Thermal stability of Vernonia galamensis seed oil

Abstract

The physicochemical changes of refined vernonia oil?RVO (which naturally contains epoxidized triglycerides) upon heating was evaluated and is reported in this manuscript. A boiling point range of 183 °C to 190 °C (at 760 mm Hg) for the vernonia oil was obtained using the Siwolobboff's method. The oil changed its physical appearance and consistency in the course of the heating. A homogenous free?flowing beige?sand shade refined vernonia oil at room temperature (25 °C) was transformed irreversibly to an intense?brown shade, becoming increasingly more viscous with increase in temperature, and ceasing to flow momentarily at 188 °C. On cooling to room temperature, the oil solidified into a brown rubber?like elastic material. The oil also exhibited a reduction in its oxirane content from 1.39±0.004 equivalent HBr kg?l at 25 °C to 0.542±0.002 equivalent HBr kg?l at 70 °C. This signifies a 61% drop in oxirane content for the 45 °C temperature rise. These findings point towards a thermally driven polymerization and/or decomposition of the refined vernonia oil (RVO).