Casein Rennet

Rennet casein is somewhat different from acid-precipitated casein and it is a relatively minor industrial product. It is obtained from skim milk by the action of the enzyme rennin (chymosin) around pH 6.6. The enzyme splits up the casein component and this destabilises the milk micelles. This is followed by aggregation and precipitation of calcium caseinate along with the calcium phosphate which is present. 

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Fig. 3. Schematic process flow diagram for an imitation cheese product having the following formulation dry ingredients, calcium caseinate (or rennet casein), 24.5 wt % tapioca flour, 3.0 wt % salt, 2.16 wt % adipic acid, 0.6 wt % vitamins and minerals, 0.1 wt % sorbic acid (mold inhibitor), 0.5 wt % fat—color blend, soybean oil hydrogenated to a Wiley melting point of 36°C, 21.3 wt % lactylated monoglycerides, 0.05 wt % red-orange coloring, 0.01 wt...

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. 

Table 30.1 Properties of rennet casein. Determined according BS1416 1961...

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). 

Coextrusion is the process of extruding two or more materials simultaneously or in tandem. It allows a combination of an ingredient such as wheat flour, which is inexpensive and easily enriched with vitamins and minerals, with dairy protein, which provides functionality and texture. For example, an early coextrusion of wheat flour and rennet casein was performed by van de Voort et al. (1984), who obtained products with varying characteristics depending on process parameters. 

Casein may be coagulated and recovered as rennet casein by treatment of milk with selected proteinases (rennets). However, one of the caseins, K-casein, is hydrolysed during renneting and therefore the properties of rennet casein differ fundamentally from those of acid casein. Rennet casein, which contains the colloidal calcium phosphate of milk, is insoluble in water at pH 7 but can be dissolved by adding calcium sequestering agents, usually citrates or polyphosphates. It has desirable functional properties for certain food applications, e.g. in the production of cheese analogues. 

The primary step in the manufacture of most cheese varieties and rennet casein involves coagulation of the casein micelles to form a gel. Coagulation... 

Rennet casein Emulsifying salt Other ingredients Water... 

Figure 10.30 Typical protocols for the manufacture of cheese analogue from rennet casein.

Commercial casein is usually manufactured from skim milk by precipitating the casein through acidification or rennet coagulation. Casein exists in milk as a calcium caseinate-calcium phosphate complex. When acid is added, the complex is dissociated, and at pH 4.6, the isoelectric point of casein, maximum precipitation occurs. Relatively little commercial casein is produced in the United States, but imports amounted to well over 150 million lb in 1981 (USDA 1981C). Casein is widely used in food products as a protein supplement. Industrial uses include paper coatings, glues, plastics and artificial fibers. Casein is typed according to the process used to precipitate it from milk, such as hydrochloric acid casein, sulfuric acid casein, lactic acid casein, coprecipitated casein, rennet casein, and low-viscosity casein. Differences... 

Australian standards have been established for both acid and rennet caseins. The standards for acid casein are much the same as those for U.S. casein. Rennet casein usually has between 7.0 and 8.3% ash compared with 2.2% for acid casein. The fact that rennet casein is essentially a calcium caseinate accounts for this comparatively large ash value. 

Gaffney, P. J., Jr. and Harper, W. J. 1966. Distribution of lipase among components of a water extract of rennet casein. J. Dairy Sci. 49, 921-924. 

Casein and caseinates are generally made from skim milk by adding hydrochloric or sulfuric acid or by lactic acid fermentation. The isoelec-trically precipitated casein is washed and dried or neutralized with sodium hydroxide, potassium hydroxide, or calcium hydroxide to produce the corresponding caseinate and spray dried. Rennet casein is... 

During the period between the first and second world wars a plastics business was developed based upon rennet casein from cow s milk, from soya beans or other pulses the reaction with formaldehyde gave a rigid plastic material which could be produced in light colours, mottle and pearlescent effects, and was capable of being machined and polished to a high gloss. 

Creamer, L.K. 1985. Water absorption by renneted casein micelles. Milchwissenschaft. 40, 589-591. 

Assay Acid Casein Not less than 90.0% protein Rennet Casein Not less than 86.0% protein Caseinate Salts Not less than 84.0% protein, calculated on the dried basis. 

Sample Solution Transfer approximately 1 g of sample, accurately weighed, into a 150-mL beaker. If the sample is Acid Casein, add 0.10 g of sodium hydrogen carbonate. If the sample is Rennet Casein, add 0.10 g of sodium tripolyphosphate. Add 25 mL of water, and dissolve the sample by gently swirling while warming to 60° to 70° on a hot plate. Cool the solution to ambient temperature, and add 15 mL of water, 8 mL of 0.1 IV hydrochloric acid, and 1 mL of a 10% solution of acetic acid. Mix well by swirling, and after 5 min, add 1 mL of 1 M sodium acetate, and mix well. 

Munro PA, Southward CR, and Elston PD. The effect of casein manufacturing variables on the properties of rennet casein plastics. NZ J. Dairy Sci. Technol. 1980 115 177-190. 

Weal BC and Southward CR. Recent Developments in Casein Manufacture. I. The production of rennet casein by a continuous cook process. NZ J. Dairy Sci. Technol. 1974 9 2-5. 

Derivation Acid casein warm skim milk is acidified with dilute sulfuric, hydrochloric, or lactic acid, the whey drawn off, and the curd washed, pressed, ground, and dried. Rennet casein warm skim milk is treated with an extract of the enzyme rennin (rennet). The curd contains combined calcium and calcium phosphate. 

Proteins can be concentrated by isoelectric precipitation, heat precipitation, alcohol precipitation, ultrafiltration, microfiltration, and freeze concentration. Numerous references report differences in function in relation to the method of concentration of the protein. Whey protein produced by acid-heat precipitation (lactalbumin) is essentially insoluble but shows high water binding capacity and for this reason is the whey protein of choice for baking and for formulation of cereal products [89]. The use of ultrafiltration instead of acid precipitation of soy protein provides products with quite different characteristics [108], However, caseinate produced via acid precipitation is nearly as suitable for the production of imitation cheese as is rennet casein produced by the action of chymosin on skim milk [88],... 

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