Optimization of microwave-assisted enzymatic extraction of polyphenols from waste peanut shells and evaluation of its antioxidant and antibacterial activities in vitro

Abstract A microwave-assisted enzymatic extraction (MAEE) method was developed and optimized to enhance the polyphenols extraction yield from waste peanut shells. The optimum conditions were as follows: irradiation time 2.6 min, amount of cellulase 0.81 wt.%, a pH of 5.5, and incubation at 66 °C for 2.0 h. Under these conditions, the extraction yield of total polyphenols could reach 1.75 ± 0.06%, which was higher than other extraction methods including heat-refluxing extraction, ultrasonic-assisted extraction and enzyme-assisted extraction. The structural changes of the plant material after different extractions observed by scanning electron microscopy provided visual evidence of the disruption effect. Moreover, the crude extract was then purified by NKA-9 resin, the polyphenols content in the purified extract increased to 62.73%. The antioxidant activities of the crude and purified polyphenols extract were evaluated by DPPH and hydroxyl radicals, reducing power and β-carotene bleaching test. The antibacterial activities of purified extract were also tested using Oxford cup method. The results indicated that the MAEE method was efficient and environment-friendly, and the polyphenols have significant antioxidant and antibacterial activities, which can be used as a source of potential antioxidant and preservative.