Beta-mannanase likely involved in the utilization of carbohydrates in the human gut. Catalyzes the hydrolysis of different beta-1,4-linked mannans, such as ivory nut mannan, konjac glucomannan, as well as carob and guar gum galactomannans, to a mixture of oligosaccharides. The dominant product from ivory nut mannan is found to be mannotriose; mannobiose and mannotetraose are produced to a lesser extent. Does not hydrolyze mannobiose, and hydrolyzes mannotriose at a significantly lower rate than the longer oligosaccharides. Random hydrolysis of (1->4)-beta-D-mannosidic linkages in mannans, galactomannans and glucomannans. Optimum pH is 5.3. Retains over 90% of its activity in the pH range of 5 to 6. Homodimer. Is likely to be cell attached, either by the sortase mechanism (LPXTG motif) or via a C-terminal transmembrane helix. The carbohydrate-binding modules (CBMs) are responsible for the affinity to carob galactomannan. Belongs to the glycosyl hydrolase 26 family.