Vitamin C Content of Walnuts (Persian) During Growth and Development

Abstract

The remarkably high concentration of vitamin C in immature walnuts and in walnut hulls was first reported by GHERGHELEZHIU (1), who noted that the walnuts developed a maximum concentration of 2.5% vitamin C (wet basis) just before hardening of the shell took place. Subsequently, there was a gradual loss of vitamin C up to maturity. HENNIG and OHSKE (2) confirmed these observations and noted that the percentage of total vitamin C (ascorbic and dehydroascorbic acid) in the green hulls decreased from 1.0% in July to 0.26%o in October; the dehydro-form represented less than one-tenth of the total vitamin C. A maximum value of 1.8%o ascorbic acid in the whole immature walnuts was reported by PYKE, MELvILLE, and SAR-SON (3). MELVLLE, WOKES, and ORGAN (4) measured the amount of reductones1 in immature walnuts ranging in weight from 2 to 40 grams, and found about 30%o of the total apparent (dichlorophenol-indophenol titratable) vitamin C to be reductones. However, LUOG and WELL.ER (5) reported that only 5-107o of the total reducing capacity of the walnut extracts could be assigned to reductones, and that only about 5% of the total vitamin C (ascorbic plus dehydroascorbic acid) occurred as dehydro-acid. Recently TUBA, HUNTER, and OSBORNE (6), using the method of LEVY (7), have published values for the non-vitamin C reductants, expressed as percentage of total indophenol dye reductants, of 38%o for the whole immature walnut of 4.2 gm. weight, and 24%o for a walnut weighing 8.5 gm.As a part of investigations dealing with the utilization of waste walnut hulls as a commercial source of vitamin C, we have measured the vitamin C content of the Persian (English) walnut at different stages of development during two seasons. The amount of reductones and the distribution of vitamin C in the differentiated structures of the maturing walnut have also been determined. The amount of biologically active vitamin C in the immature walnuts has been measured and compared with the values obtained by the chemical methods. ProcedureThe data presented in this paper were obtained from experiments with walnuts of five commercial varieties, grown in Ignacio Valley near Walnut Creek, California. Walnuts were picked from the trees and immediately 1 The term " reductones " as used in this report refers to the naturally occurring and derived substances which give the reduction of 2.6 dichlorphenol indophenol dye characteristic of vitamin C but have no vitamin C activity. 133www.plantphysiol.org on May 9, 2018 -Published by Downloaded from

Ascorbic Acid from Walnut Hulls

“…of bed volume, and the bed was loaded to 4.2 mg. per ml. Maximum purity of 47% was obtained in eluate 3, whereas the maximum concentration of ascorbic acid on a volume basis occurred in eluate 4 at 0.13%.…”

L-Ascorbic Acid: Metabolism, Biosynthesis, Function

“…Iso lated alfalfa roots {Medicago sativa), maintained in continuous culture for two years, still formed ascorbic acid (Smirnov and Ovcharov, 1960). Certain fruits accumulate substantial quantity of ascorbic acid, notably walnut hulls (Klose et al, 1948), rose hips (Jackson et al, 1961), and the West Indian cherry (Ledin, 1958) which contain over 1% on a moisture-free basis. With senescence, the ascorbic acid content declines and very little remains in the leaf following abscission (Franke, 1965).…”

Apparent vitamin C in the walnut (Juglans regia)

“…Nevertheless, the apparent vitamin C in walnuts cannot be reductone, since its dye titration value is very low at pH 2 and increases markedly as the titration pH is lowered (Wokes, 1946a), in contrast with reductone, the dye titration value of which decreases as the titration pH is lowered (Martius & von Euler, 1934;Wokes, 1946a). The use of too high a titration pH probably explains the failure of Lugg &;Weller (1943) and of Klose, Peat & Fevold (1948) to discover much apparent vitamin C in unripe walnuts, though it should be added that the latter workers complicated their results by using sulphur dioxide in the extracting fluid. On the other hand, when Tuba, Hunter & Osborne (1947) applied to walnuts Levy's (1943) method of estimating ascorbic acid in the presence of reductones and other interfering substances they found 24-38 % of the total vitamin C to be nonspecific dye reductants.…”