Production of xylanolitic enzymes and xylooligosaccharides by Aureobasidium pullulans CCT 1261 in submerged cultivation

Abstract

Endo-β-1,4-xylanases are microbial-produced enzymes capable of converting lignocellulosic biomass in value-added products of biotechnological interest, such as xylooligosaccharides (XOS). Although endo-β-1,4-xylanase production using lignocellulosic substrates is commonly studied, there are few reports investigating the production of both xylanolytic enzymes and XOS by microbial species. In this paper, the production of xylanolytic enzymes and XOS by three Aureobasidium pullulans strains was evaluated during submerged cultivation, as well as the use of untreated and alkali pretreated agricultural substrates as sources of xylan for endo-β-1,4-xylanase production. The CCT 1261 strain showed the highest endo-β-1,4-xylanase activity (74.94 U/mL), specific activity (158.65 U/mg protein), productivity (P, 1.25 U/mL.h), maximum specific growth rate (μmax, 0.18 1/h), and maximum biomass concentration (Xmax, 4.10 g/L); and a low β-xylosidase production (0.19 U/mL). XOS production by the CCT 1261 strain was verified in the first 12 h of cultivation, which reached the total concentration of 1.68 mg/mL, and the XOS produced were comprised mainly of xylobiose and xylotriose. Among the agricultural substrates evaluated, untreated rice bran showed the highest amount of hemicellulose (29.6%) and a low lignin content (12.2%), which implied in the highest endo-β-1,4-xylanase activity (11.69 U/mL) when used as substrate in submerged cultivation. Endo-β-1,4-xylanase could be produced by A. pullulans in an economical way using a by-product of rice grain milling, which can be further improved by optimization of the submerged cultivation conditions.