The following results of Mulder’s analysis of casein, when compared with those by the same chemist of albumen, gelatin and fibrin, show that there is but little difference in the ultimate chemical composition of these, so far as the constituents there named are concerned:
| Casein | ||
| Carbon | 53·83 | |
| Hydrogen | 7·15 | |
| Nitrogen | 15·65 | |
| Oxygen | 23·37 | |
| Sulphur |
| Albumen | Gelatin | Fibrin | |
| Carbon | 53·5 | 50·40 | 52·7 |
| Hydrogen | 7·0 | 6·64 | 6·9 |
| Nitrogen | 15·5 | 18·34 | 15·4 |
| Oxygen | 22·0 | 24·62 | 23·5 |
| Sulphur | 1·6 | ” | 1·2 |
| Phosphorus | 0·4 | ” | 0·3 |
We may therefore conclude that, regarding these from the point of view of nitrogenous or flesh-forming, and carbonaceous or heat-giving constituents, these chief materials of flesh and of cheese are about equal.
The same is the case as regards the fat. The quantity in the carcass of oxen, calves, sheep, lambs, and pigs varies, according to Dr. Edward Smith, from 16 per cent. to 31·3 per cent. in moderately fatted animals; while in whole-milk cheeses it varies from 21·68 per cent. to 32·31 per cent., coming down in skim-milk cheeses as low as 6·3. Dr. Smith includes Neufchâtel cheese, containing 18·74 per cent., among the whole-milk cheeses. He does not seem to be aware that the cheese made up between straws and sold under that name is a ricotta, or crude curd of skim-milk cheese. Its just value is about threepence per pound. In Italy, where it forms the basis of some delicious dishes (such as budino di ricotta[11]), it is sold for about twopence per pound, or less.
There is a discrepancy in the published analyses of casein which demands explanation here, as it is of great practical importance. They generally correspond to the above of Mulder within small fractions, as shown below in those of Scherer and Dumas:
| Scherer | Dumas | |
| Carbon | 54·665 | 53·7 |
| Hydrogen | 7·465 | 7·2 |
| Nitrogen | 15·724 | 16·6 |
| Oxygen, sulphur | 22·146 | 22·5 |
| 100·000 | 100·0 |
In these the 100 parts are made up without any phosphate of lime, while, according to Lehmann (‘Physiological Chemistry,’ vol. i. p. 379, Cavendish Edition), ‘casein that has not been treated with acids contains about 6 per cent. of phosphate of lime; more, consequently, than is contained in any of the protein compounds we have hitherto considered.’
From this it appears that we may have casein with, and casein without, this necessary constituent of food. In precipitating casein for laboratory analysis, acids are commonly used, and thus the phosphate of lime is dissolved out; but I am unable at present to tell my readers the precise extent to which this actually occurs in practical cheese-making where rennet is used. What I have at present learned only indicates generally that this constituent of cheese is very variable; and I hereby suggest to those chemists who are professionally concerned in the analysis of food, that they may supply a valuable contribution to our knowledge of this subject by simply determining the phosphate of lime contained in the ash of different kinds of cheese. I would do this myself, but, having during some ten years past nearly forsaken the laboratory for the writing-table, I have not the leisure for such work; and, worse still, have not that prime essential to practical research (especially of endowed research), a staff of obedient assistants to do the drudgery.
The comparison specially demanded is between cheeses made with rennet, and those Dutch and factory cheeses the curd of which has been precipitated by hydrochloric acid. Theoretical considerations point to the conclusion that in the latter much or even all of the phosphate of lime may be left in solution in the whey, and thus the food-value of the cheese seriously lowered. We must, however, suspend judgment in the meantime.