14. CARBOHYDRATES IN VEGETABLES.--When the composition of vegetables is considered chemically, the most striking thing about them is the carbohydrates they contain. It is this that distinguishes this class of foods from animal foods. The carbohydrate of vegetables is found in both its forms, starch and sugar. It is in the form of sugar in many of the vegetables when they are young or immature, but it turns into starch as they mature. This change can be easily observed in the case of peas. As is well known, young green peas are rather sweet because of the sugar they contain, while mature or dried peas have lost their sweetness and are starchy. The sugar that is found in large quantities in such vegetables as peas, carrots, turnips, etc. is largely cane sugar. The starch that vegetables contain occurs in tiny granules, just as it is found in cereals, and is affected by cooking in the same way. The mature vegetables in which the starch has developed, although less tender and less sweet than young ones, have a higher food value. In fact, the carbohydrate that vegetables contain constitutes a large proportion of their food value.
One of the chief sources of starch among vegetables is the potato, in which the starch grains are large and, if properly cooked, easily digested. Irish, or white, potatoes contain very little carbohydrate in the form of sugar, but in the sweet potato much of the carbohydrate is sugar. In either of these two forms--starch and sugar--vegetable carbohydrate is easily digested.
15. MINERAL MATTER, OR ASH, IN VEGETABLES.--The mineral matter in vegetables is found in comparatively large quantities, the average amount being slightly over 1 per cent. The presence of this substance is of great value, because the mineral salts of both fruits and vegetables are essential in the diet of adults in order to keep their health in a normal condition. The mineral salts of vegetables render the blood more alkaline instead of more acid, as do those contained in cereals and meat. A large number of vegetables, particularly those low in food value, such as greens, celery, etc., are very valuable for their mineral salts. In reality, this substance and the cellulose they contain are the things that recommend the use of these vegetables in the diet. Minerals of all kinds are found in solution in the water contained in vegetables, but chief among them are calcium, sodium, iron, phosphorus, and sulphur. Greens and salad vegetables are particularly high in iron, the element that assists in keeping the blood in good condition. These minerals are easily lost if the method of cookery is not planned to retain them.
16. CELLULOSE IN VEGETABLES.--The special use of cellulose, as has already been learned, is to serve as bulk in the food containing it. In vegetables, the cellulose varies greatly as to quantity, as well as to texture and the amount that can be digested. In young vegetables, it is very soft and perhaps digestible to a certain extent, but as they grow older it hardens and they become tough. This fact is clearly demonstrated in the case of beets. Those which are pulled from the garden in the summer and cooked are tender and soft, but those which are allowed to mature in the ground and are then put away for winter are, when cooked in the late winter or early spring, so hard and tough that it is almost impossible to make them soft. The quantity of cellulose that vegetables contain therefore depends largely on their age and condition. Those low in total food value contain, as a rule, larger quantities of it than those high in food value. This is due to the fact that both water and cellulose, which are usually found together in large quantities, help to detract from the fuel, or food, value of foods.
Very young persons or those who are ill sometimes find it impossible to take in its original form a vegetable that contains a large amount of bulk, or cellulose. In such a case, the vegetable may be put through a colander or a sieve in order to break up the cellulose and make it easier to digest. Under ordinary conditions, cellulose should not be avoided, but should be included in large quantities in the diet through the vegetables that are consumed daily.
17. WATER IN VEGETABLES.--The majority of vegetables contain a large quantity of water. Such vegetables as lettuce, cucumbers, tomatoes, etc., which are low in total food value, contain the most water, the average percentage being about 95. The dry vegetables, which are high in food value, average only about 10 per cent. of water. The water that is found in vegetables, whether it is much or little, is contained in cell-like structures surrounded by cellulose, and it holds in solution the mineral salts and much of the nutriment of the vegetables. In addition, the water holds in solution to a certain extent the material that gives vegetables their distinctive flavor. When any of this water is lost in the preparation of vegetables, the substances that it contains are also lost. It is therefore essential that correct methods of preparation be chosen for the cooking of this food, so as to prevent the waste of valuable food materials.
18. DIGESTIBILITY OF VEGETABLES.--The digestibility of vegetables is largely an individual matter; that is, a vegetable that agrees with one person may not agree with another. The fact that there appears to be no apparent reason for such a condition would lead to the conclusion that it is due to the peculiarities of the person. Because of this, it is not fair to make the general statement that a particular vegetable is easy to digest and another one is hard to digest.
The chief cause for difficulty in the digestion of vegetables lies in their volatile oils, which give them their flavor, but which are irritating to many persons. Vegetables having a strong flavor, such as radishes, onions, cucumbers, cabbage, and cauliflower, are the ones that disagree most frequently with persons who eat them; but sometimes the way in which some of them are cooked has more to do with this than the vegetables themselves.
Vegetables containing considerable cellulose and water do not of themselves give trouble in digestion, because they contain practically nothing to digest; but they are sometimes responsible for interfering with the digestion of other foods. Vegetables that are extremely high in starch, such as potatoes, are easily digested by most persons, provided they are properly cooked. For instance, a plain baked potato is easily digested, but the same potato sautéd in fat is more difficult of digestion.
19. TABLE SHOWING COMPOSITION AND FOOD VALUE OF VEGETABLES.--As vegetables vary considerably in the amount of the food substances they contain, so do they differ greatly in their food value. This is clearly shown in Table I, which gives the percentage of the food substances of vegetables, as well as the food value per pound, in calories, that these vegetables contain. The figures in this table are taken from Atwater's Table of American Food Materials, and refer to the edible portion of the material. In the case of several vegetables, no figures are given by this authority, but in the table here presented the percentages and the calories for the vegetables most similar are used. For example, the figures for lettuce are used for endive, as the composition and food value of this vegetable are not included and it resembles lettuce very closely. Constant reference should be made to Table I as progress is make with the study of vegetables and their preparation. Noting the difference in the composition of the different vegetables, as well as the variation in their food value, will be not only interesting but instructive. For instance, when the housewife realizes that lettuce and celery furnish only 85 to 90 calories to the pound, while dried beans and peas average more than 1,700 calories to the pound, she will understand better the place that these foods occupy in the dietary.