Activity of flavonoids and β-carotene during the auto-oxidative deterioration of model food oil-in water emulsions.

The antioxidant effects of flavonoids and β-carotene during the thermal auto-oxidation of food relevant oil-in-water emulsions were spectrophotometrically assessed by measuring the formation of primary oxidation products (conjugated dienes and lipid hydroperoxides). An oxidatively "sensitive" model emulsion was selected as substrate of this study in terms of processing and compositional factors. At a concentration of 1.5mmolkgr(-1), only quercetin among the tested compounds significantly reduced the oxidative deterioration of cottonseed oil-in-water emulsions. Structural characteristics (positioning of hydroxyl group) or partitioning behaviour between the emulsion phases may modulate the flavonoid activity. The high oxygen pressure conditions of the experimental system may explain the lack of any antioxidant activity for β-carotene. The antioxidant potential of quercetin increased with its concentration until a specific level. On the contrary, the antioxidant concentration within the same tested range (0.75-3mmolkgr(-1)) did not impact the activity of catechin and β-carotene. Mixtures of β-carotene with flavonoids did not exert a tendency for increasing the activity of each individual compound.