Microwave-assisted extraction and antioxidant activity of total phenolic compounds from pomegranate peel

Pomegranate peel is the main waste fraction of pomegranate fruits, which is an excellent source of phenolic compounds. In this study, microwave-assisted extraction was employed to extract the phenolic compounds from pomegranate peel with water. By using response surface methodology, the effects of microwave output power, extraction time, and solid-liquid ratio on total phenolic yield were investigated and the optimal conditions were determined as follows: microwave output power 600 w, extraction time 60 s, and solid-liquid ratio 20. The average experimental phenolic yield under the optimum conditions was found to be 210.36 ± 2.85 mg GAE/g, which agree with the predicted value of 214.46 mg GAE/g. Different antioxidant assays were utilized to evaluate antioxidant activity of the obtained extract. It was found the extract was an effective scavenger in quenching 1,1-diphenyl-2-picrylhydrazyl (DPPH) radicals with IC50 of 14.53 μg/ml. A linear correlation between concentration of the extract and reducing power was observed with a coefficient of r2=0.9992. In Rancimat test, the antioxidant performance of the extract was inferior to that of tertiary butylhydroquinone, which could be attributed to its poor solubility in oil.   Key words: Pomegranate peel, microwave-assisted extraction, response surface methodology, antioxidant