Minor milk proteins

Milk contains numerous minor proteins, including perhaps 60 indigenous enzymes, some of which, e.g. lipase, proteinase, phosphatases and lac-toperoxidase, are technologically important (Chapter 8). Most of the minor proteins have biological functions and probably play very significant roles (section 4.16). 

---

Bovine a-LA from the milk of transgenic mice was characterized, partially purified, and quantified as 1.0 mg/ml by Jeng et al. (1997). The N-terminal amino acid sequence of HPLC-purified bovine a-LA from mouse milk was identical to native bovine a-LA. In addition, the calcium-binding properties of this protein were also similar to the native protein. More details on the modification of minor milk protein fractions are enumerated in other segments (Section VI.A-C) of this chapter. 

Fee, C.J. and Chand, A. (2006). Intensification of minor milk protein purification processes. Proceedings of the 2nd Conference on Process Intensification and Innovation, Christchurch, New Zealand, September 24—29. 

Co-preclpltate is an insoluble milk protein product that is produced by heating skinimllk to high temperatures ( > 90 C) to denature the whey proteins and complex them with the casein micelles. The heated system is subsequently adjusted to isoelectric point conditions of pH 4.5-5 to precipitate the complexed whey protein-casein micelles, centrifuged or filtered to recover the precipitate, washed and dryed. The resulting product, which is virtually insoluble, exhibits only minor functionality in most typical emulsification applications. 

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. 

Grosclaude, F., Mahe, M.-F., Mercier, J.-C., Bonnemarie, J. and Tessier, J. H. 1976B. Polymorphism of milk proteins of Nepalese bovines. II. Polymorphism of the caseins (as-minors) Is locus as2-Cn linked to loci asrCn, 0-Cn, and x-Cn Ann. Genet. Sel. Anim. 8, 481-491 (French). 

McKenzie, H. A. 1971. Whey proteins and minor proteins (3-Lactoglobulins. In Milk Proteins Chemistry and Molecular Biology, Vol. 2. H.A. McKenzie (Editor). Academic Press, New York, pp. 257-330. 

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. 

Since the principal constituents of milk are proteins, lipids and lactose, proteinases, lipases and / -galactosidase (lactase) are the principal exogenous enzymes used in dairy technology. Apart from these, there are, at present, only minor applications for glucose oxidase, catalase, superoxide dismutase and lysozyme. Lactoperoxidase, xanthine oxidase and sulphydryl oxidase might also be included, although at present the indigenous form of these enzymes is exploited. 

In addition to the major protein fractions indicated above, some minor proteins have been isolated or identified in milk. 

At least five genetic variants of asi-casein have been identified, but in Western breeds of cattle the B variant is predominant. The protein comprises a single polypeptide chain of known amino acid sequence (Fig. 2) which is found in milk as a major and a minor fraction. The major fraction, previously designated aSi-casein, contains 8 mol P/ mol (aSi-CN-8P), whereas the minor component (previously aSo-cas-ein) has an additional phosphorylated serine residue at position 41... 

Screening for potential bioactivity among minor proteins of milk, egg, vegetables, cereals, and fruits. 

The chemical composition determines the nutritive properties of milk and its quality. The major constituents are water, fatty matter, proteins, and sugar however, they are not necessarily more important than minor constituents, such as vitamins, enzymes, and minerals, as the latter also play an important role in nutrition. The determination of such minor constituents is therefore of great significance [2-4]. 

---