Page:Popular Science Monthly Volume 12.djvu/482

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the alcoholic fermentation, even before maturity is passed. H. Gutzeit (Zeitscher Oest. Ap. Ver., 1875, p. 337; Pro. Am. Phar. Asso., 1876, p. 287) reports finding alcohol, or other simple compound of ethyl, in the fruits of a number of plants. Some of the fruits were not quite ripe, and none were overripe. De Luca (Comptes Rendus, lxxxiii., 512; Jour. Chem. Soc., 1876, ii., 649) reports obtaining products of the alcoholic and acetic fermentations from the fresh fruits, leaves, and flowers, of several plants. In all these cases the quantities of alcohol obtained were very minute. The investigator first above named found methyl-alcohol, in some cases, with the ethyl-alcohol. Pasteur states that the germs which excite alcoholic fermentation are very abundant on the bunches of ripe grapes, where very rare in the atmosphere. Also, that the fermentive germs are found on ripe strawberries, cherries, and currants, but not on the same fruits unripe. The formation of methyl-alcohol, above referred to, is closely allied to the formation of methyl-salicylate or wintergreen-oil. A number of the essential or volatile oils, with which plants and fruits are perfumed and flavored, contain alcohol radicals in union as compound ethers. It is probable, from every point of view, that the slight occurrence of the vinous fermentation in fruits belongs to an important class of chemical formations, by means of which a multitude of odor-giving substances are scattered throughout vegetation. We shall inquire more carefully into the fruit-flavor compounds and their formation further on.

2. The Pectous Substances.—These are, in general terms, the constituents of plant-jelly. As vegetable products, they correspond to the varieties of gelatine obtained from animal tissues. Unlike gelatine, however, they are non-nitrogenous. They are found in the soft parts of plants generally, as in the tuber of the potato and the root of the carrot; but it is in fruits that they have most importance for edible value. The immediate origin of the pectous substances is pretty well known, being due to a specific fermentation, a prominent feature in fruit-ripening. The material from which all the pectous substances proceed is the fermentable body called pectose, an insoluble, tasteless substance, found abundantly in unripe fruits, also to some extent in immature roots and tubers, and having no more value for food than cellulose. Now, there is formed along with this substance a "ferment," as it is called, a body which by contact induces a specific fermentation—a definite chemical change. Pectase is the name of the ferment. Just as, in the germinating seed, starch, by contact with diastase, suffers fermentation with production of sugar, and as, in bruised and wetted mustard-seeds, sinigrin, by contact with myrosin, splits up into pungent oil of mustard and sugar, etc., so the crude pectose of green fruits, by contact of their pectase at the time of ripening, changes to the edible plant-jellies or pectous substances. Long boiling with water alone effects the same change.