What happens in the chemical sense in this neutralizing process is nicely illustrated by the formation of common salt from hydrochloric acid and caustic soda, also called sodium hydroxid. When these two substances are dissolved in water, and the solutions mixed, the chemical action is as follows:

HCL +  NaOH = H₂O    + NaCl
Hydrochloric acid  +  Caustic soda   = Water  + Common salt
  (Muriatic acid)     (Sodium hydroxid) (Sodium chloride)

The strong hydrochloric acid with its pungent odor and sour taste, and the caustic alkali with its equally characteristic properties have both disappeared, Common examples of neutralization and in their place we find nothing more wonderful than common salt dissolved in water. Other forms of neutralization that are very common are vinegar (acetic acid C₂H₄O₂) and soda, or sour milk (lactic acid C₃H₆O₃) and soda. When bread is "sour," we mean that there was not enough soda to neutralize the acid.

PRINCIPLES OF NEUTRALIZING ALKALIS

If we should try many experiments of neutralizing alkalis with acids, we would discover these general rules:

1 All acids contain hydrogen.

2 All alkalis contain oxygen and hydrogen in equal proportions.

3 When these substances react, the hydrogen of the acid joins the hydrogen of the base or alkali, forming water, H₂O.

4 The metal of the base always replaces the hydrogen of the acid.

2KOH + H₂SO₄ = K₂SO₄ + 2H₂O
Potassium hydroxid  + Sulfuric acid  = Potassium Sulfate + Water
    (alkali or base) (acid) (Salt)

(In the above equation the potassium (K) of the potassium hydroxid replaces the Hydrogen (H) in the sulfuric acid.)

5 The other elements of the original compounds unite to form a new substance, which is neither acid nor alkali, but which is termed a salt.

The names of a few common acids, bases and salts, and their chemical formulas, are given here, as many of them will be important in the pursuance of this work.

Acids

Bases

(Ammonia gas dissolved in water produces this alkali.) The equation for this is as follows:

NH₃ +   H₂O  +     NH₄OH
(Ammonia) gas + Water + Ammonium hydroxid

Salts

Fluorin, Bromin, Iodin—These three elements are in many respects like chlorin. The first is a gas, the second a heavy, Formation of salts in the human body reddish-brown liquid at ordinary temperature, and the third a dark, grayish crystalline solid. These elements all form acids just as chlorin forms hydrochloric acid. These acids produce salts, and these various salts exist in small quantities in the human body.

Mineral Sulfur—This element is of no particular importance or use to the body, as it is insoluble and cannot be digested. The compounds of sulfur, however, are numerous and important. Sulfuric acid, sometimes called oil of vitriol, is one of the most active chemicals known, and is especially destructive to living tissue, as it combines with the water in the tissue so rapidly as to char or burn it.

When sulfur is burned in air it forms sulfur dioxid, SO₂, which is used for the purpose of fumigation or destroying alleged dis-ease germs. This SO₂ dissolved in water gives H₂SO₃, sulfurous acid. By oxidizing this another part of oxygen is added, forming H₂SO₄. All three of these compounds are poisonous and harmful.

Hydrogen Sulfid, H₂S, is a poisonous gas with a bad odor. It is formed by the decay of certain food substances, such as eggs. Sometimes this gas occurs in intestinal fermentation.

Carbon Disulfid, CS₂, is used extensively to kill insects. The salts of sulfuric acid, or sulfates, are quite important, and many of them are poisonous. Glauber's salt (sodium sulfate Na₂SO₄) and Epsom salts (magnesium sulfate MgSO₄) are extensively used by the medical profession as purgatives. These poisons cause the intestines to act violently in an effort to throw out the offending substances.

Vegetable Sulfur in the Human Body—I have herein mentioned a number of sulfur compounds which are foreign or harmful to animal life. In wonderful contrast to this is the fact that sulfur is an essential constituent of the human body, and in certain complex compounds with nitrogen and other elements, forms the brain, nerves, and many other body-tissues.

Phosphorus—This element is useful in the manufacture of common matches because it possesses the power to ignite by friction. The things of interest to the food scientist, however, are the salts of phosphoric acid. These enter largely into the bones, and to some extent into the nerves and other organs of the body.

Silicon is the element which, combined with oxygen, forms the greatest part of the rocks and the sand of the solid earth. It forms the shell of certain sea-animals. In the human body it is found in the teeth and in the bones in very small quantities.

