Effects of different extraction methods on yield, purity, composition, antioxidant and antimicrobial activities of phenolics from peony flowers

In the present study, microwave-assisted extraction (MAE), ultrasound-microwave synergistic extraction (UMSE) and conventional liquid–solid extraction (CLSE) methods were performed to extract the phenolics from ground peony flowers. For MAE and UMSE, the effect of extraction conditions (microwave power, extraction time, solid/solvent ratio, ethanol concentration) on the yield of phenolics was evaluated. Optimum conditions were determined in experiments where a single factor was varied. Under optimal conditions, yield, purity, composition, antioxidant and antimicrobial activities of the phenolics from the different extracts were analyzed. The antioxidant activities were determined using 2,2-diphenyl-1-picrylhydrazyl (DPPH), 2,2′-azino-bis-3-ethylbenzthiazoline-6-sulphonic acid (ABTS) and reducing power assays. Thus, the half-maximal inhibitory concentration (IC50) was defined for the different extraction procedures in both DPPH and ABTS assays. The antimicrobial activities of the extracts were determined using an agar well diffusion assay. Although CLSE extracts exhibited the strongest free radical scavenging activities for both ABTS (IC50 = 11.35 ± 0.36 μg/mL) and DPPH (IC50 = 18.07 ± 0.21 μg/mL), and displayed the greatest reducing power, they also had the weakest inhibitory activities for all tested bacteria. Conversely, MAE extracts exhibited the largest zone of inhibition for Escherichia coli (E. coli) (14.00 ± 1.00 mm), Streptococcus mutans (S. mutan) (13.75 ± 0.50 mm), and Streptococcus agalactiae (S. agalactiae) (12.00 ± 0.10 mm), indicating that MAE extracts exerted the best antimicrobial activities. Therefore, the CLSE method should be selected for producing the strongest antioxidant activities and the MAE procedure for generating the strongest antimicrobial activities.