Mango pulp-agar based model gel: textural characterisation

Acid-induced gelation behavior of casein/whey protein solutions assessed by oscillatory rheology

Gelation process of acid-induced casein gels was studied using response surface method (RSM). Ratio of casein to whey proteins, incubation and heating temperatures were independent variables. Final storage modulus (G') measured 200 min after the addition of glucono-δ-lactone and the gelation time i.e. the time at which G' of gels became greater than 1 Pa were the parameters studied. Incubation temperature strongly affected both parameters. The higher the incubation temperature, the lower was the G' and the shorter the gelation time. Increased heating temperature however, increased the G' but again shortened the gelation time. Increase in G' was attributed to the formation of disulphide cross-linkages between denatured whey proteins and casein chains; whilst the latter was legitimized by considering the higher isoelectric pH of whey proteins. Maximum response (G' = 268.93 Pa) was obtained at 2.7 % w/w, 25 °C and 90 °C for casein content, incubation and heating temperatures, respectively.

Flow behaviour of gellan sol with selected cations

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 (ηo) 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.