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Scientific American Supplement, No. 275, April 9, 1881
Various
Scientific American Supplement, No. 275, April 9, 1881
WHEAT AND WHEAT BREAD
In consequence of the interest that has been recently excited on the subject of bread reform, we have, says the London Miller, translated the interesting contribution of H. Mège-Mouriès to the Imperial and Central Society of Agriculture of France, and subsequently published in a separate form in 1860, on "Wheat and Wheat Bread," with the illustration prepared by the author for the contribution. The author says: "I repeat in this pamphlet the principal facts put forth in the notes issued by me, and in the reports furnished by Mr. Chevreul to the Academy of Science, from 1853 up to 1860."
The study of the structure of the wheat berry, its chemical composition, its alimentary value, its preservation, etc., is not alone of interest to science, agriculture, and industry, but it is worthy of attracting the attention of governments, for this study, in its connection to political economy, is bound up with the fate and the prosperity of nations. Wheat has been cultivated from time immemorial. At first it was roughly crushed and consumed in the form of a thick soup, or in cakes baked on an ordinary hearth. Many centuries before the Christian era the Egyptians were acquainted with the means of making fermented or leavened bread; afterwards this practice spread into Greece, and it is found in esteem at Rome two centuries B.C.; from Rome the new method was introduced among the Gauls, and it is found to-day to exist almost the same as it was practiced at that period, with the exception, of course, of the considerable improvements introduced in the baking and grinding.
Since the fortunate idea was formed of transforming the wheat into bread, this grain has always produced white bread, and dark or brown bread, from which the conclusion was drawn that it must necessarily make white bread and brown bread; on the other hand, the flours, mixed with bran, made a brownish, doughy, and badly risen bread, and it was therefore concluded that the bran, by its color, produced this inferior bread. From this error, accepted as a truth, the most contradictory opinions of the most opposite processes have arisen, which are repeated at the present day in the art of separating as completely as possible all the tissues of the wheat, and of extracting from the grain only 70 per cent of flour fit for making white bread. It is, however, difficult for the observer to admit that a small quantity of the thin yellow envelope can, by a simple mingling with the crumb of the loaf, color it brown, and it is still more difficult to admit that the actual presence of these envelopes can without decomposition render bread doughy, badly raised, sticky, and incapable of swelling in water. On the other hand, although some distinguished chemists deny or exalt the nutritive properties of bran, agriculturists, taking practical observation as proof, attribute to that portion of the grain a physiological action which has nothing in common with plastic alimentation, and prove that animals weakened by a too long usage of dry fodder, are restored to health by the use of bran, which only seems to act by its presence, since the greater portion of it, as already demonstrated by Mr. Poggiale, is passed through with the excrement.
With these opinions, apparently so opposed, it evidently results that there is an unknown factor at the bottom of the question; it is the nature of this factor I wish to find out, and it was after the discovery that I was able to explain the nature of brown bread, and its role in the alimentation of animals. We have then to examine the causes of the production of brown bread, to state why white bread kills animals fed exclusively on it, while bread mixed with bran makes them live. We have to explain the phenomena of panification, the operations of grinding, and to explain the means of preparing a bread more economical and more favorable to health. To explain this question clearly and briefly we must first be acquainted with the various substances forming the berry, their nature, their position, and their properties. This we shall do with the aid of the illustration given.
SECTION OF A GRAIN OF WHEAT MAGNIFIED.
EXPLANATION OF DIAGRAM.
