256 P. BISWAS ET AL.
tomatoes. It appears that in tomatoes that have reached a certain matu-
rity stage, that is, breaker/pink, delaying ripening will be less deleteri-
ous than it would be at the green stage. Perhaps sensory qualities have
already developed by the breaker/pink maturity stage.
Fatty acids are considered key precursors in the formation of tomato
aroma volatiles (Wang et al. 1996). Changes in membrane lipid compo-
sition (decrease in phospholipids, decrease in unsaturated fatty acids)
are thought to be correlated with the incidence of CI. Since chilling
alters lipid saturation, there is a possible connection between chilling-
induced lipid composition changes and aroma development following
low temperature stress. Many flavoring compounds are derived from
peroxidation of unsaturated fatty acids through the LOX/lyase enzyme
pathway (Stone et al. 1975; Vick and Zimmerman 1986). Cleavage of 13-
hydroperoxide from linoleic (18:2) and linolenic (18:3) acids produces
hexanal andcis-3-hexenal, respectively. Both hexanal and hexenal can
further be reduced by ADH to form hexanol andcis-3-hexenol (Vick and
Zimmerman 1986).Cis-3-hexenal can further be isomerized totrans-2-
hexenal with or without enzyme activity (Riley et al. 1996). Yilmaz et al.
(2001) reported that enzyme activity itself was not a good predictor of
the amount of volatiles produced and suggested that availability of pre-
cursors and composition may be more important in determining fruit
flavor composition. For instance, Sitrit et al. (2007) found that availabil-
ity of appropriate unsaturated fatty acids is an important factor affect-
ing tomato flavor and manipulation of these fatty acid metabolic path-
ways has been attempted by the expression of a yeastΔ-9 desaturase
gene. Modifying expression of휔-3 desaturase in tomato resulted in an
increase in the 18:3/18:2 ratio and altered aroma profile in addition to
enhancing chilling tolerance (Dominguez et al. 2010). These findings,
therefore, suggest that there is likely to be a direct connection between
chilling-induced fatty acid composition changes and aroma develop-
ment in tomato.
Low temperature usually reduces ethylene production, alters red
color development, and delays ripening. The questions remain as to
whether lower concentrations of some aroma compounds reported in
cool-stored tomatoes result from a direct effect of low temperature stress
or an indirect effect of delayed fruit ripening. It can be argued that fla-
vor loss of mature-green tomatoes after storage could be because of,
at least in part, failure of fruit to ripen. Many researchers recognized
these issues and they used advanced maturity stage tomatoes since it
is believed that organoleptic qualities have already developed by that
stage. Therefore, for example, if lower concentrations of carotenoid-
derived volatiles are found in chilled tomatoes harvested at advanced