Production and physicochemical properties of water-insoluble glucan from Streptococcus mutans.

Abstract

A method for the production of water-insoluble glucan was developed by utilizing the extracellular glucosyltransferase present in the culture fluid of Streptococcus mutans, and some physicochemical properties of the glucan powder were investigated.Streptococcus mutans was cultured in brain heart infusion (BHI) medium. The growth phase shifted to the logarithmic phase and the stationary phase at 6 and 14h after the inoculation of the preculture into BHI medium, respectively. The doubling time was about 180 min.Water-insoluble glucan was produced by incubation of the cell-free supernatant of the culture fluid with sucrose added as a substrate. The amount of water-insoluble glucan produced was affected by the concentration of substrate, temperature and pH; the optimum values of these factors were 15% (w/w), 37 °C and 7.5, respectively. By gas-liquid chromatographic analysis of the methylated water-insoluble glucan, the glucan chain was found to consist of 60% of α-1, 3-and 20% of α-1, 6-D-glucosidic bonds. The molar percent of each type of linkage was not affected by the pH of the reaction mixture but was affected by the incubation temperature. Among 8 strains examined, OMZ-176 and 6715 showed the best production of water-insoluble glucan. No peak was observed in the powder X-ray diffraction pattern of the freeze-dried glucan, suggesting that it is an amorphous powder. The hygroscopicity of the glucan powder was similar to that of corn starch. A rheological study showed that a dispersion of the glucan had non-Newtonian and shear-thinning behavior.