Transcribers note:

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HUMAN FOODS AND THEIR NUTRITIVE VALUE

by

HARRY SNYDER, B.S.



New York The MacMillan Company 1914 All rights reserved Copyright, 1908, by the MacMillan Company.

Set up and electrotyped. Published November, 1908. Reprinted October, 1909; September, 1910; February, 1911; September, 1912; May, December, 1913; June, 1914.

Norwood Press J. S. Cushing Co.—Berwick & Smith Co. Norwood, Mass., U.S.A.



PREFACE

Since 1897 instruction has been given at the University of Minnesota, College of Agriculture, on human foods and their nutritive value. With the development of the work, need has been felt for a text-book presenting in concise form the composition and physical properties of foods, and discussing some of the main factors which affect their nutritive value. To meet the need, this book has been prepared, primarily for the author's classroom. It aims to present some of the principles of human nutrition along with a study of the more common articles of food. It is believed that a better understanding of the subject of nutrition will suggest ways in which foods may be selected and utilized more intelligently, resulting not only in pecuniary saving, but also in greater efficiency of physical and mental effort.

Prominence is given in this work to those foods, as flour, bread, cereals, vegetables, meats, milk, dairy products, and fruits, that are most extensively used in the dietary, and to some of the physical, chemical, and bacteriological changes affecting digestibility and nutritive value which take place during their preparation for the table. Dietary studies, comparative cost and value of foods, rational feeding of men, and experiments and laboratory practice form features of the work. Some closely related topics, largely of a sanitary nature, as the effect upon food of household sanitation and storage, are also briefly discussed. References are given in case more extended information is desired on some of the subjects treated. While this book was prepared mainly for students who have taken a course in general chemistry, it has been the intention to present the topics in such a way as to be understood by the layman also.

This work completes a series of text-books undertaken by the author over ten years ago, dealing with agricultural and industrial subjects: "Chemistry of Plant and Animal Life," "Dairy Chemistry," "Soils and Fertilizers," and "Human Foods and their Nutritive Value." It has been the aim in preparing these books to avoid as far as possible repetition, but at the same time to make each work sufficiently complete to permit its use as a text independent of the series.

One of the greatest uses that science can serve is in its application to the household and the everyday affairs of life. Too little attention is generally bestowed upon the study of foods in schools and colleges, and the author sincerely hopes the time will soon come when more prominence will be given to this subject, which is the oldest, most important, most neglected, and least understood of any that have a direct bearing upon the welfare of man.

HARRY SNYDER.



CONTENTS

CHAPTER I PAGE GENERAL COMPOSITION OF FOODS 1

Water; Dry Matter; Variations in Weight of Foods; Ash; Function of Ash in Plant Life; Organic Matter; Products of Combustion of Organic Matter; Classification of Organic Compounds; Non-nitrogenous Compounds; Carbohydrates; Cellulose; Amount of Cellulose in Foods; Crude Fiber; Starch; Microscopic Structure of Starch; Dextrin; Food Value of Starch; Sugar; Pectose Substances; Nitrogen-free-extract; Fats; Fuel Value of Fats; Iodine Number of Fats; Glycerol Content of Fats; Ether Extract and Crude Fat; Organic Acids; Dietetic Value of Organic Acids; Essential Oils; Mixed Compounds; Nutritive Value of Non-nitrogenous Compounds; Nitrogenous Compounds; General Composition; Protein; Sub-divisions of Proteins; Crude Protein; Food Value of Protein; Albuminoids; Amids and Amines; Alkaloids; General Relationship of the Nitrogenous Compounds.

CHAPTER II

CHANGES IN COMPOSITION OF FOODS DURING COOKING AND PREPARATION 27

Raw and Cooked Foods compared as to Composition; Chemical Changes during Cooking; General Changes affecting Cellulose, Starch, Sugar, Pectin Bodies, Fats, Proteids; Effect of Chemical Changes on Digestibility; Physical Changes during Cooking; Action of Heat on Animal and Plant Tissues; Amount of Heat required for Cooking; Bacteriological Changes; Insoluble Ferments; Soluble Ferments; Bacterial Action Necessary in Preparation of Some Foods; Injurious Bacterial Action; General Relationship of Chemical, Physical, and Bacteriological Changes; Esthetic Value of Foods; Color of Foods; Natural and Artificial Colors; Conditions under which Use of Chemicals in Preparation of Foods is Justifiable.

CHAPTER III

VEGETABLE FOODS 37

General Composition; Potatoes; Chemical and Mechanical Composition; Uses of Potatoes in Dietary; Sweet Potatoes; Carrots; Parsnips; Cabbage; Cauliflower; Beets; Cucumbers; Lettuce; Onions; Spinach; Asparagus; Melons; Tomatoes; Sweet Corn; Eggplant; Squash; Celery; Dietetic Value of Vegetables; Nutrient Content of Vegetables; Sanitary Condition of Vegetables; Miscellaneous Compounds in Vegetables; Canned Vegetables; Edible Portion and Refuse of Vegetables.

CHAPTER IV

FRUITS, FLAVORS AND EXTRACTS 48

General Composition; Food Value; Apples; Oranges; Lemons; Grape Fruit; Strawberries; Grapes; Peaches; Plums; Olives; Figs; Dried Fruits; Uses of Fruit in the Dietary; Canning and Preservation of Fruits; Adulterated Canned Fruits; Fruit Flavors and Extracts; Synthetic Preparation of Flavors.

CHAPTER V

SUGARS, MOLASSES, SYRUP, HONEY, AND CONFECTIONS 58

Composition of Sugars; Beet Sugar; Cane Sugar; Manufacture of Sugar; Sulphur Dioxid and Indigo, Uses of, in Sugar Manufacture; Commercial Grades of Sugar; Sugar in the Dietary; Maple Sugar; Adulteration of Sugar; Dextrose Sugars; Inversion of Sugars; Molasses; Syrups; Adulteration of Molasses; Sorghum Syrup; Maple Syrup; Analysis of Sugar; Adulteration of Syrups; Honey; Confections; Coloring Matter in Candies; Coal Tar Dyes; Saccharine.

CHAPTER VI

LEGUMES AND NUTS 71

General Composition of Legumes; Beans; Digestibility of Beans; Use of Beans in the Dietary; String Beans; Peas; Canned Peas; Peanuts; General Composition of Nuts; Chestnuts; The Hickory Nut; Almonds; Pistachio; Cocoanuts; Uses of Nuts in the Dietary.