Metals—Metals, when united with oxygen and hydrogen, form the bases of nearly all the substances studied in this lesson. When these act with acids they produce the salts. It is these salts of the metals that are of most interest to us. The salts of common metals, such as copper, tin, lead, and iron do not enter into the composition of the human body, and many of these are decidedly poisonous, especially those of copper, lead, mercury, and arsenic.

The metals whose salts are found in the body are sodium, potassium, calcium, and magnesium. These metals in their elementary state are seldom seen outside a chemist's laboratory, but we can judge of their importance when we remember that the digestive juices contain these metals. The teeth and all bony substances are formed from these compounds, and the ability of all body-fluids to carry food material in solution depends upon a definite per cent of these metal salts. The study of minerals, or of mineral salts contained in food, together with their uses in the body, forms an important subdivision of food chemistry.

Iron—Iron is mentioned separately from other metals because it not only yields salts that occur in small quantities in the body, but because, like sulphur, it enters into the complex nitrogenous portions of the body to form part of the living substance itself.

This organic iron, as it is sometimes called, occurs chiefly in the red blood-corpuscles. The patent medicines which are exploited for the iron they contain, are frauds so far as nourishing the body is concerned. The popular deception is caused by the general belief that all compounds containing the same elements are alike in their uses. One might as well swallow iron filings as to endeavor to build red blood corpuscles out of the mineral solution of iron.

LESSON III

ORGANIC CHEMISTRY

CARBON

In this lesson I will consider carbon and carbon compounds, which are the bases of all foods and living matter. I will devote but little attention to theories and technicalities, but will discuss the subject from scientific and practical standpoints.

Wood, flesh, and other products of vegetable or of animal life blacken when heated to a sufficiently high temperature. This blackening is due to the presence of carbon. If such substances are heated with an abundant supply of air, the carbon combines with oxygen and forms a colorless gas; that is, the carbon burns.

The principal form in which carbon occurs in nature is in combination with other elements. It occurs not only in all living things, but in their fossil remains, as in coal. All products of plant life contain carbon, hydrogen, and oxygen. Among the more common of these are sugar, starch, wood, etc. Most products of animal life contain carbon, hydrogen, oxygen, and nitrogen. Among these are albumin, fibrin, casein, etc.

Carbon occurs in the atmosphere in the form of carbon dioxid or carbonic acid gas. It is also found in the earth in the form of salts of carbonic acid or carbonates, such as limestone, marble, and chalk.

The pure element, carbon, is found in nature in the form of diamonds, which are pure crystallized carbon. Small diamonds are now made artificially in electric furnaces. Crystallized carbon also occurs in nature in the form of graphite, from which lead pencils are made. Charcoal, lampblack, and coke are forms of amorphous carbon which contain a very small percentage of impurities.

Notwithstanding the marked difference in their appearance, the various forms of carbon have some properties in common. They are insoluble in all known liquids. They are tasteless, odorless, and infusible at ordinary temperature. When heated without access of air, they remain unchanged unless the temperature is very high, in which case they unite with oxygen and are consumed, forming carbon dioxid.

INORGANIC CARBON COMPOUNDS

CARBON DIOXID (CO₂)

The principal compound of carbon and oxygen is carbon dioxid, often called carbonic acid gas. This gas is always present in the air. It issues from the earth in many places, particularly in the neighborhood of volcanoes. With it many mineral waters are naturally charged.

Carbon dioxid is constantly formed by many natural processes. Every animal that breathes gives off carbon dioxid from its lungs. This gas is also formed whenever ordinary combustible materials are burned. The natural processes of decay of both vegetable and animal matter tend to convert the carbon contained therein into carbon dioxid, which is thrown off and absorbed into the air. The process of alcoholic fermentation, and similar processes, also give rise to the formation of this gas. When fruits ripen, fall, and decay, the sugar, which all fruit-juices contain, is changed to alcohol and carbon dioxid.

RELATION OF CARBON DIOXID TO LIFE

Carbon dioxid is an important factor in the life activity of the earth. The leaves of plants absorb carbon dioxid from the air, and by means of the chemical activity of the green coloring-matter or chlorophyl, the plant has the power of combining the carbon dioxid with water, and with the mineral salts which have been absorbed from the earth by the roots of the plant. Sunlight is necessary to this action, especially in the manufacture of starch.

