Microbial rennin

Alkali- and temperature-resistant proteases (detergent industry). Microbial rennin (cheese manufacturing),... 

Seker, S., Beyenal, H., Ayhan, R, and Tanyolac, A., Production of microbial rennin from Mucor miehei in a continnonsly fed fermenter. Enzyme Microbiol. Technol., 23,469,1998. 

Cheese is a concentrated dairy food produced from milk curds that are separated from whey. The curds may be partially degraded by natural milk or microbial enzymes during ripening, as in cured cheeses, or they may be consumed fresh, as in uncured cheeses like cottage cheese. Most commonly, a bacterial culture with the aid of a coagulating enzyme like rennin is responsible for producing the initial curd. The... 

Microbial proteinases can be classified by mechanism of action. Hartley (1960) divided them into four groups serine proteinases, thio proteinases, metalloproteinases, and acid proteinases. Morihara (1974) classified enzymes within these groups according to substrate specificity. Enzymes which split peptide substrates at the carboxyl side of specific amino acids are called carboxyendopeptidases, and those which split peptide substrates at the amino side of specific amino acids are called aminoendopeptidases. Acid proteinases, such as rennin and pepsin, split either side of specific aromatic or hydrophobic amino acid residues. The action of proteolytic enzymes on milk proteins has been reviewed by Visser (1981). 

Source. Enzymes for food applications come from all three kingdoms plant, animal, and microbial. Traditionally used plant and animal enzymes are the plant proteases such as papain, ficin and bromelain, plant amylases from malt, and animal rennin which is used in cheese manufacture. Microbial cells are the usual and most promising future source of industrial enzymes. Estimates of the number of microorganisms in the world tested as potential sources of enzymes fall around 2% with only about 25 organisms, including a dozen or so fungi, currently used for industrial enzymes. 

Although the general proteolytic activities of various milk clotting enzymes may vary, their milk clotting activities are apparently predicated on the same specific cleavage of the Phe-Met bond in -casein. Apparently rennin, pepsin, chymotrypsin, a microbial protease, proteases from Endo-thia parasitica, Mucor pusillus, and Mucor miehei exert the same type of activity on -casein (2, 169). Enzymes that are currently used commercially for cheesemaking in the United States include rennin, rennin-pepsin mixtures, and microbial proteases from Endothia parasitica, Mucor pusiUus, and Mucor miehei. 

Aspartic proteinases of microbial origin can be classified as pepsin-like or rennin-like enzymes. The latter are able to coagulate milk. The pepsin-like enzymes are produced, for example, by Aspergillus awamori, A. niger, A. oryzae, Penicillium spp, and Trametes sanguinea. The rennin-like enzymes are produced, for example, by Aspergillus usamii and Mucor spp., such as M. pusillus. 

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