The Chemistry of Food and Nutrition

by A. W. Duncan

What has been called a defect in most fruits, is the fact that the proteid is small in proportion to the other constituents. This has been too much dwelt upon, owing to the prevailing exaggerated idea of the quantity of proteid required. The tomato contains a large proportion, though the water is very high. Bananas, grapes and strawberries contain to each part of proteid from 10 to 12 parts of other solid nutritive constituents (any oil being calculated into starch equivalents); this is termed the nutritive ratio. Although this may seem a small proportion of proteid, there are reasons for believing that it is sufficient. Taking the average of 29 analyses of American apples, a nutritive ratio of 33 was obtained. If it were suggested that life should be sustained on apples alone, this small quantity of proteid would be an insurmountable difficulty. As the addition of nuts or other nutritious food sufficiently increases the proteid, no objection can with justice be made against the use of fruit. A study of our teeth, digestive organs and general structure, and of comparative anatomy, points to fruits, nuts and succulent vegetables as our original diet.

The potash and other salts of the organic acids in fruits tend to keep the blood properly alkaline. Where there is a tendency to the deposition of uric acid in the body, they hinder its formation. Citric, tartaric, malic and other organic acids exist in fruits in combination with potash and other bases, as well as in the free state. The free acids in fruits, when eaten, combine with the alkalies in the intestinal tract, and are absorbed by the body and pass into the blood, not as acids, but as neutral salts. Here they are converted into potassium carbonate or some other carbonate. Fruit acids never make the blood acid but the reverse. Fruit salts and acids are antiscorbutic. Fruits have often proved of the greatest benefit in illness. What is known as the grape cure has been productive of much good. Lemons and oranges have also been of great benefit. Strawberries have been craved for and have proved of the greatest advantage in some extreme cases of illness when more concentrated food could not be endured. Fruit is coming into greater use, especially owing to its better distribution and lessened cost. Fruit is not as cheap as it should be, as it can be produced in great abundance at little cost, and with comparatively little labour. The price paid by the public greatly exceeds the real cost of production. A very large proportion, often the greater part of the cost to the consumer, goes in railway and other rates and in middle-men's profits. It is commonly cheaper to bring fruit from over the sea, including land carriage on either side, than it is to transport English produce from one part of our country to another. English homegrown fruit would be cheaper were it not for the difficulty of buying suitable land at a reasonable price, and the cost of transit. For the production of prime fruit there is a lack of sufficient intelligence, of scientific culture and co-operation.

Vegetables—using the name in its popular sense—contain valuable saline constituents or salts. By the usual method of cooking a large proportion of the salts is lost. It is better to steam than to boil them. The fibrous portion of vegetables is not all digested, but it is useful in stimulating the peristaltic action of the bowels and lessening any tendency to constipation. Vegetables are more especially useful to non-vegetarians to correct the defects of their other food.

The potato belongs to a poisonous order—the Solanacæ. There is a little alkaloid in the skin, but this is lost in the cooking. The eyes and sprouting portions contain the most and should be cut out.

Fungi.—There are about a hundred edible species in this country, but many of the fungi are poisonous, some intensely so. It can scarcely be expected that these lowly organised plants, differing so much in their manner of growth from the green or chlorophyll bearing plants, can be particularly nourishing. It is only the fructifying part, which appears above the ground, that is generally eaten. It is of very rapid growth. Of 9 edible fungi of 4 species, obtained in the Belgrade market, the average amount of water was 89.3 per cent., leaving only 10.7 per cent. of solid matter; the average of fat was 0.55 per cent. The food value of fungi has been greatly over-rated. In most of the analyses given in text-books and elsewhere, the total nitrogen has been multiplied by 6.25 and the result expressed as proteid. The amount of nitrogen in a form useless for the purpose of nutrition is about a third of the whole. Of the remainder or proteid nitrogen, it is said much is not assimilated, sometimes quite half, owing to the somewhat indigestible character of the fungi. An analysis of the common mushroom gave proteids 2.2 per cent., amides (useless nitrogenous compounds) 1.3 per cent., and water 93.7 per cent. The fungi are of inferior nutritive value to many fresh vegetables and are much more expensive. Their chief value is as a flavouring.

Milk and Eggs are permissible in a vegetarian dietary, and as a rule, vegetarians use them. Eggs, with the exception of such as are unfertile, are of course alive; but they have no conscious existence, and cannot be said to suffer any pain on being killed and eaten. An objection to their use as food is, that on an egg and poultry farm, the superfluous male birds are killed, and as the hens become unprofitable layers they are also killed. A similar humane objection applies to the use of cow's milk by man. The calves are deprived of part of their natural food, the deficiency being perhaps made up by unnatural farinaceous milk substitutes. Many of the calves, especially the bull calves, are killed, thus leaving all the milk for human use. When cows cease to yield sufficient milk they too are slaughtered. Milch cows are commonly kept in unhealthy houses, deprived of exercise and pure air, crowded together, with filthy evil smelling floors reeking with their excrements, tended by uncleanly people. With no exercise and a rich stimulating diet they produce more milk; but it is no matter for surprise that tuberculosis is common amongst them. When the lesions of tubercle (consumption) are localised and not excessive, the rest of the carcase is passed by veterinary surgeons as fit for food; were it otherwise, enormous quantities of meat would be destroyed. As butcher's meat is seldom officially inspected, but a very small part is judged by the butchers as too bad for food. In mitigation it may be said that poultry lead a happy existence and their death is, or should be, quickly produced with but little pain, probably less pain than if left to die from natural causes. The same cannot be said of cattle and sheep when the time arrives for their transport to the slaughter man's. It is argued by vegetarians who take milk and animal products that they are not responsible for the death of the animals, as they do not eat their flesh. As vegetarians profit by conditions in which the slaughtering of the animals is a part, they cannot be altogether exonerated. Cow's milk is prone to absorb bad odours, and it forms a most suitable breeding or nutrient medium for most species of bacteria which may accidentally get therein. By means of milk many epidemics have been spread, of scarlet fever, diphtheria, cholera, and typhoid. Occasionally milk contains tubercle bacilli from the cows themselves. By boiling, all bacteria, except a few which may be left out of consideration, are destroyed. Such a temperature, however, renders the milk less digestible and wholesome for infants. By heating to 160° F. or 170° F. for a few minutes, such pathogenic germs as are at all likely to be in milk (tubercle, typhoid, diphtheria, &c.) are killed, and the value of the milk is but little affected: this is called Pasteurising. It was until quite recently a common practice to add boric acid, formaldehyde and other preservatives; this has injured the vitality and caused the death of many infants. They have not yet gone quite out of use.

