Combined Ascorbic Acid in Plant Tissues

Abstract

EVIDENCE was presented some time ago which indicated that a part of the ascorbic acid present in certain plant food materials was present in the combined state¹. Mack², however, still considers that any apparent increase in the ascorbic acid value of cabbage on cooking is to be attributed to the thermal destruction of the ascorbic acid oxidase, and Levy³, while recognizing that part of the ascorbic acid in certain plant tissues is in the combined state, records that he has observed a decrease in the ascorbic acid value of cabbage on boiling. Experiments with cabbage carried out here have, however, invariably shown a very considerable increase in ascorbic acid value on heating in a suspension of water on a boiling water bath for 15 minutes in an atmosphere of nitrogen or carbon dioxide. We believe that the oxidase theory accounts partly, but not quantitatively, for the observed increase in value. Thus alcoholic and ethereal extracts, containing no oxidase, also show increase in ascorbic acid value, on being heated for 5 minutes in an atmosphere of nitrogen on a boiling water bath, even when titrations are carried out after addition of formaldehyde or after mercuric acetate treatment, in order to eliminate interfering substances, if any (Table 1).