Margarines: A rheological study

Abstract

Time-dependent flow properties of both commercial and pilot plant-made margarines were characterized under steady shear. Flow curves were fitted to the kinetic expression = zi + a e-kit+ b e -k2t. A first-order kinetic model did not describe the observed destruction process of the margarine structure in an adequate manner. In the proposed model, two structures with different destruction rates are postulated. Each structure contributes to a part of the shear stress necessary to deform the margarine sample. The parameters "r i a and b are temperature-dependent. Decreasing temperatures produce an exponential increase of ~i, a linear increase of b and an increase of a up to a point beyond which it remains constant. A physical interpretation of the model is proposed. The role of the aqueous phase was also studied. Greater hardness was detected at higher water content. Parameter zi increased, at any selected temperature, with increasing aqueous phase content of the sample. Parameter a increased with decreasing temperatures and higher water content. On the other hand, parameter b was not affected by the amount of aqueous phase. This kinetic model could be employed to perform studies on the influence of different parameters of margarine formulation on its rheologic behavior