Effect of konjac glucomannan on heat-induced pea protein isolate hydrogels: Evaluation of structure and formation mechanisms

The roles of increasing concentration of konjac glucomannan polysaccharide (KGM) in modifying the thermal, textural, and rheological properties of heat-induced pea protein isolate (PPI) hydrogels at neutral pH and low ionic strength were investigated in this study. Differential scanning calorimetry was first applied to investigate the effect of KGM addition on the thermal properties of pea proteins, finding that an addition of 0.5 % w/v increased the glass transition temperature of pea proteins (from 150 to 154 °C) while on the contrary, higher concentrations of 1.0–1.5 % w/v reduced glass transition temperatures (from 150 ◦C to ~ 144 °C). Water holding capacity highlighted that KGM addition significantly increased water retention, reaching values up to 90 % for KGM concentration ≥ 1.0 % w/v. Confocal laser scanning microscopy showed the presence of a phase separation system with increasing concentrations of KGM. Molecular interactions and Fourier transform infrared spectroscopy analysis highlighted that the hydrogels were mainly stabilized by non-covalent intermolecular interactions. Texture analysis confirmed that KGM significantly influenced texture of the hydrogels, in which 1.5 % w/v KGM presented the highest hardness value of 1.34 N. Lastly, small amplitude rotational and oscillatory rheology was employed to evaluate the hydrogels viscosity and viscoelastic properties, which both were significantly increased with increasing KGM concentrations.