Protein milk, from

Ultrafiltration. Membranes are used that are capable of selectively passing large molecules (>500 daltons). Pressures of 0.1—1.4 MPa (<200 psi) are exerted over the solution to overcome the osmotic pressure, while providing an adequate dow through the membrane for use. Ultrafiltration (qv) has been particulady successhil for the separation of whey from cheese. It separates protein from lactose and mineral salts, protein being the concentrate. Ultrafiltration is also used to obtain a protein-rich concentrate of skimmed milk from which cheese is made. The whey protein obtained by ultrafiltration is 50—80% protein which can be spray dried. 

Milk from cows contains 3.2% protein, about 80% of which is casein. Casein is isolated by a precipitation process from milk, involving heating, rinsing to remove whey, and drying to a powder. The yield is about 3 kg/ 100 kg skim milk. Rennet casein is obtained when the casein is precipitated by chymosin enzyme, also known as rennet, and acid casein is produced when precipitation is accomplished by acidification. Acid casein is usually found in the form of sodium caseinate or calcium caseinate, which are water-soluble salts. Caseinates are made by reacting NaOH or CaOH with a slurry of casein curd or powder and then spray drying (Southward, 2010). 

A monoclonal antibody-based ELISA has been utilized to determine ceftiofur levels in milk. The authors noted that matrix interference occurred, but a 1 100 dilution lowered the interference, and a 1 1000 dilution eliminated the matrix interference. Because of the high dilution, samples could not be measured below l.Opgkg The assay measured ceftiofur, its major metabolite desfuroylceftiofur, and ceftiofur protein conjugates and has been utilized to measure residues in milk from cows treated with therapeutic doses of the drug. The results from the incurred residue correlated well with a previous study using radiolabeled ceftiofur, confirming the detection of a metabolite that was not detected by HPLC. 

It is well known that the protein content of milk from different species varies and is inversely related to the period of development of the young. The content of the B vitamins is likewise much higher in the milks of small, rapidly maturing animals63 than in human or cow s milk. There can be no serious doubt that the ability to produce milk at all, and also the composition of milk, is controlled to a large extent by genetic factors. On this basis one would expect that milk would vary in composition from individual to individual. 

Fig. 6 Transition temperature of protein unfolding measured by CE and CD. Proteins lysozyme from chicken egg (LYS), a-lactalbumin from human milk (LAL-h), a-lactalbumin type III from bovine milk (LAL-III), cytochrome c from bovine heart (CYT), recombinant dihydrofolate reductase (DHFR).

Table 4.2 Properties of some milk proteins (modified from Walstra and Jenness, 1984)... 

Milk contains, on average, 0.03 mg thiamin per 100 g. Most (50-70%) of the thiamin in bovine milk is in the free form lesser amounts are phos-phorylated (18-45%) or protein-bound (7-17%). The concentration in mature human milk is somewhat lower (c. 0.02 mg per 100 g). Human colostrum contains only trace amounts of thiamin which increase during lactation. Pasteurized milk from goats and Channel Island breeds of cow contain about 0.04 mg per lOOg, while values for raw sheep s milk are somewhat higher, with an average of 0.08 mg per 100 g. Most of the thiamin... 

At almost every meal, we look forward especially to the proteins ham and eggs for breakfast, hamburgers or frankfurters for lunch, steak or chicken for dinner. We drink milk mostly for the sake of its prot eins. Even many of our desserts are protein products — from ice cream to Jell-O. 

Seasonal Variation and the Influence of Temperature. In temperate latitudes, rather characteristic seasonal variations in milk composition are commonly observed. Both fat and solids-not-fat contents are lower in summer than in winter. In the survey by Overman (1945) of individual cows at the University of Illinois, monthly extremes for fat were 4.24 and 3.81% in January and August and for protein were 3.61 and 3.37% in January and July, respectively. Nickerson (1960) found significant seasonal differences in 18 components of bulk milks from six areas in California. Seasonal differences in fat and protein contents were similar to those observed in Illinois. Seasonal variations in milk composition could conceivably be caused by differences in temper-... 

Bortree, A. L., Carroll, E. J. and Schalm, 0. W. 1962. Whey protein patterns of milk from cows with experimentally produced mastitis. J. Dairy Sci. 45, 1465-1471. 

This chapter considers the classification, nomenclature, primary structure, and chemical and physical properties of the individual protein as they occur in the milk from the genus Bos. While some studies have been done of the proteins of the milk of other mammals, bovine milk, due to its commercial importance, has been most extensively investigated. A more comprehensive treatment of the subject is in the two-volume treatise on the chemistry and molecular biology of the milk proteins edited by McKenzie (1970, 1971A). Other reviews are Whitney (1977), Brunner (1981), and Swaisgood (1982). 

Bovine Serum Albumin. Since Polis et al. (1950) crystallized bovine serum albumin from whey and demonstrated that it was identical in all properties investigated to blood serum albumin, except in its electrophoretic behavior at pH 4.0, very little work has been done on this protein as isolated from milk. However, much work has been done on the protein isolated from bovine blood plasma. There is considerable evidence that serum albumin is heterogeneous. For example, Spencer and King (1971) have demonstrated several protein bands by electrophoretic focusing, with two major isoelectric components differing by one unit of charge. The chemical nature of this difference is not known. 

The configuration of bovine serum albumin isolated from milk has not been investigated, but extensive investigations of this protein isolated from bovine blood serum have been made. The protein exhibits at least three different kinds of heterogeneity (1) due to polymer formation, (2) related to the sulfur linkages in the molecule, and (3) microheterogeneity. Fractionation of bovine serum albumin on DEAE-Sephadex A-50 resulted in a monomer and two dimer fractions (Janatova et al. 1968),... 

Burger, R. L. and Allen, R. H. 1974. Characterization of vitamin Bi2-binding proteins isolated from human milk and saliva by affinity chromatography. J. Biol. Chem. 249, 7220-7227. 

Interpolations on mixtures of cream and skim milk from a single sample were apparently used to determine these averages. Such mixtures would have a constant ratio of each constituent of solids not-fat and would not apply to other samples (e.g., with a different protein/lactose ratio). source Data from Short (1955). 

Whitnah (1962) found high positive correlations between viscosity at 4°C of milks from individual cows and their fat and protein contents. Surprisingly, the correlation between viscosity and the content of solids other than fat or protein was negative, which he attributed to an inverse effect of lactose on viscosity. 

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

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