Abstract
An ultrasonic process for the effective extraction of phlorotannins from Agarum cribrosum with high total phlorotannin content (TPC) was optimized using response surface methodology (RSM). Optimal conditions for ultrasound extraction consisted of temperature: 30°C; time: 5.75 h; ratio of solvent to solid: 35 mL/g, where the TPC was 19.59 mg PGE/g. The crude extract was further partitioned using hexane, dichloromethane, ethyl acetate (EtOAc), and water, in that order. The EtOAc fraction with the highest TPC exhibited the strongest radical-scavenging activity against DPPH, ABTS, hydrogen peroxide, and reducing power, which was similar to that of ascorbic acid. Furthermore, the IC50 values of the EtOAc fraction against collagenase, elastase, and tyrosinase inhibitory activity were 29.63, 16.13, and 6.17 μg/mL, respectively, whereas epigallocatechin gallate (EGCG), EGCG, and kojic acid, the counterpart positive controls, were 68.90, 23.34, and 43.29 μg/mL, respectively. The EtOAc fraction was further fractionated using Sephadex LH-20 column chromatography, which yielded two major and four minor subfractions. The structure of the SF5 and SF6 subfractions were further determined through HPLC-DAD-QMS analyses and 1H and 13C NMR, in which only trifuhalol A was identified. The SF5 and SF6 subfractions exhibited significantly higher radical-scavenging activity against DPPH and reducing power than the EtOAc fraction, but no statistically significant differences were detected for ABTS, hydrogen peroxide, collagenase, elastase, and tyrosinase inhibitory activity. Based on the results, we propose that A. cribrosum phlorotannins could be a good source for natural antioxidants and cosmeceutical.