Rennet preparation

Linklater (1961) reported that bovine pepsin accounted for only 0 to 6% of the milk-clotting activity of commercial rennet extracts. He used porcine pepsin as a reference standard. Bovine pepsin has increased in use as a coagulant because of the practice of extracting the stomach from older calves and adult cattle. More recently, Sellers (1982) reported that 85 to 95% of the proteolytic activity of calf rennet is due to chymosin and the remainder is from bovine pepsin. Adult bovine rennets preparations may contain 55 to 60% bovine pepsin. Mixtures of calf rennet and porcine pepsin may contain 40 to 45% chymosin, 5 to 10% bovine pepsin, and 50% porcine pepsin. Mixtures of adult bovine rennet and porcine pepsin typically contain 20 to 25% chymosin, 40 to 45% bovine pepsin, and 30 to 40% porcine pepsin activity (McMahon and Brown 1985). 

Because of problems encountered in blending whey products containing residual M. miehei rennet with materials containing casein, this rennet preparation has been modified to decrease its heat stability (Branner-Jorgensen et al 1980 Cornelius 1982). This process involves treatment of the rennet with hydrogen peroxide under controlled conditions. Some enzymic activity is lost but the modified enzyme has about the same stability as calf rennet. Nearly all M. miehei rennet used by the cheese industry is now modified (Ramet and Weber 1981). 

Both proteolysis and lipolysis are involved in the cheese ripening process. The rate and extent of their interactions are influenced by the rennet preparation used, characteristics of the starter culture, pH, moisture range, salting practices, temperature, and the activity of adventitious microorganisms present in or on the cheese. 

Three types of coagulation were considered. The glucono(5)lactone (GDL)-induced coagulation system (GDL system) was prepared by acidification with 1.75 g/L GDL (Roquette, Lestrem, France). The rermet-induced coagulation system (rennet system) was prepared by the addition of calf rennet (SKW, Baupte, France) at 25.6/rg/L of milk. The GDL-I-rermet-induced coagulation system (mixed system) was prepared by acidification with 0.45 g/L GDL for 2h followed by the addition of rennet at 15.4/ig/L of milk. The experimental conditions for each system were selected in order to achieve gelation without syneresis. Coagulation kinetics were performed at 30°C. 

The most abundant milk protein is casein, of which there are several different kinds, usually designated a-, (1-, and K-casein. The different caseins relate to small differences in their amino acid sequences. Casein micelles in milk have diameters less than 300 nm. Disruption of the casein micelles occurs during the preparation of cheese. Lactic acid increases the acidity of the milk until the micelles crosslink and a curd develops. The liquid portion, known as whey, containing water, lactose and some protein, is removed. Addition of the enzyme rennet (chymosin) speeds up the process by hydrolysing a specific peptide bond in K-casein. This opens up the casein and encourages further cross-linking. 

Coagulate rennet puddings, prepare soybean milk Body, flavor, and nutrient development during fermentation, aid in filtration and clarification, chill proofing... 

The first company based upon applied biocatalysis also dates back to the 19 century. In 1874 Christian Hansen started a company in Copenhagen, Denmark. His company— named Christian Hansen s Laboratory to this day—was the first in the industrial market with a standardized enzyme preparation, rennet, for cheese making. Rennet, a mixture of chymosin (also called rennin) and pepsin, was and still is obtained by salt extraction of the fonrth stomach of suckling calves. 

Crude enzyme preparations have been used in food processing since prehistoric times classical examples are rennets in cheesemaking and papaya leaves to tenderize meat. Added (exogenous) enzymes are attractive in food processing because they can induce specific changes, in contrast to chemical or physical methods which may cause non-specific undesirable changes. For some applications, there is no viable alternative to enzymes, e.g. rennet-coagulated cheeses, whereas in some cases, enzymes are preferred... 

Semi-purified preparations of PGE from calf, kid and lamb are commercially available and give satisfactory results slight differences in specificity renders one or other more suitable for particular applications. Connoisseurs of Italian cheese claim that rennet paste gives superior results to semipuri-fied PGE, and it is cheaper. 

Rennets. The traditional rennets used to coagulate milk for most cheese varieties are prepared from the stomachs of young calves, lambs or kids by extraction with NaCl (c. 15%) brines. The principal proteinase in such rennets is chymosin about 10% of the milk-clotting activity of calf rennet is due to pepsin. As the animal ages, the secretion of chymosin declines while that of pepsin increases in addition to pepsin, cattle appear to secrete a chymosin-like enzyme throughout life. 

Rao, K. S. N., Krishna, N., Nand, K., Srikanta, S., Krishna-Swamy, M. A., and Murthy, V. S. 1979. Changes during manufacture and ripening of Cheddar cheese prepared with fungal rennet substitute of Rhizopus oligosporus. Nahrung 23, 621-626. 

Three illustrations are used to review the various approaches taken by the enzyme industry in tailoring enzyme preparations to meet the production and product quality needs of the food industry. Tailored enzyme preparations have been able to convert the corn syrup industry from an acid-based industry to an enzyme-based industry, to overcome the problems created in the baking industry as grain technology improved and automation was introduced, and to rescue the cheese industry as the supply of bovine rennet decreased and the demand for cheese and cheese flavor increased. 

The individual preparations usually are named according to the substance to which they are applied, such as Protease or Amylase. Traditional names such as Malt, Pepsin, and Rennet also are used, however. 

Pepsin Obtained from the glandular layer of hog stomach. Produced as a white to light tan, water-soluble powder amber paste or clear, amber to brown, aqueous liquids. Major active principle pepsin. Typical applications used in the preparation of fishmeal and other protein hydrolysates and in the clotting of milk in manufacture of cheese (in combination with rennet). 

Rennet, Calf Aqueous extracts made from the fourth stomach of calves. Produced as a clear, amber to dark brown liquid or a white to tan powder. Major active principle protease (chymosin). Typical application used in the manufacture of cheese. Similar preparations may be made from the fourth stomach of lambs or kids. 

Standard Preparation Use a standard-strength rennet, bovine rennet, microbial rennet (Endothia parasitica), or microbial rennet (Mucor species), as appropriate for the preparation to be assayed. Such standards, which are available from commercial coagulant manufacturers, should be of known activity. Dilute the standard-strength material 1 to 200 with water, and mix. Equilibrate to 300 before use, and prepare no more than 2 h before use. 

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