Agriculture Reference
In-Depth Information
Photo 15.1.
Covering cucumbers in a plastic film prevents dehydration and subsequent loss of quality.
and the death of the tissue, if they are sus-
tained beyond a certain minimum time
period. Nevertheless, many tissues tolerate
high temperatures for a small interval (min-
utes), and this is occasionally used as a
means to control insects and diseases.
Generally, the application of low tem-
peratures that limit transpiration is the most
common technology to extend the life of
vegetable products. The temperature decrease
of the product, besides decreasing respira-
tion, also reduces the evaporation of water
from the product to the surrounding air.
Regarding the composition of the
atmosphere, this is important because
the maintenance of aerobic respiration
requires adequate O
2
levels. Generally,
low O
2
levels of the order of 2-3% induce
a beneficial decrease in the respiration
rate and other metabolic reactions, in the
same way as an increase in the CO
2
levels
(Salveit, 2003a).
Physical stress produced by an injury
of the tissue generates a respiration increase,
normally associated with a higher produc-
tion of ethylene.
The respiration rate of tissue which has
a vegetative or flower meristem (asparagus,
broccoli) is very high, which means that
many products that are harvested while
they are actively growing have high respira-
tion rates. After the harvest, the respiration
rate decreases, slowly in non-climacteric
fruits and quickly in vegetative tissue and
unripe fruits. In climacteric fruits the respi-
ration rate increases if they are harvested
during the ripening process.
15.3
Ripening
Fruit ripening involves a number of
physiological, biochemical and structural
processes that occur during the last devel-
opmental stages which confer the proper
organoleptic and nutritional characteristics
for consumption.
The changes in colour and firmness,
the decrease in acidity, the increase in sug-
ars and the generation of volatiles are some
of the most common changes during fruit
ripening (Seymour
et al
., 1993).
Climacteric fruits are characterized by
the production of ethylene during the ripen-
ing process, associated with an increase in
respiration, something that does not occur
significantly in non-climacteric fruits (Biale
and Young, 1981).
Ripening of the fruit follows a geneti-
cally determined pattern, during which
