Apparent vitamin C in the walnut (Juglans regia)

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Abstract
In walnut fruits the highest concns. of vit. C occured in the epicarp and mesocarp, especially in very young fruits, in which it could form half of the total vit. C, as measured by dye titration. In leaves the highest concns. occurred in the mesophyll, from which there was usually a definite concn. gradient through the vascular tissue, rachis and petiole towards the stem. In the stem the highest concn. was in the phloem, in which the concn. gradient was generally from older to younger tissue during the early summer, but in the reverse direction in the winter. Remarkably high conens. of apparent vit. C were found in buds and catkins, in which it usually formed most of the total vit. C. The rate of reaction of apparent vit. C with the indophenol dye was found to be much slower than that of ascorbic, dihydroxymaleic, diketogulonic, hydroxytetronic or isoascorbic acids, and to lie between those of reductic acid and reductone, all determined at the normal titration pH of about 0.7. The apparent vit. C in walnut tissues differs from reductone in its stability towards, ascorbic acid oxidase, in the increase of its dye titration value as the titration pH is reduced below 2, and in the development, by the action of the indophenol dye or of the walnut enzymes, of a yellow compound which spectroscopically seemed to resemble juglone.