Response surface methodology for optimisation of total polyphenol content and antioxidant activity of extracts from Maytenus macrocarpa bark by means of ultrasound-assisted extraction

The aim of this study was to optimise the ultrasound-assisted extraction of the total polyphenol content (TPC) and antioxidant activity from Maytenus macrocarpa bark by means of response surface methodology (RSM). The effect and interactions of temperature, time, particle size, solid:solvent ratio and water:ethanol ratio were analysed by using a fractional factorial design type 2(5-1). The most significant factors were: temperature, particle size and time. The RSM was applied to the optimisation of the TPC and two total antioxidant activities [Ferric reducing antioxidant power (FRAP) and 2,2 -azino-bis (3-ethylbenthiozoline-6-sulphonic acid) (ABTS)] as response variables. Four polynomial models were applied; the quadratic model was the most adequate one, with an adjusted R (2) value of 0.9422. M. macrocarpa has a considerable TPC that contributes to its antioxidant activity. The best results from the analysis of correlations were found in the FRAP versus TPC and ABTS versus FRAP, with a Pearson's r coefficient of 0.961 and 0.953, respectively.