ANTIOXIDANT CAPACITY ASSESSMENT BY ABTS OF 9'Z-BIXIN, 9'Z-NORBIXIN, 9'ZMETHYLBIXIN AND ALL EMETHYLBIXIN FROM BIXA ORELLANA SEEDS

The 9´Z-bixin is the major pigment present in the annatto (Bixa orellana L.) seeds. Other carotenoids present in the seeds of annatto are 9´Z-norbixin and 9´Z-methylbixin. Annatto seeds extract is used as a food colorant. In this study, we extracted and isolated 9´Z-bixin from annatto seeds. 9’Z-norbixin was obtained and purified by saponification of annatto seeds extract. Then, 9’Z-methylbixin was obtained by Steglich esterification of 9´Z-bixin with EDC/DMAP. Also, all E-methylbixin was obtained by esterification of 9’Z-bixin in acid conditions with hydrochloric acid in methanol. The antioxidant capacity of 9´Z-bixin and bixin derivatives was measured in ABTS assay to determine their structure–activity relationship. We observed that the esterification of 9´Z-bixin decreases its antioxidant capacity and that the presence of the free carboxyl group is important in the antioxidant capacity of bixin derivatives.