Agriculture Reference
In-Depth Information
exposed to low temperature (but above the
freezing point) for a certain minimum
period of time. Depending on their origin,
tropical and subtropical fruits have their
threshold for chilling at 10-15°C, whereas
the threshold is lower for fruits that origin-
ate in temperate areas.
At 7°C chilling damage occurs in
cucumber, aubergine, pepper, melon or rip-
ened tomatoes, whereas for green tomatoes
damage occurs at higher temperatures
(Wang, 2003). Chilling damage can be very
relevant if the low temperatures last a long
time. If the duration of low temperatures is
short, normal metabolic capacity in these
plants is limited or cancelled, affecting their
shelf life, although the damage is only evi-
dent when the product goes back to normal
temperatures.
In general, tomatoes can be conserved
well with a RH of 90%, but the optimal ther-
mal regime varies depending on the ripen-
ing stage, the recommendation being for
less than 15°C for green and early pink-
colour stage tomatoes, and less than 10°C
for late pink-colour stage and ripened fruits
(Chaux and Foury, 1994a, b). The storage
temperature allows for regulating the ripen-
ing speed; for instance, for pink-colour stage
tomatoes, a temperature of 10°C allows
them to ripen in 10-20 days, whereas at
20°C ripening is shortened to 8-10 days
(Chaux and Foury, 1994b).
The optimal storage temperature of
greenhouse cucumbers is from 12 to 13°C,
because lower temperatures cause the
fruits to wilt and higher temperatures
accelerate their respiration and dehydra-
tion (Chaux and Foury, 1994b). Covering
them in a plastic film extends their
shelf life.
The optimal storage temperature of leafy
vegetables is lower than for fruit vegetables.
In general, while temperatures of 0-2°C, with
RH of 90-98%, are optimal for some (arti-
chokes, asparagus, broccoli, cabbage, cauli-
flower, Chinese cabbage, endives, lettuce,
carrots and cantaloupe melons), the fruit
vegetables are better conserved at 7-10°C,
with RH of 85-95% (Tompson and Kader,
2003). The usual greenhouse vegetables are
all very sensitive to freezing (Wang, 2003).
In fresh products, postharvest treat-
ments with high temperatures can be of
interest to control pests and insects and
fungal diseases, before their storage or long-
distance shipping. Washing the peppers
with water at temperatures between 50 and
65°C, while simultaneously brushing them,
has proved to be efficient for the control of
postharvest diseases; the same is true for the
treatment of tomatoes with hot water at
50°C for 2 min (Lurie and Klein, 2003).
A proper environmental humidity has a
notable influence on maintaining the post-
harvest quality of fruits and vegetables,
especially during cold storage. An inappro-
priate humidity can increase the incidence
of fungal diseases, alter the organoleptic
characteristics and induce the cracking or
cork-like texture of the fruits and vegetables
(Scharz, 1994).
Storage in a controlled atmosphere
involves the modification of the normal
composition of the air (78% N
2
, 21% O
2
and
0.03% CO
2
), in order to have less than 8% of
O
2
and more than 1% of CO
2
, while keeping
low temperature and adequate humidity
according to the product being stored,
which decreases the respiration rate of the
product and the production of ethylene
(Kader, 2003).
An optimum atmospheric composition
delays: (i) the loss of chlorophyll (green col-
our); (ii) the biosynthesis of carotenoids
(yellow and orange colours) and antho-
cyanins (red and blue colours); and (iii) the
biosynthesis and oxidation of phenolic
compounds (brown colour) (Kader, 2003).
Low levels of O
2
and/or high concentrations
of CO
2
in the air affect the flavour, decreas-
ing the loss of acidity, the conversion of
starch into sugar, the interconversions of
sugars and the biosynthesis of volatiles that
affect the flavour and aromas, resulting in
an improvement of the nutritional flavour,
as the ascorbic acid and other vitamins
remain in the fruits (Kader, 2003).
In addition to a delay in senescence,
storage under a controlled atmosphere
decreases the sensitivity to ethylene (if the
O
2
level is below 8%, and if the CO
2
level is
above 1%), and can be useful to control
pests and diseases.
