Antioxidant Effect of Microwave-assisted Extracts of Olive Leaves on Sunflower Oil

The antioxidant properties and total phenols’ content of ۸۰% methanol, acetone and water extracts of olive leaves procured through Microwave Assisted Extraction (MAE) were examined. Two varieties of olive namely: Cronaiky and Roghani were the ones studied. Various experimental models were employed for antioxidant activity evaluation of the extracts. The results revealed the highest phenolic content (۲۳۰.۵۰ mg tannic acid equivalent g-۱ extract) and the lowest IC۵۰ in DPPH (۸۶.۸۱ µg ml-۱ of extract), reducing power (۱۶۶.۴۵ µg ml-۱ extract) and total antioxidant capacity (۱۲۸.۳۲ µg ml-۱ of extract) indices were attributed to the methanol extract of Cronaiky variety. The efficacy of the extracts at three experimental levels (۲۰۰, ۵۰۰, ۱,۰۰۰ ppm) in blocking the oxidation process was investigated using peroxide value and thiobarbituric acid index for sunflower oil during its heating at ۷۰°C (oven test method). The lowest peroxide value and thiobarbituric acid index was observed for the methanol extract of Cronaiky at its ۱,۰۰۰ ppm concentration. This extract was competitively comparable with BHA and BHT at either of the tested levels (۱۰۰, ۲۰۰ ppm). Thus, methanol extract of Cronaiky olive variety can be employed in place of synthetic antioxidants to establish oxidation stability in edible oils.

Keywords:

Antioxidant activity , Microwave , Olive leaf , Sunflower oil