Modeling and optimizing the solid–liquid extraction of phenolic compounds from lignocellulosic subproducts

Solid–liquid extraction was performed in order to obtain phenolic compounds with antioxidant activity from lignocellulosic subproducts generated in forestry using aqueous ethanol solutions. Actually, these subproducts are used to produce energy by combustion of biomass. An alternative solution is to extract the antioxidants prior to combustion in order to optimize the resources. In the first stage, the kinetics of conventional solid–liquid extraction was targeted. The experimental data were fitted to Peleg's and Page's equations for modeling the extraction of phenolic compounds and FRAP (Ferric-reducing ability power) antioxidant capacity from forestry biomass. Then, the extraction of antioxidants was optimized by using response surface methodology (RSM). The optimum conditions were 75 °C, 55 min, and ethanol concentration of 30%. Predicted values under optimum conditions were the following: extraction yield (EY), 9.19%; total phenols yield (TPY), 27.8 mg GAE/g biomass; FRAP, 1.75E+5 nmol L-threoascorbic acid equivalent (TAAE)/g biomass; trolox equivalent antioxidant capacity (TEAC), 0.23 mmol of trolox (TE)/g biomass and TEAC 50% effective concentration (EC₅₀), 0.63 mg/mL. It was confirmed the abundance of several phenolic compounds, with leading role ellagic acid, found in the greatest proportion.