Hydrophilic Carotenoids: Carotenoid Aggregates - Carotenoids: Physical, Chemical, and Biological Functions and Properties - page 32

from those of the monomers (Jelley 1936, 1937, Scheibe 1936, 1937). The particular features of the
highly dynamic and elastic aggregates are studied in the discipline of “soft matters,” an emerging
branch of materials science (Hamley and Castelletto 2007).
In nature, carotenoids exist as only two varieties: (1) unelaborated hydrocarbons, or (2) with
functional groups, these are always attached via oxygen to the carotenoid skeleton. Carotenoids with
heteroatoms other than oxygen have not yet been discovered in nature, but have been synthesized
(Pfander and Leuenberger 1976, Sliwka 1999).
In nonpolar organic solvents, hydrocarbon carotenoids generally form colored monomolecular
solutions, whereas the biologically relevant solvent, water, typically remains colorless when in con-
tact with hydrocarbon carotenoids. If the water unexpectedly exhibits an orange tint (the highly
unsaturated polyene chain acting as a hydrophilic component), the carotenoid concentration obtained
will be extremely low. Strangely enough, the i rst carotenoid aggregates in water were obtained
from -carotene, 3.1 (von Euler et al. 1931). Its well-known hydrophobicity did not prevent other

studies with

β , β

-carotene, 3.1 , and lycopene, 3.2 , an acyclic carotenoid hydrocarbon (Song and
Moore 1974, Bystritskaya and Karpukhin 1975, Lindig and Rodgers 1981, Mortensen et al. 1997).
The many natural carotenols and carotenones (zeaxanthin, 3.3 , lutein, 3.4 , violoxanthin, 3.5 , astax-
anthin, 3.6 ) are undoubtedly more suited for aggregation studies in water, Scheme 3.1 (Buchwald
and Jencks 1968, Ke et al. 1968, Hager 1970, Salares et al. 1977, Mendelsohn and Van Holten 1979,
Douillard et al. 1982, Gruszecki et al. 1990, Ruban et al. 1993, Mori et al. 1996, Auweter et al. 1999,
Mori 2001, Zsila et al. 2001, Billsten et al. 2005, Köpsel et al. 2005). Yet, the hydrophilicity of these
oxygenated carotenoids shown in Scheme 3.1 is still far too low for most practical applications. More
specii cally, these carotenoids fail to color water-based aliments. In order to overcome this prob-
lem, the two big commercial carotenoid producers (BASF, F. Hoffmann-La Roche—DSM) have

β , β

β,β-carotene 3.1

Lycopene 3.2

OH

HO

Zeaxanthin 3.3

OH

HO

Lutein 3.4

OH

O

O

HO

Violaxanthin 3.5

O

OH

HO

O

Astaxanthin 3.6

SCHEME 3.1