Milk, casein content

Protein-Based Substitutes. Several plant and animal-based proteins have been used in processed meat products to increase yields, reduce reformulation costs, enhance specific functional properties, and decrease fat content. Examples of these protein additives are wheat flour, wheat gluten, soy flour, soy protein concentrate, soy protein isolate, textured soy protein, cottonseed flour, oat flour, com germ meal, nonfat dry milk, caseinates, whey proteins, surimi, blood plasma, and egg proteins. Most of these protein ingredients can be included in cooked sausages with a maximum level allowed up to 3.5% of the formulation, except soy protein isolate and caseinates are restricted to 2% (44). 

The protein content of milk is primarily influenced by the breed of cow, the stage of lactation, type of diet being fed and the health status of the cow, and is important in processing because the protein (and specifically casein) content of milk determines its cheese yield. Milk provides a highly digestible source of protein for a large proportion of the world s population, either as raw milk or processed into dairy products. In addition to this basic nutrition, milk... 

The U.S. standards for grades of edible dry casein (acid) are presented in Title 7, Part 28, of the Code of Federal Regulation (FDA 1981B) with the following specifications Grades are determined on the basis of flavor and odor, physical appearance, bacterial estimates [standard plate count (SPC) and coliform count], protein content, moisture content, milk fat content, extraneous material, and free acid. 

The high casein content of cow s milk is responsible for the formation of a large, firm curd which may be difficult for some infants to digest compared with the finer, soft curd formed from human milk. Consequently, cow s milk often is modified to conform more closely to the nutrient and physical requirements of infants (Fomon 1974). When cow s milk is heated, homogenized, or acidified to produce softer curd formation, the protein is used by infants as efficiently as that of human milk, which contains less casein than cow s milk (Fomon 1974). 

Carpenter, R. N. and Brown, R. J. 1985. Separation of casein micelles from milk for rapid determination of casein content. J. Dairy Sci. 68, 307-311. 

Raw milk is standardized to the proper fat and total milk solids content to produce a final product with a minimum of 50% fat on a solids basis and <39% moisture (CFR 1982 Packard 1975). Cheese is made from pasteurized or raw milk, but raw milk cheese must be aged a minimum of 60 days at >1.7°C (CFR, 1982). Minimum temperature and time combinations are normally used for pasteurization of milk for cheese manufacture in order not to interfere with casein micelle coagulation and curd formation. Milk is sometimes heated only to subpasteurization temperatures to dispel dissolved gases, reduce bacterial populations, and kill certain pathogens, thus resulting in a cheese product with improved flavor (Babel 1976). 

As it can be seen in Table 13.2, human milk composition is quite different from that of cow s milk. Casein and mineral contents are lower in human milk than in cow s milk, whilst the lactose content is higher in the former. With regards to fatty matter, both types of milk present similar contents, but the total protein is over three-fold higher in cow s milk. 

Animal proteins, such as milk casein, whey, albumin, collagen, gelatin, keratin, and myofibrillar, are also proposed as raw materials to form edible films (13-15). Extended stmctures formed by unfolding of protein molecules are required for film formation. Amorphous three-dimensional stmctures formed by noncovalent interactions among protein chains stabilize the films. At high water content, films are produced by casting of viscous solutions, and at low water content, films are produced by extmsion using thermoplastic properties of proteins (13). 

The casein content of milk is an important indicator of cheese yield, and cheese yield formulas are used to determine milk payment in some cheese plants. Milks of similar protein content but dissimilar casein/whey ratio do not produce the same cheese yield. The methods presently used for casein estimation are based on precipitation of casein from the milk and involve a series of steps including centrifugation, aspiration of fat, filtration, drying and weighing. Two methods for the determination of the casein content of milk with the use of a commercial IR milk analyser have been described [24,... 

