Influence of the drying method on the physical properties and immunomodulatory activity of the particulate (1→3)-β-d-glucan from Saccharomyces cerevisiae

The particulate (1→3)-β-d-glucan isolated from Saccharomyces cerevisiae cell walls was recovered from the aqueous medium as water-insoluble particles by different drying methods: solvent exchange (GE), lyophilisation (GL), and spray drying (GS). The samples were characterised by optical microscopy, FT-IR spectroscopy, swelling capacity, and rheological behaviour of aqueous dispersions. The immunological activity of the glucan samples was examined using the assay for the mitogenic and comitogenic activities. The drying method affected the microstructure of the glucan particles leading to differences in their physical properties (particle size and shape, swelling capacity, interparticle hydrogen bonding) as well as in the flow and viscoelastic properties. In comparison to GL and GE, the GS particles preserved the ellipsoid shape of yeast cells and exhibited a very low extent of interparticle hydrogen bonds. The rather liquid-like GS dispersion showed a several times lower apparent viscosity than the gel-like GE and GL dispersions. The results suggest that the physical state of the variously dried particulate glucan samples influenced significantly also their immunomodulatory activity which was found to be about twice higher with GS than with the GL and GE samples. The results indicated that for application of the particulate (1→3)-β-d-glucan as immunomodulator/adjuvans in form of aqueous suspension it is important to use spray-dried preparations.