Agriculture Reference
In-Depth Information
In relation to the way in which the
product is sold, the consignment (commis-
sion selling) and the deposit sale modes are
still relevant, although there is an increas-
ing importance of the fixed price sale, with
a previous supply contract in many cases,
when the commercial relations between
both parties and the quality of the product
permit it.
our, a result of modifications in the content
of chlorophylls, carotenoids and anthocy-
anins; (ii) the firmness, derived from altera-
tions in the cell walls; (iii) the taste, a
consequence of the metabolism of the car-
bohydrates; and (iv) the characteristic aro-
mas caused by the release of volatile
compounds. In the initiation of these ripen-
ing processes several plant hormones are
involved, mainly ethylene, apart from being
regulated by specific ripening genes (see
Chapter 15).
The intensity of the physiological pro-
cesses associated with the ripening process
is affected by external factors: mainly tem-
perature, humidity and composition of the
atmosphere (see Chapter 15). The most
widespread use of technology to extend the
storage period of plant products is the appli-
cation of low temperatures, which limits
respiration, the main postharvest physio-
logical process.
Pre-cooling is the rapid cooling opera-
tion of just-harvested products, to decrease
their ripening process and to limit their
deterioration before storage or before send-
ing them to the market.
Storage allows for more control of the
'offer' of horticultural products, within cer-
tain limits, and reduces their seasonality.
Cold storage of perishable products aims to
decrease their respiration to retard micro-
bial activity and decrease the water losses,
by means of regulating the temperature,
oxygen and CO
2
levels.
The storage temperature must be
constant, which must be permanently
monitored because respiration (although
reduced) generates heat that must be
removed. An excessively low temperature
may interfere with the ripening process.
In tomatoes, for instance, maintaining tem-
peratures above 13°C, and even up to
16-18°C is advisable, to induce the ripen-
ing of the tomatoes that were harvested
green, for their transport to very distant
markets (Janick, 1986).
The use of plastic films has contributed
to the development of controlled or modi-
fied atmosphere packaging (MAP). These
films, which are selectively permeable to
16.2.
Postharvest Alterations:
Storage
The perishable nature of vegetables is a
critical factor in the marketing process
(Plate 27). Harvesting must be done at the
proper time, keeping in mind that the con-
sumption ripening point does not have to
coincide with the physiological ripening
(see Chapter 15). Once a certain ripening
point is exceeded, the quality of these vege-
tables deteriorates very quickly.
In order to extend their postharvest life
some products are harvested before ripen-
ing (for instance, green tomatoes), which
may involve improper development and the
consumer not enjoying the best of taste,
aroma, texture and, therefore, the expected
satisfaction. Depending on the length of the
period between harvest and consumption,
the best harvest time will have to be consid-
ered. So, postharvest management is critical
to maximize the duration of the quality of
the product.
The perishable nature of greenhouse
horticultural products and their high value
have allowed the profitable use of quick and
expensive transport methods, such as refrig-
erated lorries or, even, planes, minimizing
the storage time.
Fresh horticultural products maintain,
after being harvested, a metabolic activity
which is essential to preserving their qual-
ity. The changes during the ripening pro-
cess of the fruits are very complex and
contribute to maintain (and even enhance)
the initial quality of the product. Char-
acteristics that determine the quality of
horticultural products include: (i) the col-
