Possesses endo-beta-mannanase and mannan transglycosylase activities. May be involved in cell wall degradation during fruit ripening. Random hydrolysis of (1->4)-beta-D-mannosidic linkages in mannans, galactomannans and glucomannans. Optimum pH is 5.0 for both endo-beta-mannanase and mannan transglycosylase activities. Expressed in flowers and fruit pericarp. Belongs to the glycosyl hydrolase 5 (cellulase A) family.