ANATOMICAL STRUCTURE AND CHEMICAL COMPOSITION OF WHEAT
The figure represents the longitudinal cut of a grain of wheat; it was made by taking, with the aid of the microscope and of photography, the drawing of a large quantity of fragments, which, joined together at last, produced the figure of the entire cut. These multiplied results were necessary to appreciate the insertion of the teguments and their nature in every part of the berry; in this long and difficult work I have been aided by the co-operation of Mr. Bertsch, who, as is known, has discovered a means of fixing rapidly by photography any image from the microscope. I must state, in the first place, that even in 1837 Mr. Payen studied and published the structure and the composition of a fragment of a grain of wheat; that this learned chemist, whose authority in such matters is known, perfectly described the envelopes or coverings, and indicated the presence of various immediate principles (especially of azote, fatty and mineral substances which fill up the range of contiguous cells between them and the periphery of the perisperm, to the exclusion of the gluten and the starchy granules), as well as to the mode of insertion of the granules of starch in the gluten contained in the cells, with narrow divisions from the perisperm, and in such a manner that up to the point of working indicated by the figure 1 this study was complete. However, I have been obliged to recommence it, to study the special facts bearing on the alimentary question, and I must say that all the results obtained by Mr. Bertsch, Mr. Trécul, and myself agree with those given by Mr. Payen.
ENVELOPES OF THE BERRY
No. 1 represents a superficial side of the crease.
No. 2 indicates the epidermis or cuticle. This covering is extremely light, and offers nothing remarkable; 100 lb. of wheat contain ½ lb. of it.
No. 3 indicates the epicarp. This envelope is distinguished by a double row of long and pointed vessels; it is, like the first one, very light and without action; 100 lb. of wheat contain 1 lb. of it.
No. 4 represents the endocarp, or last tegument of the berry; the sarcocarp, which should be found between the numbers 2 and 3, no longer exists, having been absorbed. The endocarp is remarkable by its row of round and regular cells, which appear in the cut like a continuous string of beads; 100 lb. of wheat contain 1½ lb. of it.
These three envelopes are colorless, light, and spongy; their elementary composition is that of straw; they are easily removed besides with the aid of damp and friction. This property has given rise to an operation called decortication, the results of which we shall examine later on from an industrial point of view. The whole of the envelopes of the berry of wheat amount to 3 lb. in 100 lb. of wheat.
ENVELOPES AND TISSUES OF THE BERRY PROPER
No. 5 indicates the testa or episperm. This external tegument of the berry is closer than the preceding ones; it contains in the very small cells two coloring matters, the one of a palish yellow, the other of an orange yellow, and according as the one or the other matter predominates, the wheat is of a more or less intense yellow color; hence come all the varieties of wheat known in commerce as white, reddish, or red wheats. Under this tegument is found a very thin, colorless membrane, which, with the testa or episperm, forms two per cent. of the weight of the wheat.
No. 6 indicates the embryous membrane, which is only an expansion of the germ or embryo No. 10. This membrane is seen purposely removed from its contiguous parts, so as to render more visible its form and insertions. Under this tissue is found with the Nos. 7, 8, and 9, the endosperm or perisperm, containing the gluten and the starch; soluble and insoluble albuminoids, that is to say, the flour.
The endosperm and the embryous membrane are the most interesting parts of the berry; the first is one of the depots of the plastic aliments, the second contains agents capable of dissolving these aliments during the germination, of determining their absorption in the digestive organs of animals, and of producing in the dough a decomposition strong enough to make dark bread. We shall proceed to examine separately these two parts of the berry.
ENDOSPERM OR FLOURY PORTION, NOS. 7, 8, 9
This portion is composed of large glutinous cells, in which the granules of starch are found. The composition of these different layers offers a particular interest; the center, No. 9, is the softest part; it contains the least gluten and the most starch; it is the part which first pulverizes under the stone, and gives, after the first bolting, the fine flour. As this flour is poorest in gluten, it makes a dough with little consistency, and incapable of making an open bread, well raised. The first layer, No. 8, which surrounds the center, produces small white middlings, harder and richer in gluten than the center; it bakes very well, and weighs 20 lb. in 100, and it is these 20 parts in 100 which, when mixed with the 50 parts in the center, form the finest quality flour, used for making white bread.
