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

Abstract

This study aims to investigate by, 1H 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 180ºC 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.L-1.h-1) was: kG = 0.088 > kV = 0.0052 > kE = 0.0037 and half-life period (h), t1/2(E) = 188.37 > t1/2 (V) = 134.56 > t1/2 (G) = 79.04. To CSO, kG = 0.0169 > kV = 0.0101 > kE = 0.0074 and t1/2(E) = 94.18 > t1/2 (V) = 68.49 > t1/2 (G) = 41.12. These results indicated that SO is more resistant to thermal oxidation [ t1/2] than CSO [> k, < t1/2]. 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 180ºC.