Agriculture Reference
In-Depth Information
levels above 5 ppm do not hasten de-greening or improve
colour, but may cause serious losses from anthracnose dis-
ease. Exogenous ethylene causes germination of the appres-
soria that will result in the onset of the infection process.
However, ethylene can also induce physiological changes
required for the development of fruit resistance (Kader
1985). The role of ethylene in anthracnose development is
complex, and well described by Timmer and Brown (2000).
(
Aonidiella auranti
). The pressures used to remove red
scale were 36 bar (525 psi) and exposure times were short
(15-20 seconds). However, pressures have been progres-
sively reduced to reduce the risk of fruit damage. Lower
pressures of 10-13.6 bar (150-200 psi) are considered
effective given longer periods of exposure (Walker
et al
.
1999). High-pressure washes remove surface pests, but are
more commonly used for the removal of sooty mould and
general fruit cleaning. Developments in hot-water immer-
sion treatment (HWT) and hot-water rinsing and brushing
(HWRB) technologies have shown to kill decay causing
pathogens, while maintaining fruit quality during pro-
longed storage and marketing (Fallik 2004). Higher tem-
peratures require shorter treatment periods which can
prevent heat damage. Cultivar, fruit maturity, fruit size and
condition during the growing season are all factors that
should be considered when determining the exposure time
and temperature of treatments (Fallik 2004).
Dumping
Citrus fruits are dumped from crates or large bins into a
hopper or receival tank at the start of a conveyor or packing
line. The dumping procedure can produce impact damage
or abrasion unless appropriate control measures are taken.
Fruit can be dumped into water to cushion impact, but
water creates greater risks to food safety and pathogen con-
trol. Wet receival is usually associated with the implemen-
tation and maintenance of an effective water quality
management system. Effective chlorination of the water
and or filtration may support a reduced need to regularly
replace the water that could impact on the water footprint
of the pack house. Water replenishment rates vary depend-
ing on the volumes of fruit handled. If water in a receival
bath is not adequately managed, biofilms could develop
and contribute to a build-up of microbial loads. Dry dump-
ing is recommended, provided the fruit velocity can be
reduced by controlling the fall, and the hard surfaces can
be padded. Fruit on fruit contact is preferred to fruit on
hard metal surfaces.
Fungicide application
Citrus fruit are often stored and transported long distances
to markets. With the more extended supply chain, sub-
stantial losses can occur unless spoilage pathogens are
controlled and the cold chain is effectively maintained.
Consumer and environmental concerns have generated
substantial interest and, consequently research activity,
into controls that leave little or no residues on fruit.
However, chemical fungicides remain the most effective
and commonly employed treatment to control post-
harvest disease. Chemical fungicides can be applied in
aqueous solutions to fruit or can be incorporated into
waxes. The aqueous application of fungicides typically
uses high volumes to ensure good coverage. Under high-
volume application, the fruit is either immersed in tanks
or drenched from above as it moves over rotating rollers.
Alternatively, low volumes of a fungicide solution can be
sprayed over fruit rotating on brushes. The brushes apply
the fungicide to the fruit and only sufficient volumes of
fungicide are applied to maintain continuous saturation of
the rotating brushes. Unlike high-volume applications, the
solutions are not recovered and re-circulated. When fun-
gicides are used as a dip treatment, it is important to mon-
itor the fungicide concentration and use adequate
replenishment rates to ensure effective control. Chemical
fungicides can also be directly incorporated into waxes.
Fungicide in wax forms a concentrated barrier on the sur-
face of the fruit, which is useful in the control of mould
sporulation (Brown & Dezman 1990; Smilanick
et al
.
1997). The application of waxes is described in the next
section.
Washing
Citrus fruit is washed inline to remove orchard spray resi-
dues, microbes, soil and other organic contaminants, such
as sooty mould (most commonly,
Capnodium citri
Penz.)
(Davies & Albrigo 1994). Effective washing includes wet-
ting of the fruit over a brushing unit. The unit consists of
transverse cylindrical brushes set at a right angle to the
fruit, and overhead water sprays. Fruit cleaning can be
assisted by the use of detergents, and recirculated water
should be sanitised to avoid the accumulation of viable
microbes. The washing process should be completed with
a fresh potable water rinse. Barkai-Golan (1966) reported
that citrus peel was almost free from spores (especially
Penicillium
) after the fruits were washed in a bath of
sodium ophenylphenate (SSOP).
High-pressure washers
Since their introduction in the 1970s, the role of high-
pressure washes has evolved. Initially, washers or 'descalers'
were primarily used to remove insects, such as red scale
