Valorization of wine lees residues into valuable products via Supercritical Water Hydrolysis.

Abstract

Wine lees are water-waste residues generated during maceration and fermentation steps of the vinification process and they constitute a source of high value compounds, such as polyphenols, mainly anthocyanins (AC). The exploitation of these dregs could contribute to the development of new wine-related products and could also lead to a sustainable growth of the wine industry due to the concentration of AC is 10 times higher in wine lees than in grape skins [1]. After the recovery of the polyphenols from wine lees, a wet solid waste remains with poor chemical potential. This residue can be recycled by a hydrolysis step. Supercritical water (SCW) has proved to be a suitable environment-friendly media for biomass hydrolysis due to its unique properties, such as a high diffusivities or low dielectric constant [2]. This hydrolysis produces a liquid product rich in sugars that can be used as feed in a fermentation step afterwards. However, the yield of this last step would be lower with wine lees than with conventional biomasses since its cellulosic fraction only constitutes 18%. The main objective of the hydrolysis of the wine lees residue is to obtain reduced sugars which are essential chemical building blocks in the so-called biorefinery cycle. A continuous pilot plant was used to carry out the hydrolysis of wine lees in SCW. This facility was based on a continuous reactor with instantaneous heating and cooling that allowed precise control of the reaction time and therefore, high recovery of sugars was achieved and avoiding sugar degradation reactions. A wine lees-water suspension (10% w/w) was continuously fed to the reactor using a pump at a flow rate of 1 kg/h and processed under 380-395ºC and 25MPa at different reaction times, between 0.056 and 0.076s. A brown liquid was obtained after the hydrolysis step, rich in hexoses (yield of 50%) such as cellobiose, glucose and fructose. It was also observed that increasing the reaction time and temperature favored the degradation of the recovered sugars into pyruvaldehyde and glycolaldehyde.