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