Investigation of antioxidant efficiency of olive leaf (Olea europea L.) with in vitro methods

In this study, antioxidant property of olive leaf (Olea europaea L.) containing many bioactive substances in it like oleuropein was investigated in vitro with various methods. Determination of total phenolic substances, DPPH radical removal activity, antioxidant activity with ferric thiocyanate (FTC) method in linoleic acid system, chelation activity of iron (II) ions, superoxide radical removal activity and reduction capacity were performed for the samples at the concentration of 100-250-500-1000 μg/mL with methanol, ethyl acetate and n-hexane extracts obtained from dried olive leaves. Percentage yields of the Olea europaea L. were found 34,59%, 26,15% and 13,21% respectively, as a result of the extractions made with methanol, ethyl acetate and n-hexane solvents. In total phenolic substance determination the highest value was found 85,27±15,03 in methanol at 1000 μg/mL concentration and the lowest value as 0,18±1,32 in n-hexane at 500 μg/mL concentration. The highest value in the DPPH radical removal activity was found 72,93±0,42 in ethyl acetate at 500 μg/mL concentration, the lowest value as 13,77±1,23 in n-hexane at 100 μg/mL concentration. The highest value linoleic acid reduction was found as 89,52±9,77 in methanol at 250 μg/mL concentration, the lowest value as 61,19±4,05 in ethyl acetate at 100 μg/mL concentration. The highest value in reduction of iron (II) ions was found as 50,53±5,53 in ethyl acetate at 1000 μg/mL concentration, the lowest value as 8,16±0,43 in n-hexane 100 μg/mL concentration. In the superoxide radical removal activity, the highest value as 72,00±1,35 in ethyl acetate at 250 μg/mL concentration, the lowest value as 13,76±2,24 in n-hexane at 500 μg/mL concentration. Finally, the highest value was found as 1,49±0,03 in methanol at 1000 μg/mL concentration and the lowest value as 0,19±0,01 in ethyl acetate at 100 μg/mL concentration for the reduction capacity. In conclusion, it was seen that total phenolic substances, linoleic acid reduction and reduction capacity of methanol extract of the antioxidant activity of the Olea europaea L. are more active when compared with other extracts. It was found out that extracts with ethyl acetate are more effective in DPPH radical retention, iron (II) chelating, linoleic acid reduction and superoxide radical removal activity. Important values were obtained only in DPPH radical retention activity and linoleic acid reduction in the extracts with n-hexane. Due to these activities, it is thought that olive leaf may be considered as a natural alternative antioxidant in nourishment, cosmetic, pharmaceutical and animal nutrition fields.