Postharvest Physiology and Storage - Tropical and Subtropical Fruits: Postharvest Physiology, Processing and Packaging - page 25

packaging containers to reduce impact damages. Com-
pression loads could be reduced by diminishing the layers
of fruit during handling and storage and by using proper
packaging materials and configuration designs. Conversely,
vibration could be reduced by immobilizing the fruit in-
side the packages, and puncture and penetration stresses
could be minimized by the analysis of the process lines
and packaging equipment and contact surfaces, looking for
any problem equipment or parts that could damage the fruit
surface.
Packaging is a key tool for fruit preservation because
it holds and protects the fruit during handling and market-
ing. Size, shape, and strength of the packaging materials are
important, as well as the smoothness of the surface, ventila-
tions and easy storage and handling features. Fruits should
be immobilized inside the packages to avoid movements,
which could cause mechanical damages, and the column
height of product inside individual packages should be such
that fruits on the bottom could resist the load. Wax coat-
ing of cardboard cartons minimizes water loss or moisture
migration from packaged fruits.
Cooling down and cold-chain maintenance at the recom-
mended storage temperature are the most efficient tools to
minimize quality changes as the fruit is transported or stored
before processing. During harvest, fruits grown in tropical
areas could reach temperatures as high as 40 ◦ C during cer-
tain months of the year. Such field heat should be removed
as fast as possible, cooling down the fruit to its optimum
storage temperature. The precooling requirements depend
on the product type and physiology, its stage of maturity,
and the final use of the product. Precooling reduces the rate
at which respiration, transpiration, enzymatic activity, and
other metabolic reactions occur; it also reduces the rate of
growth and development of micro-organisms and thus the
deterioration rate of the fruit (Brown, 1986).
In addition to temperature control, most fresh fruits are
also sensitive to water loss, which is directly related to the
relative humidity of the environment surrounding the fruit,
temperature, and the physical characteristics of the fruit.
The higher the difference in the temperature, internal and
external atmosphere, and relative humidity, the higher the
water loss is. Thus, since the internal atmosphere of the
fruit has very high relative humidity and the permeability
of the skin to water vapor vary among fruits, a high relative
humidity is usually needed for fresh fruit stored to minimize
the product water losses and wilting.
Table 2.5 shows the recommended storage temperature
and relative humidity of fresh tropical and subtropical fruits.
It also includes the recommended oxygen and carbon diox-

ide contents for controlled or modified atmosphere storage.
This type of storage does not substitute low-temperature
storage but complements it to preserve the quality of the
fruits longer by delaying senescence, product deterioration,
and decay. The reduction of O 2 and/or an increase of CO 2
content have proven to have a beneficial effect on fruits, in-
creasing the product storage life by several days or weeks,
though not many differences in quality have been found for
many fruits. The use of very low or very high O 2 content
has also found some applications to control some micro-
bial growth and insects. Table 2.5 also shows recommended
atmosphere composition for tropical fruits.
Other postharvest operations include cleaning, wash-
ing, grading, and special treatments to reduce microbial
growth or enhance fruit appearance. Proper selection of
the fruits, discarding those with open mechanical injuries,
and fruits with decay symptoms are very important before
cooling and storage. Some fruits may require special treat-
ments to reduce the rate of deterioration or as a preparation
for commercialization or processing, which might include
the use of waxes, fungicides, or controlled ripening. In all
cases, care should be taken to use only approved chemical
products in the doses allowed for the final market. Sanita-
tion of equipment and working areas also help to reduce
product decay and contamination of the fruits with micro-
organisms which might risk consumers' health.

PHYSIOLOGICAL DISORDERS
As living organs, fruits respond to surrounding conditions
in very different ways. The tolerance to oxygen and carbon
dioxide atmosphere content, water loss, range of high or
low temperature vary among fruits and even vary based on
the degree of ripening within the same fruit. Some physi-
ological disorders can result when tolerance levels are ex-
ceeded for certain periods of time during pre- or postharvest
handling of the fruit.

Chilling injury
Most tropical and subtropical fruits are very sensitive to
low storage temperatures, showing a physiological disor-
der known as chilling injury. This damage is a postharvest
physiological disorder that occurs when the fruit is stored at
a temperature below its recommended storage temperature
(Table 2.5). Even though chilling injury mechanism is not
completely understood yet, it is well known that produce
response depends on both the temperature and the time at
which the fruit is stored. Some products can tolerate brief
periods at a given temperature without problem, but if the