Hydrolysis of hemicellulose by commercial enzyme mixtures

Wood is the most abundant biomass on Earth. Besides cellulose, the main component, wood also contains a substantial amount of hemicelluloses. For paper making purpose, cellulose is the main raw material and only a minor amount of hemicelluloses is used, thus, a great part of hemicelluloses is considered as by product in paper making process. These hemicelluloses can be hydrolyzed into monomer sugars and then served as feed stock for bacterial fermentation for the accompanying production of value added bio fuels and other chemicals. Hemicellulose (xylan) can be hydrolyzed chemically or enzymatically. In chemical hydrolysis predominant applied chemicals are H2SO4 and NaOH and enzymatic hydrolysis is carried out by enzymes. Enzymatic hydrolysis occurs at mild operating conditions of temperature, pH and pressure, also it is environment friendly. Due to the complex chemical nature of xylan, its complete breakdown requires the action of a complex of several hydrolytic enzymes with diverse modes of action and specificity. This complex usually consists of the enzymes, endo 1, 4 â xylanase, â D xylosidase, acetyl xylan esterase, á glucuronidase and arabinase. In this project two commercial enzyme mixtures, Celluclast 1.5 L and Pulpzyme HC, were used. Celluclast has mainly â xylosidase activity while Pulpzyme has â 1, 4 xylanase activity. The experiments were carried out at the conditions of, temperature 40 60 °C, pH 5 7 and Celluclast to Pulpzyme ratio 0 100 %. Seventeen experiments were run. The results show that pH is the most important factor, low pH (at pH 5) result in a higher yield of xylose. Temperature and Celluclast to Pulpzyme ratio are also important factors. Celluclast to Pulpzyme ratio in the range 50–70% results high xylose yield, this can be explained by the fact that the preparation of Celluclast 1.5 L exhibits â xylosidase activity which is responsible for debranching xylobiose and short chain xylo oligisaccharides