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

An oleoresin‐cellulose model was used for studying the interacting processes which influence carotene bleaching in powdered paprika. Special attention was given to the effects of water activity and the addition of aqueous pepper extracts, copper and ascorbic acid. The stability of carotenoids in the model system increased slightly with increasing water activity, but the effect of moisture become considerable when the system also included ascorbic acid and copper sulfate. When aw in powdered paprika exceeded 0.32, carotenoid bleaching proceeded in three stages. After an initial bleaching, there was a prolonged period of stability, after which oxidation resumed. The intermediate period of stability was absent in the dry product. Results obtained with the oleoresin‐cellulose model showed that the three‐stage carotenoid bleaching at high aw values was characteristic of the combined action of copper and ascorbic acid. It is concluded that these two materials, by becoming soluble at high water activities, play an important part in the stabilization of carotenoids in powdered paprika. Under conditions of high water activity, the prooxidant effect of a water‐soluble protein is overcome by the marked antioxidant action of the ascorbic acid‐copper system. However, in the dry product the decisive factor in carotenoid bleaching is the proteinous fraction which was previously shown to have peroxidase activity. Copyright © 1978, Wiley Blackwell. All rights reserved