Isolation of casein from milk

Destruction of the casein micelles in the milk with subsequent precipitation of the casein can be accomplished in a number of ways. The action of heat or the action of alcohols, acids, salts and the enzyme rennet all bring about precipitation. In commercial practise the two techniques used employ either acid coagulation or rennet coagulation mechanisms. 

Addition of acetic or mineral acid to skimmed milk to reduce the pH value to 4.6, the isoelectric point, will cause the casein to precipitate. As calcium salts have a buffer action on the pH, somewhat more than the theoretical amount of acid must be used. Lactic acid produced in the process of milk souring by fermentation of the lactoses present by the bacterium Streptococcus lactis will lead to a similar precipitation. 

Although acid caseins are employed for a number of purposes, rennet caseins in which the protein remains associated with calcium and phosphate are preferred for plastics applications. Rennet is the dried extract of rennin, obtained from the inner lining of the fourth stomach of calves, and is a very powerful coagulant. As little as 0.2 parts per million are said to be sufficient to coagulate slightly acidic milk. Its coagulating power is destroyed at 100 C. 

In the rennet coagulation process fresh skimmed milk is adjusted to a pH of six and about 40 ounces of a 10% solution of rennet are added per 100 gallons of milk. The initial reaction temperature is about 35°C and this is subsequently raised to about 60°C. The coagulation appears to take place in two stages. Firstly the calcium caseinate is converted to the insoluble calcium paracaseinate and this then coagulates. 

Great care is essential in controlling the temperature and the coagulation process as otherwise impurities, particularly other proteins, will be brought down with the casein. Such impurities will adversely affect the transparency of the product. 

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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... 

A) Preparation of Casein from Milk. To 40 ml of milk in a 250 ml beaker, add 40 ml of water and five drops of 6iV acetic acid. The coagulated protein to which the fat adheres settles out. Filter the precipitate and wash it with water twice, so that it collects at the lower point of the folded filter paper. When most of the water has drained, remove the filtrates if it is desired to isolate the lactose. Wash twice with a 5 ml portion of alcohol and then twice with a 5 ml portion of ether. Collect the alcohol and ether washings separately and place them in a bottle provided for this... 

In the first part of this experiment, you are going to isolate casein from milk which has a pH of about 7. Casein will be separated as an insoluble precipitate by acidification of the milk to its isoelectric point (pH = 4.6). The fat that precipitates along with casein can be removed by dissolving it in alcohol. 

G. Hevesy was the first to label proteins with radionuclides as early as 1938. The Nobel Prize was awarded to him in 1943 for his discoveries in this field Hevesy fed the radionuclide of phosphorus to sheep per os and isolated P-casein from their milk. 

Isolation of Caseins. Isoelectric caseins were obtained by precipitation from whole milk or from 5g of homogenized cheese in 30 mL of water by adding 2M FICl to pH 4.6 followed by centrifugation at 3500 rpm for 15 min. To isolate the casein fractions completely from whey and eliminate the remaining fat, it was washed once with 1M sodium acetate buffer (pH 4.6) and three times with dichloromethane/1 M sodium acetate buffer (pH 4.6) (1 1, v/v). The casein fractions obtained were lyophilized and stored at -20 °C. 

Methods with the potential for the isolation of )8-casein on a large scale, leaving a residue enriched in a.i-, and K-caseins, have been published. The methods exploit the temperature-dependent association characteristics of /3-casein, the most hydrophobic of the caseins. Up to 80% of the / -casein may be recovered from sodium caseinate by UF at 2°C the / -casein may be recovered from the permeate by UF at 40°C (Figure 4.39). MF at 2°C has been used to isolate casein from milk or sodium caseinate. It is not known whether these methods are being used commercially. 

Agarwal 0. P. edition 26 (2009). Isolation of casein and lactose from milk. Adv. Pract. Org. Chem., 371-372. 

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). 

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... 

McPherson, A. V., Dash, M. C. and Kitchen, B. J. 1984A. Isolation of bovine milk fat globule membrane material from cream without prior removal of caseins and whey proteins. J. Dairy Res. 51, 113-121. 

Caseins are usually isolated from milk by methods involving urea or some similar denaturant in high concentration. The native conformation of these proline-rich proteins may therefore not be fully recovered within a reasonable time after removal of the urea. How-... 

These regenerated proteins are obtained from milk (casein), soya beans, corn, and peanuts. More or less complex chemical separation and purification processes are required to isolate them from the parent materials. They may be dissolved in aqueous solutions of caustic, and wet-spun to form fibers, which usually require further chemical... 

Thoma, C., and Kulozik, U. (2004). Methods of Obtaining Isolated Casein-Macropeptide From Milk and Whey and Functional Properties. In Bull. 389, International Dairy Federation, Brussels, pp. lA-11. 

The principal lipase in bovine milk is a lipoprotein lipase (LPL Chapter 8) which is associated predominantly with the casein micelles and is isolated from its substrate, milk fat, by the MFGM, i.e. the enzyme and its substrate are compartmentalized. However, even slight damage to the membrane permits contact between enzyme and substrate, resulting in hydrolytic rancidity. The enzyme is optimally active at around 37°C and pH 8.5 and is stimulated by divalent cations, e.g. Ca (Ca complex free fatty acids, which are strongly inhibitory). The initial turnover of milk LPL is c. 3000 s i.e. 3000 fatty acid molecules are liberated per second per mole of enzyme (milk usually contains 1-2 mg lipase 1 , i.e. 10-20 nM) which, if fully active, is sufficient to induce rancidity in about 10 s. This never happens in milk due to a variety of factors, e.g. the pH, ionic strength and, usually, the temperature are not optimal the lipase is bound to the casein micelles the substrate is not readily available milk probably contains lipase inhibitors, including caseins. The activity of lipase in milk is not correlated with its concentration due to the various inhibitory and adverse factors. 

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