Food, its composition and preparation; a textbook for classes in household science

Front matter

! iSOO )

Class Z3ZiL515^

Book IIL7

Preface

In presenting this book for the consideration of the public, the authors are well aware of the present very general practice of furnishing all necessary instructions and theory to Domestic Science classes through the medium of notes taken by the students. Indeed it is to the conviction, resulting from long experience with the problem, of the futility and inefficiency of this practice that the book owes its origin. Much of the time thus spent by the teacher in dictating, and by the student in writing, can and ought to be saved for more profitable use.

It is questionable whether the advantages derived from note taking by elementary classes are as great as popularly supposed; certainly they do not compensate for the amount of valuable experience in the broader applications of the subject that is lost when the time is thus used. Moreover, notes taken hurriedly, as under the conditions of the class room, are often incorrectly copied, and the girl's attention is unfortunately fixed upon the mechanical process of getting down all that the teacher has said, rather than upon the comprehension of what has been said.

It is believed by the authors that, if the subject is to be taught with any degree of uniformity throughout a large school or in a city where there are several teachers supposedly presenting the same subject matter, there should be some common material that may be put directly in the hands of the pupils for home study.

The text is an elaboration of the notes dictated by the authors to their own High School classes. It is designed

iii iv PREFACE

to supplement the laboratory work and to bring to the pupils a clearer conception of the relation between the cost of foods and their nutritive value.

No recipes are given for the reason that, after close association with many Domestic Science teachers, the conclusion has been reached that each one has her own special recipes and considers no others quite so good. Again, the tendency of the age is to get away from the teaching of hard and fast rules for doing things and to teach, rather, the application of well-defined principles. The general adoption of a card catalogue system for the purpose of filing recipes makes a cook book unnecessary.

No attempt has been made to deal with such matters as setting the table, table service or table etiquette, as it is believed that these can be taught satisfactorily only by actual demonstration and practice. The subject of special diets for invalids and infants is omitted as coming more properly within the scope of a treatise in dietetics.

In studying foodstuffs, it has been the experience of the writers that a consideration of the simple compound water, made up of but two elements, is the natural starting point from which the pupils may be carried by easy stages to a consideration of the more complex compounds.

A vocabulary of the subject has been inserted in the course, as familiarity with the commoner technical terms will be found of great assistance to a clear understanding of the chapters that follow.

Mary T. Dowd.

Jean D. Jameson.

New York.

Chapter I Page

Introductory 1

Definition of Food. — Classification of Foods. — Food as a Source of Energy. — How Food is Like the Body Tissue. — Composition of Foodstuffs. — Tests for Foodstuffs. — Function of Foodstuffs in the Body, — Purposes of Cooking. — Processes of Cooking. — Digestion. — Absorption. — Assimilation.

Chapter II

Composition. — Kinds of Water. — Function of Water in the Body. — W T ater in Food. — Water as a Cooking Medium.

CHAPTER III Carbohydrate in the Form of Sugar 12

Composition. — Monosaccharides. — Disaccharides. — Function of Sugar in Nutrition. — Digestion of Sugar. — Commercial Sugar. — Molasses. — Maple Sugar. — Honey. — Effects of Cooking Sugar.

Chapter IV

Composition. — Source and Structure. — Food Value. — Function in the Body. — Tests for Starch. — Cooking of Starch. — Cellulose. — Digestion and Food Value of Cellulose. — Dextrin. — Glycogen. — Some Unusual Forms of Starch. — Tapioca, Sago, and Arrowroot.

Chapter V

Cereals as Breakfast Foods. — Wheat. — Oats. — Indian Corn. — Rice. — Buckwheat. — Barley. — Rye. — Digestibility of Cere-

VI CONTEXTS

PAGE

als. — Cooking of Cereals. — Macaroni. Spaghetti, and Noodles. — Use of Double Boiler. — The Fireless Cooker. — The Thermos Bottle. — The Pressure Cooker.

Chapter VI

Definition. — Leavening Agents. — Baking Powders. — Classification of Flour Mixtures. — Hot or Quick Breads. — Cakes. — Sponge Cakes. — Butter Cakes.

CHAPTER VII Fl<>tr Mixtures — Bread and Pastry 53

Varieties of Wheat. — The Protein of Wheat. — Milling of Flour. — Yeast Bread. — Bread Mixer. — Kinds of Yeast. — Function of Yeast in Bread Making. — Digestibility of Bread. — How to Know Good Bread. — Pastry. — Digestibility of Pastry.

