Valorisation of grape pomace by the extraction of phenolic antioxidants: Application of high voltage electrical discharges

The aim of this study was to optimise the electrically assisted extraction in order to obtain grape pomace extracts with high polyphenols content, which would be potentially interesting for applications as natural antioxidants. High voltage electrical discharges (HVED) were applied for intensification of the extraction. The effects of the energy input, the electrodes distance gap and the liquid-to-solid ratio were studied. Diffusion was then carried out in different mixtures of water and ethanol for one hour at 20, 30. 40 and 60 degrees C. The most efficient extraction was (i) an HVED pre-treatment at 80 kJ/kg with an electrodes distance of 5 mm in a liquid-to-solid ratio of 5 followed by (ii) a diffusion with 30% ethanol in water at 60 degrees C for 30 min. The highest total polyphenols content reached 2.8 +/- 0.4 gGAE/100gDM with a corresponding antioxidant activity of 66.8 +/- 3.1 gTEAC/kgDM. The polyphenols extraction rate increased with temperature in accordance to an Arrhenius type of relationship: activation energy of 21.5 +/- 1.1 kJ/mol for HVED treated systems against 0.5 +/- 0.2 kJ/mol for untreated ones. (C) 2011 Elsevier Ltd. All rights reserved.