Fermentable sugars recovery from grape stalks for bioethanol production

Abstract

[EN]Three different processes were investigated for the recovery of fermentable sugars from grape stalks: autohydrolysis at 121 ºC before and after a pre-washing step and acid hydrolysis (2% H2SO4 w/w) after a pre-washing step. Moreover, optimal conditions of a charcoal-based purification process were determined by experimental design. All hydrolysates, with their corresponding synthetic liquors were used as fermentation substrates for the production of metabolites by the yeast: Debaryomyces nepalensis NCYC 1026. The main fermentation product was ethanol, where a maximum production of 20.84 g/l, a conversion yield of 0.35 g ethanol/g monomeric sugars and a productivity of 0.453 g/l h were obtained from non-purified autohydrolysate liquor. In all cases, ethanol production and cell growth were better in nonpurified liquors than in synthetic liquors. These results could be influenced by the presence of other sugars in the hydrolysates, with higher concentration in non-purified ones.