Agriculture Reference
In-Depth Information
Tomatoes will freeze at about −1°C depending on
soluble solids content. Symptoms of freezing include
water-soaked appearance, desiccated appearance of the
locular gel and excessive softening and tissue breakdown
(Grierson & Kader 1986).
flavour development occurs is 12.8°C (Grierson & Kader
1986). The build-up of volatile compounds is significantly
reduced when fruit ripen at temperatures lower than 10°C,
while temperatures higher than 20°C favour the production
of volatile compounds (Stern
et al
. 1994). The production
of volatile compounds associated with fruit taste depends
more on the final ripening temperature than on the initial
storage temperature (Stern
et al
. 1994). The optimum
relative humidity during storage and transport is 90-95%,
while the optimum relative humidity for ripening is
75-80% (Davies & Hobson 1981). Higher relative
humidity will promote infection by fungi and the
development of decay.
Heat treatments
Heat treatments applied prior to low-temperature storage
can also reduce sensitivity of tomatoes to chilling injury by
activating the antioxidant system in the cells, protecting
them from the damaging effects of reactive oxygen species
that are associated with chilling stress (Soto-Zamora
et al
.
2005a, 2005b; Yahia
et al
. 2007). Exposing tomatoes to air
at 38°C for three days (72 hours) reduced the detrimental
effects of low-temperature storage on mature-green
tomatoes (Hakim
et al
. 1995; Lurie
et al
. 1995; Lurie &
Klein 1991; Lurie
et al
. 1997). Tomatoes exposed to either
a short-term heated water treatment (42°C for one hour) or
a long-term heated air treatment (38°C for 48 hours),
stored at 2°C and then transferred to 20°C ripened
normally; the short-term hot-water treatment extended the
storage life equally as well as the long-term hot-air treat-
ment, but altered some volatile profiles (McDonald
et al
.
1996, 1998).
Post-harvest (pre-storage) heat treatments have also
been pursued to delay ripening and to enhance resistance to
low temperature and to disinfect fruit (Lurie 1998).
Pre-storage heat treatment of mature-green tomato fruit
(treated in water for 42°C for one hour) effectively reduced
fruit decay with only minimal adverse effects on fruit
quality (McDonald
et al
. 1999). However, the effect of
heat treatments on tomato fruit is variety-dependent.
Heated forced air (38°C at 50% RH for 24 hours) injured
mature-green 'Trust' tomatoes, preventing the normal
development of red colour, increasing weight loss and
decreasing the production of ascorbic acid (Soto-Zamora
et al
. 2000; Yahia
et al
. 2001b). Some pigments, especially
lycopene, and some antioxidants in tomato fruit are very
sensitive to heat treatments (Soto-Zamora
et al
. 2005a,
2005b; Yahia
et al
. 2007).
Modified or controlled atmospheres (MA or CA)
Modified atmosphere (MA) refers to an atmosphere that
is different from ambient air achieved by product respira-
tion in an environment with restricted ventilation, whereas
controlled atmosphere (CA) refers to a precisely imposed
and strictly controlled atmosphere (Kader 1986; Smock
1979). Modified atmosphere packaging (MAP) refers
to the development of a modified atmosphere around
the product through the use of packages constructed of
semi-permeable polymeric film or with restricted diffu-
sion through one or more pores (Kader
et al
. 1989). MAP
is referred to as 'passive' if the atmosphere in the package
is allowed to slowly establish itself by product respi-
ration; 'active' MAP refers to more rapid atmosphere
establishment achieved by flushing the package with
nitrogen or a gas mixture near the expected equilibrium
atmosphere.
Low O
2
reduces respiration and ethylene production,
increases tolerance to low temperature and thus extends
tomato shelf life (Grierson
et al
. 1985). Also, it reduces the
loss of chlorophyll and the synthesis of lycopene, other
carotenoids and xanthophylls, and delays ripening
(Kader
et al
. 1989). Elevated CO
2
also retards ripening by
competitively inhibiting ethylene action. An atmosphere
of 3-5% O
2
+ 0-3% CO
2
delays tomato ripening and
retards fungal growth. Tomatoes can be kept in this atmos-
phere at 12.5°C for up to six weeks. Control of
Phoma
destructera
,
Alternaria alternata
,
Botrytis cinerea
and
Fusarium
spp. can be achieved with 2.5% O
2
+ 2.5% CO
2
at 13°C. Atmospheres containing 5-10% carbon monoxide
and 4% O
2
reduced post-harvest decay incidence and
severity without adversely affecting tomato flavour
(Kader
et al
. 1978a). Mature-green tomatoes were stored
for up to seven weeks at 12.8°C in 4% O
2
+ 2% CO
2
+ 5%
CO, with acceptable quality. Nitrous oxide was also found
to be effective against fungus growth and fruit decay
Tomato post-harvest ripening
Ripening of mature-green harvested tomatoes is commonly
done at 18°C to 21°C. Tomatoes do not ripen normally
at constant higher temperatures (Grierson & Kader 1986).
Tomatoes ripened continuously at temperatures higher
than 25°C are soft and poorly coloured, as high tempera-
ture hinders pigment (lycopene) formation. Slow ripening
is done at temperatures of 14°C to 16°C. The lowest
temperature at which ripening with good colour and