ubihydroquinones inhibit lipid peroxidation only in cooperation with vitamin E [241]. However, simultaneous presence of ubihydroquinone and vitamin E apparently is not always necessary [242], although the synergistic interaction of these antioxidants may take place (see below). It has been shown that the enzymatic reduction of ubiquinones to ubihydroquinones is catalyzed by NADH-dependent plasma membrane reductase and NADPH-dependent cytosolic ubiquinone reductase [243,244]. 

At present, considerable interest is drawn to the use of natural mixtures of antioxidants isolated from various vegetable materials. Some authors claim that such mixtures manifest stronger antioxidant effects than individual components due to synergistic interactions. It is of course quite possible, but it should be noted that synergistic interactions are not a single mechanism of the interaction between components for example, the simultaneous presence of the antioxidant and prooxidant flavonoids might diminish summary antioxidant effect of the mixture. Furthermore, natural mixtures contain, as a rule, some unknown compounds, which affect the summary effect by unknown manner. 

Alpha-tocopherol is a highly lipophilic compound, and is an excellent solvent for many poorly soluble drugs.Of widespread regulatory acceptability, tocopherols are of value in oil- or fat-based pharmaceutical products and are normally used in the concentration range 0.001-0.05% v/v. There is frequently an optimum concentration thus the autoxidation of linoleic acid and methyl linolenate is reduced at low concentrations of alpha tocopherol, and is accelerated by higher concentrations. Antioxidant effectiveness can be increased by the addition of oil-soluble synergists such as lecithin and ascorbyl palmitate. " ... 

Farombi and Burton, examined the effects of several carotenoids on autoxidized triglycerides and concluded that potential prooxidant effects could occur at high concentrations. Moreover, Henry et al., suggested that at concentrations >500 ppm both P-carotene and lycopene acted as prooxidants by decreasing the induction time significantly, during the heat catalyzed oxidation of safflower seed oil. Several studies have shown that the presence of primary antioxidants and especially tocopherols stabilize carotenoids so they exhibit synergistic antioxidant character, instead of the prooxidant action that carotenoids would present individually. 

We believe that an important application of microemulsions is to provide improved antioxidation effectiveness because of the possibility of a synergistic effect between hydrophilic and lipophilic antioxidants. This is one way of simulating Nature s protection of cell membrane oxidation by tocopherols within the bilayer, which are reactivated by ascorbic acid in the water phase. We describe here how unsaturated oils can be protected, as an illustrative example. 

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