Optimum water extraction conditions for phenolics of pomegranate peels were investigated by fractional factorial and face-centered central composite designs. Five potential factors were selected for the fractional factorial design: extraction technique, extraction temperature, extraction time, particle size and solvent to solid ratio. After eliminating statistically unimportant factors, a face-centered central composite design was set up with two controllable factors and with two responses: total phenolics and α-glucosidase inhibition activity. Optimum conditions were found as 100 °C for extraction temperature and 1 min for extraction time. There were no statistically significant differences (p > 0.05) between water extracts at optimized conditions and classical methanol extracts. Total phenolic content by HPLC was192.0 mg/g of pomegranate peels on dry matter basis. Phenolics of pomegranate peels showed α-glucosidase inhibition activity with an IC50 (concentration of phenolics required to inhibit 50 % of the enzyme activity) value of 5.56 ± 2.23 μg/ml. Pomegranate peel phenolics with its antioxidant and α-glucosidase inhibition properties might be a suitable ingredient for functional food applications.
Keywords: Alpha glucosidase inhibition; Central composite design; Fractional factorial design; Pomegranate peel.