Optimization of ultrasound-assisted extraction conditions for phenolics, antioxidant, and tyrosinase inhibitory activities of Vietnamese brown seaweed (Padina australis)

摘要

This study aimed to determine the optimum ultrasound-assistedextraction (UAE)conditions for obtaining the highest yields of phenolics and antioxidants from Padinaaustralis. The effects of extraction variables including temperature (40–60°C), extractiontime (50–80 min), ethanol concentration (0%–60%)and sample-to-solventratio (1–5g/100 mL) on the total phenolic content (TPC), DPPH radical scavengingactivity (DRSA) and ferric reducing antioxidant power (FRAP) were determined andoptimized using Box-Behnkendesign in conjunction with response surface methodology(RSM). The extraction temperature, ethanol concentration and sample-to-solventratio significantly affected TPC and DRSA, while extraction time had noimpact on TPC and antioxidant activity of P. australis within the tested ranges. Theoptimal UAE conditions were determined to be ultrasonic temperature of 60°C, ultrasonictime of 60 min, solvent concentration of 60% (v/v) aqueous ethanol andsample-to-solventratio of 1 g/100 mL. The developed mathematical models werefound to be reliable predictors for TPC, DRSA and FRAP, and the predicted values fitwell with the experimental data (R~2 = 0.86–0.96).The extract was then fractionatedto generate n-hexane,ethyl acetate and aqueous fractions. Of these fractions, ethylacetate fraction was found to possess the highest values of TPC (807.20 mg GAE/g),DPPH (1,417.01 mg TE/g), FRAP (615.07 mg TE/g dry fraction) and the strongesttyrosinase inhibitory activity (29.90 mg AAE/g).