Enzymatic production of xylooligosaccharide (XO) from selected aricultural wastes
Four different agricultural wastes, namely tobacco stalk (TS), cotton stalk (CS), sunflower stalk (SS) and wheat straw (WS) were tested for the production of Xylooligosaccharide (XO). XO production was performed by enzymatic hydrolysis of xylans which were obtained by alkali extraction from the agricultural wastes. Depending on the source, it was found that these four agricultural wastes contained different amount of xylan, cellulose and lignin and the xylan obtained from these source contained different amount of sugar and uronic acid. The highest amount of arabinose was in xylan from WS while the other xylans mainly had xylose and small amount of glucose. Different xylanase preparations were evaluated for production XO from these xylan sources. Aspergillus niger xylanase produced lower amount of XO from wheat straw xylan (WSX) than cotton stalk xylan (CSX), sun flower xylan (SSX) and tobacco stalk xylan (TSX) while Trichoderma longibrachiatum xylanase hydrolyzed highly branched WSX better. The HPLC analysis of the hydrolysis products indicated that depending on structure and composition of xylan, A. niger xylanase produced less amount of xylose than T. longibrachiatum xylanase, and the hyrolysis product of A. niger xylanase contained different amount of oligosaccharides (X2>X3>X4>X5>X6, >X6). Regardless of the structural differences of the xylan types presented in this paper, all xylans generated XO with different degree of polymerization (DP), but the DP of XO depended on the enzyme specificity and the structure of substrate.