The layer No. 7, which surrounds the preceding one, is still harder and richer in gluten; unfortunately in the reduction it becomes mixed with some hundredth parts of the bran, which render it unsuitable for making bread of the finest quality; it produces in the regrinding lower grade and dark flours, together weighing 7 per cent. The external layer, naturally adhering to the membrane, No. 6, becomes mixed in the grinding with bran, to the extent of about 20 per cent., which renders it unsuitable even for making brown bread; it serves to form the regrindings and the offals destined for the nourishment of animals; this layer is, however, the hardest, and contains the largest quantity of gluten, and it is by consequence the most nutritive. We now see the endosperm increasing from the center, formed of floury layers, which augment in richness in gluten, in proportion as they are removed from the center. Now, as the flours make more bread in proportion to the quantity of gluten they contain, and the gluten gives more bread in proportion to its being more developed, or having more consistence, it follows that the flour belonging to the parts of the berry nearest the envelopes or coverings should produce the greatest portion of bread, and this is what takes place in effect. The product of the different layers of the endosperm is given below, and it will be seen that the quantity of bread increases in a proportion relatively greater than that of the gluten, which proves once more that the gluten of the center or last formation has less consistence than that of the other layers of older formation.
The following are the results obtained from the same wheat:
On the whole, it is seen, according to the composition of the floury part of the grain, that the berry contains on an average 90 parts in 100 of flour fit for making bread of the first quality, and that the inevitable mixing in of a small quantity of bran reduces these 90 to 70 parts with the ordinary processes; but the loss is not alone there, for the foregoing table shows that the best portion of the grain is rejected from the food of man that brown or dark bread is made of flour of very good quality, and that the first quality bread is made from the portion of the endosperm containing the gluten in the smallest quantity and in the least developed form.
This is a consideration not to be passed over lightly; assuredly the gluten of the center contains as much azote as the gluten of the circumference, but it must not be admitted in a general way that the alimentary power of a body is in connection with the amount of azote it contains, and without entering into considerations which would carry us too wide of the subject, we shall simply state that if the flesh of young animals, as, for instance, the calf, has a debilitating action, while the developed flesh of full-grown animals–of a heifer, for example–has really nourishing properties, although the flesh of each animal contains the same quantity of azote, we must conclude that the proportion of elements is not everything, and that the azotic or nitrogenous elements are more nourishing in proportion as they are more developed. This is why the gluten of the layers nearest the bran is of quite a special interest from the point of view of alimentation and in the preparation of bread.
THE EMBRYO AND THE COATING OF THE EMBRYO
To be intelligible, I must commence by some very brief remarks on the tissues of vegetables. There are two sorts distinguished among plants; some seem of no importance in the phenomena of nutrition; others, on the contrary, tend to the assimilation of the organic or inorganic components which should nourish and develop all the parts of the plant. The latter have a striking analogy with ferments; their composition is almost similar, and their action is increased or diminished by the same causes.
These tissues, formed in a state of repose in vegetables as in grain, have special properties; thus the berry possesses a pericarp whose tissues should remain foreign to the phenomena of germination, and these tissues show no particularity worthy of remark, but the coating of the embryo, which should play an active part, possesses, on the contrary, properties that may be compared to those of ferments. With regard to these ferments, I must further remark that I have not been able, nor am I yet able, to express in formula my opinion of the nature of these bodies, but little known as yet; I have only made use of the language mostly employed, without wishing to touch on questions raised by the effects of the presence, and by the more complex effects of living bodies, which exercise analogous actions.
With these reservations I shall proceed to examine the tissues in the berry which help toward the germination.
