Journal of Lipid Research, Vol. 10, 561-567, September 1969
Copyright © 1969 by Lipid Research, Inc.
Ascorbic acid and copper in linoleate oxidation. II. Ascorbic acid and copper as oxidation catalysts
Gottfried Haase and W. L. Dunkley
Department of Food Science and Technology, University of California, Davis, California 95616
Both ascorbic acid and copper were strong prooxidants in the oxidation of linoleate in a buffered (pH 7.0) aqueous dispersion at 37°C. Minimum concentrations at which catalytic activity was detected were 1.3 x 10-7 m for copper and 1.8 x 10-6 m for ascorbic acid. For concentrations up to 10-3 m, the increase in rate of oxidation with increase in concentration of catalyst was greater for ascorbic acid than for copper. Ascorbic acid had maximum catalytic activity at 2.0 x 10-3 m, but was still prooxidant at the highest concentration tested (5.0 x 10-2 m). Dehydroascorbic acid was a weaker prooxidant than ascorbic acid. Further degradation products of ascorbic acid were not prooxidant.
In early stages of the oxidation autocatalytic behavior was observed with copper, but not with ascorbic acid. Ascorbic acid functioned as a true catalyst, i.e., it accelerated the reaction but it was not oxidized simultaneously with the linoleate. It is proposed that the dehydroascorbic acid radical initiates the linoleate oxidation reaction.
Supplementary key words dehydroascorbic acid • semidehydroascorbic acid radical • autocatalysis • initiation of oxidation
Submitted on February 18, 1969
Accepted on June 2, 1969
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