A comparative study on the in vitro antioxidant activity of tocopherol and extracts from rosemary and Ferulago angulata on oil oxidation during deep frying of potato slices.

Abstract

There is a tendency towards the use of natural antioxidative substances due to toxic effects of synthetic antioxidants. The purpose of this research was to evaluate the effects of tocopherol and extracts from rosemary and ferulago on oxidation in a mixture (1:1, w/w) of sunflower seed oil and palm olein, during deep frying of potato slices. Besides the control groups, tertiary butylhydroquinone (TBHQ) served as a standard for comparison. The DPPH radical scavenging activities of extracts followed the order of rosemary10%>rosemary1%>rosemary0.1%>ferulago 10%>ferulago 1%>ferulago 0.1%. Frying performance of antioxidants were tested with regards to primary (peroxide value (PV)) and secondary (anisidine value (AnV), free fatty acids (FFA), total polar compounds (TPC) and volatile oxidation compounds such as hexanal and heptanal) oxidation products and by sensory evaluation. After frying process, rosemary extract treatment exhibited PV (1.2meq O2/kg), FFA content (0.124%), TPC (12.2%), hexanal concentration (62.4ng/g) and heptanal concentration (73.8ng/g), which were significantly equal or sometimes less than those of TBHQ treatment ((1.23meq O2/kg), (0.123%), (12.6%), (64.4ng/g) and (74.1ng/g), respectively). Whilst the ferulago extract showed higher PV (2meq O2/kg) than the control sample, it was efficient in delaying secondary oxidative changes. Tocopherol markedly retarded primary stage but its activity fell down toward secondary oxidation products. The overall results of this research suggest that rosemary extract may be a good natural alternative to TBHQ, but further studies are necessary to investigate the use of ferulago extract.