Oxidized yeast β-glucan: Rheological behaviors and the formation of entanglement network at different oxidation degree

Abstract

This work investigated the rheological properties of oxidized yeast β-glucans (OYG) with three different oxidation degrees (15.2%, 47.3% and 71.2%). Firstly, the intrinsic viscosities of OYG2 and OYG3 calculated by Huggins and Kraemer equations were 104 and 214 mL/g, respectively. Steady-state shear test showed that the OYG solutions exhibited shear-thinning behavior of pseudoplastic non-Newtonian fluid when concentration (c) was greater than 5 mg/mL and OYG1 had the highest apparent viscosity. By fitting viscosity data to the Cross model, the critical overlap concentration (c*) were determined to be 4.69, 3.79 and 2.25 mg/mL for OYG1, OYG2 and OYG3, respectively. From the results of dynamic frequency sweep test, the storage modulus (G′) and the loss modulus (G″) were greatly dependent on frequency and concentration, and OYG solutions represented the feature of structural fluid, an entanglement network at c ≥ 5 mg/mL. Micro-rheological test revealed that the OYG1 solutions were dominated by viscoelasticity at c ≥ 13 mg/mL and the Fluidity Index (FI) decreased with increasing concentration, indicating the increase in elasticity and viscosity. Meanwhile, as the concentration increased from 13 to 20 mg/L, shorter time and lower temperature were required for OYG1 to form a gel, as indicated as they decreased from 53′21″ and 78.60 °C to 41′34″ and 67.40 °C, respectively. Results of temperature ramp test illustrated a thermo-irreversible characteristic of OYG1/water system. The findings suggest that OYGs can be potentially employed in food or cosmetic products for various applications as thickener, stabilizer and so on.