Free Galacturonic Acid in Citrus Fruits

Authors:
  • WSWalton B. Sinclair
    Walton B. Sinclair
  • VJVirgil A. Jolliffe
    Virgil A. Jolliffe
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Abstract
1. Very little free galacturonic acid was found at any time during the normal maturation of tree-ripened Valencia oranges. An ion-exchange procedure was used to collect the organic acids, and the presence of monogalacturonic acid in the eluate was determined with a carbazole colorimetric method and a chromatographic analysis procedure. The carbazole analysis indicated the presence of microquantities of galacturonic acid, while the more sensitive and specific chromatographic analyses detected none. Fruit which was picked green and then ripened in storage likewise gave no trace of an increase in free galacturonic acid. Juice that was allowed to stand for several hours until it was obvious that the "cloud" had been broken down also showed no increase in monogalacturonic acid. 2. In the light of our present information on pectic enzyme activity in citrus it is possible to theorize how biosynthesis and degradation of the pectic substances could proceed in citrus fruits without an accumulation of free monogalacturonic acid.