Flow behaviour of gellan sol with selected cations

Abstract

An understanding of the flow behaviour of the sols before gel formation is important for developing nutrient enriched gels. The influence of cations like CaCl₂ (0.05 and 0.1 %, w/w) and FeSO₄ (0.05 and 0.1 %, w/w) on the rheological properties of 1 % gellan sol (w/w) prior to gelling was investigated. The apparent viscosity, reported at a shear-rate of 100 s^-1, indicated that the gellan dispersion without any cation possessed lower values compared to other samples containing different cations. The Cross model provided the best fit (0.97 ≤ r ≤ 0.99, p ≤ 0.01) compared to moderate fitting to power law model (0.94 ≤ r ≤ 0.98). Among the different Cross model parameters, the zero-shear viscosity (η_o) increased with the addition of CaCl₂ and FeSO₄, and with an increase in their concentrations. Zero-shear viscosity values were 0.46 Pas for gellan sol, 0.79 Pas for gellan with 0.05 % (w/w) CaCl₂, 1.41 Pas for gellan with 0.1 % CaCl₂, 3.85 Pas for gellan with 0.05 % FeSO₄ and 4.33 Pas for gellan with 0.1 % FeSO₄. An increase in cation concentration from 0.05 to 0.10 % (w/w) marginally increased the relaxation time (λ) values indicating the development of more solid characteristics in the sol.