CHAPTER VII

MILK AND DAIRY PRODUCTS 80

Importance in the Dietary; General Composition; Digestibility; Sanitary Condition of Milk; Certified Milk; Pasteurized Milk; Tyrotoxicon; Color of Milk; Souring of Milk; Use of Preservatives in Milk; Condensed Milk; Skim Milk; Cream; Buttermilk; Goat's Milk; Koumiss; Prepared Milks; Human Milk; Adulteration of Milk; Composition of Butter; Digestibility of Butter; Adulteration of Butter; General Composition of Cheese; Digestibility; Use in the Dietary; Cottage Cheese; Different Kinds of Cheese; Adulteration of Cheese; Dairy Products in the Dietary.

CHAPTER VIII

MEATS AND ANIMAL FOOD PRODUCTS 98

General Composition; Mineral Matter; Fat; Protein; Non-nitrogenous Compounds; Why Meats vary in Composition; Amides; Albuminoids; Taste and Flavor of Meats; Alkaloidal Bodies in Meats; Ripening of Meats in Cold Storage; Beef; Veal; Mutton; Pork; Lard; Texture and Toughness of Meat; Influence of Cooking upon the Composition of Meats; Beef Extracts; Miscellaneous Meat Products; Pickled Meats; Saltpeter in Meats; Smoked Meats; Poultry; Fish; Oysters, Fattening of; Shell Fish; Eggs, General Composition; Digestibility of Eggs; Use of Eggs in the Dietary; Canned Meats, General Composition.

CHAPTER IX

CEREALS 121

Preparation and Cost of Cereals; Various Grains used in making Cereal Products; Cleanliness of; Corn Preparations; Corn Flour; Use of Corn in Dietary; Corn Bread; Oat Preparations; Cooking of Oatmeal; Wheat Preparations; Flour Middlings; Breakfast Foods; Digestibility of Wheat Preparations; Barley Preparations; Rice Preparations; Predigested Foods; The Value of Cereals in the Dietary; Phosphate Content of Cereals; Phosphorus Requirements of a Ration; Mechanical Action of Cereals upon Digestion; Cost and Nutritive Value of Cereals.

CHAPTER X

WHEAT FLOUR 133

Use for Bread Making; Winter and Spring Wheat Flours; Composition of Wheat and Flour; Roller Process of Flour Milling; Grades of Flour; Types of Flour; Composition of Flour; Graham and Entire Wheat Flours; Composition of Wheat Offals; Aging and Curing of Flour; Macaroni Flour; Color; Granulation; Capacity of Flour to absorb Water; Physical Properties of Gluten; Gluten as a Factor in Bread Making; Unsoundness; Comparative Baking Tests; Bleaching; Adulteration of Flour; Nutritive Value of Flour.

CHAPTER XI

BREAD AND BREAD MAKING 158

Leavened and Unleavened Bread; Changes during Bread Making; Loss of Dry Matter during Bread Making; Action of Yeast; Compressed Yeast; Dry Yeast; Production of Carbon Dioxid Gas and Alcohol; Production of Soluble Carbohydrates; Production of Acids in Bread Making; Volatile Compounds produced during Bread Making; Behavior of Wheat Proteids in Bread Making; Production of Volatile Nitrogenous Compounds; Oxidation of Fat; Influence of the Addition of Wheat Starch and Gluten to Flour; Composition of Bread; Use of Skim Milk and Lard in Bread Making; Influence of Warm and Cold Flours in Bread Making; Variations in the Process of Bread Making; Digestibility of Bread; Use of Graham and Entire Wheat in the Dietary; Mineral Content of White Bread; Comparative Digestibility of New and Old Bread; Different Kinds of Bread; Toast.

CHAPTER XII

BAKING POWDERS 186

General Composition; Cream of Tartar Powders; Residue from Cream of Tartar Baking Powders; Tartaric Acid Powders; Phosphate Baking Powders; Mineral and Organic Phosphates; Phosphate Residue; Alum Baking Powders; Residue from Alum Baking Powders; Objections urged against Alum Powders; Action of Baking Powders and Yeast Compared; Keeping Qualities of Baking Powders; Inspection of Baking Powders; Fillers; Home-made Baking Powders.

CHAPTER XIII

VINEGAR, SPICES, AND CONDIMENTS 193

Vinegar; Chemical Changes during Manufacture of Vinegar; Ferment Action; Materials used in Preparation of Vinegars; Characteristics of a Good Vinegar; Vinegar Solids; Acidity of Vinegar; Different Kinds of Vinegars; Standards of Purity; Adulteration of Vinegar; Characteristics of Spices; Pepper; Cayenne; Mustard; Ginger; Cinnamon and Cassia; Cloves; Allspice; Nutmeg; Adulteration of Spices and Condiments; Essential Oils of; Uses of Condiments in Preparation of Foods; Action of Condiments upon Digestion; Condiments and Natural Flavors.

CHAPTER XIV

TEA, COFFEE, CHOCOLATE, AND COCOA 203

Tea; Sources of Tea Supply; Composition of Tea; Black Tea and Green Tea; Judging Teas; Adulteration of Tea; Food Value and Physiological Properties of Tea; Composition of Coffee; Adulteration of Coffee; Chicory in Coffee; Glazing of Coffee; Cereal Coffee Substitutes; Cocoa and Chocolate Preparations; Composition of Cocoa; Chocolate; Cocoa Nibs; Plain Chocolate; Sweet Chocolate; Cocoa Butter; Nutritive Value of Cocoa; Adulteration of Chocolate and Cocoa; Comparative Composition of Beverages.

CHAPTER XV

THE DIGESTIBILITY OF FOOD 214

Digestibility, how Determined; Completeness and Ease of Digestion Process; Example of Digestion Experiment; Available Nutrients; Available Energy; Caloric Value of Foods; Normal Digestion and Health; Digestibility of Animal Foods; Digestibility of Vegetable Foods; Factors influencing Digestion; Combination of Foods; Amount of Food; Method of Preparation of Food; Mechanical Condition of Foods; Mastication; Palatability of Foods; Physiological Properties of Foods; Individuality; Psychological Factors.

CHAPTER XVI

COMPARATIVE COST AND VALUE OF FOODS 231

Cost and Nutrient Content of Foods; How to compare Two Foods as to Nutritive Value; Cheap Foods; Expensive Foods; Nutrients Procurable for a Given Sum; Examples; Comparing Nutritive Value of Common Foods at Different Prices; Cost and Value of Nutrients.

CHAPTER XVII

DIETARY STUDIES 244

Object of Dietary Studies; Wide and Narrow Rations; Dietary Standards; Number of Meals per Day; Mixed Dietary Desirable; Animal and Vegetable Foods; Economy of Production; Food Habits; Underfed Families; Cheap and Expensive Foods; Food Notions; Dietary of Two Families Compared; Food in its Relation to Mental and Physical Vigor; Dietary Studies in Public Institutions.

