The present disclosure belongs to the technical field of biochemical engineering, and relates to a preparation method of ?-galactosidase. The preparation method includes the following steps: step 1, seeding Bacillus circulans into a Luria-Bertani (LB) medium for culture and activation and then into a seed tank for culture to obtain a seed culture broth; step 2, introducing the seed culture broth into a fermentor containing a fermentation medium for fermentation to obtain a fermentation broth of B. circulans; and step 3, filtering or centrifuging the fermentation broth of B. circulans to remove cells to obtain a ?-galactosidase liquid; the fermentation medium includes lactose, galactose, phytone, corn meal, yeast extract, a phosphate salt, a carbonate salt, and water. According to the method, fermentation time is short, production period is shortened, and specific activity of the resulting enzyme liquid is high. The present disclosure further provides a preparation method of an immobilized ?-galactosidase without using a crosslinking agent. The resulting immobilized enzyme has excellent stability and can be continuously used for 264 hours or more, and costs for preparing galactose by using the immobilized enzyme is substantially reduced.

The present invention has objects to provide a glucan useful as water-soluble dietary fiber, its preparation and uses. The present invention solves the above objects by providing a branched -glucan, which is constructed by glucose molecules and characterized by methylation analysis as follows: (1) Ratio of 2,3,6-trimethyl-1,4,5-triacetyl-glucitol to 2,3,4-trimethyl-1,5,6-triacetyl-glucitol is in the range of 1:0.6 to 1:4; (2) Total content of 2,3,6-trimethyl-1,4,5-triacetyl-glucitol and 2,3,4-trimethyl-1,5,6-triacetyl-glucitol is 60% or higher in the partially methylated glucitol acetates; (3) Content of 2,4,6-trimethyl-1,3,5-triacetyl-glucitol is 0.5% or higher but less than 10% in the partially methylated glucitol acetates; and (4) Content of 2,4-dimethyl-1,3,5,6-tetraacetyl-glucitol is 0.5% or higher in the partially methylated glucitol acetates; a novel -glucosyltransferase which forms the branched -glucan, processes for producing them, and their uses.