Proline Content in Citrus Fruits

Abstract

Chinard's reagent for the detection of cyclic imino acids was adopted for the estimation of proline in citrus fruits, which "contained particularly much proline, such as from the highest content in Valencia orange (about 300mg%) to the lowest in lemon (30mg%). Some differences in proline content were incidentally observed in cases of strain, fruit weight, position of the fruit on a tree or place of production of Citrus Unshiu. Its content in Citrus Unshiu varied greatly with season and storage in winter. At an early harvesting season (October) of the fruits its content was only less than 10mg% and increased in several folds at the last season (December). Proline increased also on storage of the fruits in winter. This was observed more clearly in peels, in which proline was not formed by the degradation of peel proteins. On the other hand, proline content was not changed on storage of homogenized fruits without prior heating. Also on heating of homogenized fruits it was practically unchanged.