Agriculture Reference
In-Depth Information
Table 2.1
Ripeness Classes of Tomatoes.
Class
Description*
Immature-green The surface is completely light to dark green. There is no jelly-like material in any of the locules,
and the seeds are cut upon slicing the fruit with a sharp knife.
Mature green Seeds are fully developed and are not cut upon slicing of the fruit. Jelly-like material is formed in
at least one of the locules. This is the minimum stage of harvest maturity.
Breaker Tomatoes at this stage are characterised by a definite break in the colour from green to tannish-
yellow, pink or red on not more than 10% of the surface.
Turning More than 10% but not more than 30% of the surface, in the aggregate, shows a definite change
in colour from green to tannish-yellow, pink, red or a combination thereof.
Pink More than 30% but not more than 60% of the surface, in the aggregate, shows pink or red colour.
Light-red More than 60% of the surface, in the aggregate, shows pinkish red or red colour, provided that
not more than 90% of the surface is red colour.
Red
More than 90% of the surface, in the aggregate, shows red colour.
*All percentages refer to both colour distribution and intensity.
As mentioned above, the initiation of ripening can
be accelerated in preclimacteric tomatoes by exogenous
ethylene exposure. Commercial ripening of mature-green
tomatoes may involve post-harvest application of ethylene
to ensure uniformity in ripening and colour development.
This is commonly done for domestic marketing and also
when tomatoes are to be shipped long distances interna-
tionally, in order to better manage and control the ripening
process. Maximum ethylene concentration should be
between 100 and 150 ppm for rapid and uniform ripening.
Duration of the ethylene treatment period is 24 to 48 h,
depending on temperature, ethylene concentration and
desired speed of ripening (Blankenship & Sisler 1991) -
the need for longer ethylene exposure to initiate ripening
indicates that the tomatoes were harvested immature. Good
air circulation is needed to ensure uniform temperature
throughout the room and to prevent CO
2
accumulation. The
latter is because CO
2
at >2% will inhibit ethylene action
and therefore will slow down or inhibit ripening. Adequate
air exchange in ripening rooms is important to reduce the
development of off flavours (Grierson & Kader 1986).
Mature-green tomatoes ripened with ethylene at 20°C had
more ascorbic acid content at the table-ripe stage than
those ripened without added ethylene simply because
the ethylene-treated fruit reached the red, fully ripe stage
faster than fruit that were not exposed to ethylene (Kader
et al
. 1978c; Watada
et al
. 1976).
Blossom-end rot
Blossom-end rot (BER) is a physiological disorder that
causes extensive losses in production (Dorais
et al
. 2001).
This disorder develops as a visible external depression of
necrotic tissue (Plate 2.3) affecting the distal end of the
placenta and the adjacent locular contents as well as the
pericarp (Willumsen
et al
. 1996). In internal BER, also
called 'black seeds', black necrotic tissue develops in the
adjacent parenchyma tissue around young seeds and the
distal part of the placenta (Adams & Ho, 1992). BER is
believed to be caused by fruit calcium deficiency or
stress (Saure 2001). Fruit susceptibility is related to lack of
coordination during fruit growth between cell enlargement
and calcium supply. The development is also positively
correlated with the leaf K:Ca ratio, but is weakly correlated
to the K:Ca ratio in mature fruit (Bar Tal & Pressman 1996).
Factors affecting BER include daily irradiance, air tem-
perature, water availability, salinity, nutrient ratios in the
rhizosphere, root temperature, air humidity and xylem
tissue development in the fruit. Several strategies have
been suggested to avoid this disorder (Dorais
et al
. 2001),
including (1) the use of resistant cultivars; (2) optimizing
calcium and phosphate supply; (3) maintaining a dynamic
balance between calcium and potassium and between nitrate
and ammonium that will ensure sufficient calcium uptake;
(4) the use of irrigation water or nutrient solution with low
electrical conductivity (EC); (5) optimizing irrigation
frequency; (6) avoiding high root temperature (>26°C);
(7) avoiding excessive canopy transpiration by leaf thin-
ning, shading, roof sprinkling and greenhouse fogging;
(8) maintaining proper fruit:leaf ratios that can provide
Physiological disorders
The following is a brief description of various fruit
disorders related to pre-harvest factors.
