The Isolation ofl-Quinic Acid from the Apple Fruit

Abstract

A method is described by means of which several grammes of l -quinic acid were isolated from young fruits of the Worcester Pearmain apple stored for a number of days in nitrogen. The essential stages in the method are the removal of colouring matter from extracts of the frozen ground pulp tissue of the fruit with charcoal, the removal of amino acids by absorption on cation exchange resin, and the separation of the organic acid from sugars by adsorption of the former on anion exchange resin. Finally, the quinic acid was separated from malic acid by fractional displacement from the anion exchange resin. The characterization of the isolated quinic acid, and of malic acid also isolated from the fruits, is described. Citric acid is shown to be formed by oxidation of quinic acid with hot hydrogen peroxide. The possible function of quinic acid in the apple fruit and in plants generally is discussed.