Extraction, preparative monomer separation and antibacterial activity of total polyphenols from Perilla frutescens

Polyphenols display potential functional activities especially for rosmarinic acid (RosA) and caffeic acid (CafA). In this study, two different methods including ultrasonic-assisted ethanol extraction (60%) and ultrasound-assisted cellulase (≥ 15000 U/g, 2%) hydrolysis were applied for the extraction of total phenolics from 44 species of Perilla frutescens. Folin-Ciocalteu method detection showed that the content of total phenolics extracted by cellulase hydrolysis was the highest and attained to 28.00 mgGAE/gextracts for ZB1. Continuously, the extracts were purified by XDA-8 macroporous resin and medium-pressure liquid chromatography (MPLC), and the content of total phenolics improved to 66.62 mgGAE/gextract. High-performance liquid chromatography (HPLC) assay showed that the total polyphenols were mainly composed of gallic acid, caffeic acid, rosmarinic acid, luteolin and apigenin. Besides, a sequential XDA-8 macroporous resin combined with high-speed counter-current chromatography (HSCCC)/MPLC system was established for simultaneously isolation and preparation of RosA (purity 98.29%) and CafA (purity 97.01%) from the extracts. Further, antibacterial activities of the total polyphenols were evaluated by disc diffusion method and scanning electron microscope (SEM) observation. The results verified that the total polyphenols had effective antibacterial capacity on three kinds of bacteria including E. coli, S. aureus, and B. subtilis in a concentration-dependent manner. All these results demonstrated that the ultrasound-assisted cellulase hydrolysis extraction of total polyphenols and proposed three-step separation of RosA and CafA had a high yield and good purity, and they exhibited an effective antibacterial ability.