Abstract: The depolymerization of gum derived from Gleditsia sinensis was performed by enzymatic hydrolysis with β- mannanase. The optimal hydrolysis conditions were investigated by using an L9 (34) orthogonal array design to explore the effects of substrate concentration, enzyme dosage, hydrolysis time and hydrolysis temperature on average polymerization degree of hydrolysates and reducing end glycosyl group yield. The results showed that the optimal conditions for depolymerization of the gum were substrate concentration of 50 g/L, enzyme dosage of 1300 U/g, reaction temperature of 65 ℃, and reaction time of 11 h. Under the optimal hydrolysis conditions, the reducing end glycosyl group yield was 49.92% and the average degree of polymerization 2.00. In addition, fed batch operation at the beginning could increase substrate concentration, and he reducing end glycosyl group yields in 100 g/L and 150 g/L reaction solutions after reaction for 24 h were 50.89% and 46.97%, respectively. The addition of surfactants such as gleditsia saponin and T-ween 80 could improve reducing end glycosyl group yield by 5.25% and 9.40%, respectively. Moreover, HPLC analysis indicated that the hydrolysates of Gleditsia sinensis gum mainly consisted of mannotetraose (17.25%), mannotriose (28.68%), mannobiose (4.55%) and monosaccharide (1.81%).

Key words: Gleditsia sinensis gum, enzyme hydrolysis, reducing saccharides, orthogonal array design, oligosaccharide