Stomach of calves

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. 

Rennet or rennin—an animal prolease derived from the stomachs of calves as well as from microorganisms. Rennet is used in the manufacture of cheese to clot milk. 

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. 

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. 

The most widely used animal enzyme is chymosin which is used for milk clotting in the production of cheese. Well known plant enzymes include papain, bromelain and cereal malt. Microbial enzymes have been used in the fruit and cereal processing industries since the 1950 s and offer a less expensive source. Eor example, chymosin (a relatively expensive enzyme found in the stomach of calves) have been replaced by the microbial rennet in the production of cheese. 

An example is the use of pre-gastric lipases for the production of Italian cheese types. In these cheeses the entire stomach of calves is dried and used. This results in a characteristic piquant flavour. The substrate specificity of the lipases, in terms of affinity for certain fatty acid chain lengths, determines the quality and the flavour of the final lipolyses product. 

To produce artificial horn, skimmed milk is treated at 35° C with fermenting rennin from the stomachs of calves. When the temperature is raised to 65° C, coagulation of the protein results (denaturing) with the formation of curds containing about 609 /water. They are washed, dried, and pressed in linen bags. Alternatively, the protein can also be precipitated with acids. About 1 kg of dried casein is obtained from 30 liters of skimmed milk. The commercial product contains fat and therefore has a milky yellow color. 

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. 

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. 

Cheese is made by coagulating milk by the addition of rennet to produce curds. The curds are separated from the liquid whey and then processed and matured to produce a wide variety of cheeses. The active ingredient of rennet is the enzyme chymosin. Until 1990, most rennet was produced from the stomach of slaughtered newly born calves. These days, at a cost one tenth of that before 1990, chymosin is produced by genetically engineered bacteria into which the gene for this enzyme has been inserted, and is used for making cheese in the United States, Europe, and other parts of the world. 

As it is almost time to go, we pause for a last snack of cheddar. I mention that the cheeses we are eating, like most that have been sold since 1990, were made with genetically engineered ingredients. Before that, the curdling agent was isolated from the stomach of young calves (see box 5.1). 

Rennin is absent from the human stomach, but is present in that of newborn calves (see D2). Since pepsin may perform rennins function, i.e., milk coagulation, rennin is superfluous in the stomach of man. 

Since the first scientific explanation of the favorable effects of soured milk products in humans by Metchnikoff (1907) at the beginning of the twentieth century, the most beneficial part of the intestinal flora is suggested to be LAB. LAB are also the most common organisms used for commercial DFM preparations (Anonymous, 1990 Tuschy, 1986). The emphasis on the LAB stems from evidence that LAB play a central role in the gut flora that enables them to influence the composition of the flora to the benefits of the host. The stomach of the neonatal pigs is shown to be colonized by Lactobacillus and Streptococci within 48 hours after birth (Dulcuzeau, 1985). Similarly, in newborn calves one of the first groups of microorganisms in the rumen is LAB (Nousiainen and Setala, 1993). Studies show that when the gut flora develops after birth, as the lactobacilli increase, other components of the flora decrease (Smith, 1965). The claims made for DFM effects of LAB in farm animals are many and varied. 

Enzymes derived from the stomach of suckling calves and lambs have been found to be largely responsible for the development of characteristic flavours of Italian cheese. The properties of these enzymes (Richardson and Nelson, 1967) and the chemic nature of their activities have been studied. The development of the goaty flavour of Italian cheese, for example, is attributed to the production of low molecular weight fatty acids in milk fat, presumably induced by fat lipolysis. The production of cheese flavour components such as diacetyls and acetoin is facilitated by esterases (Magee et al., 1981). Present day cheese manufacturing practices involve the addition of external esterases to augment the production of the desired flavours. Enzyme modified cheese products are employed to fortify or intensity cheddar cheese flavour in some formulations. 

Chymosin Stomach lining of calves or genetically engineered microorganisms B. Peptidases of 6-7 5.5-6.0... 

A favorite meat dish in Scotland, made of the heart, liver, and lungs of sheep or calves minced with suet, onions, oatmeal, and seasonings and boiled in the stomach of a sheep. 

Commercial casein is obtained from cow s milk, in which it is the main protein at about 3% concentration. Most of the casein for adhesives is obtained by acid precipitation however, some is precipitated from milk by rennet, a preparation made from the stomach of young calves. Only the use of acid casein is covered here, since a very limited amount of rennet casein is used for adhesives. 

Rennin is also found in the stomach. Its substrate is the casein of milk, which is converted by the enzyme to insoluble paracasein. This conversion is only a mild hydrolysis, which can be catalyzed just as well by pepsin, trypsin, and other proteases. For this reason, the very existence of rennin has been doubted periodically. However, rennin has now been obtained in crystalline form from the gastric juice of calves. For the calf at least, its existence has thus been established. 

The era of modem enzyme technology began in 1874 when the Danish chemist Christian Hansen produced the first industrial batches of chymosin by extracting dried calves stomachs with saline solutions. 

As a rule, when quinolones are administered orally, their absorption from the gastrointestinal tract is rapid and almost complete, but food in the stomach delays their absorption. In unweaned calves, fluoroquinolones are often given in the milk replacer, but oral bioavailability is slightly reduced compared with the oral drench (139). On tire other hand, fermentation in the rumen of mature ruminants precludes the oral use of fluoroquinolones. Injectable solutions are also available for systemic therapy of large animals and turkeys. 

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). 

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