Presence in Rose Hips of Substances Inhibiting the Oxidation of Ascorbic Acid

IT has been demonstrated that even AnalaR grade chemicals may contain sufficient heavy-metal impurity to catalyse the oxidation of ascorbic acid 1 ; it was found that this oxidation was diminished by the addition of an aqueous extract of the flesh from hips of Rosa canina . The protective action of the hip extract was then tested in the presence of extracts of cauliflower ascorbic oxidase, apple polyphenolase and horseradish peroxidase. In each case reaction mixtures were prepared containing the oxidase system, hip extract and added ascorbic acid (final concentration, about 1.0 mgm./ml.) buffered to p H 6.0; the mixtures were incubated at 25°C, aerated and samples taken at intervals for the assay of residual ascorbic acid. Controls were also run, containing only the oxidase system, buffer and added ascorbic acid. To confirm the effect on metal-catalysed oxidation, a further mixture was made consisting of buffer, ascorbic acid and copper sulphate (final concentration, 2×10 −9 M ). Table 1 gives the average results for a number of replicate experiments.