Cheese contains a high concentration of essential nutrients relative to its energy content. Its precise nutrient content is influenced by the type of milk used (species, stage of lactation, whole fat, lowfat, skim), method of manufacture, and to a lesser extent the degree of ripening. As outlined in detail elsewhere in this review, water-insoluble nutrients of milk (casein, colloidal minerals, fat, and fat-soluble vitamins) are retained in the cheese curd whereas the water-soluble constituents (whey proteins, lactose, water-soluble vitamins, and minerals) partition into the whey. However, loss of water-soluble B vitamins in whey may be compensated to a certain extent by microbial synthesis during ripening (Renner, 1987). 

The last paragraph can be summarized as follows bacterial protein is comparable to milk casein (Calloway and Kumar, 1969). The nucleic acid content of bacteria depends on the growth rate and can be reduced by submitting the cells to conditions of the stationary growth phase or, when growing them in a chemostat, by growing them in a... 

Human milk has a lower casein content than bovine milk and consists mainly of (3 and k varieties whose exact amino acid compositions are slightly different from those of the latter in Table 12.13. At least one phosphate group is present in all varieties of casein, which are therefore phosphoproteins. In these caseins the phosphate groups are attached to serine residues (12.18a). Phosphoserine (12.18b) can be isolated from milk. Phosphothreonine units (12.18c) may be present in the milk from some species. 

Milk type a-Lactalbumin (mg/ml) 3 -Lactoglobnlin (mg/ml) Casein content (mg/ml)... 

RP-HPLC was applied to separate and characterize 3-casein and a-lactalbumin fractions of human milk and to quantify milk protein contents.The determinations were performed in the linear range of 0.09-1.5 and 0.45-3.6 g/L for 3-casein and a-lactalbumin, respectively. Analysis of variance (ANOVA) showed significant differences (p < 0.05) between protein content in milk from different mothers at the same lactation time (l /2 months). A significant decrease (p < 0.05) was observed for the casein and a-lactalbumin concentrations during the first 6 months of lactation. 

Cavaletto, M. Cantisani, A.M. Napolitano, L. Giuffrida, M.G. Calderone, V., Fabris, C. Bertino, E. Prandi, M.G. Conti, A. Comparative study of casein content in human colostrum and milk. Milchwissenschaft 1994,49, 303-305. 

Mastitis is well known to decrease lactose content. This fact explains the relation between lactose content and determination of log SCC (4). This emphasizes the possibilities of detecting changes with lactose when analyzing milk spectra and proves its strong relation with SCC. Factors 5, 6, 8 and 10, which showed high correlation with regression coefficients, had the highest correlation with protein content. This is consistent with the fact that mastitis causes alteration of protein fractions in milk. Mastitic milk has more proteolytic activity than normal milk, due to increase of proteinase plasmin, which hydrolyzes the casein (25, 26). Harmon (6) and Urech et al. (25), have reported decreased ccs-casein and (3-casein content and elevated whey proteins and y-casein in the total protein of mastitic milk. 

The high casein content of milk can be adsorbed on the electrode and on the current bridge. This adsorbed protein layer can break down the potentiometric signal. Therefore, the dilution of the sample as well as the standards is necessary. For the milk samples, the addition of the ISAB solution, in this case, 2 volume of the diluted aqueous HNO3 solution to 1 volume of milk or standard is recommended, that is, the 2 1 ratio is recommended. The ISAB is prepared by diluting 60 cm concentrated HNO3 to 11 with de-ionized water. 

The protein-N content of fish muscle tissue is between 2-3%. The amino acid composition, when compared to that of beef or milk casein (Table 13.6), reveals the high nutritional value of fish proteins. The sarcoplasma protein accounts for 20-30% of the muscle tissue total protein. The contractile apparatus accounts for 65-75% protein the connective tissue of teleosts is 3% and of elasmobranchs, such as sharks and rays (skate or rocker), is up to 10%. The individual protein groups and their functions in muscle tissue of mammals (cf. 12.3.2) also apply to fish. 

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