Optimization of accelerated solvent extraction of bioactive compounds from Eucalyptus intertexta using response surface methodology and evaluation of its phenolic composition and biological activities

Polyphenols-rich extracts were obtained by accelerated solvent extraction (ASE) from E. intertexta leaves and analyzed by HPLC for the first time. Response surface methodology (RSM) based on central composite experimental design (CCD) was used to investigate the effect of three independent variables (temperature, extraction time, and ethanol concentration) on extraction yield, phenolic content, antioxidant, and anti-xanthine oxidase activities. The statistical analysis indicated that experimental data were well fitted to a quadratic polynomial model with regression coefficient values of more than 0.96 for all studied responses. Optimized extraction conditions, obtained by the maximization of a global desirability function, were 26.6% ethanol concentration, dynamic time of 36 min and a temperature of 179 degrees C. Under these optimal conditions the experimental values of the studied responses were 52.3 g extract/100 g DW extraction yield, 180.7 mg GAE/g extract total phenolic content, 17.2% antioxidant activity, and 55.3% anti-xanthine oxidase capacity. The HPLC analysis of all CCD extracts allowed to quantify twenty-two phenolic compounds in which eight molecules have not been reported previously in the genus of Eucalyptus. 3,4-dihydroxybenzoic, methyl ester, gallic acids, myricitrin, catechin, epicatechin, and polydatin were the most abundant phenolic compounds. The percentages of these compounds in extracts depend on the operating conditions. The best recovery of flavonoids (583 mg/g) was obtained at 100 degrees C, 10 min, and 44% ethanol, whereas phenolic acids (357 mg/g) were favored at a lower ethanol concentration of 11% and higher temperature and exposure time (180 degrees C, 36 min). The extraction of stilbenes (148 mg/g) was at its maximum at 140 degrees C, 1 min, and 27.5%.