Phenolics of pomegranate peels: extraction optimization by central composite design and alpha glucosidase inhibition potentials

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 a-glucosidase inhibition activity. Optimum conditions were found as 100 degrees 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 was 192.0 mg/g of pomegranate peels on dry matter basis. Phenolics of pomegranate peels showed alpha-glucosidase inhibition activity with an IC50 (concentration of phenolics required to inhibit 50% of the enzyme activity) value of 5.56 +/- 2.23 mu g/ml. Pomegranate peel phenolics with its antioxidant and a-glucosidase inhibition properties might be a suitable ingredient for functional food applications.