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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By the addition of sugar, sweet chocolates are made. They vary widely in composition according to the flavors and amounts of sugar added during their preparation. The average composition of cocoa nibs, standard cocoa, and plain chocolate is as follows:
Standard Cocoa Composition of
Plain Chocolate Per Cent Per Cent Per Cent Water 3.00 β 3.09 Ash 3.50 4.20 3.08 Theobromine 1.00 β β Caffein 0.50 β β Crude Protein 12.00 β β Crude fiber 2.50 5.02 2.63 Fat 50.00 32.52 49.81 Starch and other non-nitrogenous matter 27.50 β β
223. Adulteration of Chocolate and Cocoa.βThe various chocolate and cocoa preparations offer an enticing field for sophistication; they are not, however, so extensively adulterated as before the enforcement of national and state pure food laws. The most common adulterants are starch, cocoa shells, and occasionally iron dioxid and other pigments to give color, also foreign fats to replace the fat removed and to give the required plasticity for molding.
224. Comparative Composition of Beverages.βTea and coffee as beverages contain but little in the way of nutrients other than the cream and sugar used in them. The solid matter in tea and coffee infusions amounts to less than 1.2 per cent. When cocoa is made with milk, it is a beverage of high nutritive value due mainly to the milk.
Composition of Beverages[56]
Value
per Lb. % % % % Cal. Commercial cereal coffee (0.5 ounce to 1 pint water) 98.2 0.2 β 1.4 30 Parched corn coffee (1.6 ounces to 1 pint water) 99.5 0.2 β 0.5 13 Oatmeal water (1 ounce to 1 pint water) 99.7 0.3 β 0.3 11 Coffee (1 ounce 1 pint water) 98.9 0.2 β 0.7 16 Tea (0.5 ounce to 1 pint water) 99.5 0.2 β 0.6 15 Cocoa (0.5 ounce to 1 pint milk) 84.5 3.8 4.7 6.0 365 Cocoa (0.5 ounce to 1 pint water) 97.1 0.6 0.9 1.1 65 Skimmed milk 90.5 3.4 0.3 5.1 170 CHAPTER XV THE DIGESTIBILITY OF FOODS
225. Digestibility, How Determined.βThe term "digestibility," as applied to foods, is used in two ways: (1) meaning the thoroughness of the process, or the completeness with which the nutrients of the food are absorbed and used by the body, and (2) meaning the ease or comfort with which digestion is accomplished. Cheese is popularly termed indigestible, and rice digestible, when in reality the nutrients of cheese are more completely although more slowly digested than those of rice. In this work, unless otherwise stated, digestibility is applied to the completeness of the digestion process.
The digestibility of a food is ascertained by means of digestion experiments, in which all of the food consumed for a certain period, usually two to four days, is weighed and analyzed, and from the weight and composition is determined the amount, in pounds or grams, of each nutrient consumed.[72] In like manner the nutrients in the indigestible portion, or feces, are determined from the weight and composition of the feces. The indigestible nutrients in the feces are deducted from the total nutrients of the food, the difference being the amount digested, or oxidized in the body. When the food is digested, the various nutrients undergo complete or partial oxidation, with the formation of carbon dioxid gas, water, urea (CH4N2O), and other compounds. The feces consist mainly of the compounds which have escaped digestion. The various groups of compounds of foods do not all have the same digestibility; for example, the starch of potatoes is 92 per cent digestible, while the protein is only 72 per cent. The percentage amount of a nutrient that is digested is called the digestion coefficient.
In the following way the digestibility of a two-days ration of bread and milk was determined: 773.5 grams of bread and 2000 grams of milk were consumed by the subject. The dried feces weighed 38.2 grams. The foods and feces when analyzed were found to have the following composition:[62]
[A] Results on dry-matter basis.
Statement of Results of a Digestion ExperimentMaterial Protein
N Γ 6.25 Ether
Extract Carbo-
hydrates Ash Heat of
Combustion Grams Grams Grams Grams Grams Calories Bread 773.5 60.0 6.9 362.8 2.5 1895 Milk 2000.0 63.0 92.6 100.0 14.0 1585 ββ ββ ββ ββ ββ Total 38.2 123.0 99.5 462.8 16.5 3480 Feces 9.9 7.0 11.3 10.1 194 ββ ββ ββ ββ ββ Total amount digested 113.1 92.5 451.5 6.4 3286 Per cent digested or coefficients of digestibility 92.0 93.0 97.5 38.8 94.4 Available energy β β β β 90.0
In this experiment 92 per cent of the crude protein, 93 per cent of the ether extract, and 97.5 per cent of the carbohydrates of the bread and milk ration were digested and absorbed by the body. In calculating the available energy, correction is made for the unoxidized residue, as urea and allied forms. It is estimated that for each gram of protein in the ration there was an indigestible residue yielding 1.25 calories.
