Effect of concentration, temperature, pH, co-solutes on the rheological properties of Hyptis suaveolens L. mucilage dispersions

Abstract

The rheological behavior of mucilage dispersions obtained from Hyptis suaveolens L. seeds was characterized. The apparent viscosity showed a non-Newtonian shear-thinning behavior in a range of shear rate 0.1–300 s−1 at 25 °C and pH 6.5. The Cross and Herschel-Bulkley parameters (r2 > 0.9923) indicated that more physical entanglements arise with increasing concentration (0.1–0.75% w/v). Mechanical spectra were obtained by frequency sweep measurement (0.01–10 Hz) at 0.1% deformation and 25 °C. A G´-G´´ cross-over point was observed (1 Hz) for a 0.1% mucilage dispersion, suggesting a molecular transition from random coil to an entangled conformation. The tan(δ) performance for mucilage dispersion with 0.25–0.75% (w/v) concentrations, with values between 0.2 and 0.3, classified into an intermediate behavior between weak and elastic gel. The G´ values were well characterized by power-law frequency dependence (r2≥0.9628). The mucilage dispersion exhibited temperature stability between 20 and 60 °C, and activation energies with values between 7.20 and 12.85 kJmol-1 indicated that more energy was required to disrupt the formed entanglements and to induce viscous flow. For 0.5% mucilage dispersion, the NaCl addition (0–250 mM) generate more aggregates which disruption became more shear dependence as salt concentration growth, and the formed entanglements were less flexible from neutral to alkaline conditions. The sucrose addition (1, 3, 5, 10, and 20% w/v) into 0.5% mucilage dispersion produced a less shear-thinning behavior, giving a stabilizing effect and enhancing the biopolymer gel strength. These results suggest that mucilage could be applied in many food applications, such as stabilizing, thickening and gelling agents.