Optimal extraction condition for the recovery of bioactive compounds and antioxidants from coffee silverskin

Coffee silverskin (CS) is a coproduct that has been the subject of research as it contains compounds that exert beneficial effects on health. Therefore, this study aimed to determine the optimal condition for the recovery of bioactive compounds from CS. In the first step, three conventional extraction methods (at room temperature, with agitation and in Soxhlet) and four solvents (isopropanol, acetone, ethanol, and water) were tested. For the second step, the extraction curve of the total phenolic compounds was evaluated to define the extraction time, and the Peleg model was fitted. Sequentially, the temperature and concentration of the hydroalcoholic solution were optimized. The antioxidant activity (ferric reducing antioxidant power assay (FRAP) and 2,2-diphenyl-1-picrylhydrazyl assay (DPPH)), total phenolic content (TPC), and total flavonoid content (TFC) were influenced by the interaction between the type of solvent and the extraction method (p < .05). Water and ethanol and the extraction method with agitation (EM-2) were the best operating conditions obtained in the first stage. In the second step, Peleg's model was considered satisfactory to represent the extraction kinetics of the TPC, and the extraction time determined was 120 min. Higher values of extraction temperature and ethanol concentration resulted in higher recovery of bioactive compounds. The combination of the temperature of 68 degrees C and ethanol concentration of 64% resulted in the best extraction condition by the desirability function (D = 0.88). In this condition, the values obtained for FRAP, DPPH, TPC, and TFC were 0.071 mmol Fe (II)/g CS, 706.74 g CS/g DPPH, 7.22 mg GAE/g CS, and 0.81 mg QE/g CS, respectively. Practical Applications Coffee silverskin (CS) is a coproduct that has a rich composition in bioactive compounds. Various conventional extraction methods and new technologies are available for the extraction of bioactive compounds from this material. Generally, conventional extraction methods are even more employed by industries, as they are better known and cheaper than new technologies. The different conventional extraction methods and the type of solvent can affect the extraction yield of bioactive compounds from CS. Therefore, it is important to know and compare the conventional extraction methods, in order to optimize the desired variables of the process and obtain greater extraction yield of bioactive compounds.