Physicochemical and rheological properties of cross-linked inulin with different degree of polymerization

Long-chain inulin (L-In) and short-chain inulin (S-In) from native inulin was separated through the method of alcohol precipitation. Cross-linked inulin with two different degree of polymerization (average DP = 6.88 and 15.10) were prepared in aqueous solutions by using the L-In and S-In respectively as raw material and sodium hexametaphosphate as cross-linker. Structural characteristics of cross-linked inulin were determined by Fourier-transform infrared spectroscopy and scanning electron microscopy. Compared with native L-In and S-In, cross-linked inulin had a higher intrinsic viscosity, stronger stability and moisture absorption capability, but lower water solubility. Only 1% reducing sugar produced when cross-linked inulin was heated within 100 °C, and inulin hydrolysis occurred in acidic environment (pH < 6). Rheological properties of inulin dispersions with different degree of polymerization were investigated and compared. The viscoelastic properties of steady shear measurements indicated that cross-linked inulin dispersions presented shear-thinning behaviors, which could be described by a power law model with determination coefficients (R2 = 0.9312–0.9926). The viscoelastic properties of dynamic frequency sweep measurements indicated that cross-linked inulin dispersion showed more solid viscoelastic properties than corresponding native inulin dispersions.