Response surface optimization to extract antioxidants from freeze-dried seeds and peel of pomegranate (Punica granatum L.)

The seeds and peel of pomegranates, which are a byproduct of the fruit processing industry, could be used as a source of antioxidants. This study, therefore, aimed at optimizing experimental conditions to extract antioxidants from the freeze-dried powder of pomegranate seeds and peel. Extraction temperature (degrees C), time (min), and solvent types (ethanol, methanol, and acetone) were studied as independent variables to optimize the extraction conditions. The interaction between variables was examined using response surface methodology (RSM) with Box-Behnken design (BBD). The total phenolic compounds (TPC), 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity, and ferric reducing antioxidant power (FRAP) were determined to evaluate the antioxidant activities of pomegranate seeds and peel. The TPC of the pomegranate seeds and peel ranged from 1.43 +/- 0.19 to 3.98 +/- 0.06 mg GAE/100 g DM and 1.37 +/- 0.47 to 2.68 +/- 0.61 mg GAE/100 g DM, respectively. DPPH values of peel (76.51 +/- 1.58 to 85.82 +/- 1.97%) were higher than those of the seeds (38.56 +/- 4.02 to 70.41 +/- 3.64%). The FRAP values for pomegranate seeds and peel were within the range of 144.58 +/- 2.57 to 232.61 +/- 3.17 mg AAE/100 g DM and 521.42 +/- 4.89 to 798.45 +/- 4.10 mg AAE/100 g DM, respectively. The results of the RSM optimization demonstrated that under the optimized temperature (50 degrees C), time (30 min), and solvent (methanol), freeze-dried pomegranate seeds showed the maximum value of TPC (2.91 +/- 0.05 mg GAE/100 g DM), DPPH (61.26 +/- 2.65%), and FRAP (148.34 +/- 4.42 mg AAE/100 g DM). Moreover, 50 degrees C for 10 min is the optimum temperature and time for maximum antioxidant extraction from pomegranate peel when methanol was used as the solvent. The maximum TPC, DPPH, and FRAP values were 2.79 +/- 0.08 mg GAE/100 g DM, 86.19 +/- 4.17%, and 785.67 +/- 4.92 mg AAE/100 g DM, sequentially. It is clear from the results that pomegranate peel contains more antioxidants than seeds. On an industrial scale, extraction procedures that use more solvent and need time to extract antioxidants may be replaced with the optimized extraction conditions used in the present study.