472 



POTATOES, FRUITS. 



It is curious to observe that soda is absent from white wheat, its place being 

 taken by other alkalies. Rye contains more cellulose and dextrin than wheat, but 

 less sugar; rye bread is usually less porous. 



In the preparation of bread, the meal is kneaded with water until dough is 

 formed, and to it is added salt and yeast (saccharomycetes cerevisiae). When 

 placed in a warm oven, the proteids of the meal begin to decompose and act as a 

 ferment upon the swollen up starch, which becomes in part changed into sugar. 

 The sugar is farther decomposed into C0 2 and alcohol, the C0 2 forms bubbles, 

 which make the bread spongy and porous. The alcohol is driven off by the baking 

 (200), while much soluble dextrin is formed in the crust of the bread. 



2. The Pulses contain much albumin, especially vegetable casein or legumin; 

 together with starch, lecithin, cholesterin, and 91 9 per cent, water. 

 Peas contain 28*02 proteids, and 38'81 starch : beans 28*54, and 

 37'50 : lentils, 29*31, and 40, and more cellulose. Owing to the 

 absence of glutin they do not form dough, and bread cannot be 

 prepared from them. On account of the large amount of proteids 

 which they contain they are admirably adapted as food for the 

 poorer classes. 



3. Potatoes contain 70-81 per cent, water. In the fresh juicy cellular 

 tissue, which has an acid reaction, from the presence of phosphoric, 

 malic, and hydrochloric acids, there is 16-23 per cent, of starch, 2'5 

 soluble albumin, globulin (Zoller), and a trace of asparagin. The 

 envelopes of the cells swell up by boiling, and are changed into sugar 

 and gums by dilute acids. The poisonous solanin occurs in the 

 sprouts. In 100 parts of potato ash, May found 46*96 potash, 2*41 

 sodium chloride, 8-11 potassium chloride, 6-50 sulphuric acid derived 

 from burned proteids, 7'17 silica. 



4. In Fruits the chief nutrient ingredients are sugar and salts ; the 

 organic acids give them their characteristic taste, the gelatinising 

 substance is the soluble so-called pectin (C 32 H 48 32 ), which can be pre- 

 pared artificially by boiling the very insoluble pectose of unripe fruits 

 and mulberries. 



