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قراءة كتاب The Chemistry of Food and Nutrition
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that wheatmeal he ground as finely as possible, the coarse is not only to a less extent assimilated but apt to irritate the bowels. Notwithstanding that fine white bread gave only 4.2 per cent. and a coarse white bread 4.9 per cent. of waste, a fine wheatmeal bread is more economical as the same quantity of wheat produces a greater weight of flour richer in proteid and mineral matter. From a large number of experiments with man, it has been calculated that of proteids there is digested when animal food is eaten 98 per cent., from cereals and sugars 8 per cent., from vegetables and fruits 80 per cent. The difference between the proportions digested of the other food constituents was much less. Although there is here a theoretical advantage in favour of animal food, there are other considerations of far more importance than a little undigestible waste. The main question is one of health. In some dietary experiments of a girl aged 7, living upon a fruit diet, of whom we have given some particulars elsewhere, Professor Jaffa gives the following particulars. During the ten days trial the percentages absorbed were proteids 82.5, fat 86.9, nitrogen free extract 96, crude fibre 80, ash 5.7, heat of combustion in calories 86.7. He says, "generally speaking, the food was quite thoroughly assimilated, the coefficients of digestibility being about the same as are found in an ordinary mixed diet. It is interesting to note that 80 per cent. of the crude fibre appeared to be digested. The results of a number of foreign experiments on the digestibility of crude fibre by man are from 30 to 91.4 per cent., the former value being from mixed wheat and rye, and the latter in a diet made of rice, vegetables and meat."
NOTES ON THE TABLE OF ANALYSIS.—Under calories are shown kilo-calories per pound of food. In the analysis marked U the crude fibre or cellulose is included with the carbo-hydrate, the figures being those given in Atwater's table. He has found that from 30 to 91 per cent. of the crude fibre was digested, according to the kind of food. The term fibre or cellulose in analytical tables is not a very definite one. It depends upon the details of the method of analysis. In the analyses other than U, the cellulose is excluded in calculating the calories. Nutrient ratio is the proportion of the sum of the carbo-hydrate and fat, compared with the proteid as 1. The fat has first been multiplied by 2.225 to bring it to the same nutrient value as the carbo-hydrate.
U indicates that the analyses are taken from the United States Department of Agriculture Experimental Station, Bulletin 28, the tests being chiefly made by Dr. W.O. Atwater, or under his direction. They are average analyses of several samples. The refuse consists of such parts as are rejected in preparing the food; the outer leaves, skin, stalk, seeds, &c., of vegetables; the shell of eggs; the bone, &c., of meat. E, indicates that the edible portion only of the food has been analysed, and under refuse, in brackets, is shown the quantity rejected before the analysis was made.
There is considerable variation in the same kind of food, according to the variety of seed and conditions of growth &c., especially is this the case with wheat and flour; whenever it has been possible the average of the analyses of many samples have been given. The method of analysis has not always been uniform, frequently the cellulose is included with the carbo-hydrates, and the proteid sometimes includes a very appreciable quantity of non-proteid nitrogenous matter. This is the case in the analysis of the mushrooms. G.—Analyses are by John Goodfellow; it will be noticed that the wheatmeal bread is not made from the same flour as the whole-meal. D.—B. Dyer, average of 19 fine and coarse oatmeals. S, from U.S. Cons. Reports, 1899. C.—A.H. Church. The walnut kernels are in the dried condition as purchased; originally of the same composition as shewn in the fresh kernels. C.D.—Cavendish or Figi variety of banana, analysis by D.W.M. Doherty, N.S. Wales. P.—A. Petermann, U.S. Cons. Banana flour, musca paradisiaca variety. This is widely used in Central America. The flour is from the unripe fruit, and contains starch 45.7 per cent.; on ripening the starch is converted into sugar. K.—Konig, mean of 90 analysis. Milk:—Average of many thousand analyses of the pure. Butter.—Made without salt. L, from the "Lancet," 1903, I, p. 72. Oysters at 2/6 per dozen. The 8.09 per cent. includes 0.91 glycogen (animal starch). The shell was of course excluded, also the liquid in the shell. Apples.—The refuse includes seeds, skin, &c., and such edible portion as is wasted in cutting them away; the analysis was made on the rest.
Cookery.—Flesh is easier to digest raw. A few, on the advice of their doctors, eat minced raw flesh, raw beef juice and even fresh warm blood. Such practice is abhorrent to every person of refinement. Cooking lessens the offensive appearance and qualities of flesh and changes the flavour; thorough cooking also destroys any parasites that may be present. Raw flesh is more stimulating to the animal passions, and excites ferocity in both man and animals. If the old argument was valid, that as flesh is much nearer in composition and quality to our own flesh and tissues, it is therefore our best food, we do wrong in coagulating the albuminoids, hardening the muscle substance and scorching it by cooking.
Fruits when ripe and in good condition are best eaten raw; cooking spoils the flavour. Food requiring mastication and encouraging insalivation is the best. Food is frequently made too sloppy or liquid, and is eaten too hot, thus favouring indigestion and decay of the teeth. The cereals and pulses can only with difficulty be eaten raw. When cooked in water the starch granules swell and break up, the plant cells are ruptured, the fibres are separated and the nutritious matter rendered easy of digestion. The flavour is greatly improved. Cooking increases our range and variety of food. The civilised races use it to excess and over-season their dishes, favouring over-eating.
If baking powders are used they should only be of the best makes. They should be composed of sodium bicarbonate and tartaric acid, in such correct proportions that upon the addition of water only sodium tartrate and carbon dioxide (carbonic acid) should result. Some powders contain an excess of sodium bicarbonate. Self-raising flours should be avoided. They are commonly composed of—in addition to sodium bicarbonate—acid calcium phosphate, calcium superphosphate and calcium sulphate. Common baking powders often consist of the same ingredients, and sometimes also of magnesia and alum. These are often made and sold by ignorant men, whose sole object is to make money. Calcium superphosphate and acid calcium phosphate very frequently contain arsenic, and as the cheap commercial qualities are often used there is danger in this direction. A good formula for baking powder is, tartaric acid 8 ozs., sodium bicarbonate 9 ozs., rice flour 10 to 20 ozs. The last is added to baking powders to improve the keeping quality and to add bulk. The ingredients must be first carefully dried, the sodium bicarbonate at not too high a temperature or it decomposes, and then thoroughly mixed; this must be preserved in well closed and dry bottles. Another formula, which is slow rising and well adapted for pastry, is sodium bicarbonate 4 ozs., cream of tartar 9 ozs., rice flour about 14 ozs. Custard powders consist of starch, colouring and flavouring. Egg powders are similar to baking powders but contain yellow colouring. Little objection can be taken to them if they are coloured with saffron; turmeric would do if it were not that it gives a slightly unpleasant taste. Artificial colouring matters or coal tar derivatives are much used, several of these are distinctly