CHAPTER XVIII

RATIONAL FEELING OF MAN 261

Object; Human and Animal Feeding Compared; Standard Rations; Why Tentative Dietary Standards; Amounts of Food Consumed; Average Composition of Foods; Variations in Composition of Foods; Example of a Ration; Calculations of Balanced Rations; Requisites of a Balanced Ration; Examples; Calculations of Rations for Men at Different Kinds of Labor.

CHAPTER XIX

WATER 268

Importance; Impurities in Water; Mineral Impurities; Organic Impurities; Interpretation of a Water Analysis; Natural Purification of Water; Water in Relation to Health; Improvement of Waters; Boiling of Water; Filtration; Purification of Water by Addition of Chemicals; Ice; Rain Waters; Waters of High and Low Purity; Chemical Changes which Organic Matter of Water Undergoes; Bacterial Content of Water; Mineral Waters; Materials for Softening Water; Uses of; Economic Value of a Pure Water Supply.

CHAPTER XX

FOOD AS AFFECTED BY HOUSEHOLD SANITATION AND STORAGE 284

Injurious Compounds in Foods; Nutrient Content and Sanitary Condition of Food; Sources of Contamination of Food; Unclean Ways of Handling Food; Sanitary Inspection of Food; Infection from Impure Air; Storage of Food in Cellars; Respiration of Vegetable Cells; Sunlight, Pure Water, and Pure Air as Disinfectants; Foods contaminated from Leaky Plumbing; Utensils for Storage of Food; Contamination from Unclean Dishcloths; Refrigeration; Chemical Changes that take Place in the Refrigerator; Soil; Disposal of Kitchen Refuse; Germ Diseases spread by Unsanitary Conditions around Dwellings due to Contamination of Food; General Considerations; Relation of Food to Health.

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 of Commercial Cereals; Granulation and Color of Flour; Capacity of Flour to absorb Water; Acidity of Flour; Moist and Dry Gluten; Gliadin from Flour; Bread-making Test; Microscopic Examination of Yeast; Testing Baking Powders for Alum; Testing Baking Powders for Phosphoric Acid; Testing Baking Powders for Ammonia; Vinegar Solids; Specific Gravity of Vinegar; Acidity of Vinegar; Deportment of Vinegar with Reagents; Testing Mustard for Turmeric; Examination of Tea Leaves; Action of Iron Compounds upon Tannic Acid; Identification of Coffee Berries; Detecting Chicory in Coffee; Comparative Amounts of Soap Necessary with Hard and Soft Water; Solvent Action of Water on Lead; Suspended Matter in Water; Organic Matter in Water; Deposition of Lime by Boiling Water; Qualitative Tests for Minerals in Water; Testing for Nitrites in Water.

REVIEW QUESTIONS 323

REFERENCES 350

INDEX 357



HUMAN FOODS AND THEIR NUTRITIVE VALUE



CHAPTER I

GENERAL COMPOSITION OF FOODS

1. Water.—All 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 2-1/2 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 100 deg. 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.—The 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.



3. Ash.—The 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.—That 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.—All 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 COMPOUNDS

6. Occurrence.—The 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 the fats are the chief non-nitrogenous constituents.

7. Carbohydrates.—This term is applied to a class of compounds similar in general composition, but differing widely in structural composition and physical properties. Carbohydrates make up the bulk of vegetable foods and, except in milk, are found only in traces in animal foods. They are all represented by the general formula CH2n2n, there being twice as many hydrogen as oxygen atoms, the hydrogen and oxygen being present in the same proportion as in water. As a class, the carbohydrates are neutral bodies, and, when burned, form carbon dioxide and water.



8. Cellulose is the basis of the cell structure of plants, and is found in various physical forms in food materials.[3] Sometimes it is hard and dense, resisting digestive action and mechanically inclosing other nutrients and thus preventing their being available as food. In the earlier stages of plant growth a part of the cellulose is in chemical combination with water, forming hydrated cellulose, a portion of which undergoes digestion and produces heat and energy in the body. Ordinarily, however, cellulose adds but little in the way of nutritive value, although it is often beneficial mechanically and imparts bulk to some foods otherwise too concentrated. The mechanical action of cellulose on the digestion of food is discussed in Chapter XV. Cellulose usually makes up a very small part of human food, less than 1 per cent. In refined white flour there is less than .05 of a per cent; in oatmeal and cereal products from .5 to 1 per cent, depending upon the extent to which the hulls are removed, and in vegetable foods from .1 to 1 per cent. The cellulose content of foods is included in the crude fiber of the chemist's report.

9. Starch occurs widely distributed in nature, particularly in the seeds, roots, and tubers of some plants. It is formed in the leaves of plants as a result of the joint action of chlorophyll and protoplasm, and is generally held by plant physiologists to be the first carbohydrate produced in the plant cell. Starch is composed of a number of overlapping layers separated by starch cellulose; between these layers the true starch or amylose is found. Starch from the various cereals and vegetables differs widely in mechanical structure; in wheat it is circular, in corn somewhat angular, and in parsnips exceedingly small, while potato starch granules are among the largest.[4] The nature of starch can be determined largely from its mechanical structure as studied under the microscope. It is insoluble in cold water because of the protecting action of the cellular layer, but on being heated it undergoes both mechanical and chemical changes; the grains are partially ruptured by pressure due to the conversion into steam of the moisture held mechanically. The cooking of foods is beneficial from a mechanical point of view, as it results in partial disintegration of the starch masses, changing the structure so that the starch is more readily acted upon by the ferments of the digestive tract. At a temperature of about 120 deg. C. starch begins to undergo chemical change, resulting in the rearrangement of the atoms in the molecule with the production of dextrine and soluble carbohydrates. Dextrine is formed on the crust of bread, or whenever potatoes or starchy foods are browned. At a still higher temperature starch is decomposed, with the liberation of water and production of compounds of higher carbon content. When heated in contact with water, it undergoes hydration changes; gelatinous-like products are formed, which are finally converted into a soluble condition. In cooking cereals, the hydration of the starch is one of the main physical and chemical changes that takes place, and it simply results in converting the material into such a form that other chemical changes may more readily occur. Before starch becomes dextrose, hydration is necessary. If this is accomplished by cooking, it saves the body just so much energy in digestion. Many foods owe their value largely to the starch. In cereals it is found to the extent of 72 to 76 per cent; in rice and potatoes in still larger amounts; and it is the chief constituent of many vegetables. When starch is digested, it is first changed to a soluble form and then gradually undergoes oxidation, resulting in the production of heat and energy, the same products—carbon dioxide and water—being formed as when starch is burned. Starch is a valuable heat-producing nutrient; a pound yields 1860 calories. See Chapter XV.

10. Sugar.—Sugars are widely distributed in nature, being found principally in the juices of the sugar cane, sugar beet, and sugar maple. They are divided into two large classes: the sucrose group and the dextrose group, the latter being produced from sucrose, starch, and other carbohydrates by inversion and allied chemical changes. Because of the importance of sugar in the dietary, Chapter V is devoted to the subject.

