IN-VITRO MEASUREMENT OF BETA-CAROTENE CLEAVAGE ACTIVITY - METHODOLOGICAL CONSIDERATIONS AND THE EFFECT OF OTHER CAROTENOIDS ON BETA-CAROTENE CLEAVAGE

In view of controversies about assessment of the beta-carotene cleavag e activity, methodological aspects and problems of the dioxygenase ass ay are described. Using rat and hamster intestinal preparations the me thod was optimized on retinal formation, the only cleavage product we could demonstrate. It appeared that the cell fraction with the highest cleavage activity was the 9,000 g supernatant (S-9). Maximal retinal formation was obtained with SDS, taurocholate and egg lecithin in the buffer and 3 mu g beta-carotene dissolved in acetone. Ethanol, THF/DMS O (1:1) or propylene glycol as solvent for beta-carotene reduced retin al formation to 55, 24, and 19%, respectively Retinal formation increa sed proportionally with the amount of protein S-9 used and was linear up to 40-60 minutes of incubation. Incubation with a-carotene or beta- cryptoxanthin resulted in a retinal formation of 29 and 55% of the amo unt formed from beta-carotene. Addition of 9 mu g of lutein to an incu bation with 3 mu g beta-carotene reduced retinal formation. While lyco pene had no effect. In conclusion, the beta-carotene cleavage assay wi th S-9 as enzyme source described in this report, seems a useful tool to study (dietary) determinants of beta-carotene cleavage activity but for other purposes adaptation of the method is required.