THE EMBRYO (10, see woodcut) is composed of the root of the plant, with which we have nothing to do here. This root of the plant which is to grow is embedded in a mass of cells full of fatty bodies. These bodies present this remarkable particularity, that they contain among their elements sulphur and phosphorus. When you dehydrate by alcohol 100 grammes of the embryo of wheat, obtained by the same means as the membrane (a process indicated later on), this embryo, treated with ether, produces 20 grammes of oils composed elementarily of hydrogen, oxygen, carbon, azote, sulphur, and phosphorus. This analysis, made according to the means indicated by M. Fremy, shows that the fatty bodies of the embryo are composed like those of the germ of an egg, like those of the brain and of the nervous system of animals. It is necessary for us to stop an instant at this fact: in the first place, because it proves that vegetables are designed to form the phosphoric as well as the nitrogenous and ternary aliments, and finally, because it indicates how important it is to mix the embryo and its dependents with the bread in the most complete manner possible, seeing that a large portion of these phosphoric bodies always become decomposed during the baking.
COATING OF THE EMBRYO.–This membrane (6), which is only an expansion of the embryo, surrounds the endosperm; it is composed of beautiful irregular cubic cells, diminishing according as they come nearer to the embryo. These cells are composed, first, of the insoluble cellular tissue; second, of phosphate of chalk and fatty phosphoric bodies; third, of soluble cerealine. In order to study the composition and the nature of this tissue, it must be completely isolated, and this result is obtained in the following manner.
The wheat should be damped with water containing 10 parts in 100 of alcoholized caustic soda; at the expiration of one hour the envelopes of the pericarp, and of the testa Nos. 2, 3, 4, 5, should be separated by friction in a coarse cloth, having been reduced by the action of the alkali to a pulpy state; each berry should then be opened separately to remove the portion of the envelope held in the fold of the crease, and then all the berries divided in two are put into three parts of water charged with one-hundredth of caustic potash. This liquid dissolves the gluten, divides the starch, and at the expiration of twenty-four hours the parts of the berries are kneaded between the fingers, collected in pure water, and washed until the water issues clear; these membranes with their embryos, which are often detached by this operation, are cast into water acidulated with one-hundredth of hydrochloric acid, and at the end of several hours they should be completely washed. The product obtained consists of beautiful white membranes, insoluble in alkalies and diluted acids, which show under the microscope beautiful cells joined in a tissue following the embryo, with which it has indeed a striking analogy in its properties and composition. This membrane, exhausted by the alcohol and ether, gives, by an elementary analysis, hydrogen, oxygen, carbon, and azote. Unfortunately, under the action of the tests this membrane has been killed, and it no longer possesses the special properties of active tissues. Among these properties three may be especially mentioned:
1st. Its resistance to water charged with a mineral salt, such as sea salt for instance
2d. Its action through its presence.
3d. Its action as a ferment.
The action of saltwater is explained as follows: When the berry is plunged into pure water it will be observed that the water penetrates in the course of a few hours to the very center of the endosperm, but if water charged or saturated with sea salt be used, it will be seen that the liquid immediately passes through the teguments Nos. 2, 3, 4, and 5, and stops abruptly before the embryo membrane No. 6, which will remain quite dry and brittle for several days, the berry remaining all the time in the water. Should the water penetrate further after several days, it can be ascertained that the entrance was gained through the part No 10 free of this tissue, and this notwithstanding the cells are full of fatty bodies. This membrane alone produces this action, for if the coatings Nos. 2, 3, 4, and 5 be removed, the resistance to the liquid remains the same, while if the whole, or a portion of it, be divided, either by friction between two millstones or by simple incisions, the liquid penetrates the berry within a few hours. This property is analogous to that of the radicules of roots, which take up the bodies most suitable for the nourishment of the plant. It proves, besides, that this membrane, like all those endowed with life, does not obey more the ordinary laws of permeability than those of chemical affinity, and this property can be turned to advantage in the preservation of grain in decortication and grinding.
To determine the action of this tissue through its presence, take 100 grammes of wheat, wash it and remove the first coating by decortication; then immerse it for several hours in lukewarm water, and dry afterwards in an ordinary temperature. It should then be reduced in a small coffee mill, the flour and middlings separated by sifting and the bran repassed through a machine that will crush it without breaking it; then dress it again, and repeat the operation six times at least. The bran now obtained is composed of the embryous membrane, a little flour adhering to it, and some traces of the teguments Nos. 2, 3, 4, and 5. This coarse tissue-weighs about 14 grammes, and to determine its action through its presence, place it in 200 grammes of water at a temperature of 86°; afterwards press it. The liquid that escapes contains chiefly the flour and cerealine. Filter this liquid, and put it in a test glass marked No. 1, which will serve to determine the action of the cerealine.
