Mechanisms regulating carotenoid absorption

About 90% of a large but physiological amount of -carotene (10 mg), when dispersed in oil can be absorbed (Faulks et al. 1997), about 65% from cooked pur66 carrot but only about 40% from raw carrots (Liveny et al. 2003). About 25% of P-carotene was absorbed from cooked leaf spinach as measured by mass balance in ileostomy volimteers (Faulks etal. 2004). It would seem, therefore, that in normal healthy volunteers there is httle inhibition to absorption of modest doses of free P-carotene and that the poor absorption from some foods is a result of the form of the carotenoid and the absence of an effective system of extraction from the food matrix during digestion. 

It is also recognized that co-ingested dietary fat improves carotenoid bioavailability (Dimitrov et al. 1988 Prince and Frisoli, 1993 Reddy etal. 1995 Jayarajan et al. 1980). Because of their hydrophobic nature the carotenoids are constrained to the hydrophobic domains of plant tissues where they may be present as part of the photosynthetic mechanism in leaf chloroplasts (CogdeU 1988), as semicrystalline bodies in fruit and roots (Thelander et al. 1985) or dissolved in lipid droplets within plastids in ripe fruit (de Pee et al. 1998). Absorption studies would indicate that carotenoid present as semicrystalline bodies is most difficult to absorb, followed by carotenoids in leaves, with fruit carotenoids dispersed in oil droplets being most easily absorbed. 

From such a model it will be appreciated that bulk lipid, even if it is emulsified in the gastric antrum or in the duodenum in the presence of bile salts cannot effectively penetrate pieces of vegetable tissue to wash out the carotenoid. However, once the emulsion droplets 

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