If, on the other hand, the water, ash and fat in a meat sample be determined and the sum of their per cents be subtracted from 100, the difference represents the nitrogenous bodies plus all undetermined matters and errors of analysis. The assumption that meats are free of carbohydrates is not tenable since glycogen is constantly found therein and in horse flesh in comparatively large amounts. In a thoroughly scientific analysis of meats, the nitrogenous bodies should be separated and determined by groups, according to the principles developed in paragraphs [411-414]. This process requires a great amount of analytical work and in general it will be sufficient to make a cold water extract to secure the flesh bases and a hot water extract to secure the gelatin. The nitrogen is then determined in each of these portions separately. The nitrogen in the cold water extract is multiplied by four, in the hot water extract by six and in the residue by 6.25. The sum of these products represents approximately the total nitrogenous matter in the sample.

Aqueous extracts containing nitrogen are easily prepared for moist combustion by placing them in the digestion flasks, connecting the latter with the vacuum service and evaporating the contents of the flask nearly to dryness. The sulfuric acid is then added and the nitrogen converted into ammonia and determined in the usual manner.

541. Fractional Analysis of Meats.—A better idea of the composition of a meat is obtained by separating its constituents into several groups by the action of different solvents. This method has been elaborated by Knorr.[546]

The separation of the meats in edible portion and waste and the determination of moisture and fat are conducted as already described. The residue from the fat extraction is exhausted with alcohol, and in the extract are found the nitrogenous bases kreatin, kreatinin, sarkin and xanthin, and urea, lactic, butyric, acetic and formic acids, glycogen and inosit. In the residue from the alcohol extraction, the proteid nitrogen is determined in a separate sample.

A separate portion of the sample is ground to a fine paste and repeatedly rubbed up with cold water, which is poured through a tared filter. When the extraction is complete, the filter and its contents are dried and the dry residue determined. This residue represents the nitrogenous constituents of the muscle fibers and their sheaths together with any other bodies insoluble in cold water. The filtrate from the cold water extraction is heated to boiling to precipitate the albuminous matters which are collected, dried and weighed, or the nitrogen therein determined and the albuminous matters calculated by multiplying by the usual factor. The filtrate from the coagulated albuminous bodies is evaporated to dryness and weighed. It consists essentially of the same materials as the alcoholic extract mentioned above. The ash and nitrogen in the aqueous extract are also determined.

The mean content of the edible parts of common meats, expressed as per cents in groups as mentioned, follow:

Per cent.
Water73.11
Ash1.18
Total soluble matter26.89
Phosphoric acid0.49

Per cent.
Proteids insoluble in cold water13.76
Of which coagulable by heat2.24
Cold water extract3.56
Ash in water extract1.09
Of which phosphoric acid0.38

Per cent.
Fat4.93
Alcohol extract3.03
Proteids in residue from alcohol 17.88
Total nitrogen in sample3.37

542. Estimation of Starch in Sausages.—Starchy substances are sometimes added to sausages for the purpose of increasing their weight. The presence of starch in a sausage is easily detected by iodin. The quantity may be determined by the following process:[547]

The principle of the process is based upon the observation that while starch is easily soluble in an aqueous solution of the alkalies, it is insoluble in an alcoholic solution thereof. The chief constituents of meat, viz., fat and proteid matters, on the other hand, are readily soluble in an alcoholic solution of potash or soda. This renders the separation of the starch easy. The sample is warmed on a water bath with a considerable excess of an eight per cent solution of potassium hydroxid in alcohol whereby the fat and flesh are quickly dissolved. The starch and other carbohydrate bodies, remain in an undissolved state. In order to prevent the gelatinizing of the soap which is formed, the mass is diluted with warm alcohol, the insoluble residue collected upon a filter and washed with alcohol until the alkaline reaction disappears. The residue is then treated with aqueous potassium hydroxid solution, whereby the starch is brought into solution and, after filtration, is treated with alcohol until it is all precipitated. The precipitated starch is collected upon a filter, washed with alcohol and finally with ether, dried and weighed. Starch prepared in this way contains a considerable quantity of potash, the amount of which can be determined by incineration. In order to avoid this trouble, the starch, after separation in the first instance as above mentioned and solution in aqueous potassium hydroxid, is precipitated on the addition of enough acetic to render the solution slightly acid. The precipitated starch, in this instance, is practically free of potash, since potassium acetate is soluble in alcohol.

543. Detection of Horse Flesh.—Since horse flesh has become an important article of human food and is often sold as beef and sausage, a method of distinguishing it is desirable. The comparative anatomist is able to detect horse flesh when accompanied by its bones, or in portions sufficiently large for the identification of muscular characteristics. It is well known that horse flesh contains a much higher percentage of glycogen than is found in other edible meats. Niebel has based a method of detecting horse flesh upon this fact, the glycogen being converted into dextrose and determined in the usual way. Whenever the percentage of reducing sugars in the dry fat-free flesh exceeds one per cent, Niebel infers that the sample under examination is horse flesh.[548]