Integral valorization of vine pruning residue by sequential autohydrolysis stages

Abstract

Wine processing generates a large amount of residue, in particular pruning residue of vine. In this work, autohydrolysis in two sequential stages was proposed for the integral valorization of this residue. In a first stage, vine pruning residue was submitted to autohydrolysis treatment at 180 °C for 60 min (severity of 4.13) and liquid to solid ratio of 6 g water per g vine pruning residue. In these conditions, 63.7% of xylan was recovered in the liquid phase as xylooligosaccharides (17 g/L) and 2.35 g/L of phenolic compounds with antioxidant activity were also extracted. Autohydrolyzed vine pruning residue was subjected to a second autohydrolysis at temperature in the range 180–200 °C and time 30–40 min. After sequential treatments, enzymatic hydrolysis of cellulose was significantly improved from 73% to 99% of conversion. At selected conditions (severity of 4.60), ethanol production was successfully obtained from two strategies of, separately and simultaneously, saccharification and fermentation, thus achieving ethanol yield of 96 and 83%, respectively. Overall, two sequential stages of the process allowed the recovery of 13.7 kg of xylooligosaccharides, 3.1 kg of phenolic compounds, 13.1 kg of ethanol and 27 kg of lignin per 100 kg of vine pruning residue. Sequential autohydrolysis stages were shown as a suitable strategy for the integral valorization of vine pruning residue.