CAROTENOIDS IN LAND PLANTS 



too numerous to outline here, but generally carrots have been found 

 to contain between 60 and 120 (Jig./g- (wet wt) of carotene, although 

 some selected strains contain as much as 370 (J.g./g. (fresh wt.).^^" It 

 now seems certain that carotene is present in carrots in a water soluble 

 form attached to a protein. » 1 1. 3 1 2 



Puerto Rican sweet potatoes (Ipomea batatas edulis) can contain 

 between 40 and 80 [xg./g. (wet wt.) of p-carotene which is the pre- 

 dominant carotenoid present ^ ^ ^' ^ ^ ^ for only traces of xanthophylls 

 have been found. ^ ^ ^ The carotene concentration is about the same in 

 the Red Velvet variety as in the common strains, but is much less (one 

 third) in the Nancy Hall variety. ^ ^ ^ The common potato, on the other 

 hand, contains very little carotene (about 0-1 to 0-2 ;j.g./g-) the content 

 varying only a little from " white " to yellow fleshed varieties; 1 & 0. 3 1 s- 

 3 2 1 ^-carotene and probably c^-carotene are present. We see then from 

 the point of view of providing a source of vitamin A active carotenoids, 

 potatoes are of negligible value, whilst sweet potatoes and carrots are 

 potentially extremely good sources. Potatoes are useful in experimental 

 diets which will just prevent vitamin A deficiency symptoms in rats. ^ ^ • 

 Lycopene has recently been observed as the major component of the 

 complex carotenoid mixture occurring in some swedes^"^ whilst in 

 others prolycopene appears to predominate. ^ ^ ^a 



(ii) Xanthophylls 



The xanthophyll fraction of commercial carrots is quite small, being 

 only 5-10 per cent, of the total carotenoids present \^^^ however, the 

 percentage varies from xylem to phloem, being higher in the former, 

 where in the case of Danver's Half Long and Yellow Belgian, it reaches 

 30-50 per cent, of the total carotenoids. ^^'' In wild carrots at least 95 

 per cent, of the total pigments are xanthophylls, mostly monohydroxy 

 derivatives, ^ ^ ' and a similar high value (75-93 per cent.) is found for 

 the xanthophyll content of yellow carrots. ^ ° ^ 



In potatoes the xanthophyll fraction constitutes about 90-95 per 

 cent, of the pigment ; this is in contrast to the commercial carrot and 

 the sweet potato where it is the minor fraction. The concentration of 

 xanthophylls in potatoes varies, according to variety, between 0-2 and 

 2*6 ^.g./g- (fresh wt.), the yellow flesried varieties {e.g., Katahdin) 

 naturally containing most. ^^^^'^^^'^ 20.3 2 2 



The xanthophylls detected in potatoes are ^-xanthophyll* (sic), tara- 

 or violaxanthiny ^ ^ ^ lutein, auroxanthin and flavoxanthin. ^ ^ ^ A 



* 3-xanthophyll was the name given by Tswett to a strongly adsorbed pigment occuring in 

 green leaves. 



As this has now been shown to be a mixture of pigments, its use has been abandoned. 



55 



