Micellar casein concentrates and isolates: changes induced by stabilization and preservation methods
Authors:   , García Amezqueta Arantza 
Published: May 2023

The use of milk protein concentrates as ingredients is increasing due to their excellent functional and nutritional value. A good strategy for obtaining these concentrates is the use of membrane filtration as it allows to separate and concentrate specific compounds of milk maintaining their native structure. This is the case of micellar casein concentrates (MCC) or isolates (MCI), which have been partially separated from whey proteins, lactose and soluble minerals and finally spray-dried. However, these powder protein concentrates have to be dispersed and dissolved before their use to perform their function as food ingredients, which presents a problem due to their difficult reconstitution. Alternatively, their use in liquid form would provide an important completive advantage, nevertheless, their handling in liquid form makes them highly vulnerable to microbiological spoilage and other alterations. This dissertation, therefore, set out to explore the behaviour and stability of these liquid concentrates treated by high-pressure processing as well as their combination with an antibacterial such as nisin. This non-thermal technology has also been used to treat dairy bases for high-protein content yogurt manufacture. In addition, during the predoctoral stay carried out in FrieslandCampina Innovation Centre (Wageningen, The Netherlands), it has been studied in depth the effect of sequestering salts: sodium hexametaphosphate (SHMP) and trisodium citrate (TSC) on MCI solutions, as well as the heat-induced changes of SHMP on MCI and their stability over time. Concerning the most relevant findings, the treatment of liquid micellar casein concentrates (LMCC) at 600 MPa for 5 minutes managed to guarantee microbial quality; however, at these high pressures, fractionation and regrouping processes occurred in the micellar structures that affected the final texture. It was also found that the addition of nisin to LMCC allowed reducing the pressure applied to 450 MPa reaching a similar microbial reduction level that the one obtained at 600 MPa but without affecting the physicochemical properties of the concentrates. Concerning the yogurts made with LMCC treated both thermally and by high pressure, it was found that both showed high water retention capacity and firmness, and the differences were observed between the two treatments in terms of yogurt viscosity (stirred), highlighting the potential of the non-thermal treatment. As the most relevant findings of the research carried out with MCI, it has been demonstrated that both sequestering salts induced the micelle disruption but their mechanism differed. Thus, it has been hypothesized that TSC forms soluble Ca-Citrate complexes by solubilizing the inorganic phosphate in the micelle, while SHMP acts as a peptizing agent inducing the disruption of micellar calcium phosphate, but not solubilizing it. Furthermore, when SHMP was added to an MCI solution and heated at different combinations of temperature and time, simulating industrial conditions, hydrolysis of SHMP occurred resulting in a marked decrease in pH and viscosity. However, these solutions with SHMP showed very good stability during storage, demonstrating its ability as a stabilizing agent.