Date of Award:
Master of Science (MS)
Nutrition, Dietetics, and Food Sciences
Marie K. Walsh
When skim milk is filtered via microfiltration, the amount of casein (one of the major milk proteins) in solution can be concentrated. When casein content is high enough (>15%), the solution forms a gel at cold temperatures. With growing trends in the food industry towards simplistic ingredient labels, commonly used gums and stabilizers in the dairy industry are becoming less preferred. In the future, there is potential for the gelling properties of micellar casein to be applied to dairy products as a thickener or stabilizer, but the mechanism behind gel formation isn’t understood well. In this study, the gel strength, gelation temperature, and structural changes of casein in response to modifications were studied to understand how they may affect gelation. These modifications included reductions in protein content (from 18.5 to 10%), pH adjustment (from 6.2 to 6.8), addition of a calcium chelating salt (sequesters calcium, a structural component of casein), and addition of a common dairy stabilizer: kappa carrageenan. Protein content was the main determinant of gel strength; reductions from the original protein content of 18.5% to less than 15% resulted in weaker gels that required lower temperatures to form a gel. We found that as the pH increased from 6.2 to 6.8, stronger gels can be formed at a higher temperature. The addition of calcium chelating salts improved these qualities as well but increasing concentrations from moderate (25mM) to high (50mM) resulted in a reduction in gel strength. Microstructure analysis of gels via transmission electron microscopy revealed that with increasing pH, the micellar structure of casein was disintegrating, forming a dispersion of free casein fragments. Calcium chelation at moderate concentrations partially disintegrated the protein structure, but high concentrations led to the formation of large casein aggregates causing a reduction in gel strength. When kappa carrageenan was added, it allowed samples diluted to 10% protein to form a gel which was not previously possible. Kappa carrageenan had minimal interaction with casein, but it was responsible for a stronger gel. Overall, modifications of casein can increase the gel strength and temperature of gelation due to the structural changes in casein.
Pougher, Nathan, "Understanding the Impact of Physicochemical Modifications on the Cold Gelling Behavior of Micellar Casein Concentrate Dispersions" (2023). All Graduate Theses and Dissertations, Fall 2023 to Present. 23.
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