Production and characteristics comparison of crude β-glucosidases produced by microorganisms Thermoascus aurantiacus e Aureobasidium pullulans in agricultural wastes

The purified β-glucosidase of Aureobasidium pullulans ER-16 is one of more thermostable enzyme reported to date. Considering the unfeasibility of using purified enzyme for industrial application, it was interesting to analyze this property for the crude enzyme. Thermophilic fungus Thermoascus aurantiacus CBMAI-756 and mesophilic A. pullulans ER-16 were cultivated in different hemicellulosic materials on solid-state cultivation for β-glucosidase production. Wheat bran was most appropriate for β-glucosidase production by both microorganisms. T. aurantiacus exhibited maximum enzyme production (7.0 U/ml or 70 U/g) at 48–72 h and A. pullulans a maximum (1.3 U/ml or 13 U/g) at 120 h. Maximum activities were at 75 °C with optimum pH at 4.5 and 4.0, for T. aurantiacus and A. pullulans, respectively. A. pullulans's β-glucosidase was more pH stable (4.5–10.0 against 4.5–8.0) and more thermostable (90% after 1 h at 75 °C against 85% after 1 h at 70 °C) than the enzyme from the thermophilic T. aurantiacus. The t(1/2) at 80 °C were 50 and 12.5 min for A. pullulans and T. aurantiascus, respectively. These data confirm the high thermostability of crude β-glucosidase from A. pullulans. Both β-glucosidases were strongly inhibited by glucose, but ethanol significantly increased the activity of the enzyme from T. aurantiacus.