Gastric colloidal behaviour of milk protein as a tool for manipulating nutrient digestion in dairy products and protein emulsions

Abstract Not only the structure of food before ingestion but also the structure that is formed during digestion play an important role in food digestion. The coagulation or aggregation of milk proteins under gastric conditions to form a structured coagulum (clot or curd) is a unique interaction between the food source and physiological secretion and action. The interaction can take place in various types of food, such as infant formulae, solid cheeses and emulsion-type beverages, all of which contain milk proteins, resulting in a variety of colloidal phenomena, i.e. aggregation, flocculation/creaming, gelation and clotting. The protein composition, processing treatments and the presence of other food components influence the formation, the structure and the composition of the curd/clot or coagulum. These colloidal stabilizations or destabilizations in the stomach have an impact on the digestion of proteins, lipids and other nutrients, through controlling the kinetics of protein hydrolysis and disintegration of the formed structure. This article summarizes studies on the colloidal behaviour and the restructuring of components in milk, milk protein ingredients and dairy products during gastric digestion that are induced by the interactions among proteins and biological components of the gastrointestinal tract as well as the influence of food processing treatments (such as heat treatment and homogenization) on these interactions and phenomena. The potential to produce healthy foods with different nutritional outcomes by manipulating the restructuring properties of the milk proteins is discussed.