Ether-Soluble Organic Acids of Mature Valencia Orange Leaves

Abstract

In a series of studies (16,18, 20) on the organic acids of citrus fruits, the authors have pointed out that large amounts of organic acids exist in the juice of the pulp, as compared with exceptionally low concentrations in the peel. The vascular system of the fruit is confined chiefly to the mesocarp (albedo), and the latter thus serves the important function of transporting water and solutes from the tree to the juice vesicles of the pulp. Since these vesicles contain relatively large amounts of organic acids, it would appear that higher concentrations than are present should occur in the mesocarp, that is, if the total organic acid radical is transferred from leaves to vesicles. This situation led to the postulation that the organic acids of the juice are possibly synthesized in the pulp vesicles rather than in the leaves and subsequently transferred to the pulp. Quantitative determination and identification of the organic acids present in the leaves should provide fundamental data necessary for a solution to this problem. The present investigation has been concerned with the extraction of the organic acids from ground, dried Valencia orange leaves with absolute ethyl ether, and with the subsequent determination of total and individual organic acids in the water solution of the ether extract. In addition, water-soluble organic acids were extracted directly from aliquot portions of the dried leaf samples, and these data were compared with the total and individual acids extracted with ether. This information revealed the amounts of organic acids present in the leaves in soluble and insoluble states. The influence of these factors on the buffer system of the leaves is discussed. Furthermore, certain relationships are proposed concerning the synthesis and translocation of organic acids from the leaves to the fruit.