Carotenoids that contain unsubstituted beta-ionone rings ( including beta-carotene, alpha-carotene, beta-cryptoxanthin and gamma-carotene ) have vitamin A activity ( meaning that they can be converted to retinol ), and these and other carotenoids can also act as antioxidants.
12.
In general, carnivores are poor converters of ionone-containing carotenoids, and pure carnivores such as cats and ferrets lack beta-carotene 15, 15'- monooxygenase and cannot convert any carotenoids to retinal ( resulting in none of the carotenoids being forms of vitamin A for these species ).
13.
One quirk of some " Viola " is the elusive scent of their flowers; along with terpenes, a major component of the scent is a ketone compound called ionone, which temporarily desensitises the receptors of the nose, thus preventing any further scent being detected from the flower until the nerves recover.
