Bixin

Bixin is an apocarotenoid found in annatto, a natural food coloring obtained from the seeds of the achiote tree ("Bixa orellana"). Annatto seeds contain about 5% pigments, which consist of 70-80% bixin.
Bixin is chemically unstable when isolated and converts via isomerization into "trans"-bixin (β-bixin), the double-bond isomer.
Bixin is soluble in fats and alcohols but insoluble in water. Upon exposure to alkali, the methyl ester is hydrolyzed to produce the dicarboxylic acid norbixin, a water-soluble derivative.