Characterization of the non-coagulating enzyme fraction of different milk-clotting preparations

Proteolytic milk-clotting enzymes are extracted from various sources (animals, plants, fungi) and processed according to various methods that are specific to each manufacturer or cheese-maker. Chemical composition and polypeptide patterns of 24 milk-clotting preparations from animal and fungal sources: 10 commercial rennets, 9 artisanal calf rennets, 2 recombinant chymosin preparations and 3 microbial preparations, were compared in order to identify differences according to both their manufacturing process and their source. The preparation from Cryphonectria parasitica had the highest ammonia and small peptide content. Commercial rennets and preparations from Rhizomucor miehei had the highest NaCl and pH values while artisanal rennets had the lowest and recombinant chymosins were intermediate. In comparison with the other commercial preparations, commercial rennets had the highest variability in chemical composition and their polypeptide profiles showed numerous protein bands ranging from 15 kDa to 197 kDa, like artisanal rennets. Protein composition of commercial rennets revealed the presence of bovine serum albumin, either native or degraded, and degraded chymosin. The results indicated that the source of coagulating enzymes and the conditions applied for enzyme extraction led to specific chemical compositions, polypeptide patterns and protein composition which are described in this article.