same difficulty in getting at the starch for cooking. If, during the cooking of starch, as, for example, in the cooking of oatmeal, the surface is left exposed so that the top dries, the starch is changed into a hard skin which is exceedingly difficult of digestion. If the oatmeal is stirred occasion- ally and kept covered so that the steam is confined in the space above the surface, no such change occurs. When a vegetable food containing much starch, such as potatoes or cereals, is cooked, the starch granules swell in the process until they burst most of the cell walls of the plant. CHANGES OP STARCH GRAINS IN COOKING a, cells and starch grains in a raw potato ; 6, in a partially cooked potato ; c, in a thoroughly boiled potato. Starch is not soluble in cold water, but, when heated, the granules finally break down and gelatinize. This is only partial solution. When a substance really dissolves, it disappears entirely from view, as sugar does in water. It may impart a color to the solution, but it does not render it opaque. Because starch does not dissolve, it cannot pass through the lining wall of the intestines and so must be changed in digestion before it can be absorbed. A ferment called ptyalin is found in the saliva, which is capable of acting on starch and changing it to sugar. There is an intermediate stage in this action, for the starch 60 FOOD STUDY is first changed into dextrine. Dextrine is whitish like starch, but with iodine turns a beautiful wine red. Unlike starch, it is soluble in cold water. When starchy food is chewed saliva is mixed with it, and as the food lies in the fundus (or middle part) of the stomach the ptyalin has a chance to act on it. It used to be thought that this action stopped as soon as the food reached the stomach, for ptyalin cannot act in gastric juice, but it is now known that this change can go on for about two hours before the gastric juice is so mixed with the food that the action is stopped. Therefore it seems a somewhat important matter that such food should be chewed thoroughly and mixed with saliva and not swallowed whole or washed down with liquids. In the stomach, however, not all of the starch is digested. Probably most of it does not go beyond the dextrine stage. In the intestines there is another ferment, sometimes called amylopsin, which, like the ptyalin, can digest starch. We are, then, apparently, well equipped to digest starch, and this is fortunate, for starch forms a large proportion of the nutrients of our diet. Dextrine may also be formed by heating dry starch very hot, at least to 320° F. It is formed somewhat in toast, and in the crust of bread, and in browned flour, since in these cases the starch is exposed to intense heat. Some breakfast foods are partially dextrinized and this is sup- posed to make them more digestible. In reality, so small a percentage of the starch is changed that they are really not very different. Browned flour does not possess the thickening power of ordinary flour because the dextrine in it dissolves instead of gelatinizing. Since heating with acids will dextrinize starch at a much lower temperature, and only a few drops of acid are necessary to bring this about, it is sometimes J^[^ Pea Starch Bean Starch Buckwheat Starch Potato Starch STARCH GRAINS, MAGNIFIED MANY TIMES From Leach's "Food Inspection and Analysis." STARCH 61

AI-modernized reading of the original text

same difficulty in getting at the starch for cooking. If, during the cooking of starch, as, for example, in the cooking of oatmeal, the surface is left exposed so that the top dries, the starch is changed into a hard skin which is exceedingly difficult of digestion. If the oatmeal is stirred occasionally and kept covered so that the steam is confined in the space above the surface, no such change occurs. When a vegetable food containing much starch, such as potatoes or cereals, is cooked, the starch granules swell in the process until they burst most of the cell walls of the plant. CHANGES OP STARCH GRAINS IN COOKING a, cells and starch grains in a raw potato ; 6, in a partially cooked potato ; c, in a thoroughly boiled potato. Starch is not soluble in cold water, but, when heated, the granules finally break down and gelatinize. This is only partial solution. When a substance really dissolves, it disappears entirely from view, as sugar does in water. It may impart a color to the solution, but it does not render it opaque. Because starch does not dissolve, it cannot pass through the lining wall of the intestines and so must be changed in digestion before it can be absorbed. A ferment called ptyalin is found in the saliva, which is capable of acting on starch and changing it to sugar. There is an intermediate stage in this action, for the starch is first changed into dextrine. Dextrine is whitish like starch, but with iodine turns a beautiful wine red. Unlike starch, it is soluble in cold water. When starchy food is chewed saliva is mixed with it, and as the food lies in the fundus (or middle part) of the stomach the ptyalin has a chance to act on it. It used to be thought that this action stopped as soon as the food reached the stomach, for ptyalin cannot act in gastric juice, but it is now known that this change can go on for about two hours before the gastric juice is so mixed with the food that the action is stopped. Therefore it seems a somewhat important matter that such food should be chewed thoroughly and mixed with saliva and not swallowed whole or washed down with liquids. In the stomach, however, not all of the starch is digested. Probably most of it does not go beyond the dextrine stage. In the intestines there is another ferment, sometimes called amylopsin, which, like the ptyalin, can digest starch. We are, then, apparently, well equipped to digest starch, and this is fortunate, for starch forms a large proportion of the nutrients of our diet. Dextrine may also be formed by heating dry starch very hot, at least to 320° F. It is formed somewhat in toast, and in the crust of bread, and in browned flour, since in these cases the starch is exposed to intense heat. Some breakfast foods are partially dextrinized and this is supposed to make them more digestible. In reality, so small a percentage of the starch is changed that they are really not very different. Browned flour does not possess the thickening power of ordinary flour because the dextrine in it dissolves instead of gelatinizing. Since heating with acids will dextrinize starch at a much lower temperature, and only a few drops of acid are necessary to bring this about, it is sometimes J^[^ Pea Starch Bean Starch Buckwheat Starch Potato Starch STARCH GRAINS, MAGNIFIED MANY TIMES From Leach's "Food Inspection and Analysis."

Food study