Structure of peanut shell xylan and its conversion to oligosaccharides

We present here that peanut shell, an underutilized agro-residue, is suitable for the isolation of xylan and the production of prebiotic xylooligosaccharides (XOS). Two different alkaline extraction procedures coupled to delignification were applied for the extraction of xylan. A one-step extraction in the presence of sodium hypochlorite produced xylan I (14.8% yield) contaminated with other hemicelluloses, mainly xyloglucan. A twostep extraction of sodium chlorite-delignified material yielded much purer polysaccharide, assigned as xylan II (15.5% yield). This polysaccharide was characterized by NMR, and MALDI ToF MS analysis was performed on xylooligosaccharides generated by various xylanases. The polysaccharide appears to be a glucuronoxylan similar to a hardwood glucuronoxylan, however, with a relatively higher degree of substitution of the main chain with 4-O-methyl-o-glucuronic acid (Xyl:MeGlcA ratio similar to 6-7). Consequently, the peanut shell glucuronoxylan hydrolysates produced by GH10, GH11 and GH30 xylanases contained considerable portion of acidic xylooligosaccharides. A process for the production of peanut shell xylooligosaccharides from alkali extracted peanut shell xylan using a thermophilic Thermomyces lanuginosus GH11 xylanase has been proposed.