Rheological properties of concentrated milk as a function of concentration, temperature and storage time

Abstract

The flow properties of concentrated milk were evaluated between concentrations of 12.6 and 48.6% solids content, at three temperatures and through 4 weeks of storage. Three rheological models, Newton, power law and Herschel-Bulkley, were applied to fit the flow behavior of milk concentrates depending on the concentration level. The resulting flow behavior indices and consistency coefficients were correlated to concentration by a single term exponential equations, with only two concentrates, 42.4 and 48.6% solids contents exhibiting yield stress. The effect of the temperatures studied on the flow behavior index was minimal, though noticeable on the consistency coefficient, and at the three selected temperatures (5, 15 and 25 °C) the flow behavior index decreased with storage time while the consistency coefficient increased. The energy of activation for flow (evaluated with an Arrhenius type equation) increased with concentration and storage time and ranged from 2.42 to 11.8 kcal gmol −1. A nonlinear model accounting for temperature and concentration effects on the consistency coefficient was identified. The constants of the aforementioned nonlinear model were different for each week of storage. During the 4 weeks of storage the consistency coefficient showed no significant differences, in contrast to the flow behavior index.