Chapter VIII

Definition. — Classification of Vegetables. — Composition and Food Value of Vegetables. — Digestion of Vegetables. — Selection and Care. — Cooking of Vegetables. — Preserving Vegetables. — Legumes. — Food Value. — Cooking. — Soy Bean. — Tubers. — The Dasheen. — Bulbs, Leaves. Stems, and Shoots. — Fruits. — Flower Buds. — Digestion and Food Value of Green Vegetables.

CHAPTER IX Fruits 77

Definition. — Composition. — Digestibility. — Selection of Fruit. — Preparation and Cooking. — Dried Fruits. — Xuts. — Food Value of Xuts. — Use of Xuts in Cooking.

CHAPTER X Fats and Oils S

Composition. — Properties. — Function of Fats in Nutrition. — Digestibility. — Sources of Fats. — Cooking in Fats. — Preparation of Fats.

CONTENTS vii

Chapter XI Page

Milk 90

Value as Food. — Composition. — Digestibility. — The Care of Milk.— Skim Milk.— Sour Milk.— Certified Milk.— Pasteurized Milk.— Sterilized Milk.— Condensed Milk.— Milk Powder.— Modified Milk.— Malted Milk. — Milk in Cooking- Milk Products. — Butter and Cheese.

CHAPTER XII Eggs 97

Structure. — Composition and Food Value. — Digestibility. — Selection and Care. — Preparation and Cooking.

Chapter XIII

Structure. — Kinds. — Composition. — Digestion of Meat. — Food Value of Meat. — Selection of Meat. — Cooking of Meat. — Methods of Preserving Meat. — Cuts of Beef. — Cuts of Veal. — Sweetbreads. — Cuts of Lamb and Mutton. — Cuts of Pork. — Internal Organs Used as Food. — Gelatin.

CHAPTER XIV Poultry and Game 114

Definition. — Composition and Food Value. — Selection. — Picking. — Chickens. — Turkeys. — Ducks and Geese. — Squab and Guinea Fowl. — Preparation and Cooking of Poultry.

CHAPTER XV Fish 118

Quality and Flavor. — Composition. — Digestibility of Fish. — How to Choose Fish. — Cooking of Fish. — Ways of Preserving. — Common Food Fish. — Specially Prepared Fish. — Unusual Types of Fish Recommended by the Bureau of Fisheries. — Shell Fish. — Oysters. — Clams. — Mussels. — Lobsters. — Crabs. — Shrimps . — Terrapin .

viii CONTENTS

Chapter XX

Planning Meals. — Per Cent of Income for Food. — Food for Adults ajid Children. — Cost of Food. — Balanced Meals. — Variety in Diet, — The ^Esthetic Considerations. — Desirable. Foods.— Food Combinations. — Suggestions for Planning Meals — Sample Meals Showing the Approximate Number of Calories Furnished.

Chapter XXI

Why Foods Spoil.— Ways of Preserving Foods.— Canning by the Open Kettle Method.— The One-Period Cold Pack Method.— Intermittent Sterilization. — Use of Preservatives — Kinds of Preservatives. — Drying of Fruits and Vegetables.

Glossary *65

FOOD

ITS COMPOSITION AND PREPARATION

Chapter I Introductory

1. Definition of Food. — Food is any substance which, when taken into the body, is capable of building body substance, yielding energy, or regulating body processes.

2. Classification of Foods. — Foods may be classified as organic and inorganic. The organic foods, as the name implies, are derived from an organism, which organism may be a plant or an animal. As organic foods serve the purpose of replacing tissues which have been oxidized (burned) they themselves must be oxidizable.

Inorganic foods serve to replace tissue which has not been oxidized; they are water and mineral substances and are not oxidizable.

3. Food as a Source of Energy. — A plant has the power of taking carbon dioxide from the air, and with the aid of the light and heat of the sun, combining it with water from the soil, thus forming such compounds as starch, sugar and protein. Heat is absorbed during the process; therefore, when these compounds are oxidized in the body, they decompose into their original constituents, at the same time liberating the same amount of heat as was absorbed during their formation. This liberated heat is the source of all body energy.

2 FOOD

While animals cannot make use of such simple substances as are found in the air and the earth, they can use such substances when they have been transformed by the plant. The animals, in their turn, convert the simple substances into more complex substances which man designates as animal food.

