Casein isolation

Although less susceptible than / - and as2-caseins, isolated xsl -casein in solution is also readily hydrolysed by plasmin. It has been suggested that a minor ill-defined fraction of casein, called A-casein, consists of plasmin-produced fragments of asl-casein, but the situation is unclear. 

Figure 4.17 Oligosaccharides attached to casein isolated from bovine milk (1-2) or colostrum...

McKenzie, H. A. 1971C. Whole casein Isolation properties and zone electrophoresis. In Milk Proteins, Vol. II. H.A. McKenzie (Editor). Academic Press, New York. 

Bazinet, L., Lamarche, F., Ippersiel, D., and Amiot, J. 1999a. Bipolar membrane electro-acidification to produce bovine milk casein isolate. J. Agric. Food Chem. 47, 5291-5296. 

Bazinet L, Gendron C, Ippersiel D, Rene-Paradis J, Tetreault C, Beaudry J, Britten M, Mahdavi B, Amiot J, and Lamarche F. Effect of type of added salt and ionic strength on physicochemical and functional properties of casein isolates produced by electroacidification. J Agric. Food Chem. 2002 50(23) 6875-6881. 

Soybean protein is a very important binder type, especially in North America. It has properties very similar to those of casein. Isolated soybean proteins are hydrolyzed, isoelectric proteins. They are used in the form of alpha and delta proteins with four different viscosities (extra low, low, medium, and high). The viscosity refers to the dissolved soybean protein, the solvent of choice being aqueous ammonia (26 Be). Proteins dissolved in this way exhibit very low sensitivity to water after drying. like casein, soybean protein is mostly used as a mixture with polymer dispersions. This combination permits the preparation of coating colors with high sohds content and a relatively low viscosity. Solids contents ofca. 60%, suitable for blade coaters, can be achieved. 

Products prepared from soy protein products and resembling chicken, ham, frankfurters, and bacon are available commercially. Soy protein isolates are used in place of milk proteins or sodium caseinate in products such as coffee creamers, whipped toppings, yogurt, and infant formulas (see Dairy substitutes). Soy protein products also are used in snacks and in baked foods. 

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). 

A significant problem is the wide variation in properties in the same type of product both from different manufacturers and from the same source. More recendy there has been vast improvement in the consistency of these products from a given manufacturer and usage in dairy substitutes is expected to expand. These isolates do have a higher protein efficiency ratio (PER) than casein and are equal to egg protein. 

Soybean Protein Isolates. Soybean protein isolates, having a protein content of >90 wt%, are the only vegetable proteins that are widely used in imitation dairy products (1). Most isolates are derived from isoelectric precipitation, so that the soybean protein isolates have properties that are similar to those of casein. They are insoluble at thek isoelectric point, have a relatively high proportion of hydrophobic amino acid residues, and are calcium-sensitive. They differ from casein in that they are heat-denaturable and thus heat-labile. The proteins have relatively good nutritional properties and have been increasingly used as a principal source of protein. A main deterrent to use has been the beany flavor associated with the product. Use is expected to increase in part because of lower cost as compared to caseinates. There has been much research to develop improved soybean protein isolates. 

Isolated soy proteins have also been used in whipped toppings. Soy-protein-based toppings have a lower protein concentration than caseinate-based toppings. Formulations ate adjusted to protein levels, and higher protein levels can result in off-flavors. Typical formulations for a Hquid frozen, prewhipped product are given in Table 18. 

Chemical nature Isolation of casein from milk Production of casein plastics Properties of casein Applications Miscellaneous Protein Plastics Derivatives of Natural Rubber Gutta Percha and Related Materials Shellac... 

Roach, A. and Harte, F. (2008). Disruption and sedimentation of casein micelles and casein micelle isolates under high-pressure homogenization. Innovative Food Sci. Emerg. Technol. 9,1-8. 

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). 

Since the discovery of the enkephalins in 1975 [11] a large number of endogenous opioid peptides have been detected in mammals, and at present three distinct families of opioid peptides are known (for a review, See Ref. 12). These are the enkephalins, the endorphins (a-, (J-, and y-), and the dynorphins and neoendorphins. The recently discovered endomor-phins [13] also may represent endogenous opioid peptides. Peptides with opioid activity have also been isolated from tryptic digests of milk casein... 

Considerable interest has been shown in uses of vegetable food proteins in cheese-type products. Attempts have been made to coprecipitate casein and vegetable protein in the typical vat process for making cheeses (35). Rhee (36) has found that up to 50% peanut protein isolate and 25% soybean isolate can be effectively substituted for sodium caseinate in the preparation of imitation cheeses. 

Feeding studies with the rat as the test animal verified the high nutritional quality indicated by the amino acid pattern (45). Using isolates and concentrates prepared from Jewel and Centennial cultivars, PER values were equal to that of casein (milk protein) (Table IV). Examination of the amino acid patterns of sweet potato protein and casein revealed that both contained... 

The complete identification of the amino acids which are essential in the diet is due to W.C. Rose (1938). His first attempts to replace casein with its constituents were unsuccessful because an essential amino acid component in the protein hydrolysate had been missed. After threonine had been isolated by him from casein and fibrin, and shown to be essential, Rose identified val, met, his, lys, phe, leu, ile, thr, and arg as... 

Another fat-soluble vitamin, E, was found by Evans and Bishop in 1923. Pregnant rats on a defined diet (alcohol-extracted casein, cornstarch, and lard) supplemented with butter (vitamins A and D) and yeast extract (vitamin B group) produced few young because of fetal resorption. Male rats on the same diet were sterile. The disorders, which have not been identified in man, were corrected by wheat-germ oil, from which tocopherol, the active ingredient, was isolated in 1936. In spite of intensive investigations and a recognition that the vitamin is an antioxidant and destroyer of free radicals, the function of vitamin E remains obscure. 

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