This formation of food material in plants by the combination of simple chemical substances, such as carbon dioxid and water, is one of the fundamental life-processes. Animals do not possess this power of utilizing simple or inorganic chemical compounds, therefore they must take their food substances in the more complex forms which have been created by the power of sunlight acting upon the plant.

I have already explained how carbon dioxid may enter the air. Thus we see that the carbon dioxid which is withdrawn from the air, by the growth of plants, is constantly replaced by combustion, and in this way the "carbon cycle" is completed. This is one of the most beautiful adaptations in nature. If the plant did not remove the carbon dioxid from the air, it would soon accumulate in such quantities as to become detrimental to life, and, on the other hand, if this gas were not returned to the air by combustion, by the breathing of animals, and by the decay of plants, the vegetable world would soon be without carbon dioxid, which is as essential to plant life as is the oxygen of the air to animal life.

CARBON MONOXID (CO)

This compound is formed when a substance containing carbon is burned in an insufficient supply of air, as for example when the draught is partly shut off in a stove.

Carbon monoxid is a colorless gas. It burns with a blue flame, forming carbon dioxid. The blue flame seen playing over the embers of a coal fire is carbon monoxid burning. This gas is extremely poisonous. Carbon dioxid, CO₂, is not poisonous. The poisonous properties of illuminating gas are due to the carbon monoxid which it contains.

ORGANIC CARBON COMPOUNDS

The carbon compounds thus far considered have been mentioned to illustrate a few of the simpler or inorganic forms of carbon. We will now begin the study of organic chemistry or the compounds of carbon which are commonly found only in plant and animal substances.

Carbon has wonderful powers of combination with other chemical elements, and may combine with the same elements in thousands of different proportions. This property of carbon to form so many different compounds is considered one of the fundamental facts of chemistry upon which life depends. For example:

Carbon and hydrogen compounds

Oxygen can combine with hydrogen in but two proportions—peroxid of hydrogen (H₂O₂) and water (H₂O)—while carbon and hydrogen can combine in more than a hundred different compounds. The simpler of these are acetylene (C₂H₂) and marsh gas or methane (CH₄), which is the fire-damp in mines.

The compounds containing carbon, hydrogen, and oxygen number into the thousands. A great many substances formed in plants contain these three elements, such as fruit-acids, alcohol, sugar, and fats.

CLASSIFICATION OF ORGANIC CARBON COMPOUNDS

Only a few of the most important groups of the organic or life-formed carbon compounds will be considered in this work, namely:

• a Hydrocarbons
• b Alcohols
• c Glycerin
• d Aldehydes and ethers
• e Organic acids
• f Carbohydrates
• g Fats

a HYDROCARBONS

Hydrocarbons are compounds of the two elements carbon and hydrogen. These compounds are very important in industrial chemistry. They are found in petroleum, coal-tar, etc., which were originally formed from decaying and petrifying masses of plants. Gasoline, benzin, naphtha, acetylene, methane, etc., are some of the industrial forms by which hydrocarbons are known in commerce.

The industries based upon the chemistry of these hydrocarbons are very complex and interesting. Coal-tar yields, by repeated distillation and chemical reaction, thousands of compounds, many of which find important industrial usages. Coal-tar dyes are very numerous and of wonderful coloring power. They have been extensively used in the artificial coloring of manufactured foods. The Federal Pure Food Law attempted to prohibit this. In fact, it was the pernicious effect and extensive use of these poisons that stimulated the passage of the "Food and Drugs Act." Another interesting product of the coal-tar industry is saccharin. Saccharin has no food value whatever, but it is 280 times sweeter than cane-sugar, and is therefore used as a substitute in sweetening some prepared foods.

b ALCOHOLS

To the ordinary mind the term alcohol refers only to the intoxicating element in liquors. To the chemist, alcohol has a much broader significance. There are many varieties of alcohols, of which ethyl alcohol (C₂H₅.HO), which is found in liquors, is only one example. Another form of alcohol which is fairly well known is wood or methyl alcohol (CH₃.OH).

There are also higher alcohols, that is, those having more complex chemical formulas, such as butyl alcohol. In the fermentation of grains or fruits for intoxicating liquors, a small quantity of the various higher alcohols is formed. These higher alcohols are more intoxicating and more harmful to the human system than ethyl alcohol, and must be separated from the latter by careful distillation. The poisonous property of green whisky and cheap liquors is generally due to the presence of higher alcohols.

