5 VITAMINS A AND CAROTENES 



of the carotene on activated magnesia from the hydrocarbon layer and 

 elution with Skellysolve-acetone mixtures resulted in a recovery of 85 to 

 95 % of the carotene found in the original plant source. For large-scale 

 operations technical hydrated lime was recommended as the adsorbent. 

 With the lime method a concentration of carotene was obtained containing 

 30,000 to 40,000 I.U. per gram. This was increased to 160,000 to 180,000 

 I.U. per gram by low temperature fractionations. Fractional crystallization 

 at low temperatures produced a carotene, m.p. 171 to 173° (corr.). 



One of the recent large-scale industrial methods" uses dehydrated alfalfa 

 meal as the source of carotene. This is extracted with pure hexane by a 

 countercurrent process. The crude extract is concentrated to one-tenth 

 its original volume and the concentrate passed upward through a series of 

 towers containing activated carbon (20 mesh). Chlorophyll is adsorbed at 

 the bottom, xanthophyll next, and carotene at the top of the tower. Con- 

 tinuous washing with hexane separates first the lipoids, then the carotenes, 

 followed by the xanthophyll. To obtain the chlorophyll from the bottom 

 portion of the tower the flow of hexane is reversed. The carotene fraction is 

 further purified by a second chromatographic adsorption. The product 

 thus obtained contains 12 to 20 million I.U. per pound of the concentrate. 

 If purer carotene is desired, the crude concentrate is recrystallized from 

 benzene-isopropanol mixtures. Carotene prepared from alfalfa contains 

 mostly |8-carotene and very little of the a isomer. 



A very recent modification^^ of the above method makes use of tricalcium 

 phosphate, Ca3(P04)2, to adsorb chlorophyll and xanthophyll almost com- 

 pletely from hexane solutions of these substances together with carotene. 

 Adsorption is accomplished either by stirring tricalcium phosphate (1.2 

 lb. per gallon of hexane extract) with the extract and then filtering the mix- 

 ture, or by making use of the radial chromatography method. ^^ The effi- 

 ciency of the recovery of carotene is over 95 % with concentrates containing 

 over 300,000 I.U. per gram. Further purification is effected by low tempera- 

 ture fractionation or by a chromatographic adsorption through a magnesia 

 colimm. 



Carotene has also been produced industrially from palm oiP^ and from 

 carrots. ^^ However, the carotene produced from these sources contains both 

 the a and ^ isomers. 



3, Chemical Constitution of Provitamin A Carotenoids 



a. General 



All provitamin A carotenoids are structurally related to one of the three 

 carotenes, a-, (8-, or 7-carotene. The elucidation of the chemical structure 



" P. P. Hopf, Ind. Eng. Chem. 39, 938 (1947). 



" J. M. Tabor et al., U. S. Pat. 2,440,029 (April 20, 1948). 



16 H. M. Barnett, U. S. Pats. 2,348,443 (May 9, 1944), 2,412,707 (Dec. 17, 1946). 



