| Milk proteins associate with each other via several mechanisms including hydrophobic interactions. The properties of casein networks relies on the nature of these interaction forces (type, strength, number, and lifetime or relaxation behavior) between bonds within the network. Hydrophobic interactions have been included as one of the integral forces in recent models of the casein micelle. This aim of this thesis was to understand the role of hydrophobic interactions in several milk protein systems and how modifying these interactions would affect the formation, strength, and stability of the matrices. A series of salts, which mainly modifies hydrophobic interactions in protein systems by increasing or decreasing the solubility of a protein, was used as a tool to assess the role hydrophobic interactions play within several milk protein networks. Four model milk protein systems were studied: brine-salted cheese, process cheese, rennet milk gels, and protein stabilized foams. Salts were added to the protein systems at low and high concentrations. Chemical, rheological, textural and functional tests were used to assess how intrinsic or extrinsic factors affect the changes in protein-protein interaction strength. At low salt concentrations ( < 0.25 M) electrostatic interactions decrease in milk protein systems. Cheese and gel systems exhibited lower hardness and storage modulus values. Foams demonstrated increased overrun, stability, and yield stress. At high salt concentrations > 0.25 M, salt-specific effects were observed (i.e., strengthening or weakening hydrophobic interactions). Strengthening hydrophobic interactions in rennet gels and cheeses resulted in a more dense, brittle, and firmer protein network. Foams were more stable but weaker than the control. Weakening hydrophobic interactions produced softer, more meltable cheeses and prevented gelation. Foams were more voluminous but less stable and weaker. A deeper understanding of the role of hydrophobic interactions in milk protein systems helped to provide information how modulating hydrophobic interactions can influence cheese texture and melt properties, gelation and structure of rennet gels, and stability of protein stabilized foams. This research can lead to the development of milk protein products that employ functional ingredients/methods which alter hydrophobic interactions in proteins as tools to improve texture or functionality. |
