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
Read free book Β«Human Foods and Their Nutritive Value by Harry Snyder (dark academia books to read .TXT) πΒ» - read online or download for free at americanlibrarybooks.com
- Author: Harry Snyder
- Performer: -
Read book online Β«Human Foods and Their Nutritive Value by Harry Snyder (dark academia books to read .TXT) πΒ». Author - Harry Snyder
HUMAN FOODS AND THEIR NUTRITIVE VALUE
CHAPTER I GENERAL COMPOSITION OF FOODS
1. Water.βAll foods contain water. Vegetables in their natural condition contain large amounts, often 95 per cent, while in meats there is from 40 to 60 per cent or more. Prepared cereal products, as flour, corn meal, and oatmeal, which are apparently dry, have from 7 to 14 per cent. In general the amount of water in a food varies with the mechanical structure and the conditions under which it has been prepared, and is an important factor in estimating the value, as the nutrients are often greatly decreased because of large amounts of water. The water in substances as flour and meal is mechanically held in combination with the fine particles and varies with the moisture content, or hydroscopicity, of the air. Oftentimes foods gain or lose water to such an extent as to affect their weight; for example, one hundred pounds of flour containing 12 per cent of water may be reduced in weight three pounds or more when stored in a dry place, or there may be an increase in weight from being stored in a damp place. In tables of analyses the results, unless otherwise stated, are usually given on the basis of the original material, or the dry substance. Potatoes, for example, contain 2Β½ per cent of crude protein on the basis of 75 per cent of water; or on a dry matter basis, that is, when the water is entirely eliminated, there is 10 per cent of protein.
The water of foods is determined by drying the weighed material in a water or air oven at a temperature of about 100Β° C, until all of the moisture has been expelled in the form of steam, leaving the dry matter or material free from water.[1] The determination of dry matter, while theoretically a simple process, is attended with many difficulties. Substances which contain much fat may undergo oxidation during drying; volatile compounds, as essential oils, are expelled along with the moisture; and other changes may occur affecting the accuracy of the work. The last traces of moisture are removed with difficulty from a substance, being mechanically retained by the particles with great tenacity. When very accurate dry matter determinations are desired, the substance is dried in a vacuum oven, or in a desiccator over sulphuric acid, or in an atmosphere of some non-oxidizing gas, as hydrogen.
2. Dry Matter.βThe dry matter of a food is a mechanical mixture of the various compounds, as starch, sugar, fat, protein, cellulose, and mineral matter, and is obtained by drying the material. Succulent vegetable foods with 95 per cent of water contain only 5 per cent of dry matter, while in flour with 12 per cent of water there is 88 per cent, and in sugar 99 per cent. The dry matter is obtained by subtracting the per cent of water from 100, and in foods it varies from 5 per cent and less in some vegetables to 99 per cent in sugar.
Fig. 1.βApparatus used for the Determination of Dry Matter and Ash in Foods. 1, desiccator; 2, muffle furnace for combustion of foods and obtaining ash; 3, water oven for drying food materials.
3. Ash.βThe ash, or mineral matter, is that portion obtained by burning or igniting the dry matter at the lowest temperature necessary for complete combustion. The ash in vegetable foods ranges from 2 to 5 per cent and, together with the nitrogen, represents what was taken from the soil during growth. In animal bodies, the ash is present mainly in the bones, but there is also an appreciable amount, one per cent or more, in all the tissues. Ash is exceedingly variable in composition, being composed of the various salts of potassium, sodium, calcium, magnesium, and iron, as sulphates, phosphates, chlorides, and silicates of these elements. There are also other elements in small amounts. In the plant economy these elements take an essential part and are requisite for the formation of plant tissue and the production in the leaves of the organic compounds which later are stored up in the seeds. Some of the elements appear to be more necessary than others, and whenever withheld plant growth is restricted. The elements most essential for plant growth are potassium, calcium, magnesium, iron, phosphorus, and sulphur.[1]
In the animal body minerals are derived, either directly or indirectly, from the vegetable foods consumed. The part which each of the mineral elements takes in animal nutrition is not well understood. Some of the elements, as phosphorus and sulphur, are in organic combination with the nitrogenous compounds, as the nucleated albuminoids, which are very essential for animal life. In both plant and animal bodies, the mineral matter is present as mineral salts and organic combinations. It is held that the ash elements which are in organic combination are the forms mainly utilized for tissue construction. While it is not known just what part all the mineral elements take in animal nutrition, experiments show that in all ordinary mixed rations the amount of the different mineral elements is in excess of the demands of the body, and it is only in rare instances, as in cases of restricted diet, or convalescence from some disease, that special attention need be given to increasing the mineral content of the ration. An excess of mineral matter in foods is equally as objectionable as a scant amount, elimination of the excess entailing additional work on the body.
The composition of the ash of different food materials varies widely, both in amount, and form of the individual elements. When for any reason it is necessary to increase the phosphates in a ration, milk and eggs do this to a greater extent than almost any other foods. Common salt, or sodium chloride, is one of the most essential of the mineral constituents of the body. It is necessary for giving the blood its normal composition, furnishing acid and basic constituents for the production of the digestive fluids, and for the nutrition of the cells. While salt is a necessary food, in large amounts, as when the attempt is made to use sea water as a beverage, it acts as a poison, suggesting that a material may be both a food and a poison. When sodium chloride is entirely withheld from an animal, death from salt starvation ensues. Many foods contain naturally small amounts of sodium chloride.
4. Organic Matter.βThat portion of a food material which is converted into gaseous or volatile products during combustion is called the organic matter. It is a mechanical mixture of compounds made up of carbon, hydrogen, oxygen, nitrogen, and sulphur, and is composed of various individual organic compounds, as cellulose, starch, sugar, albumin, and fat. The amount in a food is determined by subtracting the ash and water from 100. The organic matter varies widely in composition; in some foods it is largely starch, as in potatoes and rice, while in others, as forage crops consumed by animals, cellulose predominates. The nature of the prevailing organic compound, as sugar or starch, determines the nutritive value of a food. Each has a definite chemical composition capable of being expressed by a formula. Considered collectively, the organic compounds are termed organic matter. When burned, the organic compounds are converted into gases, the carbon uniting with the oxygen of the air to form carbon dioxide, hydrogen to form water, sulphur to form sulphur dioxide, and the nitrogen to form oxides of nitrogen and ammonia.
5. Classification of Organic Compounds.βAll food materials are composed of a large number of organic compounds. For purposes of study these are divided into classes. The element nitrogen is taken as the basis of the division. Compounds which contain this element are called nitrogenous, while those from which it is absent are called non-nitrogenous.[2] The nitrogenous organic compounds are composed of the elements nitrogen, hydrogen, carbon, oxygen, and sulphur, while the non-nitrogenous compounds are composed of carbon, hydrogen, and oxygen. In vegetable foods the non-nitrogenous compounds predominate, there being usually from six to twelve parts of non-nitrogenous to every one part of nitrogenous, while in animal foods the nitrogenous compounds are present in larger amount.
NON-NITROGENOUS COMPOUNDS6. Occurrence.βThe non-nitrogenous compounds of foods consist mainly of cellulose, starch, sugar, and fat. For purposes of study, they are divided into subdivisions, as carbohydrates, pectose substances or jellies, fats, organic acids, essential oils, and mixed compounds. In plants the carbohydrates predominate, while in animal tissue
Comments (0)