Alcohol does not exist in normal, fresh plant or animal substances except in very minute quantities. It is formed from sugar by fermentation. This fermentation is due to a microscopic yeast-plant.

c GLYCERIN

Another form of alcohol is glycerin (C₃H₈O₃). It is of special interest to the food chemist because it enters into the formation of all fats.

d ALDEHYDES AND ETHERS

These are compounds containing carbon, hydrogen, and oxygen, and are closely related to alcohols. In fact they are formed from alcohols by a process of oxidation, hence contain a little larger proportion of oxygen than the related alcohol.

An example of aldehyde with which many are familiar is formaldehyde, which is used in laboratories for the preservation of animal-tissues for dissection. This formaldehyde is a very strong germicide; that is, it is poisonous to bacteria or germs. For this reason it is used as a preservative of milk, a use which is forbidden by the "Food and Drugs Act," because formaldehyde is also poisonous to the human system.

Ethyl ether, which is used as an anesthetic or to produce insensibility to pain, will serve as an illustration of this group of compounds. When analyzing foods in chemical laboratories, ether is commonly used for dissolving fats.

e ORGANIC ACIDS

It will be remembered that acids were studied in the second lesson. It was found that the common properties of acids are a sour taste, ability to combine with alkalis in the formation of salts, and that all acids contain hydrogen. These same properties that were studied in the second lesson in reference to mineral acids, such as hydrochloric and sulfuric, apply also to the organic acids. The organic acids, however, as a class are not so strong or active as the mineral acids.

All organic acids are compounds of carbon, hydrogen, and oxygen, the same as alcohols and ethers, the chief difference between these compounds and acids being that the acids contain a greater proportion of oxygen. One of the simplest organic acids is formic acid (HCO.OH). This acid is the active principle in the sting of the red ant, and also of stinging nettles. It produces blisters when applied to the skin.

Impure acetic acid (C₂H₄O₂) is very well known to all under the name of vinegar. Acetic acid may be obtained by distilling wood. If it could be manufactured cheaply enough, vinegar made from wood would be fully as wholesome as the best cider vinegars, but this being an expensive process of manufacture, the temptation of the food adulterator is to make the vinegar of sulfuric acid, which is much cheaper than the mild acetic acid, but much more harmful when taken into the body.

The formic and the acetic acids are examples of a series of organic acids known as fatty acids. Other members of the series are—

These fatty acids are very important to the food scientist as they combine with glycerin to form fats. When combined with alkalis under a certain temperature they form soap. Perhaps some of our older students may remember the soap kettle on the farm at home, in which lard cracklings and other fatty fragments of the animal were boiled with lye or caustic potash to form home-made soap. The chemical action that took place was a combination of these fatty acids with the caustic potash or lye. The glycerin was set free and remained in the bottom of the kettle as soft soap. Reference will be made to these acids again, in Lesson IV, where the study of fats will be taken up in detail. (See "Fats and Oils," under Lesson IV, Chemistry of Foods, p. 122).

There are some other forms of organic acids which do not belong in the fatty series; that is, they do not contain the same general proportions of carbon and hydrogen. One of these is oxalic acid (C₂H₂O₄) which is found in certain plants, such as sorrel, and is an active poison. Oxalic acid is used in the household for taking iron-rust out of cloth.

Lactic acid (C₃H₆O₃) is the acid of sour milk. Malic acid (C₄H₆O₅) is found in many fruits such as apples, apricots, currants, pears, plums, prunes, etc. Tartaric acid (C₄H₆O₆) is found principally in grapes. It is one of the constituent elements in the sediment found in wine casks, and is the active principle in cream of tartar. The latter is a potassium salt of tartaric acid.

Citric acid (C₆H₈O₇) is one of the most important of the organic acids from the standpoint of the food chemist. It is the active principle of citrus-fruits, such as grapefruit, lemons, limes, oranges, etc. Lemons contain as high as five per cent of this acid. Citric acid is often used to make lemonade, and if pure citric acid is used, the manufactured product is equal to the original, except from a sentimental standpoint of having the genuine. The danger is, as in the case of adulterated vinegar, that the manufacturer may be tempted to use cheaper mineral acids instead of citric acid.

