Circulating Polyphenols Extraction System with High-Voltage Electrical Discharge: Design and Performance Evaluation

Abstract

Spent coffee grounds (SCGs) were an abundant industrial waste material containing rich polyphenols. In this study, a novel high-voltage electric discharge (HVED) circulating extraction system with a “needle to ring electrode” treatment chamber was for the first time designed to extract polyphenols from SCGs. This new system consisted of a high-voltage pulse generator, a treatment chamber, an extracting tank, and a transport unit. The optimized conditions for circulating polyphenols extraction by single-factor analysis were as follows: 20 min extraction time, 50 mL/g liquid to solid ratio, 200 mL/min flow rate, 24% ethanol concentration, and 11 kV discharge voltage. Accordingly, the maximum yield of polyphenols was 59.83 ± 1.53 mg/g, which was higher than that by solvent extraction (53.52 ± 1.41 mg/g) by 20.03% with 150 min extraction time and that of “converged electric field type” method (49.84 ± 1.16 mg/g) by 11.78% with 91.6 min extraction time. Energy consumption of circulating extraction was 1962.1 kJ/kg, which was far lower than those of converged electric field type method (6015.9 kJ/kg) and solvent extraction (5423.5 kJ/kg). Therefore, circulating extraction could reach a highest yield with lowest extraction time and energy consumption. Results indicated that the HVED circulating extraction system was the most efficient among the three methods.