BACK EXTRUSION TEST ON EMULSIONS STABILIZED WITH WHEY-PROTEIN CONCENTRATES

A double back-extrusion test was used to study the differences in the theological behaviour of WPC stabilized emulsion. Emulsions were prepa red 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 se cond thrust immediately or after 15 and 60 min, to quantify the degree of reversible thixotropy. From the curves obtained the slope, the mea n area under the curve and the force at the change of slope were deter mined and compared for the first and second thrust. The results indica ted that the emulsions showed a different behaviour according to the p rotein concentration and the volume fractions of dispersed phase. The curves and the parameters measured for the first and second thrust wer e significantly different, thus providing a measure of thixotropy. Mor eover, it was possible to determine that the emulsions with a volume f raction of dispersed phase of 0.80 presented a degree of reversible th ixotropy. (C) 1995 Academic Press Limited