In this study, the antioxidant capacity and oxidative stability of zeaxanthin with different concentrations in soybean oil were evaluated. The oxidative or isomerization products of zeaxanthin were monitored during oxidation for 12 h at 110 °C. It was found that the ability to scavenge the free radicals (DPPH, FRAP, and ABTS) was dependent upon the concentration of zeaxanthin. However, antioxidation of zeaxanthin was observed when the concentration was less than 50 μg/g. When the concentration exceeded 50 μg/g, zeaxanthin acted as a pro-oxidant. There were three kinds of non-volatile products of zeaxanthin that were detected: (a) Z-violaxanthin, (b) 9-Z-zeaxanthin, and (c) 13-Z-zeaxanthin, and it was found that the content of 13-Z-zeaxanthin formed by isomerization was the highest. In addition, the linear ketone (6-methyl-3,5-heptadien-2-one) and cyclic volatile products (3-hydroxy-β-cyclocitral, 3-hydroxy-5,6-epoxy-7,8-dihydro-β-ionone, and 3-hydroxy-β-ionone) formed by in situ oxidative cleavage were identified.
Keywords: antioxidants; free radical scavenging; oxidative cleavage; pro-oxidants; zeaxanthin.