Steady-shear viscosity of stirred yogurts with varying ropiness

Abstract

Stirred yogurt was viewed as a concentrated dispersion of aggregates consisting of protein particles. The steady-shear behavior of three types of stirred yogurt with varying ropiness was investigated experimentally. To describe the shear-dependent viscosity, a microrheological model was used which was developed for weakly aggregating dispersions. This model was capable of successfully describing the steady-state viscosity as a function of shear rate of the stirred yogurts, the protein concentration of which ranged between 2.0% and 3.9%. The value of the fractal dimensionality df, following from the model for the aggregates is about 2.24, which was similar to the value of df found with other methods. Moreover, realistic values were found for the interaction forces (energies) describing interaction between the aggregates. The calculated size of the aggregates was close to the size found before by applying different experimental techniques. Using this model, the interpretation of the measured curves suggests that the exopolysaccharides, produced by the lactic acid bacteria in yogurt, play a significant role in the rheology of stirred yogurt.

Impact of oxidoreduction potential and of gas bubbling on rheological properties of non-fat yoghurt

“…Under N 2 -H 2 condition, the gel was as weak as under oxidizing conditions despite there being a greater production of EPS. The contribution of EPS produced by LAB to the rheological properties of yoghurt is a common assumption (Hess, Roberts, & Ziegler, 1997;Rawson & Marshall, 1997; van Marle, van den Ende, de Kruif, & Mellema, 1999) but, as reported by Hassan et al (1995) and van Marle (1998), and in the present case, no correlation between the viscosity of fermented milk and EPS concentration was found.…”

Redox Potential: Monitoring and Role in Development of Aroma Compounds, Rheological Properties and Survival of Oxygen Sensitive Strains During the Manufacture of Fermented Dairy Products

“…Indeed, the gel of yoghurts produced under N2 -H2 conditions is weaker despite greater EPS production [23]. It is a common assumption that EPS produced by bacteria contribute to the rheological properties of yoghurt [31][32][33] but, as reported by Hassan et al [34], van Marle [35] and Martin et al [23], no correlation between the viscosity of yoghurt and EPS concentrations was found.…”

Yoghurt with candied chestnut: freeze drying, physical, and rheological behaviour

“…It exhibits irreversible timedependent shear behaviour, and shear rate thinning (van Marle et al 1999 andRascon-Diaz et al 2012). Rascon-Diaz et al (2012) suggested that, visual inspection of the viscosity curves of fresh yoghurt and reconstituted natural yoghurt (without added hydrocolloids) subjected to spray drying, indicates a decrease in viscosity in both yoghurt samples.…”