Optimization of extraction and microencapsulation of bioactive compounds from spent coffee grounds

Abstract

Coffee grounds consist of a by-product produced at the time of beverage preparation. This by-product has several extractable compounds with high antioxidant action, which can be recovered and added to food and beverage formulations. In this context, this study aimed to optimize the extraction of bioactive compounds from coffee grounds and, subsequently, promote the microencapsulation of these compounds. For the extractions, the influence of different methods (extraction at room temperature, shaking incubator and soxhlet) and solvents (water, ethanol, acetone and isopropanol) was evaluated. Subsequently, using a central composite rotational design (CCRD), the effect of the water/ethanol mixture and the extraction temperature on the extraction yields were evaluated. A phenolic compounds extraction curve was built to define the ideal process time. Response surfaces were elaborated and the desirability function was applied to determine the optimal point. For the microencapsulation of the extracted bioactive compounds, drying by foam mat, spray-drying and freeze-drying of the extract and foam were used. The wall materials used were albumin, maltodextrin and gum arabic. A mixture design was used to study the concentrations of the wall materials and the desirability function was used to determine the ideal concentration. The foams were dried in a convective dryer using temperatures of 50, 60 and 70 °C and two air velocities, 1 and 2 m/s. The dried product was characterized and compared with powders produced by spray-drying and freeze-drying methods. Subsequently, a new experiment using only spray-drying and lyophilization drying was carried out. In this case, new concentrations of the wall materials were tested and the dried product was characterized and compared. The results obtained during the extraction stage indicated that the most efficient bioactive compounds extraction was achieved by using a shaker incubator and the best pure extracting agents were water and ethanol. Furthermore, according to the results of the DCCR and the extraction curve, the maximum recovery of compounds was obtained with the use of ethanol at a concentration of 45% and a temperature of 63.3 °C, for 90 min. In the microencapsulation study, the concentration of wall materials was set at 20%, consisting of 4, 6 and 10% of albumin, maltodextrin and gum arabic, respectively. The foam drying time ranged from 200 to 450 min. All drying methods resulted in products with good physicochemical properties and satisfactory encapsulation efficiency values, above 60%. In microencapsulation using spray-drying and freeze-drying the powders obtained by freeze-drying had lower moisture and water activity values and were more hygroscopic. However, the content of bioactive compounds and the encapsulation efficiency values were similar between the two methods. Among the wall materials, the use of albumin resulted in a dried product with lower bioactive content and encapsulation efficiency for both drying methods.