Effects of sesame oil on thermooxidative stability of soybean oil

초록

Effects of sesame oil on thermooxidative stability of soybean oil were studied by determining values of peroxides, free fatty acids, conjugated dienoic acids, and aldehydes as well as fatty acid composition analysis by GC. Soybean oil with 0, 10, 20, 30 or 40% sesame oil was heated at 160 ℃ for 25 h. Peroxide values of soybean oil increased with heating time upto 15 h and then decreased. Rate of increase in peroxide formation decreased with the addition of sesame oil, indicating the lowering of oil oxidation. The more the sesame oil was, the lower the rate was. Acid value of the heated oil did not change with heating time; however, more acids were formed in the oil with higher amount of sesame oil, which might be due to degradation of sesame oil heated above its smoke point. Conjugated dienoic acid value was the highest in 100% soybean oil and one blended with 10% sesame oil. A rate of increase in conjugated dienoic acid decreased with the content of sesame oil. p-Anisidine values of soybean oil increased with time during heating at 160 ℃. There was a bare difference in p-anisidine values among samples with different content of sesame oil ; however rate of increase was higher in samples without sesame oil. Ratios of unsaturated fatty acid to saturated fatty acid(U/S ratio) decreased with heating time and the rate of decrease was in the order of 30%, 10%, 20%, 40% and 0% of the sesame oil blending. The result strongly suggested that addition of sesame oil could improve the oxidative stability of soybean oil during heating.