Heat-induced changes in the calcium sensitivity of caseins

Stability of milk proteins subjected to UHT treatments: challenges and future perspectives

Ultra-high temperature (UHT) treatments are of high economic relevance for food industries because they contribute to extending the shelf life of food products and facilitating their distribution. In the dairy segment, UHT treatments are applied to a wide range of products containing variable protein amounts. In this sense, the changes in the molecular structure of milk proteins induced by the severity of UHT treatments may lead to fouling in equipment during processing or sedimentation and/or gelation during storage. Nowadays, these concerns are even more relevant due to the increasing demand for UHT-treated high-protein beverages. This review will discuss the two main strategies used by industries to increase the stability of milk proteins during and/or after UHT treatments: (i) addition of chelating agents and (ii) use of polysaccharides. Moreover, the challenges and opportunities associated with promising strategies to improve the stability of milk proteins during and/or after UHT treatments will be covered in this review. The information compiled will be useful to guide researchers and industries in developing more stable UHT dairy products in harmony with consumers' demands.

Association behavior of beta-casein

The association behavior of beta-casein, a protein with a distinct amphipathic character, was studied. beta-Casein exhibits markedly temperature-dependent association behavior; at low temperatures (<10-15 degrees C), monomers predominate, but as the temperature is increased, monomers associate, via hydrophobic bonding, into micelles. beta-Casein micelles have a hydrodynamic radius of approximately 12 nm, a radius of gyration of approximately 8.3 nm, and an interaction radius of approximately 15 nm. These data are fully consistent with a previous fluffy particle. The association behavior of beta-casein is also strongly affected by concentration and solvent quality. At low concentrations beta-casein exhibits a critical micelle concentration (CMC) of approximately 0.05%, w/v, at 40 degrees C. In the presence of 6 M urea the temperature dependence of beta-casein's association behavior is eliminated, leaving monomers predominantly. Temperature-dependent transformations in micelle morphology can be explained by changes in solvent quality, i.e., the temperature-protein hydrophobicity and temperature-voluminosity profiles of beta-casein. The results obtained are consistent with the shell model as developed by Kegeles, in which a distribution of micelle sizes is formed. They contrast with the traditional description of the micellization of beta-casein by a two-state model or by the closed-association model, i.e., monomers if micelles.