Human Foods and Their Nutritive Value by Harry Snyder (dark academia books to read .TXT) π
CHAPTER XXI
LABORATORY PRACTICE 299
Object of Laboratory Practice; Laboratory Note-book and Suggestions for Laboratory Practice; List of Apparatus Used; Photograph of Apparatus Used; Directions for Weighing; Directions for Measuring; Use of Microscope; Water in Flour; Water in Butter; Ash in Flour; Nitric Acid Test for Nitrogenous Organic Matter; Acidity of Lemons; Influence of Heat on Potato Starch Grains; Influence of Yeast on Starch Grains; Mechanical Composition of Potatoes; Pectose from Apples; Lemon Extract; Vanilla Extract; Testing Olive Oil for Cotton Seed Oil; Testing for Coal Tar Dyes; Determining the Per Cent of Skin in Beans; Extraction of Fat from Peanuts; Microscopic Examination of Milk; Formaldehyde in Cream or Milk; Gelatine in Cream or Milk; Testing for Oleomargarine; Testing for Watering or Skimming of Milk; Boric Acid in Meat; Microscopic Examination of Cereal Starch Grains; Identification
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32. General Relationship of Chemical, Physical, and Bacteriological Changes.βIt cannot be said that the beneficial results derived from the cooking of foods are due to either chemical, physical, or bacteriological change alone, but to the joint action of the three. In order to secure a chemical change, a physical change must often precede, and a bacteriological change cannot take place without causing a change in chemical composition; the three are closely related and interdependent.
33. Esthetic Value of Foods.βFoods should be not only of good physical texture and contain the requisite nutrients, but they should also be pleasing to the eye and served in the most attractive manner. Some foods owe a part of their commercial value to color, and when they are lacking in natural color they are not consumed with a relish. There is no objection to the addition of coloring matter to foods, provided it is of a non-injurious character and does not affect the amount of nutrients, and that its presence and the kind of coloring material are made known. Some foods contain objectionable colors which are eliminated during the process of manufacture, as in the case of sugar and flour. As far as removal of coloring matter from foods during refining is concerned, there can be no objection, so long as no injurious reagents or chemicals are retained, as the removal of the color in no way affects the nutritive value or permits fraud, but necessitates higher purification and refining. The use of chemicals and reagents in the preparation and refining of foods is considered permissible in all cases where the reagents are removed by subsequent processes. In the food decisions of the United States Department of Agriculture, it is stated: "Not excluded under this provision are substances properly used in the preparation of food products for clarification or refining and eliminated in the further process of manufacture." [15]
CHAPTER III VEGETABLE FOODSFig. 9.βTransverse Section
of Potato. (After Cowden
and Bussard.) a, skin; b, cortical
layer; c, outer medullary
layer; d, inner medullary layer.
34. General Composition.βVegetable 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,βouter 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.
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] KΓΆnig, "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.βGraphic
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.βThe 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.βMelons 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.βGraphic
Composition Of Tomato.
48. Tomatoes.βThe 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.βFresh, 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,β90 per cent. The principal nutrients are starch and sugar, which make up about half the
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