ENZYMATIC PRODUCTION OF XYLOOLIGOSACCHARIDES FROM CORNCOB USING ENDO-XYLANASE FROM Streptomyces thermovulgaris TISTR1948

Abstract Xylooligosaccharides (XOs) are the sugar oligomers produced from xylan hydrolysis. XOs have a characteristic of prebiotic by promoting the growth of probiotic microorganisms. Xylan containing agricultural wastes e.g. rice straw, sugarcane bagasse and corncob could be applied to produce XOs by a consecutively process of alkali-pretreatment and enzymatic hydrolysis. In this study, we emphasized on enzymatic production of XOs from corncob, a low cost raw material and relatively high xylan content. The dried corncob was ground and sieved to be <100 mesh size, then subjected to alkali-pretreatment by soaking in 10.0% (w/v) KOH solution at 100°C for 1 h, followed by adjusting pH to 7.0 by adding 5.0% (w/v) H 2 SO 4 , washed by tap water, filtered through a filter cloth and dried the filtrate at 80°C for 48 h. The recovery yield after KOH-pretreatment was 43.69±1.30% (w/w) and the major components of KOH-pretreated corncob were; cellulose (68.21±1.41%), hemicellulose (21.67±0.71%) and lignin (4.29±0.40%). The KOH-pretreated corncob was then subjected to enzymatic hydrolysis by mashing with 10 mM K-P buffer pH 6.5 (15.0% solid). Then, 100 U/g substrate of endo-xylanase from Streptomyces thermovulgaris TISTR1948 was added, the reaction was carried out at 55°C under static condition for 24 h. The samples were periodically taken and analyzed by a thin-layer chromatography (TLC). The results revealed that the suitable reaction time for XOs production was 12 h, which the xylobiose was found as the main product while few xylose contents were obtained. The optimal conditions for XOs production was studied by the response surface methodology (RSM) via the central composite design (CCD). The factors of pH and temperature (°C) were investigated with endo-xylanase concentration (U/g substrate). The results showed that all factors were significant and influenced on the quantity of XOs in term of reducing sugar content (mg/g substrate). The optimal conditions to achieve maximum yield of reducing sugar were; endoxylanase concentration 142.70 U/g substrate at 53.56°C and pH 6.51. Using this experimental design, the reducing sugar content increased from 109.89±1.87 to 130.83±1.4 mg/g substrate or 603.74±6.49 mg/g xylan content in KOH-pretreated corncob which was 19.09% higher than un-optimized condition