Effect of nettle (Urtica dioica) leaves extract on the inhibition of soybean oil oxidation

The traditional extraction method was used to evaluate the antioxidant properties of nettle leaves in soybean oil. Also the effects of three different solvents (water, 80% methanol and chloroform) on the extraction content of phenolic and flavonoid compounds from nettle leaves were examined. Water extract had the highest extraction yield, and chloroform extract had the highest extraction contents of phenolic and flavonoid compounds and the lowest IC50 for DPPH radicals. The effects of nettle extracts in three concentration levels (200, 500 and 800 ppm) and synthetic antioxidants (BHA and BHT) in two levels (100 and 200 ppm) on the stability of soybean oil were compared through the determination of peroxide value and thiobarbitoric acid index in specific periods (25 days). The results showed that different concentrations of extracts were effective in retarding the oil oxidation at 60ºC. Among the treatments, the extracts with the concentration of 800 ppm, particularly chloroform extract, had the highest antioxidant activity and were comparable with BHT, and also were more effective than BHA. Hence, the nettle leaves can be introduced as natural antioxidant source and this antioxidative effect caused by the presence of phenolic compounds in nettle leaves.