Food and drugs analysis
Ertg. Clzem., 1920,12? 977-979.)-Sugars exercise a protective action in fruit against freezing ; cane sugar disappears in rotting fruit, and is transformed irrto invert sugar during the stages of ripening and over-ripening; cane and invert sugar are differently localised in the tissues of the fruit. The method described below makes use of the fa& that freezing brings about ta very rapid transformation of cane to invert sugar, resulting from the free mingling of cane sugar with inverting acids
... invertase, or both. One half of the fruit to be examined is analysed directly, and the other half is frozen with ice and salt. Each sample of the fruit may be cut into halves, or, with very small fruit, two approximately equal samples may be set aside for the anaIysis. The directly analysed portion involves the estimation of invert sugar before and after hydrolysis; the frozen portion is also analysed for invert sugar before and after hydrolysis. In other words, the ratios of invert sugar to cane sugar before and' after freezing are compared. In all cases the estimations a m made by weighing the cuprous oxide formed after reduction. In the case of some peaches it was found that the freezing and thawing produced in fifteen hours three times as much inversion as storage for two weeks, By inspection of the values found for the percentage of inversion obtainable from the fruit before and after laboratory freezing, reliable conclusions m a y be drawn as to whether the fruit has already been subjected to cold storage or not, since the change broughh about by freezing and storage will not be repeated by laboratory freezing, provided the first freezing w&s thorough and the laboratory freezing was not delayed too long. It will also be observed that not only cane sugar is inverted during rotting, over-ripening, rotting and freezing, but inverted sugar previously present or formed by inversion may be lost by chemicd decomposition, or by metabolism of the plant, or by yeasts and moulds. The method takes advantage of divergencies in the largest components of the fruit, since inversion subtracts from the cane sugar concentration and adds to the invert sugar concentration.