Optimization of Oil Extraction from Cocoa Bean Shells Using Three Solvents with Solvent Reusability

Abstract

Cocoa bean shells from chocolate processing are byproducts of the winnowing process used to remove the shells from the cocoa nibs. The cocoa bean shells have a residual oil content of 11.30 wt % and good nutritional value for animal feed. This study aims to determine the optimal conditions for oil extraction from dried cocoa bean shells using three solvents (hexane, anhydrous ethanol, and hydrous ethanol) while reusing the solvent. The mass ratio of solvent-to-dried cocoa bean shell (2.5−29.5 g/g), stirrer speed (50−550 rpm), and extraction time (0.3−13.7 min) parameters are varied to optimize the oil yield from dried cocoa bean shell using the response surface method. The optimal conditions for hexane were 26.0:1 g/g hexane-to-dried cocoa bean shell ratio, 550 rpm stirrer speed, and 5.2 min extraction time; for anhydrous ethanol, it was 29.5:1 g/g anhydrous ethanol-to-dried cocoa bean shell ratio, 330 rpm stirrer speed, and 7.1 min extraction time; and for hydrous ethanol, it was 27.4 g/g hydrous ethanol-to-dried cocoa bean shell ratio, 550 rpm stirrer speed, and 12.1 min extraction time. The results of oil yields showed that 10.80, 10.50, and 8.90 wt % cocoa bean shell oil yields from the extraction process under optimal conditions using hexane, anhydrous ethanol, and hydrous ethanol, respectively. The high yields of cocoa bean shell oil from hexane and anhydrous ethanol conditions were selected to test the extraction efficiency using reused miscella. Therefore, the extraction efficiency of dried cocoa bean shells with reused miscella using hexane and anhydrous ethanol was examined under optimal conditions to save the amount of solvent and energy. It was found that six cycles of hexane and two cycles of anhydrous ethanol were required to extract oil from cocoa bean shells, with an efficiency of over 80%. The compositions in cocoa bean shell oil from extraction consisted of 99.53% triglycerides, 0.01% free fatty acids, 0.43% diglycerides, and 0.05% monoglycerides for the hexane condition, while the compositions in cocoa bean shell oil were found to be 98.37% triglycerides, 0.53% free fatty acids, 1.02% diglycerides, and 0.08% monoglycerides after being extracted with ethanol. In addition, cocoa bean shell was oil extracted with reused miscella of hexane and anhydrous ethanol solvents to save energy and chemicals during solvent evaporation. This study recommends ethanol over hexane because it is safer for the environment. Both dried and defatted cocoa bean shells could successfully produce feed pellets by using pelletization. The process was achieved by adding 25 wt % water to defatted cocoa bean shells before forming them with a pellet machine.