Aroma Volatiles - Fruit Ripening: Physiology, Signalling and Genomics - page 73

(Obando-Ulloa et al. , 2008). A transgenic
line of 'Royal Gala' apple fruit produced
no detectable ethylene using antisense
1-aminocyclopropane-1-carboxylic acid
(ACC) oxidase (ACO), resulting in a
signifi cant reduction in aroma volatiles
(Schaffer et al. , 2007). Furthermore, the
transgenic hybrids, produced by crossing
Charentais melons with an antisense ACO
line, showed a 60-80% lower ester content
with a low odour threshold (potent
odourants). These results showed that
enzymes located in the fi nal step of ester
biosynthesis, AATs, are regulated by
ethylene during fruit ripening (Schaffer et
al. , 2007; Lucchetta et al. , 2009).
In the case of non-climacteric fruit, a
signifi cant accumulation of volatile esters
was found during strawberry ( Fragaria
chiloensis ) fruit ripening, which was
correlated with increased AAT activity and
FcAAT1 expression (Conzález et al. , 2009).
In citrus fruit, there was induced expres-
sion of the TPS-encoding gene Cstps1
accompanying a considerable increase in
the sesquiterpene valencene in response to
exogenous ethylene treatment during fruit
growth (Sharon-Asa et al. , 2003). Ripening-
related increases in volatiles have also
been observed in other non-climacteric
fruits such as raspberry and koubo
(Defi lippi et al. , 2009a).
Loss of function of ripening inhibitor
(RIN) protein caused a delay in ripening
and extended the shelf-life by regulating
the expression of ACC synthase genes in
tomato fruit (Fujisawa et al. , 2011). A
recent report by Qin et al. (2012) demon-
strated the role of transcription factor RIN
in the regulation of the biosynthesis of
ethylene and aroma volatiles during
tomato fruit ripening. Five target gene
promoters that could be bound by RIN
were identifi ed using high-resolution two-
dimensional electrophoresis coupled with
chromatin immunoprecipitation tech-
niques. Furthermore, RIN was found to be
involved in the modulation of aroma
formation derived from the LOX pathway
through the direct and rigorous regulation
of genes such as TomLOXC , HPL and
ADH2 (Qin et al. , 2012). Increased bio-

synthesis of volatile compounds during
tomato fruit ripening depends on ethylene,
as there were no ripening-associated
increases in the ethylene-insensitive Nr
mutant (Klee and Giovannoni, 2011). The
above results taken together suggest that
ethylene preferentially controls the gener-
ation of aroma volatiles.

5.4.3 Temperature

Fruits ripen and senesce rapidly at ambient
temperature after harvest, and low-
temperature storage is the primary tech-
nology used to delay quality deterioration.
Tomato fruits were stored at 21°C (control)
and 6°C (chilled) for 3 days followed by
transfer to ambient temperature for up to
3 days to mimic storage in the retail chain.
The content of major aroma volatiles, such
as the C6 compounds isobutylthiazole and
methylbutanol, were signifi cantly reduced
after chilling storage and a subsequent
shelf-life (Boukobza and Taylor, 2002). In
the case of fruits that are susceptible to CI,
the overall levels of volatile compounds
and aroma acceptability showed a gradual
decrease during storage and transfer to
shelf-life at ambient temperature. A dis-
tinct separation between peach fruit with
CI and without CI was observed based on
E-nose analysis, and the differences were
caused mainly by decreases in volatile C6
compounds, esters and lactones during
cold storage and shelf-life after transfer
(Zhang et al. , 2011). Gradual decreases in
fruity-note esters were observed in durian
fruit with longer chilling temperature
storage (Voon et al. , 2007).
Low-temperature-induced changes in
aroma volatile profi les could be caused by
a decrease in enzyme activity or a decline
in substrate abundance. In tomato fruit, a
signifi cant decrease in ADH activity was
correlated with changes in volatile
alcohols during cold storage (León-
Sánchez et al. , 2009). Reduced levels of
fruity-note esters in peach fruit with CI
were the consequence of reduced
expression of PpLOX1 , PpLOX3 and
PpAAT1 (Zhang et al. , 2011). The content