Natural Diversity and Genetic Control of Fruit Sensory Quality - Fruit Ripening: Physiology, Signalling and Genomics - page 237

respectively, in tomato (Davies and
Hobson, 1981) and peach fruit. In mature
tomato, glucose and fructose constitute the
major sugars, whereas in peach, sucrose is
predominant at maturity, followed by
reducing sugars (glucose and fructose) and,
in smaller amounts, sorbitol (Moriguchi et
al. , 1990; Robertson et al. , 1990). Two
organic acids, citrate and malate, are
dominant in most fruit species (Tucker,
1993), as in tomato and peach. Acidity has
been related either to the fruit pH or to
titratable acidity (Baldwin et al. , 1998;
Auerswald et al. , 1999). Acidity affects not
only the sour taste of the fruit (Sweeney et
al. , 1970) but also sweetness, by masking
the taste of sugars. Thus, both sugars and
acids contribute to the sweetness and to
the overall taste intensity (Baldwin et al. ,
1998). Sweetness seems more infl uenced
by the content of fructose than of glucose,
while acidity is mostly due to citric acid,
present in higher amounts than malic acid
in mature fruits (Stevens et al. , 1977).
The other main component of fl avour is
aroma, due to volatile compounds. In
tomato, several sensory attributes have
been proposed to characterize aroma, such
as fruity, green, grassy, earthy, musty, fl oral,
candy, citrus, grapefruit and pharma-
ceutical aromas (Bucheli et al. , 1999;
Causse et al. , 2001; Baldwin et al. , 2004;
Sinesio et al. , 2010). More than 400 aroma
volatiles have been identifi ed in tomato
fruit (reviewed by Petro-Turza 1987),
among which about 30 seem to be
important for tomato aroma (Baldwin et al. ,
2000, 2004). In apple and strawberry, more
than 300 volatile compounds have been
identifi ed (Dixon and Hewett, 2000) for
which 20 volatiles are considered the
aroma fi ngerprint of strawberry (Ulrich et
al. , 1997). Volatiles can be divided into two
groups: those produced in intact tissues,
important for the fl avour of the intact fresh
fruit; and those formed when plant tissues
are disrupted, essential for the perception
of fl avour when the fruit is being chewed
(Yahia, 1994). The combination of volatiles
may be more important than their total
amount for sensory sensations. For
example, the perception of aldehydes may

be enhanced by the presence of esters
(Fellman et al. , 2000).
In apple, texture is the primary limiting
factor for acceptability by consumers.
Firmness, mealiness, juiciness, meltiness
or tough skin are the major texture attri-
butes. They are quite diffi cult to correlate
with instrumental measurements. Firmness
in the mouth is related partly to the
instrumental measure of fruit fi rmness in
tomato (Causse et al. , 2002), and mealiness
could be found to be related to the texture
parameters of the pericarp (Verkeke et al. ,
1998). Texture is related to several pro-
cesses, such as fruit morphology, cell size
and shape, cell adhesion and cell-wall
properties (Lee et al. , 1999; Devaux et al. ,
2005; Chaïb et al. , 2007).
Consumer preferences facing natural
diversity indicate the most important traits
for breeders but also the diversity of
consumer appreciation. High tomato-like
aroma intensity and sweetness but inter-
mediate acidity are the most important
characteristics for consumer preferences
(Jones 1986; Baldwin et al. , 1998; Lê and
Ledauphin, 2006). Malundo et al. (1995)
showed that given levels of sweetness
correspond to optimal acid concentrations,
beyond which acceptability decreases.
Baldwin et al. (1998) related the overall
acceptability to the ratio of sugars to
titratable acidity and to the concentration
of several aroma compounds. Verkeke et al.
(1998) pinpointed the major role of texture
traits in the preference of consumers. The
sensory evaluation of apricots revealed that
overall quality was linked mainly to
fl avour, sweetness and juiciness (Valentini
et al. , 2006). For melon, the most critical
quality traits depend on the melon type:
retronasal aroma for climacteric types and
texture for non-climateric ones (Ferrer et
al. , 2007). Each cultivar may be char-
acterized by a particular sensory profi le
and a specifi c potential of taste and texture
(Causse et al. , 2010; Sinesio et al. , 2010;
Fig. 14.1). Genetic variation is the major
source of fruit quality variation (Stevens
1986; Causse et al. , 2003), but fruit
organoleptic quality is also infl uenced by
external factors such as the environment