<![CDATA[Portulaca oleracea L. is an underutilized species with great potential as a source of phenolic compounds, but the extraction conditions strongly affect the recovery of these compounds. This study aimed to optimize the parameters of ultrasound-assisted extraction (UAE) for maximum total phenolic content (TPC) of P. oleracea by response surface methodology (RSM). Firstly, single-factor experiments were conducted to determine the suitable ranges of extraction time, ethanol concentration and extraction temperature. Total phenolic content was determined using the Folin–Ciocalteu method and expressed as mg gallic acid equivalents per gram (mg GAE/g) and these variables were optimized using a three-factor, three-level Box–Behnken experimental design comprising a total of 15 experimental trials. The experimental TPC values obtained from Box–Behnken design ranged from 158.332±19.900 to 252.450±8.260 mg GAE/g. The experimental response was well explained by a quadratic model which was statistically significant (F=14.71, p=0.0043, R2 = 0.9636, adjusted R2 = 0.8981, predicted R2 = 0.7360 and lack of fit p=0.7805). The strongest linear effect was found for the extraction time. The quadratic terms of extraction time and ethanol concentration were significant. Numerical optimization predicted extraction time of 53.045 min, ethanol concentration of 69.233 % and temperature of 13.507 °C. The predicted TPC was 231.17 mg GAE/g with overall desirability of 0.880. The experimental confirmation gave a TPC of 193.83±6.874 mg mg GAE/g (mean ± standard error of the mean (SEM), n = 3), being approximately 16.1% lower than the expected value. Overall, RSM successfully characterized the nonlinear effects of the extraction parameters and provided an optimal UAE operational zone regarding phenolic extraction from P. oleracea at about 53 min, 69% ethanol and 13–14 °C.]]>
