It is produced by newborn ruminant animals in the lining of the abomasum to curdle the milk they ingest, allowing a longer residence in the bowels and better absorption.

Chymosin is produced by gastric chief cells in newborn mammals[3] to curdle the milk they ingest, allowing a longer residence in the bowels and better absorption.

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.

[1] Listed below are the ruminant Cym gene and corresponding human pseudogene: Because of the imperfections and scarcity of microbial and animal rennets, producers sought replacements.

With the development of genetic engineering, it became possible to extract rennet-producing genes from animal stomach and insert them into certain bacteria, fungi or yeasts to make them produce chymosin during fermentation.

FPC can deliver several benefits to the cheese producer compared with animal or microbial rennet, such as higher production yield, better curd texture and reduced bitterness.