Agriculture Reference
In-Depth Information
weather can cause basal cracking between fruitlets. Fruit
affected by even minor frost damage are prone to cracking as
they ripen in spring. Juice weeping from wounds is immedi-
ately invaded by yeasts, and these fruit are severely damaged
or destroyed as they ripen. The disease may occur in the
plantation or as a post-harvest problem (Pegg et al . 1995).
Yeasts are among the most common organisms found in
nature. In damaged and overripe fruit, and in fruit with
interfruitlet cracking already present, yeasts start growing
and dividing or new yeasts invade (Paull 1997). In warm
temperature, they infect and grow in sugar solutions
causing fermentation (conversion of sugar to alcohol),
releasing carbon dioxide gas. Early symptoms of yeast rot
include the appearance of bubbles of gas and juice through
cracks or points of injury where infection occurs (Pegg
et  al . 1995). The skin turns brown and leathery (Paull
1997). With the leakage of juice, the fruit becomes spongy.
Internally, the decaying flesh is bright yellow with large
gas cavities. Finally, the shell is left surrounding a mass of
spongy fibrous tissue (Pegg et al . 1995). Some yeasts do
not produce gas but cause a glassy spoilage with a
distinctive aroma (Snowdon 1990).
The characteristic symptoms of this disorder are initially
the formation of translucent, water-soaked spots at the base
of the fruitlets and these areas become brown at later stages
(Abdullah et al . 1985; Akamine 1976). The individual
spots may enlarge and coalesce to form a dark brown to
black colour tissue mass along the core in the entire centre
of the fruit. The browning may expand both inwards and
outwards from the periphery of the core, more into the
flesh, as brown water-soaked areas. The pattern and extent
of development of internal browning symptoms may vary
with the variety. In cultivar 'Mauritius' (Queen) (Plate 7.4)
the initial symptoms appear within 7-10 days of cold stor-
age at 10°C and the intensity increases on prolonged cold
storage (Plate 7.5). The symptoms could be seen in both
core and flesh tissue covering over 75% of the fruit stored
for 3 weeks. The internal browning symptoms develop
rather slowly in certain varieties such as 'Kew' (Smooth
Cayenne) (Plate 7.4) where initial symptoms appear
following 2 weeks of storage at 10°C (Plate 7.5) and the
browning is mostly confined to the flesh tissue as isolated
patches. Internal browning symptoms are observed in the
flesh of Smooth Cayenne fruit chilled at 10°C and the
symptoms were progressively less at lower temperatures,
with no symptoms observed in the flesh of fruit stored at
0°C (Stewart et al . 2002).
Because there are no obvious external symptoms,
affected fruit is often not detected until it is sliced after
purchase, resulting in considerable customer dissatisfaction
(Stewart et al . 2002). This also restricts processing and
leads to significant wastage during processing of pineapple.
The disorder is reported from many pineapple growing
regions in the world and several commercial cultivars. In
countries like Australia field-induced internal browning is
found to be most prevalent (Swete-kelly & Bagshaw 1993).
Internal browning is a result of both cellular damage and
enzymatic browning. Pulp tissues of pineapple affected by
internal browning leak out greater amount of electrolytes
than unaffected tissues (Weerahewa & Adikaram 2005a)
and this might be due to alteration of membrane structure.
The disorder is induced by chilling and results in
browning of the flesh and core of the fruit due to the
oxidation of phenolic substances by the enzyme polyphenol
oxidase (PPO) (Stewart et al . 2001), a copper containing
enzyme which catalyses conversion of o -dihydroxyphenols
to o -quinones (Van Lelyveld & De Bruynm 1977). The
browning of most plant tissues is a result of oxidation of
colourless monophenolic compounds first to o -dihydroxy
phenol and o -dihydroxy phenolic substances to o -quinones
by polyphenol oxidase (Mayer & Harel 1979; Walker &
Ferrar 1998). The o -quinones react with amino acids,
Control
Fruit that will ripen in spring in frost-prone areas must be
protected against damage, by covering young, developing
fruit with paper bags (Pegg et al . 1995). Fruits should also
be protected from sunburn and mechanical damage. Fruit
showing even minor interfruitlet cracking should not be
consigned to the market. Any fruit showing fractures
between fruitlets should be picked at the earliest stages of
fruit maturity to minimize losses from yeasty rot (Pegg
et al . 1995).
Internal browning of fruit
Internal browning is a physiological disorder in pineapple
also known as black heart and endogenous brown spot
(EBS). Pineapple is a chilling sensitive fruit and when the
harvested fruit is exposed to low temperature 8-15°C
during storage, transport or when the developing fruit is
exposed to cool winter periods in the field, development of
internal browning occurs (Wills et al . 1985). Internal
browning is induced in ripening fruit when field
temperatures fall below 21°C for several days, followed by
a return to warmer temperatures (Teisson 1979; Rohrbach &
Paull 1982; Smith & Glennie 1987). In subtropical
Queensland, summer crops of Smooth Cayenne produce
fruits with excellent characteristics, but fruit grown in the
winter months (May-September) are particularly susceptible
to the internal browning disorder (Teisson 1979).
Search WWH ::




Custom Search