Palm oil carotenoids

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Abstract
Examination of the unsaponifiable matter of a West African plantation oil of low free fatty acid content showed the presence of [alpha]-, [beta]-, and [gamma]-carotenes, lycopene, neolycopene, lutein, neo-lutein, and the carotenoid intermediate between [gamma]- and [beta]-carotenes on the chromatogram previously observed in "Sherbro" palm oil (Hunter and Scott, Biochem. J., 1941, 35, 31). Evidence was also obtained of the presence of ergosterol. Analogy is drawn between the reversible isomerization of carotenoids and the "mobile" cis-trans isomerism of azobenzene (Hartley, Jour. Chem. Soc, 1938, 633), and it is shown that B-carotene isomerises more rapidly in a non-polar solvent such as toluene than in nitromethane. The original theory that isomerization of carotenoids is due to 3-carbon prototropy with movement of a terminal double bond out of the conjugated system (Gillam and El Ridi, Biochem. Jour., 1936, 30, 1735) is ruled out, in addition to the arguments adduced by Zech-meister et al. (Proc. Nat. Acad. Sei. Wash., 1941, 27, 468) by the fact that a-carotene gives rise to an isomer, neo-a-carotene, with retention of optical activity.