Agriculture Reference
In-Depth Information
specifications. Grading can be done manually or by us-
ing electronic sorting equipment. When hand sorting, good
lighting is essential, and sorters are provided with good
information on which fruits need to be removed. Photo-
graphic charts/posters showing the type and degree of blem-
ishes allowed on fruit are one of the methods used (Hardy,
2004).
Fruits are normally sized mechanically using belts or
rollers, electronically or by weight. Weight sizers are not
recommended when pattern packing fruits as there is too
much variation leading to poor packout presentation. Fruit
can be packed either as “loose fill” or pattern packed, de-
pending on the market being targeted. Pattern packing can
be either “open pocket” or “closed pocket.” Generally fruits
are packed in either 0.5 or 1.0 cu ft cardboard cartons,
each package graded to have a similar size, shape color,
and condition (blemish level) (Hardy, 2004; Kimball et al.,
2005). Time is an important factor in the marketing of fresh
produce, as delays add to losses. Once the fruit has been
packed, dispatch to the market should be done as soon as
possible, otherwise packed containers must be (1) protected
from the sun and rain as heat and water may cause rapid
deterioration and weaken the cardboard boxes; (2) handled
carefully during staking to avoid damaging the contents
that may lead to water loss and decay; and (3) stacked so
as to get ventilation to avoid overheating leading to dete-
rioration. Losses during packing can be minimized if fruit
is kept as cool as possible, kept dry, protected from injury,
and sent to the market quickly (FAO, 1989).
decreasing or increasing temperature causes rapid deterio-
ration due to the following disorders.
Freezing injury
Generally, fruits are high in water content with the freez-
ing point of their tissue relatively high ( 3 Cto 0.5 C).
Freezing causes the disruption, which results in immediate
collapse of the tissues and total loss of cellular integrity
(USAID, 2006). Fruit which has recovered from freezing
is highly susceptible to decay.
Chilling injury
Chilling injury is a physiological disorder that can reduce
the quality and value of plants and their products, particu-
larly tropical and subtropical species, as a result of expo-
sure to low but nonfreezing temperatures (Marangoni et al.,
1996). Limes and lemons stored at temperatures lower than
10 C develop chilling injury symptoms including rind pit-
ting and sunken, water-soaked lesions on the fruit surface
(Ladaniya, 2004). Other symptoms of chilling injury in-
clude superficial brown staining of the rind, browning of the
albedo, and watery breakdown (Porat, 2004). Lemons are
sensitive to both heat and cold, while limes are well adapted
to a tropical climate but strongly sensitive to cold. Chilling
injury in lime may be characterized by pitting (Fig. 20.4a),
initially seen in the rind as small defects, while more severe
symptoms show as brown discoloration or sunken areas of
various sizes that develop from these small injury areas.
The pits may with time coalesce and form leathery, brown,
sunken areas on the rind (Fig. 20.4b) that increases with
longer exposure to temperatures below 10 C (Arpaia and
Kader, 2000). Symptoms of chilling injury may not develop
until the produce is removed from cold storage to ambient
temperatures.
Postharvest losses: causes and remedies
The storage life of citrus fruits as well as other commodities
varies inversely with the rate of respiration since respiration
supplies compounds that determine the rate of metabolic
processes directly related to quality parameters. Commodi-
ties and cultivars with higher rates of respiration tend to
have shorter storage lives than those with low rates of res-
piration. The respiration rate of citrus at 5 Cislow;res-
piration is affected by a range of environmental factors,
including light, stress (chemical from fumigants, radiation,
water), growth regulators, and pathogen attack. However,
the most important postharvest factors that lead to damage
of fruits are temperature, mechanical injury, postharvest
pathology (diseases), and physiological disorders (FAO,
1989; Murata, 1997; Kader, 2002).
Heat injury
Sometimes fruit ripening and senescence can be delayed by
heat treatment but fruits can also be damaged by such treat-
ment; the damage can be both external and internal (Lurie,
1998). Continued exposure to high temperatures causes
phytotoxic symptoms leading to complete tissue collapse.
External symptoms of heat injury may be evident as scald
damage (surface browning) and brown sunken lesions on
the flavedo of 'Eureka' lemon (Obenland and Neipp, 2005).
Exposure of lemon and lime to high temperatures caused
by radiation will cause them to deteriorate rapidly (FAO,
1989). Fruit left in the sun after harvest may reach tempera-
tures as high as 50 C, resulting in a high rate of respiration,
and, if packed and transported without cooling or adequate
ventilation, will deteriorate.
Temperature effects
Temperature has a profound effect on the rates of biologi-
cal reactions (e.g., metabolism and respiration). Above or
below the physiological range of most crops (0 -30 C),
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