Catalyzes the conversion of the ubiquitous 5,6-epoxycarotenoids, antheraxanthin and violaxanthin, into capsanthin and capsorubin, respectively. all-trans-violaxanthin = all-trans-capsorubin all-trans-antheraxanthin = all-trans-capsanthin all-trans-violaxanthin = (5R,6S)-5,6-epoxi-capsanthin (5R,6S)-5,6-epoxi-capsanthin = all-trans-capsorubin Binds 1 FAD per subunit non-covalently. Carotenoid biosynthesis; capsanthin biosynthesis; capsanthin from antheraxanthin: step 1/1. Carotenoid biosynthesis; capsorubin biosynthesis; capsorubin from violaxanthin: step 1/1. Monomer. Belongs to the lycopene cyclase family.