Method and special complex enzyme for hydrolyzing galactomannan (GM) to prepare small-molecule GM and galactomannan oligosaccharide (GMOS)

A method for hydrolyzing a GM to prepare a small-molecule GM and a GMOS, wherein the small-molecule GM has a molecular weight of 20,000 Da or less, comprising the following steps:

• 1) conducting a fermentation with MCC and melibiose as carbon sources and T. reesei as an enzyme-producing strain to obtain a supernatant, which is an enzyme solution with enzymatic activities of β-mannanase and α-galactosidase, wherein an enzymatic activity ratio of the of the β-mannanase to the α-galactosidase is no less than 7:1, and wherein the total concentration of the MCC and the melibiose is 20.0 g/L to 35.0 g/L;
• and after the fermentation is completed, centrifuging a resulting culture solution, wherein the supernatant comprises the enzyme solution;
• and
• 2) directly using the enzyme solution obtained in step 1) for an enzymatic hydrolysis of the GM as a substrate to prepare the small-molecule GM and the GMOS.