Hydrolysis of mutan and prevention of its formation in streptococcal films by fungal α- d-glucanases

Abstract

A mixed-linkage (α-1,3, α-1,6) water-insoluble glucan (known as mutan) of streptococcal origin was hydrolysed with fungal mutanase, dextranase and a mixture of these enzymes. The basic hydrolysis parameters, i.e. pH, temperature, reaction time, and enzyme and substrate concentration, were standardised to maximise sugar yield from glucan. Thus, the highest conversion of 0.02% mutan to soluble carbohydrate fraction (88% in 36 h) was obtained when mutanase and dextranase were combined. Under such conditions, the synergistic effects of these enzymes were seen as a considerable increase in hydrolysis yield, as compared to that obtained with mutanase (62%) or dextranase (18%) alone. Steady-state measurement of the products of the enzymic reaction during hydrolysis revealed that the mutanase operated in an exo manner and that the dextranase exhibited an endo type of action on mutan. HPLC analysis showed that glucose was the primary final product of glucan hydrolysis with mutanase. Digestion of biopolymer with dextranase or a mixture of mutanase and dextranase yielded glucose and its dimer as main hydrolytic products. Mutanase, dextranase and their mixture were also tested in various in vitro application studies. The enzymes were effective in preventing mutan formation and removing glucan from mixed streptococcal films, especially when the enzymic preparations were used in combination. However, these enzymes displayed less hydrolytic activity towards mutan, which had already been formed in the biofilm.