Rennet, Calf

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. 

Microbial coagulants are now useful and are responsible for about one third of all the cheese produced worldwide, but suffer from the disadvantage of being too stable and so are threatened commercially by improved methods of produdng chymosin by recombinant DNA technology. The use of thermally destabilized microbial rennets results in residual enzyme levels in the milk product similar to or below those encountered when calf rennet is use (55). An unexpected benefit has been an increase on some occasions of the specificity of the microbial enzyme, making it virtually indistinguishable from the action of calf rennet. Also some microbial rennets help impart a flavor that is popular with consumers. 

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. 

Chymosin has now been produced in Escherichia coli (Chen et al 1984 Hayenga et al. 1984) and Saccharomyces cerevisiae (Moir et al 1985) by recombinant DNA techniques. Cheese-making trials comparing recombinant chymosin with calf rennet have found no significant differences between the two (Green et al 1985). The impact of this development on the cheese industry will be felt when the various regulatory issues have been resolved. 

Emmons (1970) experienced significant inactivation when commercial pepsin and pepsin-calf rennet mixtures were diluted with high-pH, hard water 10 min before adding them to the cheese vat. Mickelsen and Ernstrom (1972) reported that mixtures of porcine pepsin and calf rennet were stable between pH 5.0 and 6.0, but that pepsin activity was lost from the mixture aboire pH 6.0. This loss was shown to be entirely due to pepsin instability. Below pH 6.0 chymosin activity was destroyed by pepsin. 

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). 

Green (1972) reported that Cheddar cheese made entirely with bovine pepsin was only slightly inferior to that made with calf rennet and Fox and Walley (1971) found no significant difference between Cheddar cheese made with bovine pepsin and rennet. Fox (1969) found that the milk-clotting activity of bovine pepsin is less pH-dependent than that... 

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). 

Proteolysis of casein begins with the addition of rennet to the milk and the formation of a coagulum. Calf rennet is actually 80% chymosin and 20% bovine pepsin A (Grappin et al 1985). Rennet can remain active in Cheddar and Camembert cheeses for up to three months, but... 

Visser, S., Hup, G., Exterkate, F. A. and Stadhouders, J. 1983. Bitter flavor in cheese. 2. Model studies on the formation and degradation of bitter peptides by proteolytic enzymes from calf rennet, starter cells and starter cell fractions. Neth. Milk Dairy J. 37, 169-180. 

Chymosin, the principal proteinase of calf rennet, preferentially hydrolyzes the Phe105-Met10 bond to produce the para-K-casein fragment (f 1—105), which is the same whatever the degree of phosphorylation or glycosylation, and the macropeptide fragment (fl 06-169),... 

Milk Coagulation. The first step in cheese manufacture is the coagulation of milk. Traditionally, this coagulation step is catalyzed by the enzyme rennet. Rennet is a saline extract of the 4th stomach of calves, usually slaughtered before they are 30 days old. The principal protease in rennet is rennin. In an attempt to avoid confusion with the hormone peptide renin, the International Enzyme Nomenclature Committee has assigned the name chymosin to the protease in calf rennet. During the growth of calves, chymosin is replaced by pepsin, the acid protease of the mature stomach. 

Cheese is manufactured by the heat treatment or pasteurisation of milk, which is then cultured, and renneted (for coagulation). Primarily, vegetarian rennets (like Mucor Mihei) are used, as genetically engineered rennet is prohibited and vegetarians spurn calf rennet. After the curd is developed and cooked, the whey is drained and the curd is salted, aged and formed. Of course this varies dramatically between the different cheeses. Some cheeses are... 

In the past, there have been concerns over the transmissible spongiform encephalopathies (TSE) contamination of animal-derived products. However, in the light of current scientific knowledge, and irrespective of geographical origin, milk and milk derivatives are reported as unlikely to present any risk of TSE contamination TSE risk is negligible if the calf rennet is produced in accordance with regulations. ... 

Cheese making (coagulation) by casein hydrolysis with calf stomach extract Calf rennet (ch)onosin)... 

There are restrictions on some dairy ingredients. For example, enzymes used to make cheese should be of microbial origin to be acceptable as halal. Rennet from calf must be avoided. The active ingredient in rennet is Chymosin. Chymosin can also be produced in the lab, and this biotech product can be halal. Most calf rennet in the US is not halal. 

Owing to increasing world cheese production ( 4% p.a. over the past 30 years), concomitant with a reduced supply of calf rennet (due to a... 

Chicken pepsin is the least suitable of these and is used widely only in Israel. Bovine pepsin is probably the most satisfactory and many commercial calf rennets contain up to 50% bovine pepsin its proteolytic specificity is generally similar to that of calf chymosin. The proteolytic specificities of the three principal fungal rennets are considerably different from that of calf chymosin but the acceptability of most cheese varieties made using fungal rennets is fairly good. Microbial rennets are widely used in the United States but to only a limited extent in Europe. The extensive literature on rennet substitutes has been reviewed by Sardinas (1972), Emstrom and Wong (1974), Nelson (1975), Green (1977), and Phelan (1985). 

Calf rennet contains about 10% bovine pepsin (EC 3.4.23.1, Rothe et ai, 1977). The proteolytic products produced from Na-caseinate by bovine pepsin are similar to those produced by chymosin (Fox, 1%9), although as far as we are aware the specificity of bovine or porcine pepsins on bovine caseins has not been rigorously determined. 

Bines, V. E., Young, P., and Law, B. A. (1989). Comparison of cheese made with a recombinant calf chymosin and with standard calf rennet. J. Dairy Res. 56,657-664. 

Green, M. L., and Foster, P. D. M. (1974). Comparison of the rates of proteolysis during ripening of Cheddar cheeses made with calf rennet and swine pepsin as coagulants. J. Dairy Res. 41,269-282. 

Johnston, K. A., Dunlop, F. P., Coker, C. J., and Wards, S. M. (1994). Comparisons between the electrophoretic pattern and textural assessment of aged Cheddar made using various levels of calf rennet or microbial coagulant (Rennilase 46L). Int. Dairy J. 4, 303-327. 

Rennet is used extensively in the production of cheese. This enzyme is found in the fourth stomach of the calf it converts casein into paracasein, which, in the presence of calcium, precipitates to form an elastic curd. Much commercial rennet is contaminated with pepsin which tends to act strongly on casein and thereby produces a weak curd with off flavor. Many microbial proteases can clot milk, but only recently have microbial preparations been produced which can replace calf rennet to prepare cheeses of good flavor. Microbial preparations from Endothia parasitica and Mucor pusillus var. Lindt seem to be the most promising, and these have been used commercially. The new sources of rennet were reviewed recently (Sardinas, 1969). 

Morris HJA, Anderson K (1991) A comparative study of Cheddar cheeses made with fermentation produced calf chymosin from Kluyveromyces lactis and with calf rennet. Cult Dairy Prod J... 

The course of coagulation according to the temperature is given in the preceding table by Fleischmann. This experiment is made with a milk, with addition of parts of neutral calf rennet, exposing to temperatures varied by means of suitably regulated water-baths. 

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