The other above-named groups of organic compounds which are formed from the three elements carbon, hydrogen, and oxygen—(f) carbohydrates and (g) fats—are very important to the food chemist. These will be considered in detail in Lesson IV. See pages 107-125.

ORGANIC NITROGENOUS COMPOUNDS

If to the three elements carbon, hydrogen, and oxygen, the element nitrogen is added, it still further increases the number of possible compounds that may be formed upon the base of the wonderful carbon atom. With this additional nitrogen factor, a new and a distinct quality is obtained.

The chief characteristic of the element nitrogen is the ease with which its compounds change their chemical form. To quote the chemist, "the compounds of nitrogen are very unstable." Nearly all explosives are nitrogenous compounds. When this element, nitrogen, is combined with the wonderful variety of compounds formed by carbon, we have not only a great many intimately related yet distinct substances, but compounds which readily change from one form to another. These are the distinctive qualities or conditions necessary, from a chemical standpoint, to make the processes of life possible. Protoplasm, which is the basis of all life, is formed by an intimate mixture of a number of complex chemical compounds, the chief elements of which are carbon, hydrogen, oxygen, and nitrogen.

The organic compounds containing nitrogen are very numerous and very interesting. As all tissues and substances of the animal body contain nitrogen as a necessary element, we can see why this group of compounds is of great importance to the student of food science.

Some of the nitrogenous compounds which are not available as nutritive substances, and many of which are poisonous or harmful to animal life, will be considered in Lesson IX, under "Alkaloids and Narcotics." (See Vol. II, p. 349.) The principal nutritive substances, and proteids or compounds containing available food nitrogen, will be considered in Lesson IV.

LESSON IV

CHEMISTRY OF FOODS

The chemistry of carbon compounds and the general composition of plant and of animal substances were discussed in Lesson III. We are now prepared to take up the chemistry of food. The chemistry of food substances will be considered under the common divisions of carbohydrates, fats, proteids, and mineral salts. (See "Classification of Organic Carbon Compounds," Lesson III, p. 89.)

In the food tables and analyses commonly published, the above terms are used with very little explanation, and read by the average person with meager comprehension. When one reads that a food is composed of glucose, citric acid, or globulin, he is likely to become confused, not being able to understand how a food at one time can be said to be composed of carbohydrates, proteids, and fats, and at another time to be composed of other substances. The explanation is that the first classification does not refer to definite chemical substances, but to groups of related compounds having properties in common.

There is still another way of giving the chemical composition of a food, namely, to specify the chemical elements that it contains. It will be remembered that the relation between chemical elements and chemical compounds was explained in the first lesson. As an example, I will take the analysis of milk. We will first say that milk contains a certain percentage of protein, carbohydrates, and fat. We might then say that the proteid of milk is part casein and part albumin, and that the albumin contains certain percentages of oxygen, sulfur, etc.; also that the chief carbohydrate in milk is milk-sugar, which in turn is composed of carbon, hydrogen, and oxygen. Or, we could consider the milk as a whole, without dividing it into groups, and give the per cent of each chemical element in the milk. Thus, the carbon of the proteid, milk-sugar, and fat would be all considered together, and show a certain per cent of carbon in the milk as a whole.

CARBOHYDRATES

The word carbohydrate means carbon combined with water; that is, the element carbon is combined with hydrogen and oxygen, which exist in the carbohydrate compound in the same proportion as they exist in water.

The carbohydrates are closely related chemically to the aldehydes and the alcohols, so far as their composition is concerned (See "Aldehydes and Ethers," Lesson III, p. 93), but this does not imply that they have the same physiological effect in the animal body.

CLASSIFICATION OF CARBOHYDRATES

The carbohydrates are divided by the chemist into three classes known as

• a Monosaccharids
• b Disaccharids
• c Polysaccharids

The principal subdivisions found in these classes of carbohydrate foods are given in the following table, arranged in the order of their importance:

a MONOSACCHARIDS

1 GLUCOSE OR GRAPE-SUGAR (C₆H₁₂O₆)

Glucose or grape-sugar is the most important sugar known from the standpoint of the physiological chemist. This sugar is normally found in considerable quantities in human blood, and is absolutely essential to the life-process, a fact which forms an amusing contrast with the popular conception of the term glucose as something injurious or poisonous.

Glucose is found in honey, and in nearly all fruits, grains, and sweets. (For "Sweets" see Lesson VIII, Vol. II, p. 324). It may be taken into the human body directly from such fruits, or it may originate by the digestion of other carbohydrates.

