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Antioxidant properties of arylhydrazones in sunfl ower oil oxidation and regular trends in variation of the antioxidant activity of arylhydrazones in the process in comparison with ethybenzene oxidation were examined.

The presence of a synergistic effect of binary mixtures of quercetin–monosaccharide in the model reaction with the 2,2'-diphenyl-1-picrylhydrazyl radical in deoxygenated ethanol was established. It was shown that the studied carbohydrates related to the tetrose, pentose and hexose groups exhibit a synergistic effect to some extent enhancing the anti-radical effect of quercetin. The synergistic effect of the mixture is determined by the number of hydroxyl substituents and by the presence of aldehyde or ketone groups in carbohydrate molecules. The synergistic compositions of quercetin with glucose and galactose in the ratio of 60:40% showed the highest antiradical activity. The maximum synergistic effect of the mixture is 75%.  It is achieved due to the fact that, firstly, when dissolved in water, quercetin transforms into a tautomeric diketo form where hydrogen bonds form between its carbonyl groups and hydroxy groups of the monosaccharide, promoting the formation of molecular complexes, improving solubility of flavonoid in water and the manifestation of a synergistic effect in a mixture with carbohydrate. Secondly, reducing carbohydrates are able to restore oxidized forms of quercetin, which is confirmed by the great synergistic effect of aldose in comparison with ketoses, regardless of the number of hydroxy groups in the molecule. The synergistic effect of the quercetin–monosaccharide compositions, established in a model reaction with a hydrazyl radical, was compared to that in the autoxidation process of cottonseed oil. In the reaction with the peroxy radicals of cottonseed oil, the synergistic effect of the quercetin monosaccharide compositions increases up to 300% only for sugars capable of reducing quercetin radicals and reacting with air oxygen, reducing the steady-state concentration of peroxy radicals in the system.

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