Optimization of Conditions for Xylanase Production Using Aspergillus tubingensis Under Different Carbon Sources

Abstract

Xylanases are hydrolytic enzymes with wide range of applications in food processing, bleaching of pulp in paper manufacturing industry, bio-conversion of biomass wastes to fermentable sugars and enhancing nutrient digestibility in animal feeds. The optimization of growth conditions and evaluation of an appropriate substrate as carbon source among cassava peels, corn cobs, wheat bran and rice husk on xylanase production by novel strain of Aspergillus tubingensis under Solid State Fermentation (SSF) was investigated. The fungal isolate was identified based on ribosomal RNA gene and ITS gene sequencing analysis as Aspergillus tubingensis. Results showed that Corn cobs had the highest xylanase production among the four substrates. Corn cobs recorded the highest value of xylanase production at pH of 6.0 (107.97 U/g), after incubation period of 72 hour (111.23 U/g), at temperature of 30 oC (44.26 U/g) and at ratio 1:3 (45.68 U/g). The optimum growth conditions for xylanase production by Aspergillus tubingensis were: pH 6.0, incubation period of 72 hours, temperature of 30 oC and substrate concentration of 1:3 (4g of substrate per 12mL of fermentation medium). Corn cobs showed the highest yield of xylanase activity (111.23±0.31 U/g), followed by Rice husk (101.91±0.72 U/g), Wheat bran (89.30±1.16 U/g) and Cassava peel (87.03±0.57 U/g). In conclusion, among the various agro residues that were used as carbon sources, Corn cobs had maximum xylanase activity. Various culture conditions were optimized by using one factor at a time method and the maximum xylanase production was obtained at pH of 6.0, incubation period of 72 hour, temperature of 30 oC and substrate concentration of 1:3 under solid state fermentation. It is therefore suggested that some other notable environmental and fermentation factors that influence metabolism-mediated production yields of xylanase like aeration, agitation, carbon and nitrogen sources, metal ion requirement, inoculum size etc. should be optimized for maximum production of enzyme. Keywords: Solid State Fermentation, Cassava peels, Corn cobs, Wheat bran, Rice husk