528. General Analysis.—The cereals are prepared for analysis by grinding until the fragments pass a sieve having circular perforations half a millimeter in diameter. The moisture, ash, ether extract, proteids and carbohydrates are determined by some one of the processes already described in detail. In this country the methods of the Association of Official Agricultural Chemists are generally followed.[535] For convenience these methods are summarized below.
Moisture.—Dry from two to three grams of the fine-ground sample for five hours, at the temperature of boiling water, in a current of dry hydrogen. If the substance be held in a glass vessel, the latter should not be in contact with the boiling water.
Ash.—Char from two to three grams of the sample and burn to whiteness at the lowest possible red heat. If a white ash can not be obtained in this manner, exhaust the charred mass with water, collect the insoluble residue on a filter, burn it, add this ash to the residue from the evaporation of the aqueous extract and heat the whole to low redness until the ash is white.
Ether Extract.—Pure ether is prepared by washing the commercial article four or five times with water to free it of the chief part of the alcohol it contains. The residual water is mostly removed by treating the liquid with caustic soda or potash. Any residual alcohol or water is finally removed by the action of metallic sodium. The ether thus prepared is stoppered, after the evolution of hydrogen has ceased, and is kept over metallic sodium. Immediately before use it should be distilled out of contact with moist air.
The residue from the determination of moisture, as described above, is extracted in an appropriate apparatus ([39]) with the pure ether for sixteen hours. The extract is dried to constant weight. The weight may be checked by drying and weighing the extraction tube and its contents before and after the operation.
Crude Proteids.—Proceed as in the method of determining nitrogen in the absence of nitrates and multiply the weight of nitrogen obtained by 6.25. This factor is a general one, but should not be rigidly applied. In each instance, according to the nature of the cereal, the appropriate factor, pointed out in paragraph [407] should be used, and the factor 6.25 be applied only in those cases where a special factor is not given. The factors for the common cereals are wheat 5.70, rye 5.62, oats 6.06, maize 6.22, barley 5.82 and flaxseed 5.62.
For separating the proteid matters consult paragraphs [392-410]. In the case of wheat the methods of Teller may be consulted.[536]
Amid Nitrogen.—The albuminoid nitrogen is determined as directed in paragraph [203] of volume II. The difference between this number and that representing the total nitrogen gives the nitrogen as amids.
Fiber and Carbohydrates.—The methods of analysis are described in detail in Part Third.
529. Bread.—In general, the same processes are followed in bread analysis as are used with cereals and flours. In addition to the regular analytical processes, breads are to be examined for adulterants, bleaching and coloring matters, and for the purpose of determining the changes which have taken place in their nutrient constituents in the processes of fermentation and cooking.