Back extrusion test on emulsions stabilized with whey protein concentrates

Abstract

A double back-extrusion test was used to study the differences in the rheological behaviour of WPC stabilized emulsion. Emulsions were prepared with protein concentrations of 25 and 40 g/L in distilled water at pH 7 and volume fractions of dispersed phase of 0.67 and 0.80. After the first thrust, the emulsions were manually mixed and underwent a second thrust immediately, or after 15 and 60 min, to quantify the degree of reversible thixotropy. From the curves obtained the slope, the mean area under the curve and the force at the change of slope were determined and compared for the first and second thrust. The results indicated that the emulsions showed a different behaviour according to the protein concentration and the volume fractions of dispersed phase. The curves and the parameters measured for the first and second thrust were significantly different, thus providing a measure of thixotropy. Moreover, it was possible to determine that the emulsions with a volume fraction of dispersed phase of 0.80 presented a degree of reversible thixotropy.