11. Pectose Substances are jelly-like bodies found in fruits and vegetables. They are closely related in chemical composition to the carbohydrates, into which form they are changed during digestion; and in nutrition they serve practically the same function. In the early stages of growth the pectin bodies are combined with organic acids, forming insoluble compounds, as the pectin in green apples. During the ripening of fruit and the cooking of vegetables, the pectin is changed to a more soluble and digestible condition. In food analysis, the pectin is usually included with the carbohydrates.

12. Nitrogen-free-extract.—In discussing the composition of foods, the carbohydrates other then cellulose, as starch, sugar, and pectin, are grouped under the name of nitrogen-free-extract. Methods of chemical analysis have not yet been sufficiently perfected to enable accurate and rapid determination to be made of all these individual carbohydrates, and hence they are grouped together as nitrogen-free-extract. As the name indicates, they are compounds which contain no nitrogen, and are extractives in the sense that they are soluble in dilute acid and alkaline solutions. The nitrogen-free-extract is determined indirectly, that is, by the method of difference. All the other constituents of a food, as water, ash, crude fiber (cellulose), crude protein, and ether extract, are determined; the total is subtracted from 100, and the difference is nitrogen-free-extract. In studying the nutritive value of foods, particular attention should be given to the nature of the nitrogen-free-extract, as in some instances it is composed of sugar and in others of starch, pectin, or pentosan (gum sugars). While all these compounds have practically the same fuel value, they differ in composition, structure, and the way in which they are acted upon by chemicals and digestive ferments.[1]



13. Fat.—Fat is found mainly in the seeds of plants, but to some extent in the leaves and stems. It differs from starch in containing more carbon and less oxygen. In starch there is about 44 per cent of carbon, while in fat there is 75 per cent. Hence it is that when fat is burned or undergoes combustion, it yields a larger amount of the products of combustion—carbon dioxid and water—than does starch. A gram of fat produces 2-1/4 times as much heat as a gram of starch. Fat is the most concentrated non-nitrogenous nutrient. As found in food materials, it is a mechanical mixture of various fats, among which are stearin, palmitin, and olein. Stearin and palmitin are hard fats, crystalline in structure, and with a high melting point, while olein is a liquid. In addition to these three, there are also small amounts of other fats, as butyrin in butter, which give character or individuality to materials. There are a number of vegetable fats or oils which are used for food purposes and, when properly prepared and refined, have a high nutritive value. Occasionally one fat of cheaper origin but not necessarily of lower nutritive value is substituted for another. The fats have definite physical and chemical properties which enable them to be readily distinguished, as iodine number, specific gravity, index of refraction, and heat of combustion. By iodine number is meant the percentage of iodine that will unite chemically with the fat. Wheat oil has an iodine number of about 100, meaning that one pound of wheat oil will unite chemically with one pound of iodine. Fats have a lower specific gravity than water, usually ranging from .89 to .94, the specific gravity of a fat being fairly constant. All fats can be separated into glycerol and a fatty acid, glycerol or glycerine being common constituents, while each fat yields its own characteristic acid, as stearin, stearic acid; palmitin, palmitic acid; and olein, oleic acid. The fats are soluble in ether, chloroform, and benzine. In the chemical analysis of foods, they are separated with ether, and along with the fat, variable amounts of other substances are extracted, these extractive products usually being called "ether extract" or "crude fat."[5] The ether extract of plant tissue contains in addition to fat appreciable amounts of cellulose, gums, coloring, and other materials. From cereal products the ether extract is largely fat, but in some instances lecithin and other nitrogenous fatty substances are present, while in animal food products, as milk and meat, the ether extract is nearly pure fat.

14. Organic Acids.—Many vegetable foods contain small amounts of organic acids, as malic acid found in apples, citric in lemons, and tartaric in grapes. These give characteristic taste to foods, but have no direct nutritive value. They do not yield heat and energy as do starch, fat, and protein; they are, however, useful for imparting flavor and palatability, and it is believed they promote to some extent the digestion of foods with which they are combined by encouraging the secretion of the digestive fluids. Many fruits and vegetables owe their dietetic value to the organic acids which they contain. In plants they are usually in chemical combination with the minerals, forming compounds as salts, or with the organic compounds, producing materials as acid proteins. In the plant economy they take an essential part in promoting growth and aiding the plant to secure by osmotic action its mineral food from the soil. Organic acids are found to some extent in animal foods, as the various lactic acids of meat and milk. They are also formed in food materials as the result of ferment action. When seeds germinate, small amounts of carbohydrates are converted into organic acids. In general the organic acids are not to be considered as nutrients, but as food adjuncts, increasing palatability and promoting digestion.

15. Essential Oils.—Essential or volatile oils differ from fats, or fixed oils, in chemical composition and physical properties.[6] The essential oils are readily volatilized, leaving no permanent residue, while the fixed fats are practically non-volatile. Various essential oils are present in small amounts in nearly all vegetable food materials, and the characteristic flavor of many fruits is due to them. It is these compounds which are used for flavoring purposes, as discussed in Chapter IV. The amount in a food material is very small, usually only a few hundredths of a per cent. The essential oils have no direct food value, but indirectly, like the organic acids, they assist in promoting favorable digestive action, and are also valuable because they impart a pleasant taste. Through poor methods of cooking and preparation, the essential oils are readily lost from some foods.

16. Mixed Compounds.—Food materials frequently contain compounds which do not naturally fall into the five groups mentioned,—carbohydrates, pectose substances, fats, organic acids, and essential oils. The amount of such compounds is small, and they are classed as miscellaneous or mixed non-nitrogenous compounds. Some of them may impart a negative value to the food, and there are others which have all the characteristics, as far as general composition is concerned, of the non-nitrogenous compounds, but contain nitrogen, although as a secondary rather than an essential constituent.

17. Nutritive Value of Non-nitrogenous Compounds.—The non-nitrogenous compounds, taken as a class, are incapable alone of sustaining life, because they do not contain any nitrogen, and this is necessary for producing proteid material in the animal body. They are valuable for the production of heat and energy, and when associated with the nitrogenous compounds, are capable of forming non-nitrogenous reserve tissue. It is equally impossible to sustain life for any prolonged period with the nitrogenous compounds alone. It is when these two classes are properly blended and naturally united in food materials that their main value is secured. For nutrition purposes they are mutually related and dependent. Some food materials contain the nitrogenous and non-nitrogenous compounds blended in such proportion as to enable one food alone to practically sustain life, while in other cases it is necessary, in order to secure the best results in the feeding of animals and men, to combine different foods varying in their content of these two classes of compounds.[7]

NITROGENOUS COMPOUNDS

18. General Composition.—The nitrogenous compounds are more complex in composition than the non-nitrogenous. They are composed of a larger number of elements, united in different ways so as to form a much more complex molecular structure. Foods contain numerous nitrogenous organic compounds, which, for purposes of study, are divided into four divisions,—proteids, albuminoids, amids, and alkaloids. In addition to these, there are other nitrogenous compounds which do not naturally fall into any one of the four divisions.



