Antioxidant activity of carotenoids against the oxidative destabilization of sunflower oil-in-water emulsions

The antioxidant activity of carotenoids (β-carotene, lycopene, paprika, marigold, bixin- and norbixin-rich annatto extracts) was estimated in sunflower oil-in-water emulsions (o/w) stabilized either by Tween 20 or by a mixture of Tween 20 and sodium caseinate at equal concentrations. Both polar (paprika, marigold, bixin, norbixin) and hydrophobic (β-carotene, lycopene) carotenoids exerted a clear antioxidant effect during thermal accelerated autoxidation (60 °C) of o/w emulsions stabilized by Tween 20, while in the protein-based emulsions only polar carotenoids acted as antioxidants against the production of primary and secondary oxidation products. Furthermore, o/w emulsions, containing different concentration of paprika and bixin-rich annatto extract (0.25-1.5 g/L) in the lipid phase oxidized slower than the control emulsions. Meanwhile, the rate of carotenoids' degradation revealed that polar carotenoids, which presented antioxidant effect in both protein and Tween 20 stabilized emulsions, presented a higher rate of degradation than the hydrophobic carotenoids.

► Polar carotenoids exerted a clear antioxidant effect in both series of emulsions. ► Hydrophobic carotenoids prevented oxidation in Tween 20-o/w emulsions. ► Increased concentrations of paprika and bixin increased antioxidant activity. ► The rate of carotenoids' degradation was related to their antioxidant effect.