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66. Composition.—The following table gives the minimum, maximum and average analyses of 310 American grown samples of grain and seven samples of wheat straw:1
67. Water.—The analyses sho .v chat wheat contains ten to eleven per cent of water. This represents the moisture in the samples as analyzed, often after they have stood in the dry room of the laboratories. What percentage of water wheat contains as it goes on the market cannot be stated, but it has been shown to vary largely from day to day with varying conditions of the atmosphere. In California, where the atmosphere inland is very dry at harvest, this subject is a matter of considerable commercial importance. It is claimed that the moisture that this California wheat will absorb during a voyage from San Francisco to Liverpool will sometimes increase its weight enough to pay the entire cost of freight. Wheat bought inland and kept in warehouses all the season would increase in a similar manner upon exposure.
Experiments by Hilgard and O'Neil, of the University of California, indicated that wheat of the inland of California might increase twenty-five per cent in weight by the absorption of water when transported to a temperate climate, while a gain of five to fifteen per cent might be looked for with absolute certainty. A difference of nine per cent was observed in twenty-four hours. Brewer found a difference of from five to
1 U. S. Dept. of Agr., Office of Exp. Stations E. S. B. 11.
eight per cent of water in wheat in a room in which the moist air of New Haven circulated in September and in February when the room was heated by a furnace. Richardson found that two days were sufficient to equalize the moisture in samples of flour which originally varied from less than eight to over thirteen per cent. Afterward the water in the samples fluctuated with the humidity of the air.
68. Ash.—Lawes and Gilbert give the average composition of the ash of the grain and straw of wheat on an unmanured plat during twenty years as follows:1
Fifty per cent more phosphoric acid than potash is laid up in the grain, while in the straw five times as much potash as phosphoric acid is accumulated. A relatively large amount of magnesia is stored in the grain, while relatively more lime is to be found in the straw. More than two-thirds of the ash of straw is silica. Formerly it was held that the silica helped to stiffen the straw. This view is no longer held, since the accumulation of silica is greater in the upper portion of the stem.
It has been shown that the ash constituents of normally ripened seeds of wheat are remarkably uniform, but vary some
» Jour. Am. Chem. Soc. VoL XLV (1888), p. 100.
what with the season, as does the nitrogen, on account of irregularities in the ripening of the seed, and only slightly on account of different modes of manuring except in cases of abnormal soil exhaustion. From three plats manured as indicated in the table below, Lawes and Gilbert found the average annual yield of total mineral constituents during sixteen years to be as follows:1
Where ammonium salts alone were used the grain showed exhaustion both of potash and phosphoric acid—especially the latter, while in the straw there was a marked deficiency of the former.
69. Protein.—In 310 analyses of American grown wheats compiled to September 1st, 1890, the protein (N x 6.25) varied from 8.1 to 17.2 per cent, with an average of 11.9 per cent in samples containing an average of 10.5 per cent water, or in other words, the protein was 13.3 per cent of the dry matter of the grain. Koenig reports the range in protein of the wheat grain from various parts of the world to be from five to twentyfour per cent, but that seventy-five per cent of all analyses fall within eight to fourteen per cent.2
The nitrogenous compounds of wheat consist principally, if not wholly, of proteids, of which five have been recognized and studied by Osborne and Voorhees as follows:8 (1) a globulin, 0.6-0.7 per cent of the grain; (2) an albumin, 0.3-0.4 per cent; (3) a proteose, 0.2-0.4; (4) gliadin, 4.25 per cent; and (5) glutenin, 4-4.5 per cent. (71, 72)
1 Jour. Am. Chem. Soc. Vol. XLV (1888), p. 20. 2 U. S. Dept. of Agr., Div. of Chem. Bui. 4, p. 69.
« The Proteids of the Wheat Kernel. By Thomas B. Osborne and Clark C Voorhees. Am. Chem. Jour. XV (1893), pp. 392-471.
70. Gluten.—Wheat flour has the property in common only with rye flour of forming a dough when mixed with water which on leavening and baking produces a porous bread. This is due to the gluten which imprisons the carbonic acid gas caused by the fermentive action of the yeast. The gas expanding during leavening and during baking causes the bread to become porous.
