Effect of a glassy gellan/polydextrose matrix on the activity of a-d-glucosidase

An investigation of the ability of the enzyme α-d-glucosidase to act on the substrate 4-nitrophenyl α-d-glucopyranoside (pNPG) while embedded in glassy carbohydrate matrices (deacylated gellan with polydextrose and polydextrose alone) is presented. Physicochemical characterisation of the matrices was achieved using the techniques of modulated differential scanning calorimetry, small deformation dynamic oscillation on shear, Fourier transform infra-red spectroscopy, wide angle X-ray diffraction and scanning electron microscopy. A UV-vis spectrophotometric procedure was adapted for the analysis of the activity of α-d-glucosidase in hydrolysing pNPG in the condensed carbohydrate systems. In order to derive a relationship between the structural properties of the matrix and the enzymatic activity, mechanical spectra were recorded using the combined framework of the Williams, Landel and Ferry equation with the time-temperature superposition principle. Theoretical modelling and experimental observations strongly argue for a pronounced effect of the gelling polysaccharide/co-solute mixture on enzymatic activity near the mechanical Tg of the matrix.