Whey proteins denaturation

NFDM, which retains casein micelles similar to those in fresh milk, is produced by pasteurization of sklmmllk, vacuum concentration and spray drying under processing conditions that result in either "low heat" or "high heat" product. Low heat NFDM is required for most applications that depend upon a highly soluble protein, as the case for most emulsification applications, since it is manufactured under mild temperature conditions to minimize whey protein denaturation and complexation with casein micelles. 

Whey protein concentrates (WPC) are produced by a variety of processing treatments to remove both lactose and minerals (20) as indicated in Figure 5. Even though it would be highly desireable to remove most of the lactose and minerals in these processes, it is not practical from an economic standpoint and thus most of these products only range in protein content from 35 to 50 %.The major objective of most of these processes is to produce a WPC with minimal protein denaturation in order to obtain a product with maximum protein solubility and functionality. However, from a practical consideration this objective is not readily obtainable, and thus most WPC products commercially available exhibit variable whey protein denaturation and functionality (20). 

Addition of CaCl2 to about 0.2 M causes aggregation of the casein such that it can be readily removed by low-speed centrifugation. If calcium is added at 90°C, the casein forms coarse aggregates which precipitate readily. This principle is used in the commercial production of some casein co-precipitates in which the whey proteins, denatured on heating milk at 90°C for 10 min, co-precipitate with the casein. Such products have a very high ash content. 

Hillier, R. M. and Lyster, R. L. J. 1979. Whey protein denaturation in heated milk and cheese whey. J. Dairy Res. 46, 95-102. 

Instantized milk powder normally exhibits low bulk density but higher water dispersibility than conventionally spray-dried powder. However, the extra heat exposure from the agglomeration and redrying treatments causes additional Maillard reaction, whey protein denaturation, and related chemical and physicochemical reactions that tend to lower product quality. 

N Parris, MA Baginski. A rapid method for the determination of whey protein denaturation. J Dairy Sci 74 58-64, 1991. 

Tziboula, A. and Home, D. S. 1999. Influence of whey protein denaturation on re-carrageenan gelation. Colloid Surf. B Biointeifaces 12 299-308. 

Generally a decrease in the pH of milk systems prior to heating results in more association of the denatured whey proteins to the casein micelle (Corredig and Dalgleish, 1996 Oldfield et al., 2000 Vasbinder and de Kruif, 2003). Even small changes in pH can shift the distribution of the association of the denatured whey protein with the casein micelle. For example, at a level of 95% whey protein denaturation, there is 70% of the denatured whey proteins associated with the casein micelle at pH 6.55 and this is decreased to 30% when the pH of milk prior to heating was... 

Heat treatment of milk above 60 °C, which promotes whey protein denaturation and its complexation with K-casein at normal milk pH (6.6), also affects renneting properties. An increase in rennet coagulation time and a decrease in gel firmness were observed with increased heat treatment of milk (Menard and Gamier, 2005). Ultra-high temperature (UHT) treated milk failed to coagulate completely but the coagulation properties were restored by threefold concentration of the UHT milk (McMahon ef al., 1993). 

McMahon, D.J., Yousif, B.H., and Kalab, M. (1993). Effect of whey protein denaturation on structure of casein micelles and their rennetability after ultra-high temperature processing of milk with or without ultrafiltration. Int. Dairy J. 3, 239-256. 

Lopez-Fandino, R., Carrascosa, A.V., and Olano, A. The effects of high pressure on whey protein denaturation and cheese-making properties of raw milk, /. Dairy Sci, 79, 929,1996. 

Anema (2008b) showed that application of combined process involving heat and high pressure to skim milk resulted in higher level of whey protein denaturation than that of heat or pressure treatment alone. High-pressure treatment alone decreased the casein micelle size, whereas the change in casein micelle size was not prominent for thermal or combined treatment. 

Anema, S.G. 2008a. Effect of milk solids concentration on whey protein denaturation, particle size changes and solubilization of casein in high-pressure-treated skim milk. International Dairy Journal 18 228-235. 

Moatsu, G., Bakopanos, C., Katharios, D., Katsaros, G., Kandarakis, 1., Taoukis, R, and Politis, 1. 2008. Effect of high pressure treatment at various temperatures on indigenous proteolytic enzymes and whey protein denaturation in bovine milk. Journal of Dairy Research 75 262-269. 

Labropoulos, A. E., Palmer, J. K., and Lopez, A. (1981b). Whey protein denaturation of UHT processed milk and its effect on rheology of yogurt. /. Text. Stud. 12, 365-374. 

Whey proteins denature at temperatures above 70°C and become insoluble and form thermally irreversible gels. 

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