Antioxidant activity of some medicinal plant extracts on oxidation of olive oil

Total phenolic contents, free radical scavenging activities and antioxidant capacities of Origanum onites extracts prepared using different methods were determined. Total phenolics ranged from 79.93 to 141.80 mg GAE/g, radical scavenging activities (IC50) were between 624.83 and 1080.16 mu g/ml and antioxidant capacities ranged from 107.31 to 161.71 mg AAE/g extract. The highest total phenolics and antioxidant activity were found in aceton:water:acetic acid (95:4.5:0.5) extract of O. onites using ultra-sonication bath. Total phenolic contents, free radical scavenging activities and antioxidant capacities of Satureja thymbra extracts were between 84.32 and 104.27 mg GAE/g, IC50 = 370.46 and 697.29 mu g/ml, 104.03 and 123.34 mg AAE/g extract, respectively. In terms of the highest total phenolics and antioxidant properties, extracts of Satureja thymbra prepared using ethanol:water:acetic acid (95:4.5:0.5) Soxhlet extraction showed the highest values. Butylated hydroxytoluene (BHT) and extracts (600 and 1200 ppm O. onites and S. thymbra) exhibited a strong antioxidant activity in olive oil. The highest value of peroxide is found in butylated hydroxy anisole (BHA) containing oils, when monitored from 0 to 28 days and values were in order of 2.98-29.59 and 2.98-29.64 meq O-2/kg oil. Absorbance value at the 0th day of all samples was 1.68 and increased till 28th Day. Acid values of oils including BHA, BHT, 600 and 1200 ppm O. onites extract and 600 ppm S. thymbra extract were found as 1.89 mg KOH/g at 28th day for second control.