Xylooligosaccharide production from cotton and sunflower stalks

Ak, Özlem
In this study, the aim was enzymatic xylooligosaccharide production from cotton and sunflower stalks, two of main agricultural residues in Turkey. In first two parts of the study, alkali extracted xylan from both of the stalks was hydrolyzed by commercial xylanases Veron and Shearzyme. The effect of temperature, pH, enzyme and substrate concentrations were investigated to determine optimum enzymatic hydrolysis conditions of xylan. Sunflower and cotton stalk xylans were hydrolyzed by Shearzyme more efficiently than Veron under the conditions studied. Shearzyme produced different product profiles containing xylobiose (X2), xylotriose (X3), xylotetrose (X4) and xylopentose (X5) from cotton and sunflower stalk xylan. On the other hand, Veron hydrolyzed both xylan types to produce X2, X3, X5, X6 and larger xylooligosaccharides without any change in product profiles. In the third part of the study, home produced xylanase from Bacillus pumilus SB-M13, was also investigated for the production of xylooligosaccharides from both cotton and sunflower stalk xylan. The main products obtained by hydrolysis of both substrates by pure B. pumilus xylanase were X5 and X6, while crude B. pumilus xylanase generated X4 and X5 as the main products. Xylooligosaccharide production from pretreated cotton stalk without alkali extraction of xylan was the final part of the study. Three different pretreatment methods including biomass pretreatment by Phanerochaete chrysosporium fermentation, cellulase pretreatment and hydrothermal pretreatment were investigated to break down complex lignocellulosic structure of cotton stalk to improve the subsequent enzymatic hydrolysis of xylan in pretreated cotton stalk for xylooligosaccharide production. However, xylooligosaccharide was not effectively produced from pretreated cotton stalk. Shearzyme inhibiton was observed after all the pretreatment methods during further hydrolysis of pretreated cotton stalk probably due to production of inhibitory compounds of the enzyme.


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Citation Formats
Ö. Ak, “Xylooligosaccharide production from cotton and sunflower stalks,” Ph.D. - Doctoral Program, Middle East Technical University, 2008.