Proteins in milk

While Little Miss Muffet may have enjoyed the whey proteins in milk in her own way, modern consumers enjoy whey proteins as the important element in the foam of a cappuccino. 

A pale yellow solid, the main protein in milk. It is used as a stabilising agent in latex compounding. Casting... 

Similarly, the protein in milk is very rich in colloidal chemistry. Most of the protein is bound within aggregates called casein micelles (see p. 512). The colloids in milk are essentially stable even at elevated temperatures, so a cup of milky tea, for... 

Milk is a remarkably complex biological fliud. It contains several hundred different molecules including enzymes and also different cells, e.g. inunune cells. In particular, it contains proteins, fat, lactose, both the indispensable and dispensable amino acids, essential fatty acids, micronutrients, cholesterol and phospholipids. Milk is essential for the first four months of life. The major protein in milk is... 

Identification and quantification of Milk Centrifugation at 4°C (for skimming) major bovine milk proteins in milk samples... 

Several of the minor proteins of the MFGM have been isolated and partially characterized (Keenan and Dylewski, 1995). A systematic nomenclature has not been developed for the MFGM proteins and most are referred to by their relative electrophoretic mobility on SDS-PAGE and whether or not they are glycoproteins. The proteins of the MFGM represent approximately 1 % of the total proteins in milk. 

Initially, it was believed that milk contained only one type of protein but about 100 years ago it was shown that the proteins in milk could be fractionated into two well-defined groups. On acidification to pH 4.6 (the isoelectric pH) at around 30°C, about 80% of the total protein in bovine milk precipitates out of solution this fraction is now called casein. The protein which remains soluble under these conditions is referred to as whey or serum protein or non-casein nitrogen. The pioneering work in this area was done by the German scientist, Hammarsten, and consequently isoelectric (acid) casein is sometimes referred to as casein nach Hammarsten. 

Figure 9.14 The denaturation of the total ( ) and individual whey proteins in milk, heated at various temperatures for 30 min /l-lactoglobulin ( ), a-lactalbumin (O). proteose peptone ( ), immunoglobulins (A), and serum albumin ( ) (from Webb and Johnson, 1965).

MILK IS AN IMPORTANT SOURCE OF PROTEIN. THE PROTEIN IN MILK IS CALLED CASEIN. CHEESE IS SPECIALLY TREATED CASEIN. 

Thomas, P. C. 1980. Influence of nutrition on the yield and content of protein in milk Dietary protein and energy supply. In Factors Affecting the Yields and Content of... 

During the nineteenth and early twentieth centuries, separation of the proteins was limited to casein and the classical lactalbumin and lacto-globulin fractions of the whey proteins. Subsequent work has resulted in the identification and characterization of numerous proteins from each of these fractions. A classification system of the known proteins in milk developed by the American Dairy Science Association s (ADSA) Committee on Milk Protein Nomenclature, Classification, and Methodology (Eigel et al 1984) is summarized and enlarged to include the minor proteins and enzymes in Table 3.1. 

Bell, K. and McKenzie, H. A. 1976. The physical and chemical properties of whey proteins. In Milk Protein Workshop, Tanunda, South Australia. Northfield Research Laboratories, South Australian Department of Agriculture. 

Addition of specific compounds to milk has been used to allow spec-trophotometric measurement of lactose as the osazone (Wahba 1965) and fat by fluorescence (Bakhiren and Butov 1968 Konev and Kozlova 1970). The dye-binding method for measuring protein in milk is based on the ability of sulfonic acid dyes to complex with the basic amino acid residues of milk proteins at low pH (Fraenkel-Conrat and Cooper 1944). Dye binding correlates well with Kjeldahl (Sherbon 1970) and infrared (Mogot et al. 1982 Grappin et al. 1980) results, but variations are caused by the different compositions of the different milk proteins (Ashworth 1966 Vanderzant and Tennison 1961). 

Bakalor, S. 1965. The estimation of protein in milk from its fluorescence in the ultraviolet region. Aust. J. Dairy Technol. 20, 151-153. 

Koops, J. and Wijnand, H. P. 1961. Determination of protein in milk by fluorescence. Neth. Milk Dairy J. 15, 333-357. 

The primary proteins in milk are the caseins. These may be removed from milk by acid and heat-induced precipitation at pH 4.6 followed by centrifugation. The remaining supernatant (called whey) contains primarily a-lactalbumin and /3-lactoglobulin. These two proteins may be separated by gel filtration or with a Cu(II)—IDA-agarose affinity column. 

The presence of a-lactalbumin in a fraction cannot be confirmed until further characterization. However, if you know that a-lactalbumin is among the smallest proteins in milk (molecular weight is 14,200), can you determine which protein peak contains a-lactalbumin ... 

Haasnoot, W., Olieman, K., Cazemier, G., and Verheijen, R. 2001. Direct biosensor immunoassays for the detection of nonmilk proteins in milk powder. J Agric Food Chem 49 5201-5206. 

Bullen, J.J., Rogers, H.J., and Leigh, L. 1972. Iron-binding proteins in milk and resistance to Escherichia coli infections in infants. Br. Med. J. 1, 69—75. 

Reiter, B. 1985. Protective proteins in milk—biological significance and exploitation. IDF Bull. 191, 1-35. 

Discuss the relevance of knowing the amount of iodine that is bound by protein in milk in measuring the 131I in milk samples by chemical processing. Make suggestions that could overcome this issue. 

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