KANNER, J., Div. of Food Technology, Agricultural Research Organization Volcani Center, P.O. Box 6, Bet Dagan, 50-200, Israel
BUDOWSKI, P., Faculty of Agriculture, Hebrew University of Jerusalem, P.O.B. 12, Rehovot, 76-100, Israel

The carotene‐bleaching activities of ascorbic acid and copper were investigated in a solid model consisting of carotene and linoleic acid adsorbed on powdered cellulose. The effects depended on the water activity (aw) of the system. Ascorbic acid in the presence of Cu++ had very little activity in the dry model but displayed increasing bleaching effects as the aw value of the system was raised. However this bleaching activity in the moist model reached a maximum as the ascorbic acid concentration rose to about 1 μmol/g cellulose, or 1.4 μmol ascorbic acid/mmol linoleic acid. At higher concentrations of ascorbic acid, the bleaching activity decreased and was eventually converted into an antioxidant effect. A peroxidase‐like protein extracted from pepper was also tested in the present model and found to exhibit prooxidant activity, which was little affected by changes in aw. The antioxidant system composed of copper and ascorbic acid at high concentrations was able to overcome the pro‐oxidant effect of peroxidase. Copyright © 1978, Wiley Blackwell. All rights reserved