Agriculture Reference
In-Depth Information
Post-harvest heat treatment, in the form of a hot water
dip, induced pineapple cv. Mauritius fruit tolerance to cold
injury and, in turn, reduced internal browning during
prolonged low-temperature storage (Weerahewa &
Adikaram 2005b). Several temperature-time combinations
were found effective, but the best was 38°C for 60 minutes.
The results indicated that an internal tissue temperature of
38°C is a prerequisite for the induction of cold tolerance.
Heat treatment, however, slowed down fruit ripening and
increased water loss. Wrapping heat-treated fruits in
polythene exposing only the crown, prior to cold storage
reduced internal browning further and also the water loss
giving the fruit a better appearance (Weerahewa & Adikaram
2005b). Akamine (1976) also found that exposure of fruits
to hot air at 37.2°C and 33% humidity reduced internal
browning. Heat treatment after refrigeration was found
more effective than before refrigeration.
More recently, treatment with 1-methylcyclopropane
(1-MCP), an inhibitor of the ethylene receptor, has been
reported to effectively control internal browning of
pineapple (Selvarajah
et al
. 2001). 1-MCP has delayed the
decline of ascorbic acid and acted as an inhibitor of
ethylene receptors in pineapple (Selvarajah
et al
. 2001).
The use of breeding to develop resistant cultivars of
pineapple provides an attractive alternative to the costly
and often inefficient post-harvest treatments used to control
the disorder. The major challenge facing the pineapple
breeders is to produce cultivars that not only show resistance
to the disorder, but also retain desirable agronomic and
eating quality characteristics (Stewart
et al
. 2002).
Control of internal browning (blackheart) was attempted
by inhibiting the expression of PPO in genetically
engineered pineapple plants (Graham
et al
. 1998).
A transformation technique for the introduction of
transgenes to control blackheart by particle bombardment
has been developed for Smooth Cayenne pineapple. Leaf
callus cultures capable of high frequency organogenesis
with a short regeneration time were used as explant material
(Ko
et al
. 2006).
(Py
et al
. 1987). The condition appears more often in large
fruit (Teisson 1979). The condition in Hawaii has been
associated with cultivar, high nitrogen, large vigorous
plants, winter- and spring-ripened fruit, treatment with
fruit enlarging growth regulators, irrigation rate and
planting density (Paull & Reyes 1996).
Affected fruit is more susceptible to pre-harvest
sunburn (Keetch 1977) and more prone to mechanical
damage after harvest, and the fruit has poor flavour due to
low acids and low esters (Bowden 1969). Impact damage
of translucent fruit is characterized by leaking of juice
from the damaged area (Paull & Reyes 1996). Leakage
could lead to bacterial and yeast development and may
also play a role in some fungal diseases of harvested fruit
(Paull & Reyes 1996).
Detection of pineapple fruit translucency using X-ray
images was investigated. Ninety-two pineapples were
imaged with X-ray and after imaging, each pineapple
was cut open to determine the true level of the disorder
and rated on a scale from 1 (no translucency) to 5
(extremely translucent). There was a high correlation
(R
−2
= 0.96) between the likelihood of a sample being
rated as good and the actual level of translucency
observed. Samples with no translucency were correctly
identified 95% of the time, while those with extreme
translucency were correctly identified 86% of the time.
The results indicate that X-ray imaging is a useful nonde-
structive method for industry for selecting pineapples
that are most likely to be free of translucency or extremely
translucent (Haff
et al
. 2006).
Crown removal either at an early or late stage of fruit
development did not have any significant effect on fruit weight
or translucency occurrence (Chen & Paull 2001). Waxing
does not influence the increase of translucency of less mature
fruit after harvest, but did reduce the severity in more mature
fruit stored at 8°C for 2-3 weeks (Rohrbach & Paull 1982).
Knobbiness
Knobbiness, a formation of knobs in the base of fruits, is a
result of genetic off type (Soler 1992). This is not a very
common disorder, and observed occasionally in a small
number of plants. However, if the plants are used for
propagation, the incidence of knobby fruit will increase
(Pegg
et al
. 1995). Therefore culling of the crowns of these
fruits is recommended. Knobs usually occur on the base of
fruit in off types. These fruits are not marketed, since
trimming generally breaks the fruit skin and allows rots to
develop (Pegg
et al
. 1995).
Plants showing knobbiness should be culled from the
field or separated from planting material. Knobby fruit
Fruit translucency
Translucence or water-soaking of the flesh is a problem in
fresh fruit market. The condition occurs before fruit harvest
and does not increase after harvest (Rohrbach & Paull
1982). Chen and Paull (2001) found that pineapple fruit
translucency begins to appear 2-4 weeks before harvest.
The basal flesh is the first to show translucence, and in
severe cases the whole fruit is affected. The translucence
has been regarded as being due to premature ripening
(Soler 1994) of the flesh, irrespective of skin colour
