Casein fraction, composition

Tarrassuk, N. P., Yaguchi, M. and Callis, J. B. 1965. Effect of temperature on the composition of casein fractions eluted from DEAE-cellulose column. J. Dairy Sci. 48, 606-609. 

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. 

Fractionation of milk and titration of the fractions have been of considerable value. Rice and Markley (1924) made an attempt to assign contributions of the various milk components to titratable acidity. One scheme utilizes oxalate to precipitate calcium and rennet to remove the calcium caseinate phosphate micelles (Horst 1947 Ling 1936 Pyne and Ryan 1950). As formulated by Ling, the scheme involves titrations of milk, oxalated milk, rennet whey, and oxalated rennet whey to the phenolphthalein endpoint. From such titrations, Ling calculated that the caseinate contributed about 0.8 mEq of the total titer of 2.2 mEq/100 ml (0.19% lactic acid) in certain milks that he analyzed. These data are consistent with calculations based on the concentrations of phosphate and proteins present (Walstra and Jenness 1984). The casein, serum proteins, colloidal inorganic phosphorus, and dissolved inorganic phosphorus were accounted for by van der Have et al (1979) in their equation relating the titratable acidity of individual cow s milks to the composition. The casein and phosphates account for the major part of the titratable acidity of fresh milk. 

Protein Composition of Milk. Skim milk is a colloidal suspension of extreme complexity. The particulate phase, the casein micelles, consists primarily of a mixture of asi, as2, / , and x-caseins combined with calcium ions and an amorphous calcium-phosphate-citrate complex. The soluble phase contains lactose, a fraction of the caseins and calcium, and, in raw milk, the whey proteins, which are predominantly /3-lacto-globulin and a-lactalbumin. When milk is centrifuged at high speed (in our experiments, 30 min at 110,000 X gravity), the casein micelles sediment. This permits one to separate the two physical phases of skim milk and to measure changes in composition of the phases resulting from... 

As a result of the close packing of the aqueous-phase droplets, the composition of the water phase is critical. Protein concentrates, caseinate, gelling agents, and special emulsihers have been recommended to simplify the emulsification and to stabilize the end product (93-98). For manufacture, the basic material for production is a mix that is chemically identical to the end product. This mix consists of mUkfat in the form of butter, butter oil, and fractionated butter oil or cream, in many cases, it also has milk solids, milk concentrates (including dissolved milk powder and caseinates), and emulsifiers (see Figure 10) (81). The fat mix (i.e., butter, butter oil, etc.) is melted and pasteurized. 

A major emphasis in the utilization of MF in the dairy industry that is of relevance to cheesemaking is changing the casein to whey protein ratio or the casein to fat ratio in mUk fractions [91]. MF of whole or skim mUk produces a retentate that is rich in native micellar casein, which improves the cheesemaking process, and a crystal clear and sterile permeate with composition close to that of sweet whey but with greater amount of native whey proteins that is suitable for direct manufacmre of whey protein isolate [8,52,92-95]. In processing skim mUk using MF membranes of 0.2 p,m pore size or smaller, the permeation of... 

A rapid FTIR method for the direct determination of the casein/whey ratio in milk has also been developed [26]. This method is unique because it does not require any physical separation of the casein and whey fractions, but rather makes use of the information contained in the whole spectrum to differentiate between these proteins. Proteins exhibit three characteristic absorption bands in the mid-infrared spectrum, designated as the amide I (1695-1600 cm-i), amide II (1560-1520 cm-i) and amide III (1300-1230 cm >) bands, and the positions of these bands are sensitive to protein secondary structure. From a structural viewpoint, caseins and whey proteins differ substantially, as the whey proteins are globular proteins whereas the caseins have little secondary structure. These structural differences make it possible to differentiate these proteins by FTIR spectroscopy. In addition to their different conformations, other differences between caseins and whey proteins, such as their differences in amino acid compositions and the presence of phosphate ester linkages in caseins but not whey proteins, are also reflected in their FTIR spectra. These spectroscopic differences are illustrated in Figure 15, which shows the so-called fingerprint region in the FTIR spectra of sodium caseinate and whey protein concentrate. Thus, FTIR spectroscopy can provide a means for quantitative determination of casein and whey proteins in the presence of each other. 

Monolayer techniques were used to characterize the interfacial properties of the resultant Fractions. Fraction I contained highly cohesive complexes that did not unfold at the interface and had an average diameter of 9.1 nm. These particles are thought to represent submicelles, previously identified in micelle formation. Fraction II showed interfacial properties that are characteristic of spread casein monomers, and contained mainly a -casein. The results are discussed in relation to casein interactions and micellar formation. Mixed monolayers of sodium caseinate/glyceride monostearate (NaCas/GMS) were also examined at different composition ratios. The results show that for low surface pressures (0-20 mNm ), there is a condensation ascribable to hydrophobic interactions in the mixed film. At high surface pressures, the hydrophobic interaction is modified and the protein is expelled from the monolayer into the subphase. These results are discussed in relation to emulsion stability. 

A better knowledge of casein micelle structure is a prerequiste for further characterization of casein derivatives. One way to study the structure of the micelle is by inducing controlled dissociation. The analysis of resultant Fractions provides information on the initial state of aggregation. Removal of calcium phosphate has been used to dissociate the micelle (6). The resultant complexes have been separated by chromatography, and their composition, and average size evaluated (7,8,9). However, the nature of interactions leading to their formation is still obscure. In the present work, we removed calcium to induce dissociation of the micelle, but afterwards, we paid attention to the interactive properties of the isolated complexes. ... 

Casein is a naturally occurring macromolecule that accounts for approximately 80% of the protein content of cow s milk it is a phosphoprotein that can be separated into various electrophoretic fractions, such as aj-casein, /c-casein, fi-casein, and y-casein in which each constituent differs in primary, secondary, and tertiary structure, amino acid composition, and molecular weight (Ghosh et al., 2009 Audic et al., 2003 Barreto et ai., 2003]. It finds use in making adhesives and paper coatings. 

Milk protein films are widely used in food and non-food sectors such as textile, paper, leather etc. These films and composites are used in different scopes of food science such as coating of meat and fresh-cut fruits, bread wrapping and preparation of antimicrobial packaging. Cow s milk proteins are divided into 2 parts caseins and whey proteins. The major fraction of milk proteins (approximately 80 %) belongs to casein group which consists of si-, s2-, ) -, and jc-casein and their portions are nearly 38, 10, 36 and 12, respectively with the corresponding molecular masses of 23,164, 25,388, 23,983 and 19,038 Da [78]. 

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