246 P. BISWAS ET AL.
downregulation of genes encoding those enzymes or over-expression of
some genes related to blotchiness.
B. Abnormal Texture
Tomato fruit is a fleshy berry consisting of parenchymatous tissues
which include the inner wall, columella, radial wall, septa, and the
outer wall. Fruit softening is a consequence of the combination of loss of
turgor, loss of cell wall rigidity by degradation of polymer constituents
of the cell wall, and reduction of cell-to-cell adhesion caused by sol-
ubilization and depolymerization of the pectin-rich middle lamella
(Shackel et al. 1991; Jackman et al. 1992; Brummell and Harpster 2001).
Various methods used to evaluate changes in textural properties include
puncture, compression, extrusion, shear, and others (Bourne 1994) and
it is important to know which measurement techniques determine what
characteristics of textural properties. Some of these methods apply a
large deforming force (e.g., via puncture) and are therefore destructive.
In contrast, some tests that apply a small amount of deformation or force
have usually been considered as non-destructive (e.g., compression
firmness). The puncture test, the most frequently used method for textu-
ral evaluation, is determined by the force required to push a probe into a
fruit to a specific depth causing irreversible damage or failure (Jackman
and Stanley 1995). When a probe is punctured through the flesh of a
pericarp, it possibly measures cell wall rigidity, cell packing, and cell–
cell adhesion. As tomato texture depends not only on flesh firmness, but
is also influenced by skin toughness and the ratio of pericarp/locular
material (Grierson and Kader 1986), it is important to know whether
the puncture was performed from outside the epidermis or inside the
tomato pericarp (without adhering locular gel). Flat plate compres-
sion usually squeezes (compresses) the fruit and measures fruit turgor
and overall fruit firmness. Although flat plate compression firmness is
widely used to measure tomato firmness, compression measurement of
tomato fruit may not be very sensitive to tissue properties as such (Jack-
man and Stanley 1995). Acoustic stiffness sensor or sonic transmission,
another commonly used method, is based on resonance theory (a body
that possesses both mass and elasticity is capable of vibrating). Depend-
ing on the specific physicomechanical properties of the fruit, free vibra-
tion may be exhibited at one or more frequencies and fruit firmness
is mainly correlated with the two lowest frequencies. Overall elastic
behavior or stiffness factors are commonly used as indices of textural
quality (Jackman and Stanley 1995). Use of microscopy to study fruit
texture has also been reported (Barrett et al. 1998).