Optimization of Continuous Extraction of Polyphenols from Grape Pomace by a Pulsed Electrical Discharge System with a “Needle-Ring Type” Treatment Chamber

Abstract

Grape pomace (GP) is an industrial waste containing abundant polyphenols, which is usually used as low-lucrative fertilizer and animal feed. If the polyphenols of GP have been fully recycled, it would produce tremendous economic benefits. Conventional maceration extraction is time-consuming and energy-wasting, while pulsed electrical discharge (PED) is demonstrated to be a highly efficient extraction method. For utilizing the GP more conveniently, a PED continuous extraction system with a “needle-ring type” treatment chamber is designed for the first time and optimized for polyphenols extraction from GP. The optimized conditions are liquid to solid ratio of 40 mL/g, ethanol concentration of 30%, bore diameter of ring electrode of 4 mm, flow rate of 50 mL/min, and discharge voltage fixed at 12 kV. Under these conditions, it obtains a maximum polyphenols yield of 6.78 ± 0.17% in 6 min, which is higher than those of the “converged electric field type” design (6.49 ± 0.09%), which is the continuous operation mode previously recommended by our group for 25 min and maceration extraction (6.03 ± 0.12%) for 120 min. However, its energy consumption (504 kJ/kg) is lower than those of the “converged electric field type” design (1462 kJ/kg) and maceration extraction (6720 kJ/kg). The HPLC chromatograms reveal that the chemical compositions of polyphenols of the three extraction methods are similar, and the “needle-ring type” design has the highest 1,1-diphenyl-2-picrylhydrazyl (DPPH) scavenging activity. The results indicate that the PED continuous extraction with a “needle-ring type” treatment chamber is efficient and promising for GP polyphenols extraction.