4. How Food is Like the Body Tissues. — If food is to build body tissue, it must bear some likeness to that tissue. As this likeness docs not lie in appearance it must in composition, and chemical analysis shows this to be the case. Food and the body tissues are made up of similar elements and compounds.

The elements are: Oxygen, hydrogen, nitrogen, carbon, sulphur, phosphorus, chlorine, sodium, potassium, calcium, magnesium, iron, fluorine, silicon, and iodine.

The compounds arc: Water, fat, carbohydrates, protein, and mineral matter. These compounds, when spoken of in connection with food, are called foodstuffs and must not be confused with food materials, such as eggs, meat, cereals, etc.

5. Composition of Foodstuffs.— Water is composed of the two elements oxygen and hydrogen.

Fat is composed of the three elements oxygen, hydrogen, and carbon.

Carbohydrates j which include starch and sugar, are composed of the same three elements that form fat, but in the carbohydrates the oxygen and hydrogen occur in the proper proportion to form water.

Water, fat, and carbohydrates are the first of the great foodstuffs which the plant manufactures from the simple inorganic compounds.

Proteins are the most complex of all the foodstuffs. They contain, in addition to the three elements found in fats and carbohydrates, other elements, the chief of which are nitrogen and sulphur. The nitrogen occurs in simpler substances called amino acids, and these by different combinations form the various proteins.

INTRODUCTORY 3

Mineral Matter includes such chemical elements as iron, calcium, magnesium, potassium, sodium, chlorine, sulphur, and phosphorus. Some of these occur as elements while others are found only in combination; some occur in organic material while others exist only in their inorganic form.

6. Tests for Foodstuffs.— Water may be detected in food by heating a small amount of the food in a test tube. Drops of water will form on the sides of the tube.

Starch may be detected by adding to the food, or a solution of the food, a few drops ol iodine. The material will turn blue if starch is present.

Sugar may be detected by boiling a small portion of the food in water and then adding Folding's solution.* A reddish brown precipitate is formed if sugar is present.

Fat may be deleted in the following way: stir some of the food with ether or benzine, allow it to stand ten minutes, then filter it and allow the ether to evaporate. The fat will remain.

Protein may be detected by the use of nitric acid and ammonia. The substance turns yellow if protein is present.

Mineral Matter may be detected by burning a sample of the food. The residue which will not burn is mineral matter.

7. Functions of the Foodstuffs in the Body. — The function of water in the body is to build tissue and regulate body processes.

The chief function of fat is to yield energy, but it may be stored in the body as fatty tissue.

The chief function of carbohydrate is to supply energy to the body, but it may furnish building material also.

The chief function of protein is to build tissue, but it may also furnish energy.

The chief function of mineral matter is to furnish building material and to regulate body processes.

Vitamines are substances essential to growth and nerve activity.

* Fehling's solution is copper sulphate, Rochelle salts, and caustic soda.

4 FOOD

8. The Means by which Food is Made Available. — Food, in order to become available to the body, must undergo certain physical and chemical changes. These changes are brought about by such processes as cooking, digestion, absorption, and assimilation.

Cooking is the preparation of food by the aid of heat. Such foods as milk, eggs, and certain fruits and vegetables may be eaten without cooking, but this is possible only because they have previously been subjected to a process similar to cooking. In the cases of the first two the heat coming from the body of the animal really did the cooking, and in the third the heat from the sun during the process of ripening performed the same operation.

9. Purposes of Cooking. — Cooking is necessary for three distinct purposes:

1. To kill micro-organisms.

2. To make the food more digestible.

3. To improve and develop flavor in the food.

10. Processes of Cooking. — The different methods of applying heat to food arc known as processes of cooking, and are:

1. Boiling. — Cooking in boiling water or at a temperature of 212° F.

2. Broiling. — Cooking directly over or under a flame.

3. Pan-broiling. — Cooking on a very hot frying pan without any fat.

4. Baking. — Cooking in a hot oven.

5. Roasting. — Cooking in a very hot oven.

6. Frying. — Cooking in sufficient hot fat to cover the food.

7. Sauteing. — Cooking in a frying pan in a small amount of fat.

8. Steaming. — Cooking over steam.

(a) Dry, as in a double boiler.

(b) Moist, as in a steamer.

