(a) The useless (from a nutrient point of view) nitrogenous bodies, including ammonia, nitric acid, the phenylamido-propionic acids, tyrosin, leucin and other amid bodies.
(b) The albumoses and peptones, products of fermentation soluble in boiling water.
(c) The caseins and albuminates, insoluble in boiling water.
The group of bodies under (a), according to Stutzer, may be separated from the groups (b) and (c) by means of phosphotungstic acid. For this purpose a portion of an intimate mixture of fine sand and cheese (100 cheese, 400 sand) corresponding to five grams of cheese, is shaken for fifteen minutes with 150 cubic centimeters of water. After remaining at rest for another fifteen minutes 100 cubic centimeters of dilute sulfuric acid (one acid, three water) are added, followed by treatment with the phosphotungstic acid as long as any precipitate is produced. The mixture is thrown on a filter and the insoluble matters washed with dilute sulfuric acid until the filtrate amounts to half a liter. Of this quantity an aliquot part (200 cubic centimeters) is used for the determination of nitrogen. From the quantity of nitrogen found, that representing the ammonia, as determined in a separate portion, is deducted and the remainder represents the nitrogen present in the cheese as amids.[526]
Albumoses and Peptones.—Albumoses and peptones are determined in cheese by the following method:[527] A quantity of the sand mixture already described, corresponding to five grams of the cheese, is treated with about 100 cubic centimeters of water, heated to boiling, and the clear liquid above the sand poured into a flask of half a liter capacity. The extraction is continued with successive portions of water in like manner until the volume of the extract is nearly half a liter. When cold, the volume of the extract is completed to half a liter with water, the liquor filtered, 200 cubic centimeters of the filtrate treated with an equal volume of dilute sulfuric acid (one to three) and phosphotungstic acid added until no further precipitate takes place. The nitrogen is determined in the precipitate after filtration and washing with dilute sulfuric acid.
Casein and Albuminates.—The quantity of casein and albuminates in cheese is calculated by subtracting from the total nitrogen that corresponding to ammonia, amids, that in the indigestible residue and that corresponding to the albumose and peptone. In three samples of cheese, viz., camembert, swiss, and gervais, Stutzer found the nitrogen, determined as above, distributed as follows:[528]
| Camembert. | Swiss. | Gervais. | |
| N as ammonia | 13.0 | 3.7 | 1.6 |
| N as amids | 38.5 | 9.0 | 5.2 |
| N as albumose peptone | 30.5 | 8.6 | 15.5 |
| N indigestible | 4.0 | 2.4 | 8.6 |
| N as casein, albuminates | 14.0 | 76.3 | 69.1 |
Ammoniacal Nitrogen.—The ammoniacal nitrogen is determined by mixing a quantity of the sand-cheese corresponding to five grams of cheese, with 200 cubic centimeters of water, adding an excess of barium carbonate and collecting the ammonia by distillation in the usual way.
Digestible Proteids.—The digestible proteids in cheese are determined by the process of artificial digestion, which will be described in the part of this volume treating of the nutritive value of foods.
These data show the remarkable changes which the proteids undergo where the ripening is carried very far as in the camembert cheese.