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

218 S. A. Ordoudi and M. Z. Tsimidou
one to five glucose molecules, and differentiated their trans and cis isomers. Van
Calsteren et al. (1997) reported also on the structure of some already known crocetin
derivatives from saffron stigmas and compared their findings with carotenoids
present in Gardenia jasminoides seeds.
Crocins dissolve readily in water to give an orange-red solution. This is the reason
for its application as a food colorant. Crystals of crocin (m.p. 186 °C) contain
water, which is only given up on prolonged drying in vacuum at 100 °C. On acid
hydrolysis in absence of air, crocins yield crocetin and glucose, while hydrolysis
with alcoholic ammonia results in crocetin and gentiobiose (Sampathu et al., 1984;
Solinas and Cichelli, 1988). Crocins are extremely sensitive to dilute aqueous potassium
hydroxide giving a quantitative yield of crocetin (potassium salt). Crocins,
as a-carotene, dissolve in concentrated sulfuric acid, forming a deep blue solution,
which on standing changes to violet, red and finally brown. Crocins are coloured
green by nitric acid (Sampathu et al., 1984). The absorbance maxima of crocins
are at about 440 nm in distilled water (ISO, 1993). The antioxidant properties of
crocin have also been investigated (Pham et al., 2000). Weber and Grosch (1976)
have reported a carbonyl compound as a product of crocin bleaching during cooxidation
with linoleic acid by a soybean lipoxygenase. On the other hand, quenching
properties of water extracts of saffron may not be related to crocins but to other
ingredients (Kumar and Nultsch, 1985).
The levels of each pigment in saffron vary due to the different origin of the
plant and the overall processing conditions and storage length. Pfander and Rychener
(1982) found that crocin 1 represents the 40–45% of the saffron aqueous extract,
followed by the crocetin-(β-D-gentiobiosyl)-(β-D-glucosyl) ester (35%), the crocetindi-(β-D-glucosyl)
ester (ca. 10%), as well as the crocetin-mono-(β-D-gentiobiosyl)
and mono-(β-D-glucosyl) esters (each ca. 2%). On the other hand, Alonso et al.
(2001) examined the content of Spanish, Indian and Iranian saffron in crocin derivatives
and gave results for trans- and cis-crocins (trans-crocin: 0,46–12,12%;
cis-crocin: 0,04–8,53%; trans-(β-D-gentiobiosyl)-(β-D-glucosyl) ester: 0,01–9,44%;
cis-(β-D-gentiobiosyl)-(β-D-glucosyl) ester: 0,01–2,26%).
2.3. Bitter compounds
The colourless glycoside picrocrocin (C 16H 26O 7, 4-(β-D-glucopyranosyloxy)-2,6,6trimethyl-1-cyclohexene-1-carboxaldehyde)
is the major bitter compound of saffron.
The compound was firstly crystallised (m.p. 156 °C) and separated by Winterstein
and Teleczky in 1922. Kuhn and Winterstein (1934) examined its chemical properties.
UV absorption maxima for picrocrocin are at 254 nm/ε = 7124 (Alonso et
al., 1999a) or 250.5 nm/ε = 10100 (Buchecker and Eugster, 1973). The latter in their
work on the absolute configuration of picrocrocin, reported the following structure,
with the R-configuration at the aglycon O link.
The formation of picrocrocin is related to degradation of zeaxanthin (Pfander
and Schurtenberger, 1982). Its decomposition gives rise to compounds responsible
for the aroma of saffron. Removal of the sugar moiety takes place during processing
(drying, storage) of saffron (Zarghami and Heinz, 1971; Sampathu et al.,
1984; Iborra et al., 1992a, b; Iborra et al., 1993; Raina, 1996; Ríos et al., 1996;