INTRODUCTORY

-Cooking in water below the boiling-point,

-A combination of stewprocess of changing pii —

10. Braising (or pot roasting;. ing and baking.

11. Fricasseeing. — A combination of stewing and sauteing.

11. Digestion. — Digest ion is the insoluble foods to soluble. This process takes place in that part of the body known as the alimentary canal, Fig. 1. This canal measures from twenty to twentyfive feet in length. Into this canal is poured secretions from such organs as the salivary gland-, the pancreas, and the liver, all of which aid in the work of digestion.

The parts of the alimentary canal are the mouth, the oesophagus, the stomach, the small intestine, and the large intestine.

12. Work of the Alimentary Canal. — Each part of the alimentary canal has its special work to do and is furnished with mechanical and chemical agents for accomplishing its task. The foodstuffs are acted upon chemically in different parts of the canal.

The Month..- — In the mouth all food is acted upon mechanically by the teeth, which grind it, and by the saliva, which moistens it.

The starchy foods are further

acted upon chemically by an enzyme called ptyalin, which is found in the saliva, and which has the power of changing

Fig. 1. — Front view of the digestive orgjjj.

a, r } e, colon ;

d, duct of the srall bladder;

a, gall bladdi

i, small intestine;

/, i :, liver;

o, e, esophagus;

p, n, pancreas;

st, stomach.

6 FOOD

the insoluble starch into a form of sugar called maltose. From the mouth the food passes through the oesophagus into the stomach.

The Stomach. — In the stomach the food is kept in motion by the muscular walls, which by their churning bring all the food in contact with the gastric juice. The connective tissue of meat is here dissolved, and the meat fibres loosened. The walls of fat cells are also dissolved, as well as certain mineral salts such as phosphate of lime. The protein foods are acted upon chemically by two enzymes found in the gastric juice. The first of these, pepsin, has the power of changing, in the presence of hydrochloric acid, the nondialyzable proteins into dialyzable peptones. The second enzyme, rennin, coagulates the caseinogen of milk, which is a necessary change before the milk can be digested by the pepsin. It is thought by some that a third enzyme is present in the gastric juice which acts upon emulsified fats.

After the food has remained in the stomach from one to five hours the mass is reduced to a grayish, semi-liquid state in which condition it is known as chyme, and begins to pass in small amounts into the small intestine.

The Small Intestine. — Here the food comes in contact with the pancreatic juice, an important digestive fluid furnished by the pancreas; with the bile, a fluid manufactured by the liver; and with the intestinal juice, which is secreted by the glands that line the small intestine.

Pancreatic juice contains three enzymes: trypsin, amylopsin, and steapsin or lipase. The trypsin acts upon any proteins which may have escaped the action of the pepsin; the amylopsin acts upon undigested starch, changing it into maltose even more quickly than the ptyalin can; and the lipase serves to emulsify fats and to some extent break them up into fatty acids and glycerin. The action of the bile is to help in the absorption of fats and by its alkalinity to counteract the acidity of the chyme.

The intestinal juice has no special action except upon the

INTRODUCTORY 7

sugars, converting maltose into grape sugar. After the food has been acted upon by the various fluids in the small intestine, it changes from acid clrymc into alkaline chyle, in which condition much of it is absorbed. Food which is by nature indigestible, or which has been made so by improper cooking, passes from the small intestine into the large.

The Large Intestine. — While the large intestine has no enzyme of its own, the walls furnish a fluid which helps to complete digestive changes which have already begun. Absorption takes place here to some extent and the residue of the food is here evacuated from the body.

13. Absorption. — Much of the digested food is absorbed from the small intestine. All the digested carbohydrate and protein foods are taken up by the epithelial cells, and the fats are taken by the lacteals or lymph vessels. These are tiny thread-like tubes which convey the fats to the thoracic duct, lying in front of and to one side of the back bone. From there the fats are poured into the blood stream. The other foods are absorbed by the blood capillaries which carry them by the portal system to the liver and thence to the heart to be sent with the blood to nourish all parts of the body.

14. Assimilation. — Assimilation is the process by which each part of the body works over into its own substance material derived from the food eaten.

Chapter II Water

15. Composition. — In composition water is the simplest of the foodstuffs, as it is made up of but two elements, oxygon and hydrogen.

While water is not capable of yielding energy because it contains no unoxidized hydrogen, its function in the body is c>f such vital importance that it must l>e considered most essential.

