Whey proteins casein effect

Skim milk was initially used as the aqueous phase in margarine. Where the law allows, margarines may contain caseinates, whey proteins, or soy proteins as the proteins component in the aqueous phase. The addition to margarine of 0.01—0.1 wt % sodium caseinate in place of milk has been proposed to eliminate sticking during frying. Substituting soy proteins for milk would have the same effect. 

Studies into the effect of frequency of milking on milk quality compared once-daily and twice-daily milking and showed that milk yield was significantly reduced and milk fat and protein concentrations were increased, with once-daily milking compared with twice-daily. Furthermore, casein concentrations in the milks were similar, but once-daily milk had higher whey protein content (O Brien et al., 2002). 

Whey protein concentrates (WPC), which are relatively new forms of milk protein products available for emulsification uses, have also been studied (4,28,29). WPC products prepared by gel filtration, ultrafiltration, metaphosphate precipitation and carboxymethyl cellulose precipitation all exhibited inferior emulsification properties compared to caseinate, both in model systems and in a simulated whipped topping formulation (2. However, additional work is proceeding on this topic and it is expected that WPC will be found to be capable of providing reasonable functionality in the emulsification area, especially if proper processing conditions are followed to minimize protein denaturation during their production. Such adverse effects on the functionality of WPC are undoubtedly due to their Irreversible interaction during heating processes which impair their ability to dissociate and unfold at the emulsion interface in order to function as an emulsifier (22). 

Figure 9.19 Effect of pH on the heat stability of type A milk (A), type B milk ( ) and whey protein-free casein micelle dispersions (O) (from Fox, 1982).

The viscosity of milk and creams tends to increase slightly with age, due in part to changes in ionic equilibria. Heating skim milk to an extent that denatures most of the whey proteins increases its viscosity by about 10%. Homogenization of whole milk has little effect on its viscosity. The increase in the volume fraction of fat on homogenization is compensated by a decrease in the volume fractions of casein and whey proteins because some skim milk proteins are adsorbed at the fat-oil interface. Pasteurization has no significant effect on the rheology of whole milk. 

Lowering the pH of milk to 4.6 solubilizes colloidal calcium phosphate. This removes its neutralizing effect, allowing electrostatic interactions between micelles. Under these conditions, micelles coagulate and precipitate from solution. Kudo (1980C) showed that release of whey proteins and K-casein from casein micelle surfaces as the pH is increased from 6.2 to 7.2 allows micelles to stick together and precipitate from solution. 

Dzurec, D. J. and Zall, R. R. 1985. Effect of heating, cooling, and storing milk on casein and whey proteins. J. Dairy Sci. 68. 273-280. 

Heating milk to > 100°C for 15 to 20 min, as in the forewarming of milk for evaporated milk manufacture, effectively denatures and complexes whey proteins with casein micelles and causes simultaneous aggregation and disaggregation of these complexed milk protein aggregates (Morr 1975). 

PJ de Koning, J Koops, PJ van Rooijen. Some features of the heat stability of concentrated milk. III. Seasonal effects on the amounts of casein, individual whey proteins and NPN and their relation to variations in heat stability. Neth Milk Dairy J 28 186 -202, 1974. 

Extraction of a portion of whey proteins, peptides, and amino acids Suitable for extraction of caseins and peptides from young cheeses. Not as effect as water Extraction of bitter and astringent peptides... 

Reynolds, E.C. and Del Rio, A. 1984. Effect of casein and whey protein solutions on the caries experience and feeding patterns of the rat. Arch. Oral Biol. 29, 927-933. 

Figure 5.3. Schematic illustration of the relative effects of heating and homogenization on fat globules in milk. MFG = milk fat globule, CM = casein micelle, WP = whey protein, dWP = denatured whey protein.

K-casein also contains two Cys residues per monomer subunit and is thus capable of interacting with the whey proteins, e.g., mainly g-lactoglobulin, via the disulfide interchange mechanism at temperatures at or above 65°C. This latter phenomenon is believed to be important in providing colloidal stability to the milk casein micelle system, as well as to the whey proteins, in high temperature processed milk products. It has also been postulated that this latter interaction with g-lactoglobulin may alter the availability of K-casein in the micelle, and thus has a detrimental effect upon the cheese making properties of milk (4). 

It is therefore postulated that whey proteins, which lack an amphiphilic conformation, do not orient sufficiently well at air/ water interfaces to stabilize foam or emulsion systems as effectively as caseinates. 

It was further found that an upstream heat treatment also helps to improve the Tg effect in milk with the casein present in micellar form, in addition to integrating the whey proteins in the gel. The increased Tg effect in milk, which was heat treated at higher levels above pasteurisation level. The same applies for milk which was UHP treated, as shown by Lauber (2002). This can be explained by the heat inactivation of a so-called Tg-inhibitor substance present in milk (De Jong et al. 2003). BOnisch et al. (2006) also proved that the inhibitor substance is located in the milk serum and demonstrated the effect of heat treatment for systems, where only the miUc serum... 

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