Microwave-assisted extraction of phenolics from pomegranate peels: Optimization, kinetics, and comparison with ultrasounds extraction

Recently, there has been much interest in the phenolics of pomegranate peels, because of their health benefits, such as antioxidant activity. Thus, the objective of this work is to optimize an efficient alternative and "green" technique for the extraction of phenolics from pomegranate peels. Microwave-assisted method was found to increase extraction yield, but mainly to shorten the treatment time by over 60 times compared to conventional extraction methods. The effects of solvent type, solvent/solid ratio, and microwave power on the yield of phenolics extraction were studied. The optimum operating conditions were found to be: solvent type, 50% aqueous ethanol; solvent/solid ratio, 60/1 mL/g; power, 600 W. The efficiency of the proposed extraction protocol was compared with that of the ultrasound-assisted extraction, another "green" extraction approach, studied in our previous work. The microwaves method had a yield about 1.7 times higher obtained in a shorter process time (4 min) in comparison to ultrasound-assisted extraction (10 min). These differences were attributed to the intense cell destruction of microwave-treated plant material observed by SEM analysis. The obtained extract presented a high antioxidant activity (radical scavenging activity of 94.91%), due to the high content of punicalagin (143.64 mg/g dry matter) measured by HPLC analysis, that was equivalent to that of the ultrasounds extract (radical scavenging activity, 94.77%; punicalagin content, 138.8 mg/g dry matter).