Evaluating the extraction of oil and sugars from spent coffee grounds

About six million tons of spent coffee grounds are discharged into the environment every year. Spent coffee grounds contain many useful components such as polysaccharides, protein, and bioactive compounds. This research aimed to exploit the important products such as coffee oil, sugar and phenolic compounds from spent coffee grounds, contributing to improve the economic efficiency of the coffee industry and reducing the environmental pollution. Coffee oil was extracted using four different methods including maceration, Soxhlet, ultrasonic-assisted and microwave-assisted extraction. The solid residue from the oil extraction process was hydrolyzed by Cellulast and Viscozyme enzyme. Monosaccharides, total phenolic content, and antioxidant activity in the hydrolysate were measured and evaluated. The results showed that ultrasonic-assisted extraction gave the highest yield of coffee oil of 9.64%; the coffee oil had a density of 0.94 kg/L; the acid value of 7.80 mg KOH/g; saponification value of 16.33 mg KOH/g and ester value of 8.57 mg KOH/g. The highest enzymatic hydrolysis yield was obtained by using 2% Viscozyme within 24 h. The spent coffee ground hydrolysate contained 2016.4 mg/L reducing sugars including 464.2 mg/L mannose; 947.1 mg/L glucose and 256.3 mg/L galactose; 401.70 mg/L total phenolic content and showed the antioxidant activity of 564.3 mg/L ascorbic acid equivalent. This study demonstrated a feasible process to obtain 96 kg of coffee oil, 48 kg of sugar and 10 kg of phenolic compounds from 1 ton of dry spent coffee grounds.