Sterculia striata seed kernel oil: Characterization and thermal stability

Abstract

The objective of the present work was to characterize sterculia seed kernel oil. The chemical composition of the seeds, physicochemical properties as well as the fatty acid composition of the kernel oil was determined. The chemical composition of kernel flour presented about 25.8% lipid content. The physicochemical parameters such as acid, iodine, peroxide and saponification values were 0.82 (% as oleic acid), 69.2 (g iodine/100 g oil), 4.20 (m eq./kg) and 136.1 (mg. KOH/g oil), respectively. With respect to fatty acid composition, the oil contained 36.2, 43.7 and 10.9% saturated, monounsaturated and polyunsaturated fatty acids, respectively. Palmitic acid (31.9%), oleic acid (41.7%) and linoleic acid (10.73%) were the principal saturated, monounsaturated and polyunsaturated fatty acids. Two cyclopropanoid fatty acids i.e. sterculic and malvalic acid were identified at a concentration of 5.3 and 2.3%, respectively. With regards to the thermal stability of the oil, a thermogravimetric analysis (TGA) has shown that the oil was stable until about 284 °C, above that the oil started loosing mass, while a differential thermogravimetric analysis (DTGA) revealed three stages of degradation with an increase in temperature. These stages corresponded to the degradation of polyunsaturated, monounsaturated and saturated fatty aids. The Differential Scanning Calorimetric (DSC) analysis showed the existence of two exothermic events of energy transition, one of which is related to the oxidation reactions and another to the decomposition of the oil. Exothermic transitions in the oil were initiated at a temperature (Ti) of 287.79 °C, and terminated at 347.81 °C, with an enthalpy variation of 11.69 joules.g-1 and at initial temperature (Ti) of 384.87 °C, peak temperature (Tp) 415.71 °C, final temperature (Tf) 448.9 °C and an enthalpy of 200.83 Joules, g-1.