Apolar carotenoids

With apolar carotenoids With polar carotenoids... 

Chemical properties of carotenoids play an important role in carotenoid micellarization and, therefore, bioavailability. Apolar carotenoids (carotenes) are generally incorporated in the central region, which is highly hydrophobic, of the oil droplets, whereas polar carotenoids (xanthophylls) are localized on the surface, and therefore xanthophylls are more easily micellarized and absorbed than carotenes (Borel and others 1996). van het Hof and others (2000) found in humans that lutein is five times more bioavailable than (3-carotene. 

The extinction coefficients of carotenoids have been listed completely bnt solvent effects can shift the absorption patterns. If a colorant molecnle is transferred into a more polar environment, then the absorption will be snbjected to a bathochro-mic (red) shift. If the colorant molecnle is transferred into a more apolar enviromnent, the absorption will be subjected to a hypsochromic (blue) shift. If a carotenoid molecule is transferred from a hexane or ethanol solution into a chloroform solution, the bathochromic shift will be 10 to 20 nm. 

Both intact carotenoids and their apolar metabolites (retinyl esters) are secreted into the lymphatic system associated with CMs. In the blood circulation, CM particles undergo lipolysis, catalyzed by a lipoprotein lipase, resulting in the formation of CM remnants that are quickly taken up by the liver. In the liver, the remnant-associated carotenoid can be either (1) metabolized into vitamin A and other metabolites, (2) stored, (3) secreted with the bile, or (4) repackaged and released with VLDL particles. In the bloodstream, VLDLs are transformed to LDLs, and then HDLs by delipidation and the carotenoids associated with the lipoprotein particles are finally distributed to extrahepatic tissues (Figure 3.2.2). Time-course studies focusing on carotenoid appearances in different lipoprotein fractions after ingestion showed that CM carotenoid levels peak early (4 to 8 hr) whereas LDL and HDL carotenoid levels reach peaks later (16 to 24 hr). 

FIGURE 2.2 Model representation of organization of the lipid membrane containing apolar and polar carotenoid pigments. 

Carotenes are soluble in apolar solvents such as petroleum ether and hexane, while xan-thophylls dissolve best in polar solvents such as ethanol and methanol (5). The stability of carotenoids is low they are especially sensitive to light, oxygen, and peroxide, so special precautions have to be taken when handling them. 

Lycopene is the major carotenoid pigment found in tomatoes, along with lesser amounts of a-, P-, y-, and -carotene, phytoene, phytofluene, neurosporene, and lutein (Trombly and Porter, 1953 Kargl et al., 1960). The basic physicochemical information on lycopene is fairly well established and is outlined in Table 4.1. Lycopene is dispersible in edible oils and soluble in apolar organic solvents. In aqueous systems, lycopene tends to aggregate and to precipitate as crystals this behavior is suspected to inhibit the bioavailability of lycopene in humans (Zumbrunn et al., 1985). In fresh tomatoes, the crystalline form of lycopene is responsible for the typical bright red of the ripe fruits. 

Carotenoids are very soluble in apolar solvents, including edible fats and oils, but they are not soluble in water. Hence, they are denoted lipochromes . Carotenoids are readily extracted... 

There are very small numbers of chylomicrons present in plasma from fasting volunteers and they are generally carotenoid free, the bulk of carotenoids being carried by the LDL and HDL. The apolar and polar carotenoids show different distributions between these two lipoproteins. LDL carries around 80% of plasma -carotene and lycopene but only about... 

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