Effects of processing on oxidative stability of sesame oil extracted from intact and dehulled seeds

Oxidative stability of oils extracted from intact and dehulled sesame seeds was determined by monitoring changes in fatty acid composition, iodine value (IV), peroxide value (PV), conjugated diene (CD), para-anisidine value (p-AV), and 2-thiobarbituric acid (TEA) value and by nuclear magnetic resonance spectroscopy after storage under Schaal oven conditions at 65 degrees C for up to 35 d. The oils from coated seeds were more stable, as reflected in PV, CD, p-AV and TEA values, than those extracted from dehulled seeds after roasting at 200 degrees C, steaming at 100 degrees C, roasting at 200 degrees C plus steaming, or microwaving at 2450 MHz, except for TEA values of oil from microwaved seeds. After 35 d of storage at 65 degrees C, the CD, p-AV, and TEA values of extracted oil from dehulled microwaved seeds were 17.72, 10.20, and 1.22, respectively, while those of their coated counterparts-were significantly (P < 0.05) different at 14.20, 16.47, and 1.26, respectively. Few significant changes were evident in the fatty acid composition of oil obtained from either coated and dehulled seeds subjected to different treatments. Nuclear magnetic resonance analyses found that R(ao) (aliphatic to olefinic protons) and R(ad) (aliphatic to diallylmethylene protons) ratios increased steadily over the entire storage period, which indicated progressive oxidation of unsaturated fatty acids.