Gluten is a mixture of gliadin and glutenin and may be obtained in a crude state from wheat meal or flour, by washing the dough made by kneading the meal with water, which removes starch and other non-gluten compounds. Moist gluten contains about sixty-six per cent of water and certain other impurities which are in fairly constant proportions in different samples. A good gluten has a light yellow color, is tenacious and elastic, while poor gluten is dark in color, is sticky but not elastic.
"The gliadin with water forms a sticky medium, which by the presence of salts is prevented from becoming wholly soluble. This medium binds together the particles of flour, rendering the dough and gluten tough and coherent. The glutenin Imparts solidity to the gluten, evidently forming a nucleus to which the gliadin adheres and from which it is consequently not washed away by water. Gliadin and starch mixed in the proportion pf 1:10 form a dough, but yield no gluten, the gliadin being washed away with the starch. The flour freed from gliadin gives no gluten, there being no binding material to hold the particles together so that they may be brought into a coherent mass.
"Soluble salts are also necessary in forming gluten, as in distilled water gliadin is readily soluble. In water containing salts it forms a very viscid, semi-fluid mass, which has great power to bind together the particles of flour. The mineral constituents of the seeds are sufficient to accomplish this purpose, for gluten can be obtained by washing a dough with distilled water."
The amount and quality of gluten—especially the latter—is what gives the flour its baking qualities. The quality of the gluten is due in part at least to the proportion of gliadin and glutenin. M. E. Fleurent states that the most favorable ratio of glutenin to gliadin is twenty-five of the former to seventy-five of the latter. He gives analyses of two varieties which are in the ratio of 23 : 77 and 30 : 70 respectively, and suggests that
the breadmaking value of the flour may in such cases be increased by mixing in proper proportions the wheat or the flour made therefrom.1 Snyder states that the most valuable wheats for breadmaking are those in which eighty to eightyfive per cent of the protein is gluten and the gluten is composed of thirty-five to forty per cent glutenin and sixty to sixty-five per cent gliadin. He reports a variety of wheat from India with a ratio of 27 :73 and one from the Argentine Republic with a ratio of 58 :42.2 The value of a flour depends, therefore, more relatively upon the quality of the gluten than upon the per cent of the nitrogenous compounds contained.
71. Gliadin.—With water containing salts or mineral matter gliadin is a plastic substance which may be drawn out into sheets or strings. By proper chemical manipulation it may be reduced to a snow-white powder. When distilled water is added to this powder it becomes sticky, but if a ten per cent solution of salt (sodium chloride) is added, it is non-adhesive, although plastic. Gliadin is soluble in distilled water, very soluble in seventy to eighty per cent alcohol, but is insoluble in water containing salts or in absolute alcohol. It is soluble in dilute acid and alkalis and may, therefore, be soluble in wheats that have undergone fermentation.
72. Glutenin.—Is the proteid which is left after dissolving the gliadin from the gluten with dilute alcohol. It is distinguished from gliadin by its lesser solubility, its darker color, and by being non-adhesive and non-plastic. It is insoluble in water, saline solutions and dilute alcohol, but is soluble in dilute acids and alkalis, from which it may be precipitated by neutralization. 3
73. Relation of Weight Per Bushel to Nitrogen Content.—
The usual and commercial standard of quality in wheat is the weight per bushel, high weight being associated with qualities desired by the miller. The following table gives the results of eight favorable seasons for wheat and eight unfavorable seasons with three conditions of fertility at Rothamsted:4
1 Compt. Rend. Acad. Sci., Paris, 126 (1898), No. 22, pp. 1592-1595.
2 The Chemistry of the Wheat Plant, pp. 276-277.
8 The Proteids of the Wheat Kernel. By Thomas B. Osborne and Clark C. Voorhees. Am. Chem. Jour. XV (1893), pp. 470-471.
* Lawes, Sir J. B., and J. H. Gilbert. On the composition of the ash of wheat, grain and straw, grown at Rothamsted in different seasons and by different manures. London (1884), pp. 105.