Optimal extraction condition and encapsulation of bioactive compounds from coffee silverskin

Abstract

Coffee silverskin is the main co-product generated during the roasting process. This co-product has a rich nutritional composition, mainly in antioxidant compounds, and can be considered a rich natural source for the extraction of these compounds. Therefore, the aim of this study was to determine an optimal condition for the extraction of bioactive compounds from coffee silverskin and to compare different encapsulation methods (foam mat drying, spray drying and freeze drying). Initially, the effect of traditional methods of solid-liquid extraction (room temperature, with agitation and Soxhlet extraction method) and the use of more friendly solvents (water, ethanol, acetone and isopropanol) were investigated. An optimal treatment was chosen by desirability function. Afterwards, the effect of the extraction temperature and the concentration of the hydroalcoholic solution were studied. In addition, the extraction kinetics of phenolic compounds were also evaluated to determine the extraction time. The desirability function was applied to determine the optimal extraction condition of bioactive compounds from coffee silverskin. The extracted bioactive compounds were subjected to different encapsulation methods (foam mat drying, spray drying and freeze drying). Maltodextrin, gum arabic and egg albumin were used as wall materials. For foam mat drying, the agents were combined according to the treatments established by mixture design and an optimal concentration was determined. The foams were dried at temperatures of 50, 60, 70 and 80 ºC in a convective dryer. Spray drying and freeze drying of the optimal condition of the wall materials combination was also performed. The powders were characterized, and a comparison of methods was performed. For the extraction, the highest content of bioactive compounds recovered from coffee silverskin was through the method with agitation. Furthermore, ethanol was the best extraction solvent, followed by water. In the subsequent step, the optimal conditions obtained for the hydroalcoholic concentration, temperature and extraction time were 64%, 68 °C and 120 min, respectively. Regarding the encapsulation methods, the ideal condition obtained from the feed mixture for foam formation was 7.6% gum arabic, 2% maltodextrin and 10.4% egg albumin. The powders obtained by different encapsulation methods showed good quality and high encapsulation efficiency.