Comparison of two posthydrolysis processes of Brewery's spent grain autohydrolysis liquor to produce a pentose-containing culture medium

A readily fermentable pentose-containing hydrolysate was obtained from Brewery's spent grain by a two-step process consisting of an auto-hydrolysis (converting the hemicelluloses into oligosaccharides) followed by an enzymatic or sulfuric acid-catalyzed posthydrolysis (converting the oligosaccharides into monosaccharides). Enzymatic hydrolyses were performed with several commercial enzymes with xylanolytic and cellulolytic activities. Acid-catalyzed hydrolyses were carried out at 121°C under various sulfuric acid concentrations and reaction times, and the effects of treatments were interpreted by means of a corrected combined severity factor (CS ¹), which varied in the range of 0.80–2.01. Under the tested conditions, chemicalhydrolysis allowed higher pentose yields than enzymatic hydrolysis. Optimized conditions (defined by CS ¹=1.10) allowed both complete monosaccharide recovery and low content of inhibitors. Liquors subjected to posthydrolysis under optimal conditions were easily fermented by Debaryomyces hansenii CCMI 941 in semiaerobic shake-flask experiments, leading to xylitol and arabitol as major fermentation products. The bioconversion process was improved by hydrolysate concentration and supplementation of fermentation media with casamino acids. The authors wish it to be known that the first two authors should be regarded as joint First Authors.