Antioxidant activities of annatto and palm tocotrienol-rich fractions in fish oil and structured lipid-based infant formula emulsion

The abilities of annatto and palm tocotrienol-rich fractions (TRFs), as natural antioxidants, to inhibit lipid oxidation in menhaden fish oil and structured lipid-based infant formula emulsion, were evaluated and compared. The peroxide and anisidine values of the bulk oil and oil-in-water emulsion samples stored at 37 °C were measured over a 28-day period. The results showed that annatto TRF was a more effective antioxidant than palm TRF and α-tocopherol in both food systems at 0.02% and 0.05%. Factors, including structural differences in chromanol head and isoprenoid tail, polarity, concentration, oxidation time, and the method used to monitor lipid oxidation, were responsible for the different behaviours of tocopherols and tocotrienols. In contrast to the reported findings in vivo, addition of α-tocopherol (0–75%) did not interfere with the antioxidant activity of tocopherol-free annatto TRF in foods. Our findings may lead to the development of new natural antioxidant products for food applications.