Composition of milk

Milk consists of 85—89% water and 11—15% total soflds (Table 1) the latter comprises soflds-not-fat (SNF) and fat. Milk having a higher fat content also has higher SNF, with an increase of 0.4% SNF for each 1% fat increase. The principal components of SNF are protein, lactose, and minerals (ash). The fat content and other constituents of the milk vary with the animal species, and the composition of milk varies with feed, stage of lactation, health of the animal, location of withdrawal from the udder, and seasonal and environmental conditions. The nonfat soflds, fat soflds, and moisture relationships are well estabhshed and can be used as a basis for detecting adulteration with water (qv). Physical properties of milk are given in Table 2. 

Casein. Milk contains proteins and essential amino acids lacking in many other foods. Casein is the principal protein in the skimmed milk (nonfat) portion of milk (3—4% of the weight). After it is removed from the Hquid portion of milk, whey remains. Whey can be denatured by heat treatment of 85°C for 15 minutes. Various protein fractions are identified as a-, P-, and y-casein, and 5-lactoglobulin and blood—semm albumin, each having specific characteristics for various uses. Table 21 gives the concentration and composition of milk proteins. 

Milk. Imitation milks fall into three broad categories filled products based on skim milk, buttermilk, whey, or combinations of these synthetic milks based on soybean products and toned milk based on the combination of soy or groundnut (peanut) protein with animal milk. Few caseinate-based products have been marketed (1,22,23). Milk is the one area where nutrition is of primary concern, especially in the diets of the young. Substitute milks are being made for human and animal markets. In the latter area, the emphasis is for products to serve as milk replacers for calves. The composition of milk and filled-milk products based on skim milk can be found in Table 10. Table 15 gives the composition of a whey /huttermilk-solids-hased calf-milk replacer, which contains carboxymethyl cellulose (CMC) for proper viscosity of the product. 

Table 15. Dry Mass Composition of Milk-Substitute Formulation, ...

There have been relatively few studies comparing the mineral and vitamin composition of milk from different dairy systems. Toledo et al. (2002) compared milk samples from organic and conventional dairy systems in Sweden, for iodine and selenium, and found that levels of selenium but not iodine were lower in organic milk. Studies in Denmark compared the vitamin E... 

Kirchgessner M, Friesecke H and Koch G (1967), Nutrition and the Composition of Milk, Lockward, London. 

Vegetable fats are mainly used in bakery products as a substitute for milk fat. This is particularly so in the EU where the CAP increases the price of milk fat. Because vegetable fats can be blended hydrogenated and interesterified it is possible to produce a vegetable fat with almost any desired range of properties. In general, the fats that are used as a substitute to milk fat are not an attempt to match the composition of milk fat but are designed to provide the best blend of properties for the product. 

Studies related to the possible differences between the chemical composition of milks from individual animals of the same species have been few. It is well known that among farm animals some individual mothers supply milk on which their offspring and foster offspring thrive, while the milk from other mothers is deficient for this purpose. It is commonly supposed that the deficiency is purely that of the quantity of milk, and little evidence is available one way or the other with respect to whether deficiencies of quality may also be involved. 

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. 

The role of milk in nature is to nourish and to provide immunological protection to the mammalian young. The nutritional value of milk is high. It comes from various sources, such as human, goat, buffalo, sheep, and yak, and has been a food for humans since prehistoric times. It is also a very complex food with many thousands of different molecular species found in it. There are several factors that can affect milk composition. An approximate composition of milk can be given as follows ... 

The composition of milk salts is influenced by a number of factors, including breed, individuality of the cow, stage of lactation, feed, mastitic infection and season of the year. The more important factors are discussed below. 

Ca-ion electrode. Ca2 + activity (rather than concentration) can be determined rapidly and accurately using a Ca2 + ion-specific electrode. Care must be exercised to ensure that the potentiometer is properly standardized using solutions that simulate the composition of milk serum. The Ca2 + activity is lower than the Ca2 + concentration - values of about 2 mM have been reported. 

Equations have been developed to estimate the total solids content of milk based on % fat and specific gravity (usually estimated using a lactometer). Such equations are empirical and suffer from a number of drawbacks for further discussion see Jenness and Patton (1959). The principal problem is the fact that the coefficient of expansion of milk fat is high and it contracts slowly on cooling and therefore the density of milk fat (Chapter 3) is not constant. Variations in the composition of milk fat and in the proportions of other milk constitiuents have less influence on these equations than the physical state of the fat. 

Milk is secreted by all species of mammals to supply nutrition and immunological protection to the young. It performs these functions with a large array of distinctive compounds. Interspecies differences in the quantitative composition of milk (Jenness and Sloan 1970) probably reflect differences in the metabolic processes of the lactating mother and in the nutritive requirements of the suckling young. 

The lipids of milk are composed of about 98% triglycerides, with much smaller amounts of free fatty acids, mono-and diglycerides, phospholipids, sterols, and hydrocarbons. Chapter 4 deals in detail with the composition of milk lipids. 

Table 1.10. Gross Composition of Milks of Various Species. 

Inherited Variation. Genetically controlled variation in milk composition is evident from both interbreed and intrabreed studies. Some comparative studies of breed differences involve sampling from individual cows others use herd milk comparisons. Surveys with both kinds of sampling, summarized in Table 1.12, give a reasonably consistent picture of differences among breeds in the gross composition of milk. 

Table 1.12. Gross Composition of Milk of Various Breeds (g/100 g).

Armstrong, T. V. 1959. Variations in the gross composition of milk as related to the breed of the cow A review and critical evaluation of literature of the United States and Canada. J. Dairy Sci. 42, 1-19. 

Cerbulis, J. and Farrell, H. M., Jr. 1975. Composition of milks of dairy cattle. I. Protein, lactose, and fat contents and distribution of protein fraction. J. Dairy Sci. 58, 817-827. 

Jenness, R. 1974. The composition of milk. In Lactation A Comprehensive Treatise, Vol. 3. B.L. Larson and V.R. Smith (Editors). Academic Press, New York. 

Jenness, R. and Sloan, R. E. 1970. The composition of milks of various species. A review. Dairy Sci. Abstr. 32, 599-612. 

Legates, J. E. 1960. Genetic and environmental factors affecting the solids-not-fat composition of milk. J. Dairy Sci. 43, 1527-1532. 

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