Use of Polyphenol Extracts from Dioscorea steriscus and Plecranthus esculentus N.E.Br Tubers to Curb Oxidative Deterioration of Sunflower Oil

Abstract

Aim: The aim of the present study was to determine the possibility of using polyphenol extracts from Dioscorea steriscus and Plecranthus esculentus N.E.Br tubers of Zimbabwe as preservatives for sunflower oil under oven and kitchen storage conditions. Methodology: Polyphenols were extracted from Dioscorea steriscus and Plecranthus esculentus tubers, screened using polyphenol screening assays and added to virgin sunflower oil at 100 ppm dose.  Oxidative stability was determined using peroxide values and UV-Vis absorbances a 232 nm. Results: Polyphenol screening assays of aqueous acetone extracts from Dioscorea steriscus and Plecranthus esculentus tubers revealed the presence of flavonoids, phenolic acids, tannins, lignans and anthocyanins. Oxidative stability of sunflower oil under kitchen storage conditions (room temperature) and oven storage conditions (65°C) as measured by peroxide values and UV-Vis absorbances at 232 nm followed the order D. steriscus fortified ˃ BHT fortified ˃ P. esculentus fortified ˃ unfortified. The lowest mean peroxide value (17.72±0.05 mEq/kg oil) over a 5 week storage duration under kitchen storage conditions was recorded in D.steriscus fortified sunflower oil and the highest (31.17±0.16 mEq/kg oil) was recorded in unfortified sunflower oil. Conclusion: Polyphenol extracts from Dioscorea steriscus and Plecranthus esculentus tubers showed high preservative potential on virgin sunflower oil under both kitchen and oven storage conditions. Polyphenol extracts from D. steriscus and P. esculentus tubers may be used as alternative sources of antioxidants for the preservation of sunflower oil.