Purification of xylanases from Aureobasidium pullulans CCT 1261 and its application in the production of...

Xylanolytic enzymes are involved in xylan hydrolysis, the main ones being endo-β-1,4-xylanases (xylanases). This can be applied in the bioconversion of lignocellulosic materials into value-added products such as xylooligosaccharides (XOS). This study aimed to establish a protocol for the purification of xylanases, as well as to characterize and apply the purified enzyme extract in the production of XOS. The enzyme purification techniques studied were ammonium sulfate ((NH₄)₂SO₄) and ethanol precipitation. Purification of xylanase by fractional precipitation (20-60%) with (NH₄)₂SO₄ was more efficient than with ethanol because the salt precipitation reached a purification factor of 10.27-fold and an enzymatic recovery of 48.6% The purified xylanase exhibited optimum temperature and pH of 50 °C and 4.5, respectively. The Michaelis-Menten constant using beechwood xylan for the enzyme was 74.9 mg/mL. The addition of salts such as CaCl₂, ZnCl_2, and FeCl₃ in the reaction medium increased the xylanase activity. Xylanase showed greater thermal stability (half-life = 169 h) at 45 °C and pH 4.5. Under these conditions and in the presence of Ca²⁺ (10 mmol/L) the enzyme was even more stable (half-life = 231 h). Total XOS contents (6.7 mg/mL) and the conversion of xylan to XOS (22.3%) between 2 and 24 h were statistically equal. The hydrolysates showed the majority composition of xylobiose, xylotriose, and xylose. The addition of Ca²⁺ ions did not contribute to an increase in the total XOS content or to a greater conversion of xylan into XOS, but the hydrolysate was richer in xylobiose and had a lower xylose content.