226. Available Nutrients.βA food may contain a comparatively large amount of a compound, and yet, on account of its low digestibility, fail to supply much of it to the body in an available form. Hence it is that the value of a food is dependent not alone on its composition, but also on its digestibility. The digestible or available nutrients of a food are determined by multiplying the per cent of each nutrient which the food contains by its digestion coefficient. For example, a sample of wheat flour contains 12 per cent protein, 88 per cent of which is digestible, making 10.56 per cent of available or digestible protein (12 Γ 0.88-10.56). Graham flour made from similar wheat contains 13 per cent total protein, and only 75 per cent of the protein is digestible, making 9.75 per cent available (13 Γ 0.75 = 9.75). Thus one food may contain a larger total but a smaller available amount of a nutrient than another.
227. Available Energy.βThe available energy of a food or a ration is expressed in calories. A ration for a laborer at active out-of-door work should yield about 3200 calories. The calory is the unit of heat, and represents the heat required to raise the temperature of a kilogram of water 1Β° C., or four pounds of water 1Β° F. The caloric value of foods is determined by the calorimeter, an apparatus which measures heat with great accuracy. A pound of starch, or allied carbohydrates, yields 1860 calories, and a pound of fat 4225 (see Section 13). While a gram of protein completely burned produces 7.8 calories, digested it yields only about 4.2 calories, because, as explained in the preceding section, not all of the carbon and oxygen are oxidized.[59] The caloric value or available energy of a ration can be calculated from the digestible nutrients by multiplying the pounds of digestible protein and carbohydrates by 1860, the digestible fat by 4225, and adding the results. For determination of the available energy of foods under different experimental conditions, and where great accuracy is desired, a specially constructed respiration calorimeter has been devised, which is built upon the same principle as an ordinary calorimeter, except it is large enough to admit a person, and is provided with appliances for measuring and analyzing the intake and outlet of air.[74] The heat produced by the combustion of the food in the body warms the water surrounding the calorimeter chamber, and this increase in temperature is determined by thermometers reading to 0.005 of a degree or less.
Fig. 55.βCalorimeter.
228. Normal Digestion and Health.βWhile the process of digestion has been extensively studied, it is not perfectly understood. Between the initial compounds of foods and their final oxidation products a large number of intermediate substances are formed, and when digestion fails to take place in a normal way, toxic or poisonous compounds are produced and various diseases result. It is probable that more diseases are due to imperfect or malnutrition than to any other cause. There is a very close relationship between health and normal digestion of the food.
The cells in the different parts of the digestive tract secrete fluids containing substances known as soluble ferments, or enzymes, which act upon the various compounds of foods, changing them chemically and physically so that they can be absorbed and utilized by the body. (See Section 31.) Some of the more important ferments are: ptyolin of the saliva, pepsin of the stomach, and pancreatin and diastase of the intestines. In order that these ferments may carry on their work in a normal way, the acidity and alkalinity of the different parts of the digestive tract must be maintained. The gastric juice contains from 0.1 to 0.25 per cent of hydrochloric acid, imparting mildly antiseptic properties; and while the peptic ferment works in a slightly acid solution, the tryptic ferment requires an alkaline solution. To secrete the necessary amount and quality of digestive fluids, the organs must be in a healthy condition. Many erroneous ideas regarding the digestion of foods are based upon misinterpretation of facts by persons suffering from impaired digestion, and attempts are frequently made to apply to normal digestion generalizations applicable only to diseased conditions.
229. Digestibility of Animal Foods.βThe proteids and fats in animal foods, as meats, are more completely digested than the same class of nutrients in vegetables. In general, about 95 per cent of the proteids of meats is digestible, while those in vegetables are often less than 85 percent digestible. The amount of indigestible residue from animal foods is small; while from vegetables it is large, for the cellulose prevents complete absorption of the nutrients and, as a result, there is much indigestible residue. Animal foods are concentrated, in that they furnish large amounts of nutrients in digestible forms. There is less difference in the completeness with which various meats are digested than in their ease of digestion; the proteins all have about the same digestion coefficients, but vary with individuals as to ease of digestion and time required. It is generally considered that the digestible proteins, whether of animal or vegetable origin, are equally valuable for food purposes. This is an assumption, however, that has not been well established by experimental evidence. In a mixed ration, the proteins from different sources appear to have the same nutritive value, but as each is composed of different radicals and separated into dissimilar elementary compounds during the process of digestion, they would not necessarily all have the same food value.
There is but little difference between the fats and proteins of meats as to completeness of digestion,βthe slight difference being in favor of the proteins. Some physiologists claim that the fat, which in some meats surrounds the bundles of fiber (protein), forming a protecting coat, prevents the complete solvent action of the digestive fluid. Very fat meats are not as completely digested as those moderately fat. It is also claimed
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