Improvement of polyphenols extraction from grape pomace using Pulsed Arc Electro-hydraulic Discharges

This work aims at producing high dynamic shock waves by Pulsed Arc Electro-hydraulic Discharges (PAED) in a water based mixture in order to increase polyphenols extraction from grape pomace. Grape pomace is the main winemaking by-product composed of skins, seeds and stems. They contained valuable compounds like polyphenols. These molecules have attracted interest for their antioxidant activity. A triggered air-gap switch was used to discharge capacitors into the mixture containing grape pomace and water. The gap switch breakdown (40 kV maximum pulse voltage) produced a high dynamic shock wave in the liquid. The pulse energies were set to 160 J and 4 kJ with a pulse repetition frequency of 0.5 Hz. The contents of total solutes and total polyphenols of extracts were obtained by the values of degree Brix and absorbance at 280 nm respectively. Results point out the intensification of the extraction of total solutes and total polyphenols from grape pomace after PAED treatment. However, maintaining constant the ratio of energy to product mass (in our case, it was equal to 0.53 J/g) was not enough to obtain similar results for laboratory and semi-pilot experiments. Other parameters should be taken into account (treatment chamber design, pressure wave distribution ...). For example, a treatment of 53 kJ/kg at the laboratory scale gives similar results as a treatment of 160 kJ/kg at the pilot scale. In these conditions, the content of polyphenols in extracts is approximately 300 mg/L and the degree Brix is 1.2%.