Also in some foods there are small amounts of nitrogen in mineral forms, as nitrates and nitrites.

19. Protein.—The term "protein" is applied to a large class of nitrogenous compounds resembling each other in general composition, but differing widely in structural composition. As a class, the proteins contain about 16 per cent of nitrogen, 52 per cent of carbon, from 6 to 7 per cent of hydrogen, 22 per cent of oxygen, and less than 2 per cent of sulphur. These elements are combined in a great variety of ways, forming various groups or radicals. In studying the protein molecule a large number of derivative products have been observed, as amid radicals, various hydrocarbons, fatty acids, and carbohydrate-like bodies.[8] It would appear that in the chemical composition of the proteins there are all the constituents, or simpler products, of the non-nitrogenous compounds, and these are in chemical combination with amid radicals and nitrogen in various forms. The nitrogen of many proteids appears to be present in more than one form or radical. The proteids take an important part in life processes. They are found more extensively in animal than in plant bodies. The protoplasm of both the plant and animal cell is composed mainly of protein.

Proteids are divided into various subdivisions, as albumins, globulins, albuminates, proteoses and peptones, and insoluble proteids. In plant and animal foods a large amount of the protein is present as insoluble proteids; that is, they are not dissolved by solvents, as water and dilute salt solution. The albumins are soluble in water and coagulated by heat at a temperature of 157 deg. to 161 deg. F. Whenever a food material is soaked in water, the albumin is removed and can then be coagulated by the action of heat, or of chemicals, as tannic acid, lead acetate, and salts of mercury. The globulins are proteids extracted from food materials by dilute salt solution after the removal of the albumins. Globulins also are coagulated by heat and precipitated by chemicals. The amount of globulins in vegetable foods is small. In animal foods myosin in meat and vitellin, found in the yolk of the egg, and some of the proteids of the blood, are examples of globulins. Albuminates are casein-like proteids found in both animal and vegetable foods. They are supposed to be proteins that are in feeble chemical combination with acid and alkaline compounds, and they are sometimes called acid and alkali proteids. Some are precipitated from their solutions by acids and others by alkalies. Peas and beans contain quite large amounts of a casein-like proteid called legumin. Proteoses and peptones are proteins soluble in water, but not coagulated by heat. They are produced from other proteids by ferment action during the digestion of food and the germination of seeds, and are often due to the changes resulting from the action of the natural ferments or enzymes inherent in the food materials. As previously stated, the insoluble proteids are present in far the largest amount of any of the nitrogenous materials of foods. Lean meat and the gluten of wheat and other grains are examples of the insoluble proteids. The various insoluble proteids from different food materials each has its own composition and distinctive chemical and physical properties, and from each a different class and percentage amount of derivative products are obtained.[1] While in general it is held that the various proteins have practically the same nutritive value, it is possible that because differences in structural composition and the products formed during digestion there may exist notable differences in nutritive value. During digestion the insoluble proteids undergo an extended series of chemical changes. They are partially oxidized, and the nitrogenous portion of the molecule is eliminated mainly in the form of amids, as urea. The insoluble proteins constitute the main source of the nitrogenous food supply of both humans and animals.

20. Crude Protein.—In the analysis of foods, the term "crude protein" is used to designate the total nitrogenous compounds considered collectively; it is composed largely of protein, but also includes the amids, alkaloids, and albuminoids. "Crude protein" and "total nitrogenous compounds" are practically synonymous terms. The various proteins all contain about 16 per cent of nitrogen; that is, one part of nitrogen is equivalent to 6.25 parts of protein. In analyzing a food material, the total organic nitrogen is determined and the amount multiplied by 6.25 to obtain the crude protein. In some food materials, as cereals, the crude protein is largely pure protein, while in others, as potatoes, it is less than half pure protein, the larger portion being amids and other compounds. In comparing the crude protein content of one food with that of another, the nature of both proteids should be considered and also the amounts of non-proteid constituents. The factor 6.25 for calculating the protein equivalent of foods is not strictly applicable to all foods. For example, the proteids of wheat—gliadin and glutenin—contain over 18 per cent of nitrogen, making the nitrogen factor about 5.68 instead of 6.25. If wheat contains 2 per cent of nitrogen, it is equivalent to 12.5 per cent of crude protein, using the factor 6.25; or to 11.4, using the factor 5.7. The nitrogen content of foods is absolute; the protein content is only relative.[9]

21. Food Value of Protein.—Because of its complexity in composition, protein is capable of being used by the body in a greater variety of ways than starch, sugar, or fat. In addition to producing heat and energy, protein serves the unique function of furnishing material for the construction of new muscular tissue and the repair of that which is worn out. It is distinctly a tissue-building nutrient. It also enters into the composition of all the vital fluids of the body, as the blood, chyme, chyle, and the various digestive fluids. Hence it is that protein is required as a nutrient by the animal body, and it cannot be produced from non-nitrogenous compounds. In vegetable bodies, the protein can be produced synthetically from amids, which in turn are formed from ammonium compounds. While protein is necessary in the ration, an excessive amount should be avoided. When there is more than is needed for functional purposes, it is used for heat and energy, and as foods rich in protein are usually the most expensive, an excess adds unnecessarily to the cost of the ration. Excess of protein in the ration may also result in a diseased condition, due to imperfect elimination of the protein residual products from the body.[10]

22. Albuminoids differ from proteids in general composition and, to some extent, in nutritive value. They are found in animal bodies mainly in the connective tissue and in the skin, hair, and nails. Some of the albuminoids, as nuclein, are equal in food value to protein, while others have a lower food value. In general, albuminoids are capable of conserving the protein of the body, and hence are called "protein sparers," but they cannot in every way enter into the composition of the body, as do the true proteins.

23. Amids and Amines.—These are nitrogenous compounds of simpler structure than the proteins and albuminoids. They are sometimes called compound ammonia in that they are derived from ammonia by the replacement of one of the hydrogen atoms with an organic radical. In plants, amids are intermediate compounds in the production of the proteids, and in some vegetables a large portion of the nitrogen is amids. In animal bodies amids are formed during oxidation, digestion, and disintegration of proteids. It is not definitely known whether or not a protein in the animal body when broken down into amid form can again be reconstructed into protein. The amids have a lower food value than the proteids and albuminoids. It is generally held that, to a certain extent, they are capable, when combined with proteids, of preventing rapid conversion of the body proteid into soluble form. When they are used in large amounts in a ration, they tend to hasten oxidation rather than conservation of the proteids.

