VEGETABLE FOODS
Fig. 9.—Transverse Section
of Potato. (After Cowden
and Bussard.) a, skin; b, cortical
layer; c, outer medullary
layer; d, inner medullary layer.
34. General Composition.—Vegetable foods, with the exception of cereals, legumes, and nuts, contain a smaller percentage of protein than animal food products. They vary widely in composition and nutritive value; in some, starch predominates, while in others, sugar, cellulose, and pectin bodies are most abundant. The general term "vegetable foods" is used in this work to include roots, tubers, garden vegetables, cereals, legumes, and all prepared foods of vegetable origin.
35. Potatoes contain about 75 per cent of water and 25 per cent of dry matter, the larger portion being starch. There is but little nitrogenous material in the potato, only 2.25 per cent, of which about half is in the form of proteids. There are ten parts of non-nitrogenous substance to every one part of nitrogenous; or, in other words, the potato has a wide nutritive ratio, and as an article of diet needs to be supplemented with foods rich in protein. The mineral matter, cellular tissue, and fat in potatoes are small in amount, as are also the organic acids. Mechanically considered, the potato is composed of three parts,—outer skin, inner skin, and flesh. The layer immediately beneath the outer skin is slightly colored, and is designated the fibro-vascular layer. The outer and inner skins combined make up about 10 per cent of the weight of the potato.
A large portion of the protein of the potato is albumin, which is soluble in water. When potatoes are peeled, cut in small pieces, and soaked in water for several hours before boiling, 80 per cent of the crude protein, or total nitrogenous material, is extracted, rendering the product less valuable as food. When potatoes are placed directly in boiling water, the losses of nitrogenous compounds are reduced to about 7 per cent, and, when the skins are not removed, to 1 per cent. Digestion experiments show that 92 per cent of the starch and 72 per cent of the protein are digested.[[12]] Compared with other foods, potatoes are often a cheap source of non-nitrogenous nutrients. If used in excessive amounts, however, they have a tendency to make the ration unbalanced and too bulky.
Mechanical Composition of the Potato
| Per Cent | |
| Unpeeled potatoes | 100.0 |
| Outer, or true skin | 2.5 |
| Inner skin, or fibro-vascular layer[A] | 8.5 |
| Flesh | 89.0 |
Chemical Composition of the Potato
| Carbohydrates | ||||||
|---|---|---|---|---|---|---|
| Water | Crude Protein | Fat | Nitrogen- free- extract | Fiber | Ash | |
| % | % | % | % | % | % | |
| Outer, or true skin | 80.1 | 2.7 | 0.8 | 14.6 | 1.8 | |
| Inner skin, or fibro-vascular layer | 83.2 | 2.3 | 0.1 | 12.6 | 0.7 | 1.1 |
| Flesh | 81.1 | 2.0 | 0.1 | 15.7 | 0.3 | 0.8 |
| Average of 86 American analyses[B] | 78.0 | 2.2 | 0.1 | 18.8 | 0.9 | |
| Average of 118 European analyses[C] | 75.0 | 2.1 | 0.1 | 21.0 | 0.7 | 1.1 |
[A] Including a small amount of flesh.
[B] From an unpublished compilation of analyses of American food products.
[C] König, "Chemie der Nahrungs-und Genussmittel," 3d ed., II, p. 626.
36. Sweet Potatoes contain more dry matter than white potatoes, the difference being due mainly to the presence of about 6 per cent of sugar. There is approximately the same starch content, but more fat, protein, and fiber. As a food, they supply a large amount of non-nitrogenous nutrients.
37. Carrots contain about half as much dry matter as potatoes, and half of the dry matter is sugar, nearly equally divided between sucrose and levulose, or fruit sugar. Like the potato, carrots have some organic acids and a relatively small amount of proteids. In carrots and milk there is practically the same per cent of water. The nutrients in each, however, differ both as to kind and proportion. Experiments with the cooking of carrots show that if a large amount of water is used, 30 per cent or more of the nutrients, particularly of the more soluble sugar and albumin, are extracted and lost in the drain waters.[[12]] The color of the carrot is due to the non-nitrogenous compound carrotin, C26H38. Carrots are valuable in a ration not because of the nutrients they supply, but for the palatability and the mechanical action which the vegetable fiber exerts upon the process of digestion.
