Optimization of Extraction of Phenolics from Walnut Pellicle Using Response Surface Methodology and Their Antioxidant Capacities

Using temperature,time and liquid/solid ratio as independent variables,a Box-Behnken design was applied to optimise the extraction of phenolics from walnut pellicle by using response surface methodology.The results indicated that when the ultrasonic power was set at 100 W,the optimum ultrasonic extraction conditions for walnut pellicle phenolics were as follows: extraction temperature 53℃,extraction time 55 min,liquid/solid ratio 58∶1(mL∶g).Under this optimum condition,the extraction yield was 30.79%.It was found that the phenolics extracted from walnut pellicle behaved stronger antioxidant activities than ascorbic acid when they were under the same concentration.The IC50 values of scavenging activity of pellicle phenolics on DPPH free radicals and ABTS were 3.38 mg/L and 36.44 mg/L,respectively,while those of ascorbic acid were 4.72 mg/L and 82.23 mg/L,respectively.