24. Alkaloids.—In some plant bodies there are small amounts of nitrogenous compounds called alkaloids. They are not found to any appreciable extent in food plants. The alkaloids, like ammonia, are basic in character and unite with acids to form salts. Many medicinal plants owe their value to the alkaloids which they contain. In animal bodies alkaloids are formed when the tissue undergoes fermentation changes, and also during disease, the products being known as ptomaines. Alkaloids have no food value, but act physiologically as irritants on the nerve centers, making them useful from a medicinal rather than from a nutritive point of view. To medical and pharmaceutical students the alkaloids form a very important group of compounds.



25. General Relationship of the Nitrogenous Compounds.—Among the various subdivisions of the nitrogenous compounds there exists a relationship similar to that among the non-nitrogenous compounds. From proteids, amids and alkaloids may be formed, just as invert sugars and their products are formed from sucrose. Although glucose products are derived from sucrose, it is not possible to reverse the process and obtain sucrose or cane sugar from starch. So it is with proteins, while the amid may be obtained from the proteid in animal nutrition, as far as known the process cannot be reversed and proteids be obtained from amids. In the construction of the protein molecule of plants, nitrogen is absorbed from the soil in soluble forms, as compounds of nitrates and nitrites and ammonium salts. These are converted, first, into amids and then into proteids. In the animal body just the reverse of this process takes place,—the protein of the food undergoes a series of changes, and is finally eliminated from the body as an amid, which in turn undergoes oxidation and nitrification, and is converted into nitrites, nitrates, and ammonium salts. These forms of nitrogen are then ready to begin again in plant and animal bodies the same cycle of changes. Thus it is that nitrogen may enter a number of times into the composition of plant and animal tissues. Nature is very economical in her use of this element.[5]



CHAPTER II

CHANGES IN COMPOSITION OF FOODS DURING COOKING AND PREPARATION

26. Raw and Cooked Foods Compared.—Raw and cooked foods differ in chemical composition mainly in the content of water. The amount of nutrients on a dry matter basis is practically the same, but the structural composition is affected by cooking, and hence it is that a food prepared for the table often differs appreciably from the raw material. Cooked meat, for example, has not the same percentage and structural composition as raw meat, although the difference in nutritive value between a given weight of each is not large. During cooking, foods are acted upon chemically, physically, and bacteriologically, and it is usually the joint action of these three agencies that brings about the desirable changes incident to their preparation for the table.

27. Chemical Changes during Cooking.—Each of the chemical compounds of which foods are composed is influenced to a greater or less extent by heat and modified in composition. The chemistry of cooking is mainly a study of the chemical changes that take place when compounds, as cellulose, starch, sugar, pectin, fat, and the various proteids, are subjected to the joint action of heat, moisture, air, and ferments. The changes which affect the cellulose are physical rather than chemical. A slight hydration of the cellular tissue, however, does take place. In human foods cellulose is not found to any appreciable extent. Many vegetables, as potatoes, which are apparently composed of cellular substances, contain but little true cellulose. Starch, as previously stated, undergoes hydration in the presence of water, and, at a temperature of 120 deg. C., is converted into dextrine. At a higher temperature disintegration of the starch molecule takes place, with the formation of carbon monoxid, carbon dioxid, and water, and the production of a residue richer in carbon than is starch. On account of the moisture, the temperature in many cooking operations is not sufficiently high for changes other than hydration and preliminary dextrinizing. In Chapter XI is given a more extended account of the changes affecting starch which occur in bread making.

During the cooking process sugars undergo inversion to a slight extent. That is, sucrose is converted into levulose and dextrose sugars. At a higher temperature, sugar is broken up into its constituents—water and carbon dioxide. The organic acids which many fruits and vegetables contain hasten the process of inversion. When sugar is subjected to dry heat, it becomes a brown, caramel-like material sometimes called barley sugar. During cooking, sugars are not altered in solubility or digestibility; starches, however, are changed to a more soluble form, and pectin—a jelly-like substance—is converted from a less to a more soluble condition, as stated in Chapter I. Changes incident to the cooking of fruits and vegetables rich in pectin, as in the making of jellies, are similar to those which take place in the last stages of ripening.

The fats are acted upon to a considerable extent by heat. Some of the vegetable oils undergo slight oxidation, resulting in decreased solubility in ether, but since there is no volatilization of the fatty matter, it is a change that does not materially affect the total fuel value of the food.[11]

There is a general tendency for the proteids to become less soluble by the action of heat, particularly the albumins and globulins. The protein molecule dissociates at a high temperature, with formation of volatile products, and therefore foods rich in protein should not be subjected to extreme heat, as losses of food value may result. During cooking, proteids undergo hydration, which is necessary and preliminary to digestion, and the heating need be carried only to this point, and not to the splitting up of the molecule. Prolonged high temperature in the cooking of proteids and starches is unnecessary in order to induce the desired chemical changes. When these nutrients are hydrated, they are in a condition to undergo digestion, without the body being compelled to expend unnecessary energy in bringing about this preliminary change. Hence it is that, while proper cooking does not materially affect the total digestibility of proteids or starches, it influences ease of digestion, as well as conserves available energy, thereby making more economical use of these nutrients.



28. Physical Changes.—The mechanical structure of foods is influenced by cooking to a greater extent than is the chemical composition. One of the chief objects of cooking is to bring the food into better mechanical condition for digestion.[12] Heat and water cause partial disintegration of both animal and vegetable tissues. The cell-cementing materials are weakened, and a softening of the tissues results. Often the action extends still further in vegetable foods, resulting in disintegration of the individual starch granules. When foods are subjected to dry heat, the moisture they contain is converted into steam, which causes bursting of the tissues. A good example of this is the popping of corn. Heat may result, too, in mechanical removal of some of the nutrients, as the fats, which are liquefied at temperatures ranging from 100 deg. to 200 deg. F. Many foods which in the raw state contain quite large amounts of fat, lose a portion mechanically during cooking, as is the case with bacon when it is cut in thin slices and fried or baked until crisp. When foods are boiled, the natural juices being of somewhat different density from the water in which they are cooked, slight osmotic changes occur. There is a tendency toward equalization of the composition of the juices of the food and the water in which they are cooked. In order to achieve the best mechanical effects in cooking, high temperatures are not necessary, except at first for rupturing the tissues; softening of the tissues is best effected by prolonged and slow heat. At a higher temperature many of the volatile and essential oils are lost, while at lower temperatures these are retained and in some instances slightly developed. The cooking should be sufficiently prolonged and the temperature high enough to effectually disintegrate and soften all of the tissues, but not to cause extended chemical changes.



