Lipoxygenase-catalysed degradation of carotenoids from tomato in the presence of antioxidant vitamins.

Carotenoid extract from ripe tomato fruit was subjected to a lipoxygenase-catalysed co-oxidation in the presence of vitamin C and vitamin E at different concentrations. Relative retention (%) of major carotenoids by the experimental mixture was used as an index of their degradation and interaction with the antioxidants. Oxidation-prevention activity of each antioxidant against pigment co-oxidation as impacted by their molar concentration was studied. beta-Carotene was found to be the most sensitive pigment, followed by lycoxanthin and lycopene. Ascorbic acid when added in the range of 0-1.8 mM interacted with the different carotenoids by different modes. Evidence was given on regeneration, by ascorbic acid, of lycopene during the course of co-oxidation. The concentration required for alpha-tocopherol acetate to exhibit antioxidative effect was 10 times higher than that of ascorbic acid. beta-Carotene was prevented, by alpha-tocopherol acetate, faster than lycoxanthin and lycopene. The latter carotenoids differed substantially in their interaction with the lipophilic antioxidant at only the lowest concentration (0.3 mM). It was established that under the given conditions there is no synergism between vitamin C and vitamin E that improves their oxidation prevention against co-oxidation of carotenoids. Moreover, the combined use of antioxidants caused more oxidative degradation of beta-carotene.