Journal : Lebensmittel-Wissenschaft + Technologie , vol. 38 , p. 29–39 , 2005
Publisher : Academic Press
International Standard Numbers
Printed : 0023-6438
Electronic : 1096-1127
Publication type : Academic article
Issue : 1
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When high fat (40 g oil /100 g) food dressings emulsified by whey protein were heat-filled (80°C) into plastic-bottles, large visible cracks developed in the dressings after cooling. The occurrence of cracks was dependent on the length of the heat treatment, pH and protein concentration. Heating (2 h at 80°C), low pH (pH 3) and high protein concentrations (1.5 g/100 g) increased the number of cracks. Dressings with cracks were more viscous and had a broader particle size distribution than dressings devoid of cracks. During heating at 80°C the complex modulus (G∗) measured at low deformation increased sharply, signifying the formation of a three-dimensional network as a result of aggregation of whey protein bridging the fat-droplets. Confocal laser scanning microscopy revealed differences in microstructure dependent on cooling rate and pH. At slow cooling and pH 3 the network structure was inhomogeneous with large voids, while at pH 4, closer to the isoelectrical point, the structure was more compact aggregated and homogeneous. The gels at pH 3 were strain sensitive and seemed more prone to localized fracture. A strong (r=0.86) relationship between a visible quality defect called cracks and the gel properties of the emulsion was found. Avoiding cracks called for a strict control of protein concentration, pH and holding time at higher temperatures.