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

Straubinger et al., 1997; Straubinger et al., 1998) or even during flower development
(Himeno and Sano, 1987). The hydrolysis of picrocrocin may also occur due
to the activation of β-glucosidase. Iborra et al. (1992a) proposed a method for the
immobilisation of this enzyme in order to increase the rate of hydrolysis yielding
thus higher levels of safranal. Himeno and Sano (1987) studied the picrocrocin
content in intact stigmas of saffron during the flower development and observed a
stepwise increase in the content before anthesis. Then, an appreciable decrease in
picrocrocin level coincided with the appearance of volatiles. Alonso et al. (2001),
who examined several samples of Spanish, Indian and Iranian saffron found their
picrocrocin content: 0.79–12.94% in Spanish saffron, 1.07–2.16% in Indian and
2.18–6.15% in Iranian saffron.
2.4. Volatiles
Saffron Quality 219
Figure 6. Chemical structure of picrocrocin.
The characteristic delicate aroma of saffron comes from an essential oil, which
mainly contains terpene aldehydes (Zarghami and Heinz, 1971). Safranal is the main
responsible compound for the aroma of saffron, even though there are other more
volatile constituents which provide saffron with its final odour (Zarghami and Heinz,
1971; Sampathu et al., 1984; Curro et al., 1986; Tarantilis and Polissiou, 1997;
Sraubinger et al., 1998). Tarantilis and Polissiou reported the presence of 23 volatile
components 13 of which were ketones and 6 aldehydes. The molecular weights of
these compounds ranged from 122–208 and their presence was directly related to
the method of volatile isolation. Five compounds, namely, 2,6,6-trimethyl-1,3-cyclohexadien-1-carboxaldehyde
(safranal) (ca. 70%); 3,5,5-trimethyl-2-cyclohexen-1-one
(isophorone) (ca. 14%); 3,5,5,-trimethyl-3-cyclohexene-1-one (isomer of isophorone)
(5%); 2,6,6-trimethyl-2-cyclohexene-1,4-dione (4%); and 2,6,6-trimethyl-1,4-cyclohexadiene-1-carboxaldehyde
(isomer of safranal) (3%) were the major compounds
the chemical structures of which, elucidated by MS, are given in Figure 7.
These volatiles with a common nucleus possibly originate from picrocrocin
and are formed either by enzymic activity or by oxidative degradation process. A
scheme for the formation of safranal has been repeatedly presented in literature
(Figure 8). According to this scheme, an intermediate volatile precursor of safranal
namely 2,6,6-trimethyl-4-hydroxy-1-carboxaldehyde-1-cyclohexene (HTCC) may be
formed.
The levels of safranal and of the other aroma compounds of saffron vary
depending mainly on the conditions of processing, storage and the methods of
analysis of saffron. In any case, safranal is the most abundant volatile component
in the stigmas of saffron (>60% of essential oil) (Zarghami and Heinz, 1971; Corradi