38. Parsnips contain more solid matter than beets or carrots, of which 3 to 4 per cent is starch. The starch grains are very small, being only about one twentieth the size of the potato starch grains. There is 3 per cent of sugar and an appreciable amount of fat, more than in any other of the vegetables of this class, and seven times as much as in the potato. The mineral matter is of somewhat different nature from that in potatoes; in parsnips one half is potash and one quarter phosphoric acid, while in potatoes three quarters are potash and one fifth phosphoric acid.
Fig. 10.—Graphic
Composition of Cabbage.
39. Cabbage contains very little dry matter, usually less than 10 per cent. It is proportionally richer in nitrogenous compounds than many vegetables, as about two of the ten parts of dry matter are crude protein, which makes the nutritive ratio one to five. During cooking 30 to 40 per cent of the nutrients are extracted. Cabbage imparts to the ration bulk but comparatively little nutritive material. It is a valuable food adjunct, particularly used raw, as in a salad, when it is easily digested and retains all of the nutrients.[[12]]
40. Cauliflower has much the same general composition as cabbage, from which it differs mainly in mechanical structure.
41. Beets.—The garden beet contains a little more protein than carrots, but otherwise has about the same general composition, and the statements made in regard to the losses of nutrients in the cooking of carrots and to their use in the dietary apply also to beets.
42. Cucumbers contain about 4 per cent of dry matter. The amount of nutrients is so small as to scarcely allow them to be considered a food. They are, however, a valuable food adjunct, as they impart palatability.
43. Lettuce contains about 7 per cent of solids, of which 1.5 is protein and 2.5 starch and sugar. While low in nutrients, it is high in dietetic value, because of the chlorophyll which it contains. It has been suggested that it is valuable, too, for supplying iron in an organic form, as there is iron chemically combined with the chlorophyll.
44. Onions are aromatic bulbs, valuable for condimental rather than nutritive purposes. They contain essential and volatile oils, which impart characteristic odor and flavor. In the onion there are about 1.5 per cent of protein and 9.5 per cent of non-nitrogenous material. Onions are often useful in stimulating the digestive tract to action.
45. Spinach is a valuable food, not to be classed merely as a relish. Its composition is interesting; for, although there is 90 per cent water, and less than 10 per cent dry matter, it still possesses high food value. Spinach contains 2.1 per cent crude protein, or about one part to every four parts of carbohydrates. In potatoes, turnips, and beets there are ten or more parts of carbohydrates to every one part of protein.
46. Asparagus is composed largely of water, about 93 per cent. The dry matter, however, is richer in protein than that of many vegetables. Asparagus contains, too, an amid compound, asparagin, which gives some of the characteristics to the vegetable.
47. Melons.—Melons contain from 8 to 10 per cent of dry matter, the larger portion of which is sugar and allied carbohydrates. The flavor is due to small amounts of essential oils and to organic acids associated with the sugars. Melons possess condimental rather than nutritive value.
Fig. 11.—Graphic
Composition Of Tomato.
48. Tomatoes.—The tomato belongs to the night-shade family, and for this reason was long looked upon with suspicion. It was first used for ornamental purposes and was called "love-apple." Gradually, as the idea of its poisonous nature became dispelled, it grew more and more popular as a food, until now in the United States it is one of the most common garden vegetables. It contains 7 per cent of dry matter, 4 per cent of which is sucrose, dextrose, and levulose. It also contains some malic acid, and a small amount of proteids, amids, cellulose, and coloring material. In the canning of tomatoes, if too much of the juice is excluded, a large part of the nutritive material is lost, as the sugars and albumins are all soluble and readily removed.[[16]] If the seeds are objectionable, they may be removed by straining and the juice added to the fleshy portion. The product then has a higher nutritive value than if the juice had been discarded with the seeds.
