Bioprocessing of Agro-Residual Wastes for Optimisation of Xylanase Production by Aspergillus brasiliensis in Shake Flask Culture and Its Scaling up Elucidation in Stirred Tank Bioreactor

Abstract

Objective:Xylanase is a hydrolytic enzyme that breaks down backbone of xylan into xylose sugars. This extracellular enzyme possesses many applications in pulp and paper, food and beverage industries. Malaysia as an agricultural country contributes more than 5 million tons of agricultural wastes per year, thus, it is feasible to utilize agro-residual wastes to produce xylanase. Methods:In the present study, Aspergillus brasiliensis ATCC 16404 was investigated for the production of xylanase in shake flask culture using different agro-residual wastes including wheat bran, sawdust, rice bran, sugarcane bagasse, barley husks, soybean hulls and palm kernel cake. A. brasiliensis was cultured at initial pH 6.5, agitation speed of 150 rpm at 30°C for 144 h. Thereafter, the optimised carbon sources obtained from earlier experiments were further elucidated in stirred tank bioreactor. This scaling up study was conducted using 1 L culture medium at initial pH 6.5, agitation speed of 200 rpm and aeration rate of 1 vvm. Results: Based on our results, the highest xylanase activity of 11.2128 ± 1.7030 U/mL at 72 h was observed using pure substrate of xylan in shake flask culture. Agro-residual wastes of wheat bran and sawdust possessed appreciable xylanase activity of 1.1162 ± 0.0034 and 1.2343 ± 0.0809 U/mL in small scale of submerged fermentation [SmF], respectively. In order to replace the expensive xylan as the prime carbon source, wheat bran and sawdust were thus elucidated as the alternative carbon source in the scale up production of xylanase using stirred tank bioreactor system. Based on the result findings, A. brasiliensis yielded relatively higher and faster xylanase production of 3.1126 ± 0.2462 U/mL at 72 h using wheat bran compared to 1.1668 ± 0.0270 U/mL from sawdust at 96 h in bioreactor. Conclusion:Hence, our study showed that wheat bran was the optimum cost effective substrate for the production of xylanase by A. brasiliensis in shorter fermentation period using large scale SmF in stirred tank bioreactor.