Pure glucose crystallizes and resembles cane-sugar, but is not so sweet. The glucose of commerce, sold as sirup, is a product manufactured from corn, or other starches, and will be considered more in detail under the heading starch. (See "Polysaccharids," p. 114).

2 PENTOSES (C₅H₁₀O₅)

Pentoses form a group of sugars, the chemical formula of which contains five atoms of carbon. Each different pentose could be studied in detail by the chemist, but the pentoses are of no particular interest to the food scientist. They exist, however, in the coarse parts of plants, such as stalks and leaves, and are of considerable importance in animal feeding. From the standpoint of human food we will remember that the carbohydrates of green plants contain a percentage of these pentoses, but as they are never removed from the plant separately, as are other sugars, we must consider their physiological effect in the particular plant rather than separately.

3 LEVULOSE (C₆H₁₂O₆)

This is the companion sugar to glucose and exists in many fruits. Levulose is often called "fruit-sugar." The composition of levulose is exactly the same as glucose, but the atoms are combined in different ways.

Levulose, for all practical purposes, may be considered the equivalent of glucose in the human body. It is sweeter than glucose and more closely resembles cane-sugar.

4 GALACTOSE (C₆H₁₂O₆)

Galactose, which is of the same composition as levulose, is another companion sugar to glucose, and is formed by the digestion of lactose or milk-sugar.

b DISACCHARIDS

1 CANE-SUGAR (C₁₂H₂₂O₁₁)

Just as there are three monosaccharid sugars with six carbon atoms each, so there are three disaccharid sugars which have twelve carbon atoms each. The first of these is cane-sugar. It is commercially made from either sugar-cane or sugar-beets, and is identical in chemical composition from either source.

Cane sugar, when digested in the human body, or by artificial means, combines with water, and forms glucose and levulose, as shown by the following equation:

   C₁₂H₂₂O₁₁  + H₂O    = C₆H₁₂O₆  + C₆H₁₂O₆
Cane-sugar + Water = Glucose  + Levulose

2 MALTOSE (C₁₂H₂₂O₁₁)

Maltose is the second member of the disaccharid group, and is of the same composition as the other two. Maltose derives its name from malt. It is formed from the starch of grains by a process of digestion which may be performed in the animal body, or by the process of malting. Maltose, like cane-sugar, can be further digested into monosaccharid sugars, but upon such digestion, instead of forming two separate simple sugars, it is wholly converted into glucose.

The reader will now understand the meaning of the terms monosaccharid, disaccharid, and polysaccharid. MONO, which means one, is the simplest form of carbohydrates. Disaccharids (DI, meaning two), split up to form two simple sugars. Polysaccharids (POLY, meaning many) are complex compounds which form many simple sugars.

3 LACTOSE (C₁₂H₂₂O₁₁)

Lactose exists in milk and has the same formula as cane-sugar. Milk contains about five per cent of this sugar.

When lactose is digested it combines with water as does cane-sugar, but instead of yielding glucose and levulose, it yields glucose and galactose.

c POLYSACCHARIDS

1 STARCH

The chemical formula of starch and other polysaccharids is written (C₆H₁₀O₅)n. This means that the proportion of the elements is according to the figures given, but the number of atoms that are supposed to be combined is many times greater than five, and is not accurately known. This is purely theoretical, and of no practical importance, except that it shows that the polysaccharid is capable of being digested or broken up into many simple carbohydrate compounds.

Starch is the most abundant carbohydrate known. It is the chief constituent of all cereals, and is found in large quantities in green fruits and tuberous plants. Starch occurs in small granules, varying greatly in size in different foods.

Potatoes are composed chiefly of starch and water. The starch grains of potatoes can almost be distinguished with the naked eye. These starch granules are not atoms or molecules in the chemical sense, but are small receptacles in which starch has been deposited by the growing plant. When cooked or boiled in water these starch grains swell into a mushy, pasty or gelatinous mass; when cooked in dry heat until they begin to turn brown, they are changed into a compound related to the gum group, known as dextrin.

Starch does not dissolve in water as do sugars. If starch is treated with digestive fluids, such as saliva, or with certain acids, it goes through a complex process of digestion in which it is first turned into soluble starch, then into the various forms of dextrin or gums, and finally into maltose or malt-sugar.