There is often an unnecessarily large amount of heat lost through faulty construction of stoves and lack of judicious use of fuels, which greatly enhances the cost of preparing foods. Ovens are frequently coated with deposits of soot; this causes the heat to be thrown out into the room or lost through the chimney, rather than utilized for heating the oven. In an ordinary cook stove it is estimated that less than 7 per cent of the heat and energy of the fuel is actually employed in bringing about physical and chemical changes incident to cooking.[13]

29. Bacteriological Changes.—The bacterial organisms of foods are destroyed in the cooking, provided a temperature of 150 deg. F. is reached and maintained for several minutes. The interior of foods rarely reaches a temperature above 200 deg. F., because of the water they contain which is not completely removed below 212 deg. One of the chief objects in cooking food is to render it sterile. Not only do bacteria become innocuous through cooking, but various parasites, as trichina and tapeworm, are destroyed, although some organisms can live at a comparatively high temperature. Cooked foods are easily re-inoculated, in some cases more readily than fresh foods, because they are in a more disintegrated condition.

In many instances bacteria are of material assistance in the preparation of foods, as in bread making, butter making, curing of cheese, and ripening of meat. All the chemical compounds of which foods are composed are subject to fermentation, each compound being acted upon by its special ferment body. Those which convert the proteids into soluble form, as the peptonizing ferments, have no action upon the carbohydrates. A cycle of bacteriological changes often takes place in a food material, one class of ferments working until their products accumulate to such an extent as to prevent their further activity, and then the process is taken up by others, as they find the conditions favorable for development. This change of bacterial flora in food materials is akin to the changes in the vegetation occupying soils. In each case, there is a constant struggle for possession. Bacteria take a much more important part in the preparation of foods than is generally considered. As a result of their workings, various chemical products, as organic acids and aromatic compounds, are produced. The organic acids chemically unite with the nutrients of foods, changing their composition and physical properties. Man is, to a great extent, dependent upon bacterial action. Plant life also is dependent upon the bacterial changes which take place in the soil and in the plant tissues. The stirring of seeds into activity is apparently due to enzymes or soluble ferments which are inherent in the seed. A study of the bacteriological changes which foods undergo in their preparation and digestion more properly belongs to the subject of bacteriology, and in this work only brief mention is made of some of the more important parts which microoerganisms take in the preparation of foods.

30. Insoluble Ferments.—Insoluble ferments are minute, plant-like bodies of definite form and structure, and can be studied only with the microscope.[1] They are developed from spores or seeds, or from the splitting or budding of the parent cells. Under suitable conditions they multiply rapidly, deriving the energy for their life processes from the chemical changes which they induce. For example, in the souring of milk the milk sugar is changed by the lactic acid ferments into lactic acid. In causing chemical changes, the ferment gives none of its own material to the reacting substance. These ferment bodies undergo life processes similar to plants of a higher order.



All foods contain bacteria or ferments. In fact, it is impossible for a food stored and prepared under ordinary conditions, unless it has been specially treated, to be free from them. Some of them are useful, some are injurious, while others are capable of producing disease. The objectionable bacteria are usually destroyed by the joint action of sunlight, pure air, and water.

31. Soluble Ferments.—Many plant and animal cells have the power of secreting substances soluble in water and capable of producing fermentation changes; to these the term "soluble ferments," or "enzymes," is applied. These ferments have not a cell structure like the organized ferments. When germinated seed, as malted barley, is extracted, a soluble and highly nitrogenous substance, called the diastase ferment, is secured that changes starch into soluble forms. The soluble ferments induce chemical change by causing molecular disturbance or splitting up of the organic compounds, resulting in the production of derivative products. They take an important part in animal and plant nutrition, as by their action insoluble compounds are brought into a soluble condition so they can be utilized for nutritive purposes. In many instances ferment changes are due to the joint action of soluble and insoluble ferments. The insoluble ferment secretes an enzyme which induces a chemical change, modified by the further action of the soluble ferment. Many of the enzymes carry on their work at a low temperature, as in the curing of meat and cheese in cold storage.[14]

32. General Relationship of Chemical, Physical, and Bacteriological Changes.—It 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.—Foods 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 FOODS

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 Fat Nitrogen-free- Protein 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 ================================================================

[Footnote A: Including a small amount of flesh.]

[Footnote B: From an unpublished compilation of analyses of American food products.]

[Footnote C: Koenig, "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, C{26}H{38}. 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.

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.



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.



CHAPTER IV

FRUITS, FLAVORS, AND EXTRACTS

57. General Composition.—Fruits are characterized by containing a large amount of water and only a small amount of dry matter, which is composed mainly of sugar and non-nitrogenous compounds. Fruits contain but little fatty material and protein. A large portion of the total nitrogen is in the form of amid compounds. Organic acids, as citric, tartaric, and malic, are found in all fruits, and the essential oils form a characteristic feature. The taste of fruits is due mainly to the blending of the various organic acids, essential oils, and sugars. Although fruits contain a high per cent of water, they are nevertheless valuable as food.[20] The constituents present to the greatest extent are sugars and acids. The sugar is not all like the common granulated sugar, but in ripe fruits a part is in the form known as levulose or fruit sugar, which is two and a half times sweeter than granulated sugar. Sugars are valuable for heat-and fat-producing purposes, but not for muscle repairing. Proteids are the muscle-forming nutrients. The organic acids, as malic acid in apples, citric acid in lemons and oranges, and tartaric acid in grapes, have characteristic medicinal properties. The sugar, proteid, and acid content of some of our more common fruits is given in the following table:[21]

COMPOSITION OF FRUITS

============================================================== WATER PROTEIDS SUGAR ACID IN KIND OF JUICE ACID - Per Cent Per Cent Per Cent Per Cent Apples (Baldwin) 85.0 0.50 10.75 0.92 Malic Apples, sweet 86.0 0.50 11.75 0.20 Malic Blackberries 88.9 0.90 11.50 0.75 Malic Currants 86.0 1.96 5.80 Tartaric Grapes 83.0 1.50 10 to 16 1.2 to 5 Tartaric Strawberries 90.8 0.95 5.36 1.40 Malic Oranges 85.0 1.10 10.00 1.30 Citric Lemons 84.0 0.95 2.00 7.20 Citric ==============================================================

In addition to sugars, acids, and proteids, there are a great many other compounds in fruits. Those which give the characteristic taste are called essential or volatile oils.

58. Food Value.—When the nutrients alone are considered, fruits appear to have a low food value, but they should not be judged entirely on this basis, because they impart palatability and flavor to other foods and exercise a favorable influence upon the digestive process. In the human ration fruits are a necessary adjunct.

