Amido acids. Protein derivations soluble in water, least complex except ammonia.
Ammonia. The simplest protein derivations.
From the discussion of the constituents in the milk and cheese, it is evident that practically all the principal ripening changes are concerned with those taking place in the proteins.
236. Causes of ripening changes.—Authorities disagree as to the exact agents which cause the ripening changes. Some think they are due to the action of the enzymes in the rennet and those secreted in the milk. Others hold that these changes are due entirely to bacterial action. A combination of the two seems probable. The action of the rennet extract renders the casein insoluble and in the ripening process the proteins become soluble, the degree depending on the length of time the cheese is ripened. The amount of water-soluble proteins and protein derivatives is used as a measure of the extent of cheese ripening, considered from a chemical standpoint.
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 ReneetExtracts on the Rate of Formation of SolubleNitrogen Compounds in Cheese Ripening | ||||
| Quantity of Rennet Added per 100 Lb. of Milk | Per Cent of Water Soluble Nitrogen Compounds in the Cheese | |||
| Initial | 32 days | 80 days | 270 days | |
2 oz | 0.14 | 0.47 | 0.68 | 1.30 |
| 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.
238. The action of the bacteria.—Authorities[112] disagree as to the groups of bacteria found in Cheddar cheese. This may be due to lack of proper classification. Some of the groups are: Bacterium lactis acidi, B. coli communis, B. lactis aerogenes, B. casei, Streptococci, B.[113] Bulgaricum and Micrococci. Authorities agree that the B. lactis acidi group is the most prominent. This group makes up 90 per cent or more of the total bacteria flora of the cheese in the early stages of ripening. In the course of a few weeks, however, this group is largely replaced by the B. casei group.[114]