766 ANNUAL, REPORT OF THE Off. Doc. 



Department of Agriculture, I quote the followiug, by Dr. Lang- 

 worthy, of the Office of Experiment Stations: 



^'Coolving of I'otatoes. — Altliougli the potato owes its nutritive 

 value principally to carbo-hydirates, it will be remembered that it 

 contains some nitrogenous matter also. According to the investiga 

 tions of Lawes and Gilbert, the juice of the potato contains more 

 proteid or albuminoid nitrogen than the flesh. This is an important 

 matter, since albuminoid nitrogen is more valuable for the body than 

 non-albumiuoid nitrogen. In general, it may be said that 85 per 

 cent, of both protein and mineral matter in the potato (the latter 

 being valuable for dietetic reasons, though not a nutrient) is in the 

 juice. More or less of the juice of any food may be accidentally 

 lost when it is prepared for the table; and the possibility' of loss in 

 cooking, due to this and other factors, is a matter of importance. 

 Any sugar or other soluble carbo-hydrates might be removed if po- 

 tatoes were cooked by boiling. Ko considerable loss of starch as 

 such is to be expected, since starch is insoluble in water. Some 

 starch is changed to a soluble body, dextrin, a sort of sugar, 'by the 

 action of dry heat, possibly also when water is present. 



''The principal ways of cooking potatoes are baking, boiling and 

 frying, or some modifications of these processes. The objects sought 

 are principally to soften tire tissues and render them more suscep 

 tible to the action of the digestive juices and to improve the flavor. 

 Just why cooking changes the flavor, as it does, has apparently never 

 been made the subject of investigation. In potatoes, as in other 

 foods, the cooked starch is more agreeable to the taste than the raw. 

 Possibly also there are volatile bodies of more or less pronounced 

 flavor, which are removed or produced by the heat of cooking. The 

 physical condition of the potato is much affected by heat. In the 

 raw^ potato the separate starch grains are inclosed in cells with walls 

 composed of crude fiber, a material resistant to digestive juices. If 

 potatoes were eaten raw% the digestive juices would not reach the 

 starch as easily unless the cell walls happened to be ruptured me- 

 chanically, as in mastication. Heat, however, expands the water 

 present, ruptures the cells, and breaks up the starch, expanding the 

 granules, which, w^hen raw, consist of tightly-packed concentric 

 layers, to a mass of much less solid structure. 



"The albuminoids in foods are coagulated by heat, and so are 

 rendered insoluble in water in which food is cooked. This explains 

 why foods, meat especially, should be plunged into boiling water if it 

 is desired to retain the albuminoids. The heat at once coagulates 

 the albumen on the surface, thus preventing more or less completely 

 the extraction of materials in the inner portion. It seems probable 

 that this reasoning w^ould apply to potatoes as well as to meat, al- 

 though they contain much less albumen. The effects of cooking po- 