16. Kinds of Water. — Water is hard or soft, according to the amount of mineral matter present in it. The hardness oi some water is due to the presence of lime salts which, if in excess, may interfere with the general health. These salts may be eliminated by boiling the water. This process will drive off the carbon dioxide which holds the carbonates in solution and the lime will he precipitated. Boiling also removes organic impurities. To remove the insipid taste which results from boiling, the water, after having been cooled, may be shaken vigorously.

17. Functions of Water in the Body. — Water serves as building material, two-thirds of the body weight being made up of water. It gives firmness and elasticity to the tissues and constitutes four-fifths of the blood.

Water acts as a great solvent in the body, carries nutriment to all the tissues, and conveys the effete matter to the organs through which it is eliminated. It also keeps the Quids of the body in their liquid state.

Water acts as a body regulating substance and a stimulant; particularly is it important in the digestive tract where experiment has shown that the production of hydro-

S chloric acid in the stomach is greatly accelerated after drinking a glass of water. There is proof also that water aids digestion by acting as a diluent on certain digestive juices, thereby increasing their solvent power.

18. Amount of Water Required. — The amount of water which the body requires varies and is dependent upon the surrounding temperature, the amount of muscular activity indulged in, and the nature of the food eaten.

One of the most prevalent dietary errors is the use of too little water in the diet. The daily requirement is approximately four pints. About one-fourth this amount is obtained from the food eaten.

19. Water in Food. — All foods, no matter how dry they may appear to be, contain some water, and some vegetables, such as asparagus, contain as high as 94 per cent of water. The keeping quality of all foods depends largely upon the amount of water they contain. Foods containing more than 20 per cent of water cannot be stored, owing to their tendency to mold. Flour or cereals that are to be kept any length of time must not contain higher than 10 to 12 per cent of water.

TABLE I.— FOODS HAVING A HIGH WATER CONTEXT

Weight in ounces of the 100-calorie portion

Watermelon 28| ozs.

Cucumbers 20 \ ozs.

Celery 19 ozs.

Lettuce 18| ozs.

Muskmelon 18 ozs.

Asparagus 16 ozs.

Rhubarb 15 \ ozs.

Tomatoes 14i ozs.

Egg plant 14£ ozs.

Spinach 14f ozs.

Radishes 12 ozs.

Peaches 10§ ozs.

Cabbage, l\\ ozs.

Buttermilk 9| ozs.

10 FOOD

20. Water as a Cooking Medium. — Water is necessary in the preparation of food and for this purpose soft water is preferable.

All foods are not cooked at the same temperature, and the degree of heat must be adapted to the food in question. If water is raised slowly to the boiling-point, the following changes will be observed. Tiny bubbles will appear on the bottom and sides of the vessel but will break before reaching the surface. These bubbles are caused by the air and gases which have been confined in the water being driven off by the heat (it is the loss of these which causes the flat taste of boiled water). As the temperature rises, the bubbles in the water will become larger and more nearly spherical and will reach the surface before they break. At this point the water is said to boil, and a thermometer introduced into it will register 212° F. or 100° C; for an open vessel at sea level, no matter how rapidly the water may boil, the temperature, under ordinary conditions, will rise no higher, the surplus heat being used to convert the water into steam.

21. Raising the Boiling-point. — The boiling-point of water may be raised: (1) By increasing the pressure — for example boiling in a confined space, as in a steam boiler under a pressure of five pounds of steam, when the water will not boil until it reaches 227° F.

(2) By increasing the density — for example a very strong salt solution will not boil until it reaches 22G° F., and a sugar solution may have a boiling-point between 215° and 350° F.

22. Lowering the Boiling-point. — The boiling-point of water is lower than 212° F. when the pressure of the atmosphere is less than fifteen pounds to the square inch. In high altitudes, as in Denver, Colorado, water boils at a temperature of 202° F., and on some points in the Himalaya Mountains it boils at a temperature as low as 180° F. Under such conditions it is difficult to properly cook foods which require a high temperature.

Experiment 1. To Show the Effect of Boiling on Hard Water. — ■ Half fill a beaker with lime water. Blow through a glass tube into the water until it loses its cloudy appearance and becomes clear. (This shows that excess of carbon dioxide keeps lime in solution.) Boil this water and notice the deposit of carbonate of lime on the bottom and sides of the beaker. Add a little acid to this deposit and observe the effervescence that takes place.

Half fill an evaporating dish with water from the faucet. Let it evaporate over a Bunsen burner, and test the residue as in the above experiment.

Experiment 2. To Show Effect of Density on the Boiling-point of Water. — -(a) Boil water, taking the temperature.

