Effect of temperature and composition on rheological behaviour and sagging capacity of glaze materials for foods

Abstract

In this work, the effect of temperature and composition on rheological behaviour and sagging capacity of glaze materials used for food coating applications was studied. Full-fat and low-fat formulations with 0, 3, 6, and 9% of vegetable fat or microparticulated whey protein as fat replacer were prepared. Dynamic and rotational rheometry was performed at 20, 30, 40, and 50 °C. Viscoelastic behaviour was analysed through phase angle, elastic modulus, and viscous modulus. In order to describe the flow behaviour, a concentration-temperature superposition technique was used with the Carreau-Yasuda, Krieger-Dougherty, and Williams-Landel-Ferry models. The theoretical evaluation of the sagging capacity, considered as a possible flow defect that alters the film homogeneity, was carried out. The characteristic viscosity that influences this phenomenon was calculated by estimating the theoretical average film thickness (using a mechanistic mathematical model previously published) and the gravitational shear stress of glaze materials. The obtained results have shown that formulations behaved as viscoelastic fluids as vegetable fat and microparticulated whey protein content increased and temperature decreased. This phenomenon was partially explained by the independence of elastic modulus with temperature, indicating that glaze materials are near the transition region between glassy and rubbery state. Flow curves could be described by the Carreau-Yasuda model; master curves of apparent viscosity data superimposed at different temperatures and compositions were achieved. Formulations with the same values of average film thickness (but higher values of sagging viscosity) could be obtained, indicating less probability for the sagging phenomenon to occur in those samples.