Production of xylose through enzymatic hydrolysis of glucuronoarabinoxylan from brewers' spent grain

Xylose is an abundant bioresource for obtaining diverse chemicals and added-value products. The production of xylose from green alternatives like enzymatic hydrolysis is an important step in a biorefinery context. This research evaluated the synergism among four classes of hydrolytic purified enzymes-endo-1,4-β-xylanase, α-L-arabinofuranosidase, β-xylosidase, and α-D-glucuronidase-over hydrolysis of glucuronoarabinoxylan (GAX) obtained from brewers' spent grain (BSG) after alkaline extraction and ethanol precipitation. First, monosaccharides, uronic acids and glycosidic-linkages of alkaline extracted GAX fraction from BSG were characterized, after that different strategies based on the addition of one or two families of enzymes-endo-1,4-β-xylanase (GH10 and GH11) and α-L-arabinofuranosidase (GH43 and GH51)-cooperating with one β-xylosidase (GH43) and one α-D-glucuronidase (GH67) into enzymatic hydrolysis were assessed to obtain the best yield of xylose. The xylose release was monitored over time in the first 90 min and after a prolonged reaction up to 48 h of reaction. The highest yield of xylose was 63.6% (48 h, 40 ℃, pH 5.5), using a mixture of all enzymes devoid of α-L-arabinofuranosidase (GH43) family. These results highlight the importance of GH51 arabinofuranosidase debranching enzyme to allow a higher cleavage of the xylan backbone of GAX from BSG and their synergy with 2 endo-1,4-β-xylanase (GH10 and GH11), one β-xylosidase (GH43) and the inclusion of one α-D-glucuronidase (GH67) in the reaction system. Therefore, this study provides an environmentally friendly process to produce xylose from BSG through utilization of enzymes as catalysts.