Production Practices and Quality Assessment of Food Crops. Vol. 1

216 S. A. Ordoudi and M. Z. Tsimidou
(8,8′-diapocarotene-8,8′-dioic acid) (Figure 4), D-glucose and D gentiobiose being
the sugar moieties. These derivatives are known as crocins.
α-Carotene, β-carotene, lycopene and zeaxanthin are also present in trace amounts
(Sampathu et al., 1984) and mangicrocin, a xanthone-carotenoid glycosidic conjugate
(Ghosal et al., 1989) has also been identified.
Crocetin is insoluble in water and in most organic solvents, with the exception
of pyridine, from which it separates in red coloured leaves (m.p. 275 to 276 °C).
When rubbed with a drop of concentrated H 2SO 4, crocetin produces a strong indigo
colour, turning violet, then brown after a few seconds (Sampathu et al., 1984).
Crocetin monomethyl ester (β-crocetin) melts at 218 °C and separates as reddish
yellow plates from a mixture of chloroform and methyl alcohol. Besides the trans
crocetin isomer, 13-cis-crocetin isomer (Speranza et al., 1984) has been reported.
The structure of dimethylcrocetin (C 11H 14O 2) 2, a purple compound, prepared by
alkaline hydrolysis in methanol of an extract of saffron, has been elucidated by
Fourier transform-IR and Raman spectroscopy and also crystal structure analysis
(Tarantilis et al., 1994c). This compound, which crystallises in the orthorhombic
space, has the all-trans configuration and forms a long planar conjugated system.
Crocetin is reported to occur to a limited extent freely in the spice (Speranza et
al., 1984). Côté et al. (2000) have reported on the properties of a glucosyltransferase
which is involved in the glucosylation of crocetin. This enzyme (uridine-5′-diphosphoglucose-crocetin
8,8′-glucosyltransferase), which glucosylates the carboxylic ends
of crocetin, has been isolated from cell cultures of saffron. The glucosylation of
crocetin into crocin by UDP-glucose takes place according to the following sequence:
monoglucosyl ester; monogentiobiosyl and diglucosyl esters; gentiobiosylglucosyl
ester and crocin (Dufresne et al., 1999).
2.2.1. Crocins
Saffron colouring properties are mainly attributed to the water-soluble crocins.
The chemistry of the digentiobiosyl derivative, known as α-crocin or crocin 1,
was dated back in the beginning of 19th century. Karrer, Kuhn and their co-workers
achieved isolation in the crystalline state in early 30s. Since then many other derivatives
have been identified in the aqueous or alcohol extracts of saffron. Structures
of major crocins as reported by various investigators (1, 2: Pfander and Wittwer,
1975a, b; 3: Pfander and Rychener, 1982; 4: Speranza et al., 1984; 5: Morjani et
al., 1990; 6, 7: Tarantilis et al., 1994b, 1995; 8: Pfister et al., 1996;) are shown in
Figure 5.
Tarantilis et al. (1995) used HPLC-UV-visible photodiode-array detection on-line
with mass spectrometry for the analysis of crocetin glycosides (crocins), carrying
Figure 4. Chemical structure of crocetin.