Improving the semi-continuous flow-through subcritical water hydrolysis of grape pomace (Vitis vinifera L.) by pH and temperature control

Abstract

This study investigated how pH (6−10) and temperature (150–210 °C) could be explored to improve yields and reduce the formation of inhibitory compounds during the semi-continuous flow-through subcritical water hydrolysis of grape pomace (Vitis vinifera L.). The results showed that the highest sugar (cellobiose, glucose, fructose, arabinose) concentration (34.64 g 100 g-1) was obtained at pH 6 and 150 °C. The use of higher temperatures (210 °C) at pH 10 allowed to produce low inhibitory compounds (furfural and 5-hydroxymethylfurfural, 1.59 g 100 g-1) and high organic acid content (290.76 g 100 g-1). Thermogravimetric analysis indicated that the biomass structure was modified by subcritical hydrolysis, with a hemicellulose reduction of approximately 75%. In conclusion, subcritical water hydrolysis at pH 10 and 210 ºC ate the optimal conditions to recover sugars and organic acids from grape pomace.