Improving oxidative stability of soya and sunflower oil using<i> Temnocalyx obovatus</i> extracts

Abstract

Recently an increasing interest in formulations of medicinal plant origin and other plant additives as antioxidants has been observed in the food market and pharmaceutical fields. This is as a result of the realization that synthetic antioxidants can participate as mutagenic and genotoxic agents. In this study Temnocalyx obovatus extracts were compared with rosemary (Rosmarinus officinallis) and tert- butyl-hydroquinone (TBHQ) as possible antioxidants in sunflower and soya oil. Upon addition of 200 ppm of dried leaf extract, acetone extract yielded protection of the samples against oxidation more efficiently as compared to rosemary, ethanol, methanol and TBHQ extracts added at the same concentration for both peroxide value determinations and Rancimat method. Higher induction periods, 12.45 and 17.17 h were achieved with acetone extracts. Increasing the concentration from 50 to 200 ppm increased the antioxidant effect of the extracts. On analyzing ultra-violet (UV) absorption at 232 nm, acetone extract showed the least absorbance implying greater protection against oil oxidation. Results of the present study are interesting as they may lead to isolation and identification of bioactive compounds present in T. obovatus that can be used to prolong shelf lives in oil based foods which are susceptible to rancidification.

Key words: Oxidative stability, Temnocalyx obovatus, peroxidation, antioxidant.