Rennet

From Free net encyclopedia

Rennet is a substance used to coagulate milk, causing it to separate into solids (curds) and liquid (whey). The active enzyme in rennet is called rennin or chymosin (Template:EC number). The chief use of rennet is in the making of cheese and junket. The enzyme reacts with κ-casein on the surface of the casein micelle particles in the milk. This in the presence of calcium ions causes the coagulation of the casein micelles to form a curd. Commercially, rennet is sold in liquid, powder, and tablet forms.

Rennin reacts specifically with κ-casein, cleaving the protein between the amino acids phenylalanine(105) and methionine (106), producing two fragments. The soluble fragment (residules 106-169) which becomes part of the whey is known as glyco macro peptide and contains the glycosylation sites for κ-casein. The other component (residules 1-105) is insoluble.

The most common source of rennet is the abomasum (fourth stomach) of slaughtered, milk-fed new-born cow calves or other young ruminants such as camels or goats. Traditionally rennet was prepared by washing and salting the stomachs of animals shortly after slaughter. The rennet was then hung up and dried until needed.

Alternative Rennets

Many plants have coagulating properties. Some examples include fig tree bark, nettles, thistles, and mallow. Commercial vegetable rennets usually contain rennet from the mold Mucor miehei. Rennet from thistle or cynara is used in traditional cheese production throughout the Mediterranean.

In recent times, the genes responsible for rennet production have been transferred from calf cells to bacterial cells. The daughter cells of these bacteria produce rennin that is identical to that of calves. Some trade names for this kind of rennet include Chy-Max, Chymostar Classic, and Chymogen.

See also: pepsin

References

Carroll, Ricki. Making Cheese, Butter, & Yogurt.Storey Publishing 2003.fr:Présure ja:レンネット pl:Podpuszczka