Exoglucanase activity in international units (IU) was assayed by a DNS method. In particular, 40 mL of enzyme solution was added to test tubes, and 160 mL of 1.25% avicel (cellulose substrate) was diluted with 0.1 M acetate buffer (pH 4.8). The mixture was incubated at 50 C for 2 h, and 0.2 mL of 3,5-dinitrosalicylic acid (DNS) reagent was added to stop the reaction. The tubes were transferred to boiling water at 100 C for 5 min, 0.6 mL of distilled water was added, the contents of the tubes were mixed to yield a red color,and absorbance was measured at 540 nm. One unit of activity was defined as the amount of enzyme required to release 1 mmol glucose per min under the conditions of the assay