(b) Boil a saturated salt solution and take the temperature.

Experiment 3. To Show the Rapidity of Evaporation. — Put the same amount of water in each of two vessels; one deep and exposing but little surface, the other shallow and exposing a large surface. Boil both slowly and observe in which vessel the water boils away first.

Chapter III Carbohydrate In The Form Of Sugar

23. Composition. — Carbohydrate foodstuffs are a combination of the three elements, carbon, hydrogen, and oxygen. The hydrogen and oxygen are present in the common foods of this class in the proportion to form water.

For purposes of more thorough study, the carbohydrates are sometimes divided into three main groups according to their molecular weight.

Group 1. Monosaccharides. — These comprise simple sugars which cannot be split into other sugars of the same or simpler form. They are: glucose, fructose, and galactose.

Group 2. LHsaccharides. — These comprise the complex sugars which may be split into two simple sugars. They include: sucrose, maltose, and lactose.

Group 3. Polysaccharides. — These are substances which yield an unknown number of simple sugars. Included in the group are: starch, dextrin, and glycogen.

24. Monosaccharides. — Monosaccharides are soluble crystalline substances which are absorbed into the blood stream without further change.

The members of this group have the common formula of C6H12O6. The source and distinguishing characteristics of each of the simple sugars will be considered in turn.

Glucose, sometimes called dextrose, is the most important of the simple sugars as it is in this form that sugar appears in the blood. Normal blood contains about 0.1 per cent of glucose which is being burned continually to produce body energy. Any surplus of glucose absorbed from the digestive tract is stored in the body as glycogen, which is

CARBOHYDRATE IN THE FORM OF SUGAR 13

in turn reconverted into glucose to be burned as needed for energy.

Fructose, or levulose, like glucose, is found as such in some plants and vegetables and in large quantities in honey.

Galactose is of considerable importance in nutrition since it is a product of the digestion of milk. It is utilized in the formation of glycogen in the liver.

25. Disaccharides. — The disaccharides are complex sugars having a formula of C12H22O11. They are soluble substances and are changed to simple sugars in the process of digestion.

Sucrose, or cane sugar, is found in nature in the juices of certain plants. Sugar cane and the sugar beet yield large quantities of sucrose and form the chief sources of the commercial sugars.

Maltose is formed from starch by the action of acids and enzymes. Maltose also occurs in malt and malt extracts.

Lactose, or sugar of milk, is found in the milk of mammals. It is obtained for commercial use from the whey of milk after the curd has been removed in the making of cheese. Lactose is not easily fermented and is, therefore, used in modifying cow's milk for infants.

26. Polysaccharides. — Polysaccharides are complex substances. They are considered at length in Chapter IV.

27. Functions of Sugar in Nutrition. — (1) As a Source of Energy. The chief function of sugar in nutrition is to supply energy to the body. It is especially well adapted for use as an energy producer because it is ready for almost immediate absorption into the blood stream. Theoretically, sugar is not essential in a modern dietary where starches are used, since all starches are changed to sugar in the process of digestion. It is recommended that sugar be used in small amounts for flavoring and to give variety to the diet rather than as a source of energy.

(2) As a building material. Sugar, in the form of galac-

14 FOOD

tose, is found in the growth stimulating part of the nerve cells. An excess of sugar in the system is converted into fat and stored in the body substances.

(3) As a body regulating substance. Without carbohydrate, fat cannot burn normally in the body. In other words, fat must burn in a flame of carbohydrate. Unless the calories furnished by carbohydrate exceed those furnished by fat, an abnormal condition of nutrition known as acidosis is liable to obtain. This condition is caused by the presence of acid in the body substances rather than in the blood.

28. Digestion of Sugar. — There is no ferment or digestive juice in the body that acts upon the monosaccharides, glucose, fructose, and galactose. These substances are absorbed from the intestines without further change, and pass into the portal vein by which they are carried to the liver. Some of this sugar is changed to glycogen and stored in the liver, and the rest is passed on through the blood stream to the tissues, where it is burned to CO2 and HoO to yield energy for work, or is stored in the muscular tissue as glycogen or fat.

In the case of the complex sugars or disaccharides, there is no digestive action in the mouth or in the stomach, but the intestinal membrane secretes a substance known as succus entericus, or intestinal juice, containing the three enzymes, sucrose, maltose, and lactase, which act in turn upon the disaccharides and change these double sugars into two single sugars as follows: