The moisture content of grain products is subject to considerable variation. Bailey finds moisture in flour in equilibrium with air to vary from about 5.25 per cent when the air showed 30 per cent relative humidity to 15 per cent when the relative humidity of the air was 80 per cent. Nutritive Value of Grain Products and Their Economy as Food The quantitative composition of the grains and of the chief food products made from them has already been given. The grains themselves, their chief mill products, and the dry cereal preparations made from them show considerable similarity in the general features of their chemical composition, and they vary but little from an average fuel value of about 1650 Calories per pound. The 100-Calorie portion of all these (dry) products is very nearly one ounce (varying only from 25 grams for oatmeal to 29 grams for rice). The cooked products naturally show greater differences, chiefly because of the presence of added water or fat. The chemical nature and nutritive value of the carbohydrates (chiefly starch in all of the grains) and of the fat do not offer any problem requiring further discussion. The chemical structure of the proteins of the cereal grains has been investigated with great thoroughness by Osborne, from whose results are taken the percentages of amino acids obtained on hydrolysis of these proteins as shown in Table 45. That glycine is absent in some cases is, as has been seen in earlier chapters, a matter of no consequence so far as food value is concerned. When, however, we find little or no lysine, as in gliadin, hordein, and zein, or find tryptophane absent as in zein, we are confronted with a deficiency which affects seriously the nutritive value. TABLE 45. AMINO ACIDS FROM PROTEINS OF GRAINS (OSBORNE) Osborne and Mendel have used these proteins largely in their feeding experiments with isolated food substances and have found: (1) that when zein (lacking tryptophane) is the only protein of the diet, it does not suffice for the needs either of a growing or a full-grown animal; (2) that when hordein or gliadin (containing tryptophane but very little lysine) is the sole protein fed, full-grown animals can be maintained, but young animals cannot grow. That these deficiencies in food value are actually due to the lack of the amino acids named has been shown by experiments in which the simple addition of the amino acid to the dietary was found to correct the deficiency. This successful correlation of the chemical structure and nutritive function of the proteins is an accomplishment of the greatest importance to the scientific development of food chemistry. 1Edestin occurs also in wheat. |