Certain physical and chemical changes during growth, storage and ripening of Bosc pears

Graduation date: 1935This investigation was undertaken to determine, from a dietetic\ud standpoint, the amounts and proportions of dextrose, levulose and\ud sucrose present in Bosc pears, and to furnish information that might\ud be of value in the development of by-products from the off-grade\ud fruit of this variety.\ud The attempt was made to carry out this work in such a way that\ud fundamental information might be obtained concerning the physiological\ud changes occuring during growth, storage, and ripening. Such information,\ud it was hoped, might lead to a better understanding of the physiology\ud of pears, and. in addition, shed some light on the dynamics of\ud carbohydrate changes in fruit.\ud The investigation has been carried on for two seasons and may\ud be divided, into three general parts: (1) a study of the physical and\ud chemical changes occuring during the latter stages of growth; (2) a\ud study of the chemical changes occuring during storage; and. (3) a\ud study of the chemical changes occuring during the ripening process.\ud (1) The results of the study of the physical and chemical \ud changes during one growing season show that the amounts of dextrose\ud remain approximately constant during growth while the amounts of\ud levulose increase steadily during most of this period, but decrease\ud markedly during the last week on the tree. Sucrose is present in\ud increasing amounts during the last seven weeks on the tree and increases\ud very rapidly during the last week.\ud (2) The results of the study of the chemical changes as observed\ud during two storage seasons, show that there are marked differences\ud between pears of two successive seasons and that the sugar\ud content of fruit may show quite different changes during storage,\ud depending upon the time of picking. It is apparent, however, that\ud levu1ose increases during storage, in most cases, and that dextrose\ud either remains constant or increases slightly. The behavior of\ud sucrose appears to depend, to a considerable extent, upon the time\ud of picking.\ud (3) The results of the study of the ripening of pears show\ud that chemical changes took place during ripening of fruit that attained\ud prime eating condition, which are quite different than those\ud which were observed during the ripening of fruit which developed\ud mediocre eating quality. These changes were studied during two seasons\ud and indicate that the conditions associated with the inversion\ud of sucrose during ripening are correlated with the physical and.\ud chemical changes involved in attaining good. eating quality. The\ud chemical changes involved in ripening include a hydrolysis of some \ud undetermined carbohydrate to yield sucrose which may or may not be\ud inverted. Levulose increases in all cases, while dextrose either\ud remains constant or increases, depending upon the extent of inversion\ud of sucrose. The identity of the material yielding the increasing\ud amounts of sugars, observed in ripening, was not determined. It\ud is suggested that the substance is a soluble non-sugar carbohydrate\ud which is transformed into sugar during the ripening process