unstable, the vitamin is found in tissues in a form of retinyl ester. It is also commercially produced and administered as esters such as retinyl  acetate  or  palmitate . The  carotenes  alpha-carotene, beta-carotene, gamma-carotene; and the  xanthophyll  beta-cryptoxanthin (all of which contain beta-ionone rings), unds to  retinal . In general, carnivores