Enhanced production of cellulase-free thermoactive xylanase using corncob by a black yeast, Aureobasidium pullulans CBS 135684

Our aim was to optimize the production of cellulase-free thermoactive xylanase by Aureobasidium pullulans CBS 135684 with statistical methodology based on experimental designs. Among eleven variables, the nutrient sources that had significant effect on xylanase production were corncob, (NH₄)₂SO₄, xylose, KH₂PO₄ and tween 80, identified by the initial screening method of Plackett-Burman. The optimum concentrations of these five components were subsequently investigated using response surface methodology. The optimal concentrations (g·l^-1) for maximum production of xylanase were corncob, 39.0; (NH₄)₂SO₄, 3.0; xylose, 1.8; KH₂PO₄ 1.4; and tween 80, 1.4, respectively. An improved xylanase yield of 8.74 ± 0.84 U·ml^-1 was obtained with optimized medium which is 2.1-fold higher production than previously obtained results (4.10 ± 0.10 U·ml^-1) after 48 h of cultivation. In addition, the xylanase production under optimal condition reached 10.09 ± 0.27 U·ml^-1 after 72 h of cultivation.