The bran should now be washed until the water issues pure, and until it shows no bluish color when iodized water and sulphuric acid are added; when the washing is finished the bran swollen by the water is placed under a press, and the liquid extracted is placed, after being filtered, in a test tube. This test tube serves to show that all cerealine has been removed from the blades of the tissue. Finally, these small blades of bran, washed and pressed, are cast, with 50 grammes of lukewarm water, into a test tube, marked No. 3; 100 grammes of diluted starch to one-tenth of dry starch are then added in each test tube, and they are put into a water bath at a temperature of 104° Fahrenheit, being stirred lightly every fifteen minutes. At the expiration of an hour, or at the most an hour and a half, No. 1 glass no longer contains any starch, as it has been converted into dextrine and glucose by the cerealine, and the iodized water only produces a purple color. No. 2 glass, with the same addition, produces a bluish color, and preserves the starch intact, which proves that the bran was well freed from the cerealine contained. No. 3 glass, like No. 1, shows a purple coloring, and the liquid only contains, in place of the starch, dextrine and glucose, i. e, the tissue has had the same action as the cerealine deprived of the tissue, and the cerealine as the tissue freed from cerealine. The same membrane rewashed can again transform the diluted starch several times. This action is due to the presence of the embryous membrane, for after four consecutive operations it still preserves its original weight. As regards the remains of the other segments, they have no influence on this phenomenon, for the coating Nos. 2, 3, 4, and 5, separated by the water and friction, have no action whatever on the diluted starch. Besides its action through its presence, which is immediate, the embryous membrane may also act as a ferment, active only after a development, varying in duration according to the conditions of temperature and the presence or absence of ferments in acting.
I make a distinction here as is seen, between the action through being present, and the action of real ferments, but it is not my intention to approve or disapprove of the different opinions expressed on this subject. I make use of these expressions only to explain more clearly the phenomena I have to speak of, for it is our duty to bear in mind that the real ferments only act after a longer or shorter period of development, while, on the other hand, the effects through presence are immediate.
I now return to the embryous membrane. Various causes increase or decrease the action of this tissue, but it may be said in general that all the agents that kill the embryous membrane will also kill the cerealine. This was the reason why I at first attributed the production of dark bread exclusively to the latter ferment, but it was easy to observe that during the baking, decompositions resulted at over 158° Fah., while the cerealine was still coagulated, and that bread containing bran, submitted to 212° of heat, became liquefied in water at 104°. It was now easy to determine that dark flours, from which the cerealine had been removed by repeated washings, still produced dark bread. It was at this time, in remembering my experiences with organic bodies, I determined the properties of the insoluble tissue, deprived of the soluble cerealine, with analogous properties, but distinguished not alone by its solid organization and state of insolubility, but also by its resistance to heat, which acts as on yeast. There exists, in reality, I repeat, a resemblance between the embryous membrane and the yeast; they have the same immediate composition; they are destroyed by the same poisons, deadened by the same temperatures, annihilated by the same agents, propagated in an analogous manner, and it might be said that the organic tissues endowed with life are only an agglomeration of fixed cells of ferments. At all events, when the blades of the embryous membrane, prepared as already stated, are exposed to a water bath at 212°, this tissue, in contact with the diluted starch, produces the same decomposition; the contact, however, should continue two or three hours in place of one. If, instead of placing these membranes in the water bath, they are enveloped in two pounds of dough, and this dough put in the oven, after the baking the washed membranes produce the same results, which especially proves that this membrane can support a temperature of 212° Fah. without disorganization. We shall refer to this property in speaking of the phenomena of panification.
