Page:Popular Science Monthly Volume 12.djvu/479

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THE CHEMISTRY OF FRUIT RIPENING.

often termed grape-sugar. It is the same compound that is largely manufactured from starch, and called starch-sugar. It is much less sweet than cane-sugar, and less abundantly soluble in water, having an oily or "mealy" taste. As made from starch, it is now much used in certain candies. When in the uncrystallizable form, glucose (lœvulose) is the same as "fruit-sugar," the uncrystallizable product obtained to some extent in manufacturing cane-sugar, and which forms a part of the sirups of the market. Many of the fruits contain cane-sugar (which is the same as beet-sugar and maple-sugar), and certain rare varieties of sugar are found in some fruits.

Buignet decided that the apple, peach, plum, raspberry, orange, and pineapple, contain cane-sugar, with glucose (mostly as lœvulose). The sugar of the grape, cherry, gooseberry, and fig, consists wholly of glucose.

The average proportion of sugars in ripe fruits is given, by Fresenius, as follows (the smallest percentages being placed first):

Peaches, 1.6 per cent, (not varying very widely).
Apricots, 1.8 per cent, (from 1.1 to 2.7).
Plums, round red, 2.1 per cent, (from 2.0 to 3.5).
Greengages, 3.1 per cent.
Raspberries, 4.0 per cent, (from 3.0 to 5.0).
Blackberries, 4.4 per cent.
Strawberries, 5.7 per cent, (from 3.2 to 7.0).
Currants, 6.1 per cent, (from 4.8 to 6.6).
Gooseberries, 7.1 per cent, (from 6.0 to 8.2).
Pears, red, 7.4 per cent.
Apples, 8.4 per cent, (from 5.9 to 10.4).
Cherries, 9.8 per cent, (from 8.5 to 13.1).
[Summer peaches, 11.6 per cent. Berard's analysis.]
Grapes, 14.9 per cent, (from 13 to 19).

It is seen from this list that the sweetness of fruit has but slight correspondence with its proportion of sugar. Currants were found to have more sugar than raspberries, blackberries, or strawberries, and over three times as much as the peaches examined by Fresenius. All analysts agree in the predominance of grapes for their quantity of sugar. The sweetness of fruit is probably favored less by large proportions of sugar than by three other conditions, namely: 1. Small proportions of acids; 2. Large proportions of pectous substances; 3. Presence of cane-sugar instead of grape-sugar.

The sugar of fruits is chiefly formed or deposited in them during their ripening. Berard found that the pulp of cherries, unripe, contained only 1.1 per cent, of sugar; ripe, 18.1 per cent.; gooseberries, unripe, 0.5 per cent.; ripe, 6.02 per cent. In 1862 Hilger determined the sugar of grapes, at ten periods during their growth and ripening, as follows (Landw. Versuchsstat, xvii., 245; Journal of the Chemical Society, xxviii., 281):