+237. Action of the rennet extract.+--Some authorities hold that rennet extract contains two enzymes, rennin and pepsin, while others think it is a single peptic ferment. These enzymes produce effects[108] closely related to, if not identical with, those of pepsin in the following particulars: neither the rennet enzyme nor pepsin causes much, if any, proteolytic change except in the presence of acid; the quantitative results of proteolysis furnished by the rennet enzyme and pepsin agree closely, when working on the same material under comparable conditions; the classes of soluble nitrogen compounds formed by the two enzymes are the same, both quantitatively and qualitatively; neither enzyme forms any considerable amount of amido compounds and neither produces any ammonia; the soluble nitrogen compounds formed by both enzymes are confined to the group of compounds known as paranuclein, caseoses and peptones. Rennet exerts a digestive effect on the casein[109] which is intensified by the development of acid in the curd. The soluble nitrogenous products formed in Cheddar cheese by the rennet enzymes are the albumoses and the higher peptones. Experiments show that no flavor develops until the amido acids and ammonia are formed. When the rennet enzymes were the only digesting ferments in the cheese, there was no trace of cheese flavor. This is probably due to the fact that the rennet enzyme changed the casein into caseoses and peptones but did not form amido acids and ammonia. Some authorities[110] think that the enzyme galactase carries the ripening of the protein from this stage. The question arises whether these intermediate compounds must be found before other agents can form the amido acids and ammonia. TABLE XV[111] SHOWING THE EFFECT OF DIFFERENT AMOUNTS OF RENEET EXTRACTS ON THE RATE OF FORMATION OF SOLUBLE NITROGEN COMPOUNDS IN CHEESE RIPENING ========================================================= | PER CENT OF WATER SOLUBLE NITROGEN QUANTITY OF | COMPOUNDS IN THE CHEESE RENNET ADDED PER +--------------------------------------- 1000 LB. OF MILK | Initial | 32 days | 80 days | 270 days -----------------+---------+---------+---------+--------- 2 oz. | 0.14 | 0.47 | 0.68 | 1.30 4 oz. | 0.16 | 0.75 | 1.13 | 1.74 8 oz. | 0.16 | 0.90 | 1.50 | 1.97 16 oz. | 0.14 | 1.26 | 1.70 | 2.04 ========================================================= The above table shows that the more rennet extract used the faster the cheese cures, measured by the amount of water-soluble nitrogen compounds formed in the cheese.