The synergistic gelation of okra polysaccharides with kappa-carrageenan and its influence on gel rheology, texture behaviour and microstructures

In this work, the gelling capacity of okra polysaccharides (OPs) and their interaction with the commonly used additive kappa-carrageenan in aqueous solution were studied. In rheology research, pure OPs solutions were found to always remain in liquid state, showing an elasticity performance during heating-cooling cycles. However, OPs formed stable synergistic gels with kappa-carrageenan in a wide range of pH values (5.0–9.0). OPs remarkably increased the texture parameters of the blend gels and influenced the water holding capacity (WHC) by altering the water distribution. The hardness and WHC of the OPs/kappa-carrageenan blend gels reached to the highest and lowest, respectively, at the ratios of 0.6/1.4 and 1.0/1.0. Dynamic rheology measurements and differential scanning calorimetry (DSC) revealed that the blend gels at ratios of 0.6/1.4 and 1.0/1.0 both exhibited higher sol/gel transition temperatures, gel/sol transition enthalpy (ΔH), critical gel strength (n) and fractal dimension (df) values than pure kappa-carrageenan and displayed similar trends of viscoelastic modulus (G′, G″) to those of kappa-carrageenan gel. Blend gels at the ratios of 0.6/1.4 or 1.0/1.0 also showed a sole endothermic peak in differential scanning calorimetry (DSC) spectra, representing melting temperatures at 62.3 °C and 56.1 °C, respectively. AFM observation confirmed that OPs and κ-carrageenan formed denser and irregular network structures in mixed solution, which is obviously different from the sparse meshwork formed by OPs self-assembly and could have contribute to the synergistic gelation of OPs with κ-carrageenan.