Effects of milk heat treatment and solvent composition on physicochemical and selected functional characteristics of milk protein concentrate

Abstract

Milk protein concentrate (MPC) powders (∼81% protein) were made from skim milk that was heat treated at 72°C for 15 s (LHMPC) or 85°C for 30 s (MHMPC). The MPC powder was manufactured by ultrafiltration and diafiltration of skim milk at 50°C followed by spray drying. The MPC dispersions (4.02% true protein) were prepared by reconstituting the LHMPC and MHMPC powders in distilled water (LHMPC and MHMPC, respectively) or milk permeate (LHMPC and MHMPC, respectively). Increasing milk heat treatment increased the level of whey protein denaturation (from ∼5 to 47% of total whey protein) and reduced the concentrations of serum protein, serum calcium, and ionic calcium. These changes were paralleled by impaired rennet-induced coagulability of the MHMPC and MHMPC dispersions and a reduction in the pH of maximum heat stability of MHMPC from pH 6.9 to 6.8. For both the LHMPC and MHMPC dispersions, the use of permeate instead of water enhanced ethanol stability at pH 6.6 to 7.0, impaired rennet gelation, and changed the heat coagulation time and pH profile from type A to type B. Increasing the severity of milk heat treatment during MPC manufacture and the use of permeate instead of water led to significant reductions in the viscosity of stirred yogurt prepared by starter-induced acidification of the MPC dispersions. The current study clearly highlights how the functionality of protein dispersions prepared by reconstitution of high-protein MPC powders may be modulated by the heat treatment of the skim milk during manufacture of the MPC and the composition of the solvent used for reconstitution.

Invited review: Understanding the behavior of caseins in milk concentrates

“…After heating, the concentrates show a slight shift of the buffering peak toward a lower pH ( Figure 2). It is important to note that these results were obtained on fresh concentrates, and this may not be the case for reconstituted concentrates as more dissociation of colloidal calcium phosphate may occur during reconstitution (Lin et al, 2018).…”

“…This applies for both fresh as well as systems reconstituted after drying. In reconstituted systems, there is an additional opportunity to modify functionality, by manipulating solvent conditions (Sandra and Corredig, 2013;Lin et al, 2018).…”

“…Colloidal calcium phosphate seems to be a major factor in the techno-functional properties of the micelles, for example, the melting properties or stretchability of cheese (Choi et al, 2007;Lucey and Horne, 2018). Furthermore, it has been demonstrated that by changing the mineral equilibrium it is possible to modify the interactions between the caseins during spray drying with consequences on their reconstitution properties (Shuck et al, 2002;Havea, 2006;Schokker et al, 2011;Sikand et al, 2013;Lin et al, 2018). For example, replacing 30% of calcium with sodium during concentration results in improved hydration of the reconstituted MPC powders (Sikand et al, 2013), and demineralization of concentrates by pre-acidification of skim milk before membrane filtration has also shown significant changes to MPC functionality, such as solubility or gelling properties (Eshpari et al, 2014;Liu et al, 2019).…”

“…Regardless of the mode of concentration, the viscosity of casein micelle suspensions increases with concentration, with a dramatic change from a Newtonian to a non-Newtonian behavior (Karlsson et al, 2007;Dahbi et al, 2010;Krishnakutti Nair et al, 2014). Similarly, the viscosity of reconstituted MPC also increases with protein concentration, and it can be altered by modifications to the serum (Deshpande and Walsh, 2018;Lin et al, 2018). The semi-empirical equation has been used to describe the dependence of viscosity as a function of concentration, with a maximum packing volume fraction for casein micelles of about 0.79 (Snoeren et al, 1982).…”

“…In particular, the effect of pre-acidification, the use of calcium chelating agents, or changes in salt balance have been studied on changes in solubility and functionality of milk concentrates (Eshpari et al, Marella et al, 2015;Ramachandran et al, 2017;Liu et al, 2019). Further changes in the ionic composition of the serum phase during reconstitution can also affect the solubility and functional properties (i.e., gelation, heat stability) of concentrates (Crowley et al, 2015b;Lin et al, 2018).…”