The isomerization of carotenes

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Abstract
In the present study, the isomerization of [beta]-carotene was re-examined in the light of the new observations of Zechmeister and Tuzson that the isomerization of B-carotene was spontaneous and not due to adsorption. This was confirmed as was the fact that the change was an equilibrium between 2 opposing reactions. The effect of temp. on the forward reaction ([beta]-carotene to [PSI][alpha]-carotene) was studied and it was found that whereas at [long dash]2[degree] some 2.5% of the carotene was isomerized in 12 wks., at room temp. some 11% was changed in 7 wks. At 80[degree] the isomerization reached equilibrium in less than 3 hr. when 31% of [PSI][alpha]-carotene was present. The reverse change of a-carotene to [beta]-carotene was found to proceed more rapidly; 5-6% of this pigment, in soln., was changed in 2 mos. at [long dash]2[degree]. At 80[degree] the equilibrium was reached in about 1/2 hr. In order to reduce the tendency of carotene sols, to isomerize spontaneously they should therefore be stored as near to 0[degree] as possible and conc. of the solns. should only be carried out at low temp. When partial isomerization occurred one adsorption of alumina or Ca(0H)2 immediately before use gave [beta]-carotene in pure form, while crystallization of the equilibrium mixture yielded practically pure B-carotene in each crop of crystals, provided the mother liquor was brought to equilibrium by raising to the boiling point between crystallizations. [alpha]-Carotene and [PSI][alpha]-carotene were separated and differentiated by chromatographic methods with absorption spectra control.

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