A novel thermostable β-1,3-1,4-glucanase from Thermoascus aurantiacus and its application in oligosaccharide production from oat bran.

Fermentation conditions for β-1,3-1,4-glucanase (TaGlu34) production in submerged culture by a thermophilic fungus, Thermoascus aurantiacus CAU830 were optimized. The highest enzyme activity of 3741 U/mL was obtained, and the crude enzyme was purified to homogeneity with a purification fold of 7.3 and a recovery yield of 11.6%. The molecular mass of the purified enzyme was estimated to be approximately 34 kDa on SDS-PAGE. TaGlu34 was most active at pH 6.0 and 75 °C, respectively. It showed excellent thermostability with thermal denaturing half-lives of 209, 130 and 69 min at 50, 60 and 70 °C, respectively. TaGlu34 exhibited strict substrate specificity towards barley β-glucan (13,527 U/mg), oat β-glucan (12,502 U/mg) and lichenan (9225 U/mg), but displayed no activity on other tested polysaccharides including laminarin, xylan, pullulan, CMC and starch. TaGlu34 hydrolyzed barley β-glucan and lichenan to yield both mainly disaccharide and trisaccharide, suggesting that it should be an endo type β-1,3-1,4-glucanase. Furthermore, TaGlu34 efficiently degraded the β-glucan component in oat bran to produce mainly oligosaccharides with degrees of polymerization (DP) 3-5, with the highest conversion ratio of 47.1%. The high yield and excellent enzymatic properties of TaGlu34 may make it a good candidate in industries.