59. Apples.—Apples vary in composition with the variety and physical characteristics of the fruit. In general they contain from 10 to 16 per cent of dry matter, of which 75 per cent, or more, is sugar or allied carbohydrates. Among the organic acids malic predominates, and the acidity ranges from 0.1 to 0.8 per cent. Apples contain but little protein, less than 1 per cent. There is some pectin, or jelly-like substance closely related to the carbohydrates. The flavor of the apple varies with the content of sugar, organic acids, and essential oils. During storage some apples appear to undergo further ripening, resulting in partial inversion of the sucrose, and there is a slight loss of weight, due to the formation of carbon dioxide. The apple is an important and valuable adjunct to the dietary.[22]



60. Oranges contain nearly the same proportion of dry matter as apples, the larger part of which is sugar. Citric acid predominates and ranges in different varieties from 1 to 2.5 per cent. The amounts of protein, fat, and cellulose are small. In some varieties of oranges there is more iron and sulphur than is usually found in fruits. All fruits, however, contain small amounts, but not as much as is found in green vegetables. The average composition of oranges is as follows:

=========================================================== PHYSICAL COMPOSITION CHEMICAL COMPOSITION OF EDIBLE PORTION - Per Cent Per Cent Rind 20 to 30 Solids 10 to 16 Pulp 25 to 35 Sugars 8 to 12 Juice 35 to 50 Citric acid 1 to 2.5 Ash 0.5 ===========================================================

61. Lemons differ from oranges in containing more citric acid and less sucrose, levulose, and dextrose. The ash of the lemon is somewhat similar in general composition to the ash of the orange, but is larger in amount. The average composition of the lemon is as follows:

=========================================================== PHYSICAL COMPOSITION CHEMICAL COMPOSITION OF EDIBLE PORTION - Per Cent Per Cent Rind 25 to 35 Solids 10 to 12 Pulp 25 to 35 Sugar 2 to 4 Juice 40 to 55 Citric acid 6 to 9 ===========================================================

62. Grape Fruit.—The rind and seed of this fruit make up about 25 per cent, leaving 75 per cent as edible portion. The juice contains 14 per cent solids, of which nearly 10 per cent is sugar and 2.5 per cent is citric acid. There is more acid in grape fruit than in oranges and appreciably less than in lemons. The characteristic flavor is due to a glucoside-like material. Otherwise the composition and food value are about the same as of oranges.



63. Strawberries contain from 8 to 12 per cent of dry matter, mainly sugar and malic acid. The protein, fat, and ash usually make up less than 2 per cent. Essential oils and coloring substances are present in small amounts. It has been estimated that it would require 75 pounds of strawberries to supply the protein for a daily ration. Nevertheless they are valuable in the dietary. It has been suggested that the malic and other acids have antiseptic properties which, added to the appearance and palatability, make them a desirable food adjunct. Strawberries have high dietetic rather than high food value.

64. Grapes contain more dry matter than apples or oranges. There is no appreciable amount of protein or fat, and while they add some nutrients, as sugar, to the ration, they do not contribute any quantity. Their value, as in the case of other fruits, is due to palatability and indirect effect upon the digestibility of other foods. In the juice of grapes there is from 10 to 15 per cent or more of sugar, as sucrose, levulose, and dextrose. Grapes contain also from 1 to 1.5 per cent of tartaric acid, which, during the process of manufacture into wine, is rendered insoluble by the alcohol formed, and the product, known as argole, is used in the preparation of cream of tartar. Differences in flavor and taste of grapes are due to variations in the sugar, acid, and essential oil content.

65. Peaches contain about 12 per cent of dry matter, of which over 10 per cent is sugar and other carbohydrates. There is less than 1.5 per cent of protein, fat, and mineral matter and about 0.5 per cent of acid. The peach contains also a very small amount of hydrocyanic acid, which is more liberally present in the kernel than in the fruit. Flavor is imparted mainly by the sugar and essential oils. Peaches vary in composition with variety and environment.[23]

66. Plums contain the most dry matter of any of the fruits, about 22 per cent, mainly sugar. About one per cent is acid and about 0.5 per cent are protein and ash. There are a great many varieties of plums, varying in composition. Dried plums (prunes) have mildly laxative properties.

67. Olives.—The ripe olive contains about 15 per cent of oil, exclusive of the pit, which makes up 20 per cent of the weight. In green, preserved olives there is considerably less oil. Because of the oil the olive has food value. Olive oil is slightly laxative and assists mechanically in the digestion of foods.

68. Figs.—Dried figs contain about 50 per cent of sugar and 3.5 per cent of protein. The fig has a mildly laxative action.

69. Dried Fruits.—Many fruits are prepared for market by drying. The dried fruit has a slightly different composition from the fresh fruit because of loss of the volatile and essential oils, and minor chemical changes which take place during the drying process. When free from preservatives, dried fruits are valuable adjuncts to the dietary and can be advantageously used when fresh fruits are not obtainable.

70. Canning and Preservation of Fruits.—To obtain the best results in canning, the fruit should not be overripe. After the ripened state has been reached fermentation and bacterial changes occur, and it is more difficult to preserve the fruit than when not so fully matured.[24] When a fruit has begun to ferment, it is hard to destroy the ferment bodies and their spores so as to prevent further ferment action. The chemical changes that occur in the last stages of ripening are similar to those which take place during the cooking process whereby the pectin or jelly-like substances are rendered more soluble and digestible.

71. Adulterated Canned Fruits.—Analyses of a number of canned fruits, made by various Boards of Health, show the presence of small amounts of arsenic, tin, lead, and other poisonous metals. The quantity dissolved depends upon the kind, age, and condition of the canned goods and the state of the fruit when canned. The longer a can of fruit or vegetable has been kept in stock, the larger is the amount of tin or metal that has been dissolved. When fresh canned, there is usually very little dissolved tin, but in old goods the amount may be comparatively large. The tin used for the can is occasionally of poor quality and may contain some arsenic, which also is dissolved. The occasional use of canned goods preserved in tin is not objectionable, but they should not be used continually if it can be avoided. Preservatives, as borax, salicylic acid, benzoic acid, and sodium sulphate, are sometimes added to prevent fermentation and to preserve the natural appearance of the fruit or vegetable.[18]

72. Fruit Flavors and Extracts.—Formerly all fruit extracts and flavors were obtained from vegetable sources; at present many are made in the chemical laboratory by synthetic methods; that is, by combining simpler organic compounds and radicals to produce the material having the desired flavor and odor. The various fruit flavors are definite chemical compounds, and can be produced in the laboratory as well as in the cells of plants. When properly made, there is no difference in chemical composition between the two. As prepared in the laboratory, however, traces of acids, alkalies, and other compounds, used in bringing about the necessary chemical combination, are often present, not having been perfectly removed. Hence it is that natural and artificial flavors differ mainly in the impurities which the artificial flavors may contain.