Define the major source of vitamin A?

The major source of vitamin A, as you may be aware, is the carotenoid pigments which are synthesized by plants. Several carotenoid possess vitamin A activity and include alpha, beta and gama carolene, lycopene and  cryptoxanthin to name a few. The primary and most efficient pro vitamin A or carotenoid is the beta-carotene (molecular weight 536.9) which has two molecules of retinal attached tail to tail.

Unlike retinol, most carotenoid can quench singlet oxygen and act as antioxidants because of their long chain of conjugated double bonds, as can be seen in Figure. Upon hydsolysis, each molecule of beta- carotene theoretically yields two molecules of vitamin A. The other casotenoid precursors we about half as active as β-carotene.