182. Production of Volatile Nitrogenous Compounds.--When fermentation is unnecessarily prolonged, an appreciable amount of nitrogen is volatilized in the form of ammonia and allied bodies, as amids. During the process of bread making, the yeast appears to act upon the protein, as well as upon the carbohydrates, and, as previously stated, losses of dry matter fall alike upon these two classes of compounds, nitrogenous and non-nitrogenous. Analyses of the flours and materials used in bread making, and of the bread, show that ordinarily about 1.5 per cent of the total nitrogen is liberated in the form of gas during the bread-making process, and analyses of the gases dispelled in baking show approximately the same per cent of nitrogen. When bread is dried, as in a drying oven, a small amount of volatile nitrogen appears to be given off,--probably as ammonium compounds formed during fermentation. The nitrogen lost in bread making under ordinary conditions is not sufficient to affect the nutritive value of the product. The losses of both nitrogen and carbon are more than offset by the increased solubility of the proteids and carbohydrates, the preliminary changes they have undergone making them more digestible and valuable for food purposes. The nitrogen volatilized in bread making appears to be mainly that present in the flour in amid forms or liberated as the result of fermentation processes. The more stable proteids undergo only limited changes in solubility and are not volatilized.
183. Oxidation of Fat.--Flour contains about 1.25 per cent of fat mechanically mixed with a small amount of yellow coloring matter. During the process of bread making the fat undergoes slight oxidation, accompanied by changes in both physical and chemical properties. The fat from bread, when no lard or shortening has been added, is darker in color, more viscous, less soluble in ether, and has a lower iodine number, than fat from flour. The change in solubility of the fat is not, however, such as to affect food value, because the fat is not volatilized, and is only changed by the addition of a small amount of oxygen from the air. When wheat fat and other vegetable and animal fats are exposed to the air, they undergo changes known as aging, similar to the slight oxidation changes in bread making.[64]