For infants the only satisfactory food is that of a healthy mother. On account of physical defects in the mother, or often for merely selfish reasons, the infant is deprived of its natural food. Many attempts have been made to bring cow's milk to approximately the same composition as human milk. It can be done by adding water, milk sugar and cream of known composition, in certain proportions. Great difficulties are met with when this is put into practice. The simplest method is that of Professor Soxhlet. The proper quantity of milk sugar is added, but instead of adding the right quantity of cream or fat—a very difficult thing to do—the equivalent quantity of extra milk sugar is used. Although not theoretically satisfactory, in practice it answers very well. We have found it to agree very well with infants. To cow's milk of pure average quality, add half its volume of water containing 12.3 per cent. of milk sugar; or, what amounts to the same thing, to a pint of cow's milk add one and a quarter ounce of milk sugar and half-a-pint of water. It is preferable to Pasteurise by placing the bottle of milk in a vessel of water. This water is to be heated until the milk shows a temperature of about 75° C. or 165° F., but must not exceed 80° C. or a change in the albumen of the milk takes place which affects its digestibility. Keep at this temperature for about ten minutes. If not required at once, a plug of cotton wool should be placed in the neck of the bottle, and it should be kept in a cold place until required. Professor Soxhlet does not advise the addition of lime water. The proteids are not of the same composition as in human milk (the calf being a ruminating animal)—and it is a common plan to add water or barley water to milk until it is so watered down that it cannot curdle into tough curds. An infant has thus either to distend its stomach with a large quantity of watery nourishment, or else to get insufficient food. Sometimes it is necessary to peptonise the milk a little. At the Leipzig infants hospital, and also the Hygienic Institute, they give to infants, up to 9 months old, Prof. Soxhlet's mixture, except that an equal volume of water is added to the milk. Milk, cheese, and especially hen's eggs contain a very large proportion of proteid. When added to food poor in proteid they improve its nutritive quality. It has often been said, and with truth, that some vegetarians by the profuse use of animal products, consume as much, or even more proteid of animal origin than the average person who includes flesh food in his dietary. An excess of proteid from these sources is less injurious as eggs contain no purins, and milk but a very small quantity. In support of the use of animal products, it may be said that we have become so fond of animal foods and stimulating drinks, that the use of milk, butter, cheese and eggs renders the transition to a dietary derived from the vegetable kingdom much easier. By means of these, cooked dishes can be produced which approach and sometimes can scarcely be distinguished from those of cooked flesh.

In the present state of society, when really good vegetarian fare is difficult to procure away from home, eggs, cheese, and milk are a great convenience.

Digestion.—The digestive juices contain certain unorganised ferments, which produce chemical changes in the food. If the food is solid, it has to be liquefied. Even if already liquid it has generally to undergo a chemical change before being fitted for absorption into the body. The alimentary canal is a tubular passage which is first expanded into the mouth, and later into the stomach. As the food passes down, it is acted upon by several digestive juices, and in the small intestine the nutritive matter is absorbed, whilst the residue passes away.

The saliva is the first digestive juice. It is alkaline and contains a ferment called ptyalin. This acts energetically on the cooked and gelatinous starch, and slowly on the raw starch. Starch is quite insoluble in water, but the first product of salivary digestion is a less complex substance called soluble-starch. When time is allowed for the action to be completed, the starch is converted into one of the sugars called maltose. In infants this property of acting on starch does not appear in effective degree until the sixth or seventh month, and starch should not be given before that time. Only a small quantity should be provided before the twelfth month, when it may be gradually increased. Dr. Sims Wallace has suggested that the eruption of the lower incisors from the seventh to the eighth month, was for the purpose of enabling the infant—in the pre-cooking stage of man's existence—to pierce the outer covering of fruits so as to permit his extracting the soluble contents by suction; and accordingly when these teeth are cut we may allow the child to bite at such vegetable substances as apples, oranges, and sugar cane. Dr. Harry Campbell says that starch should be given to the young, "not as is the custom, as liquid or pap, but in a form compelling vigorous mastication, for it is certain that early man, from the time he emerged from the ape till he discovered how to cook his vegetable food, obtained practically all his starch in such a form. If it is given as liquid or pap it will pass down as starch into the stomach, to setup disturbance in that organ; while if it is administered in a form which obliges the child to chew it properly, not only will the jaws, the teeth, and the gums obtain the exercise which they crave, and without which they cannot develop normally, but the starch will be thoroughly insalivated that much of it will be converted within the mouth into maltose. Hard well baked crusts constitute a convenient form in which to administer starch to children. A piece of crust may be put in the oven and rebaked, and spread with butter. Later, we may give hard plain biscuits." Dr. Campbell continues, that he does not say that starch in the pappy form, or as porridge, should find no place whatever in man's dietary at the present day, but we should arrange that a large proportion of our food is in a form inviting mastication.