Antioxidant activity of various plant extracts under ambient and accelerated storage of sunflower oil

The present study was conducted to inverstigate the antioxidant potential of 11 medicinally or economically important plant materials indigenous to Pakistan. The materials were extracted with 80% methanol and examined for their antioxidant activity under different storage conditions using sunflower and soybean oils as oxidation sustrates. Preliminary antioxidant activity assessment among the extracts was conducted with the TLC-test and by measuring percent inhibition of linoleic acid peroxidation. The rhizome of Iris germanica, leaves of lawsonia alba, and M. oleifera coffee (Coffee arabica) beans, rice (Oryza sativa) bran what bran and oats (Avenis sativa) groats and hull, which showed higher antioxidant activity among the extracts were further evaluated using soybean and sunflower oils as oxidation substrates. The vegetable oils were stabilized with extracts at a dosage of 0.12% (w/w), and individually subjected to accelerated (65 degrees C, 15 days)and ambient (6 months) storage. The oxidative deterioration level was monitored for the measurement of antioxidant activity index (AI), peroxide "value" (PV) conjugated dienes and trienes contents. Overall, the extracts of coffee leaves wee found to be the most effective in extending oxidative stability, and retarding PV, primary and secondary oxidation products of soybean and sunflower oils. The order of efficiency of the plant extracts for stabilization of the subject oils was as follows: oat groats and hull > coffee beans > M.oleifera leaves > Lawsonia alba > Iris germanica > rice bran > wheat bran. Significant differences in the antioxidant potential of some of the extracts for stabilization of substrate oils were observed unde the ambient and accelerated storage conditions and thus demonstrated a variable antioxidant prospective of the extracts under different analytical protocols.