Through the agency of the myrosin, another constituent of brown seed, when the two are brought in contact through the medium of water, we have vegetable albumen, a bitter principle, a little gum and sugar, and a peculiar green substance, cellulose, and mineral water, called sulphocyanide of sinapine.[[8]] The aqueous extract of yellow mustard seed yields with a solution of ferric chloride a deep, blood-red coloration, which is scarcely perceptible with similar extract of black mustard. The aqueous extract of white mustard acquires a powerful odor of sulphurated hydrogen in a few hours, while that of the black seed smells only of the pungent mustard oil.
[8]. Sinapaline sincaline.
White mustard seed contains from 25 per cent. to 35 per cent. of an inodorous fixed oil with a little tendency to become rancid and of little pungency, which it will not give up in water. In place of myronic acid converted into volatile oil of mustard, it contains a non-volatile, bitter and acrid salt termed sulphocyanide of sinapine (C17H24N2SO5 or C16H23NO5CNHS), myrosin gum cellulose and mineral matter. Now, as it is on the volatile oil and the acrid and somewhat bitter salt that the pungency and acridity of mustard depend, we can see a strong reason why in the mustard of commerce the farina of the two species, black and white seed, should be blended together, in the proportion of two parts of white to one of black. The black seed does contain some of the acrid principle as well as the volatile oil, as has been verified by the action of nitric acid, caustic potash, and ferric chloride, on the alcoholic extract. It is, therefore, the most valuable of the two seeds on account of the little volatile oil in the yellow seed. The acrid principle of white mustard appears to possess but little stability, although it has been said to bear a temperature of 130 degrees C. We find that it is readily affected by heat and that it is not safe to evaporate the alcoholic solution containing it at a higher temperature than about 30 degrees C., for, if subjected to a much higher temperature, it quickly loses its acridity and acquires a bitter, caramel-like taste.
The oil extracted by ether from the brown seed is of a bright and beautiful emerald-green color, owing to the peculiar green principle described as one of its constituents. So deep and remarkable is the color of the oil that it would be easy by means of a graduated scale of tints to determine with very tolerable certainty the percentage of brown mustard contained in any sample of mixed mustard. Specific gravity, 1.017; boils at 148 degrees.
Myronate of potash decomposes under the influence of the nitrogenous matter contained in brown mustard into volatile oil, glucose, and acid sulphate of potash. The quantity of each of these products of decomposition gives, therefore, by simple calculation, the quantity of myronic acid; one hundred parts of this acid yield 23.85 parts of volatile oil.
Place forty to fifty grammes of mustard farina in a flask of about one-half liter capacity; 250 cubic centimeters of tepid water should be poured over it, then close the flask with a cork and shake well. After twenty-four hours’ standing connect the flask with a Liebig’s condenser and heat to boiling. Pour thirty cubic centimeters strong ammonia into the receiver, the end of the condenser being dipped below the surface of the liquid. Water and the volatile oil will pass over, the oil at first floating in the shape of oily drops on the surface of the liquid, which soon sinks to the bottom, especially when the liquid is gently agitated. When no more oil globules pass over, the distillation has finished. The receiver should be closed with a cork and allowed to stand twenty-four hours; at the end of this time all the oil will be dissolved and is now contained in the liquid in the form of thiosinamine (C4H8N2). This solution is evaporated on the water bath in a weighed platinum basin, the residue dried and weighed, and the quantity of thiosinamine obtained, minus one molecule of ammonia, represents the amount of volatile oil. To estimate the amount of myrosin or albumen and sulphocyanide of sinapine, the amount of nitrogen and sulphur in the mustard should first be obtained, the former by combustion with soda lime in the well-known manner, and the latter by deflagration of the mustard and oxidation of its sulphur in a mixture of nitrate of soda and carbonate of potash. First, dissolve the mass in water or diluted acid, and the sulphuric acid contained in the solution is estimated by means of chloride of barium, and, from this data the amount of the myrosin and of the sulphocyanide of sinapine, the acrid principle is calculated. As much sulphur and nitrogen are first deducted from the totals of these substances obtained as is contained in the quantity of myronic acid previously determined.
Next, the whole remaining sulphur, and as much of the nitrogen as is required, are estimated in the acrid principle, and, lastly, the surplus nitrogen is calculated into myrosin, which has the same formula as vegetable albumen. But now, having the amount of the acrid principle and of the myrosin, a further calculation has to be made, since myrosin contains about 1 per cent. of sulphur, and this can be deducted from the total acrid principle, a corresponding quantity of nitrogen being in turn calculated into myrosin.
Chemical composition of white mustard: