Effects of quercetin or rutin on the oxidative stability of stripped or non-stripped soybean oils containing α-tocopherol

This study investigated the effects of stripping treatment and the presence of alpha-tocopherol on oxidative stability of stripped or non-stripped soybean oils containing quercetin or rutin (0.4 mM) stored at 25 degrees C for 45days. The degree of oxidation of oils was determined by analyzing headspace oxygen content, conjugated dienoic acid, and p-anisidine values. The contents of remaining a-tocopherol and the moisture content in soybean oils were also determined. Added quercetin or rutin acted as an antioxidant in stripped soybean oils and as a prooxidant in non-stripped soybean oils. The presence of 0.05 and 0.1 mM alpha-tocopherol accelerated the rates of lipid oxidation in non-stripped oils containing quercetin or rutin. Moisture content in non-stripped oils with rutin was significantly higher than that in other samples, and increased with the concentration of alpha-tocopherol (p < 0.05). In addition, quercetin and rutin helped increase the moisture content in stripped oils, but not in non-stripped oils. Quercetin and rutin accelerated the decomposition of alpha-tocopherol in both stripped and non-stripped oils. The oxidative stability of oils containing tocopherols and phenolic compounds depended on the stripping process.