Acid coagulation behavior of homogenized milk: effect of interacting and non-interacting droplets observed by rheology and diffusing wave spectroscopy (original) (raw)
2011, Dairy Science and Technology
This study analyzes the early stages of the acid coagulation behavior of milk containing homogenized fat globules. By addition of Tween 20 to homogenized milk, it was possible to create two similar colloidal systems with completely different interfacial properties. Control experiments using skim milk demonstrated that the presence of Tween did not overly affect the acid coagulation behavior of the casein micelles. The initial stages of aggregation were also similar for the two homogenized milk systems, indicating that the casein micelles were the main driving force behind early gel formation. For the case of homogenized milk without Tween, the fat globules were fully incorporated in the network. The stiffness of the gel was higher than the control and the overall spatial distribution of the fat droplets was not largely affected by the developing gel matrix. In contrast, the homogenized milk with added surfactant contained fat globules which did not interact directly with the casein micelles but rather became trapped inside the pores of the ensuing network. This gel showed a lower elastic modulus than the homogenized milk case and freediffusing fat globules. Although the presence of interacting and non-interacting droplets did not overly affect the coagulation kinetics of the casein micelles, the acid gels did show different final properties which fully reflected the presence of "active" or "inert" fillers. The knowledge derived from this work will be the first step towards developing novel textures for dairy gels, modulating the extent of the interactions between the fat globules and the protein network.
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