Comparing the efficiency of extracting antioxidant polyphenols from spent coffee grounds using an innovative ultrasound-assisted extraction equipment versus conventional method

Abstract

Two extraction approaches were compared, ultrasound-assisted extraction (UAE) and conventional extraction (CE), for the recovery of natural antioxidant phenolic compounds from spent coffee grounds (SCG), which could be used as cosmetics additives or nutritional supplements. Two factorial designs were used to investigate the effect of the varied process parameters on performances of UAE and CE processes, which were evaluated and compared regarding total polyphenols recovery, antioxidant activity of the obtained extracts and energy consumption. Polyphenols recovery was influenced mostly by ethanol content in the solvent, then ultrasound power for UAE and heating temperature for CE. Optimal operating conditions were identified as 400 W ultrasound power, 50% (v/v) ethanol in the solvent and 40 mL/g dm (dry matter) liquid to solid ratio for UAE, and about 50 °C heating temperature and 50% (v/v) ethanol in the solvent for CE. Under these optimal conditions for each process, more than 83% and 64% of available polyphenols in SCG were recovered with UAE and CE, respectively. Ultrasound assistance thus allowed about 33% enhancement of polyphenols recovery, while dividing energy consumption by more than 2. Hence, UAE process was demonstrated to be an efficient and sustainable method to recover antioxidant polyphenols from spent coffee grounds.