Effect of Methanolic Extract obtained from Cynodon dactylon (L) Pers. Rhizomes on Oxidative Stability of Soybean Oil under Thermal Conditions

In this study, first extraction from the C. dactylon rhizomes was performed with methanol solvent using maceration method, and total phenolic compounds in the extract were identified and determined. Then the antioxidant effects of the extract in different concentrations (0, 100, 200, 400, 800 and 1000 ppm) on the oxidative stability factors of soybean oil including peroxide value, acidity value, thiobarbituric acid index (TBA) and rancimat value during kept of oil in an oven at 60 °C for 72 hours was evaluated and compared with the synthetic antioxidant BHT (200 ppm). The identification results of phenolic compounds by GC/MS showed that the total amount of phenolic compounds in the C. dactylon rhizomes extract was measured as 917.08 mg/kg and the major phenolic compounds of the extract including Hydroquinone (66.89%), Thymol (1.23%), Levoglucosenone (2.48%) and Vanillic acid (1.35%) were identified. With increasing the concentration of the extract, the amount of polyphenolic compounds and as a result, the free radical scavenging activity of the extract increased. Evaluation of soybean oil stability against oxidation also showed that among the studied concentrations of methanolic extract, the concentration of 1000 ppm due to having the highest amount of phenolic compounds and therefore the highest antioxidant activity, was determined as the most effective concentration level of the extract in increasing the oxidative stability of soybean oil, so that better results were obtained than BHT synthetic antioxidant at a concentration of 200 ppm. Thus, the methanolic extract of the C. dactylon rhizomes can be used as a cheap and available antioxidant source in the edible oils industry.