Retinaldehyde from 3-carotene cleavage

Figure 2.4. Potential products arising from enzymic or nonenzymic symmetrical (a) or asymmetric (b to d) oxidative cleavage of, 6-carotene. Apocarotenals can undergo side chain oxidation to yield retinoic acid, but cannot form retinaldehyde or retinol.

Central oxidative cleavage of 3-carotene, as shown in Figure 11.3, should give rise to two molecules of retinaldehyde, which can be reduced to retinol. However, the biological activity of P-carotene, on a molar basis, is considerably lower than that of retinol, not twofold higher as might be expected. In addition to the relatively poor absorption of carotene from the diet, three factors may account for this ... 

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