THERMAL OXIDATION KINETIC OF SESAME OIL (Sesamum indicum L.) BY H-1 NMR

This study aims to investigate by, H-1 NMR the thermal oxidation kinetics of sesame oil (SO) and commercial sesame oil (CSO) obtained from roasted and unroasted seeds, respectively. The samples were heated at 180 degrees C by 8 hours/day for 15 days. The 1H NMR data analysis indicated that the hydrogen concentration decreases during 96 h of heating, remaining at 69.51%, 60.63% and 42.69% of allylic (E), vinylic (V) and bis-allylic (G) hydrogen in SO, and 49.29%, 38.51%, 18.58% in CSO, respectively. Behaving as the first order oxidation kinetics, SO average rate constant (k = mol center dot L-1 center dot h(-1)) was: k(G) = 0.088 > k(V) = 0.0052 > k(E) = 0.0037 and half-life period (h), t(1/2)(E) = 188.37 > t(1/2) (V) = 134.56 > t(1/2) (G) = 79.04. To CSO, k(G) = 0.0169 > k(V) = 0.0101 > k(E) = 0.0074 and t(1/2)(E) = 94.18 > t(1/2) (V) = 68.49 > t(1/2) (G) = 41.12. These results indicated that SO is more resistant to thermal oxidation [<k, > t(1/2)] than CSO [> k, < t(1/2)]. The study allowed to conclude that sesame oil obtained from unroasted samples has higher thermal-stability than commercial sesame oil from roasted seeds and that their cannot be used after 14.3 and 3.6 hours, respectively, for deep-frying purposes at 180 degrees C.