Effect of polar lipids on heat induced changes in concentrated milk systems

During the last decades, several researchers tried to clarify and fully explain the exact mechanism of the heat-induced coagulation which occurs during heating milk at elevated temperatures. Based on literature data, this phenomenon is mainly a consequence of heat denaturation and unfolding of the globular whey protein fraction of milk, which results in the exposure of the previously buried hydrophobic and free thiol groups. As the denaturation process proceeds, several interactions start to take place leading to the formation of a product with modified organoleptic and physicochemical characteristics. The most important interactions which are believed to take place during heating milk at high temperatures are the interactions between denatured whey proteins with themselves and/or the complex formation of denatured whey proteins (or whey protein aggregates) with casein micelles. The heat-induced network between milk proteins is essentially built due to the hydrophobic bonding between the denatured whey proteins, as well as the thiol-disulfide exchange between the denatured whey proteins with themselves and/or with the κ-caseins. In order to be able to apply high temperatures and at the same time to decrease the degree of protein complexation, the application of surface active molecules (surfactants) has been proposed. Previous studies described that the effect of surfactants on the heat stability of whey protein containing emulsions is based on the protein displacement or interaction with proteins bound on the oil interface, and/or interaction with free proteins in solution

Sensitivity analysis of a small-volume objective heat stability evaluation test for recombined concentrated milk

To quantify the stability towards heat coagulation, an objective test method was developed. The combined use of emulsion preparation by microfluidisation and heat stress by immersion of capped samples in an oil bath enabled small-volume heat stability evaluation of milk formulations. From experimental data, it became obvious that a heating period of about 9min was necessary for the samples to acquire the requested temperature (i.e. 121 degrees C). Similarly, both viscosity and particle size analyses showed an increased aggregation tendency when samples were heated for longer than 10min, whereby their positioning and the cooling medium seemed to have an insignificant effect