Heat treatment of concentrated milk protein system affect viscosity and enzymatic coagulation properties

International audience; Dairy ingredients with highly concentrated protein contents are high added value products with expanding market. They are known to have specific properties adapted for a multitude of applications (cheese, bakery, infant formulae, nutritional products for the elderly and sportspeople...). Fabricationof such dairy protein ingredients is conducted by a succession of unit operations where heat treatment is a key step that induces major changes in protein structures and thus ingredients functionalities. However, due to an incomplete understanding of phenomena taking place at these high proteinconcentrations, shedding light on these mechanisms is simultaneously a scientific challenge and an industrial need. For this purpose, we used an original approach to investigate the influence of heat treatment and mineral environment of concentrated milk protein system on viscosity and enzymatic coagulation properties. Experiments were conducted with fresh whey protein isolates (WPI) and native phosphocaseinates (NPC) according to the ratio 20:80 (WPI:NPC) using 4 different technological routes: without heat treatment (Control); with one heat treatment at 10% w/w protein; with one heat treatment at 20% w/w protein and with two heat treatments at 10% and 20% w/w protein. Interestingly, the protein concentration of the heat-treated solution greatly modulates the denaturation and aggregation process of whey proteins, which modifies the association mechanismsbetween WPI and NPC. Indeed, the increase of protein content leads to a higher particles collision probability and a shorter inter-protein distance modifying protein-protein interactions. Furthermore, the nature of complexes formed during the heat treatment and the amount of aggregates present in solution are two parameters that can modulate the rheological properties (here viscosity and enzymatic coagulation ie, gel time and gel strength) of the system. Influence of lactose and mineral environment is discussed in a second time.