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Chymosin is used to bring about the extensive precipitation and curd formation in cheese-making. The native substrate of chymosin is K-casein which is specifically cleaved at the peptide bond between amino acid residues 105 and 106, phenylalanine and methionine. [9] The resultant product is calcium phosphocaseinate.
Chymosin, its key component, is a protease enzyme that curdles the casein in milk. In addition to chymosin, rennet contains other enzymes, such as pepsin and a lipase . Rennet has traditionally been used to separate milk into solid curds and liquid whey , used in the production of cheeses.
Κ-casein, or kappa casein, is a mammalian milk protein involved in several important physiological processes. Chymosin (found in rennet ) splits K-casein into an insoluble peptide (para kappa-casein) and water-soluble glycomacropeptide (GMP).
When coagulated with chymosin, casein is sometimes called paracasein. Chymosin (EC 3.4.23.4) is an aspartic protease that specifically hydrolyzes the peptide bond in Phe105-Met106 of κ-casein, and is considered to be the most efficient protease for the cheese-making industry (Rao et al., 1998).
During the fermentation process, once sufficient lactic acid has been developed, rennet is added to cause the casein to precipitate. Rennet contains the enzyme chymosin which converts κ-casein to para-κ-caseinate (the main component of cheese curd, which is a salt of one fragment of the casein) and glycomacropeptide, which is lost in the ...
GMP is formed when the casein micelle that encapsulates milk protein is cleaved by the enzyme chymosin. The 64 terminal peptides of Kappa-casein are removed by the enzyme to create GMP. The remaining peptides form para-kappa-casein. [2] Vegetable rennets cleave at the same location and thus also produce GMP.
In this reaction, the substrate is a milk protein (e.g., casein) and the enzyme is rennin. The products are two polypeptides that have been formed by the cleavage of the larger peptide substrate. Another example is the chemical decomposition of hydrogen peroxide carried out by the enzyme catalase.
Found in rennet, chymosin is the enzyme responsible for hydrolysis of κ-casein to produce para-κ-casein and glycomacropeptide, which is the first step in formation of cheese, and subsequently curd, and whey. [16] It was the first genetically engineered food additive used commercially.