49. Sweet Corn.—Fresh, soft, green, sweet corn contains about 75 per cent of water. The dry matter is half starch and one quarter sugar. The protein content makes up nearly 5 per cent, a larger proportional amount than is found in the ripened corn, due to the fact that the proteids are deposited in the early stages of growth and the carbohydrates mainly in the last stages. Sweet corn is a vegetable of high nutritive value and palatability.
50. Eggplant contains a high per cent of water,—90 per cent. The principal nutrients are starch and sugar, which make up about half the weight of the dry matter. It does not itself supply a large amount of nutrients, but the way in which it is prepared, by combination with butter, bread crumbs, and eggs, makes it a nutritious and palatable dish, the food value being derived mainly from the materials with which it is combined, the eggplant giving the flavor and palatability.
51. Squash and Pumpkin.—Squash has much the same general composition and food value as beets and carrots, although it belongs to a different family. Pumpkins contain less dry matter than squash. The dry matter of both is composed largely of starch and sugar and, like many other of the vegetables, they are often combined with food materials containing a large amount of nutrients, as in pumpkin and squash pies, where the food value is derived mainly from the milk, sugar, eggs, flour, and butter or other shortening used.
52. Celery.—The dry matter of celery is comparatively rich in nitrogenous material, although the amount is small, and the larger proportion is in non-proteid form. When grown on rich soil, celery may contain an appreciable quantity of nitrates and nitrites, which have not been converted into amids and proteids. The supposed medicinal value is probably due to the nitrites which are generally present. Celery is valuable from a dietetic rather than a nutritive point of view.
53. Sanitary Condition of Vegetables.—The conditions under which vegetables are grown have much to do with their value, particularly from a sanitary point of view. Uncooked vegetables often cause the spread of diseases, particularly those, as cholera and typhoid, affecting the digestive tract. Particles of dirt containing the disease-producing organisms adhere to the uncooked vegetable and find their way into the digestive tract, where the bacteria undergo incubation. When sewage has been used for fertilizing the land, as in sewage irrigation, the vegetables are unsound from a sanitary point of view. Such vegetables should be thoroughly cleaned and also well cooked, in order to render them sterile. Vegetables to be eaten in the raw state should be dipped momentarily into boiling water, to destroy the activity of the germs present upon the surface. They may then be immediately immersed in ice-cold water, to preserve the crispness.
54. Miscellaneous Compounds in Vegetables.—In addition to the general nutrients which have been discussed, many of the vegetables contain some tannin, glucosides, and essential oils; and occasionally those grown upon rich soils have appreciable amounts of nitrogen compounds, as nitrates and nitrites, which have not been built up into proteids. Vegetables have a unique value in the dietary, and while as a class they contain small amounts of nutrients, they are indispensable for promoting health and securing normal digestion of the food.
55. Canned Vegetables.—When sound vegetables are thoroughly cooked to destroy ferments, and then sealed in cans while hot, they can be kept for a long time without any material impairment of nutritive value. During the cooking process there is lost a part of the essential oils, which gives a slightly different flavor to the canned or tinned goods.[[17]] In some canned vegetables preservatives are used, but the enactment and enforcement of national and state laws have greatly reduced their use. When the cans are made of a poor quality of tin, or the vegetables are of high acidity, some of the metal is dissolved in sufficient quantity to be objectionable from a sanitary point of view.[[18]]
56. Edible Portion and Refuse of Vegetables.—Many vegetables have appreciable amounts of refuse,[[19]] or non-edible parts, as skin, pods, seeds, and pulp, and in determining the nutritive value, these must be considered, as in some cases less than 50 per cent of the weight of the material is edible portion, which proportionally increases the cost of the nutrients. Ordinarily, the edible part is richer in protein than the entire material as purchased. In some cases, however, the refuse is richer in protein, but the protein is in a less available form. See comparison of potatoes and potato skins.