Agriculture Reference
In-Depth Information
Waxing
The appearance of fruit is important in attracting the eye of
the buyer. The aim of citrus waxing is to provide a good
shine and reduce weight loss during storage. Most wax for-
mulations used are water-based emulsions containing car-
nauba, shellac and/or polyethylene depending on the
regulations of the country. The application of wax is very
important, with the amount of wax and uniformity of cov-
erage critical factors to success. Waxes are usually dripped
or sprayed onto fruit over a bed of slowly rotating brushes.
A bank of fixed dippers or spray jets can be employed,
spray jets can be mounted on travelling arms that move
across the fruit in a 'wig-wag' fashion, or waxes can be
applied using controlled droplet spinning disks. Spinning
disks use centrifugal forces to disperse a fine mist of wax
emulsion onto fruit. It is important to monitor fruit flow
rates and adjust the wax rates accordingly.
mechanical sizing. Mechanical sizing is carried out with
belt or roller sizing or expanding roller equipment.
Quality standards
Several international quality standards exist for citrus and
are based on Codex Alimentarius product quality stand-
ards. Codex standards are available for oranges, grapefruits
and limes (CODEX STAN 213-1999 [CODEX Standard
for Limes 1999], CODEX STAN 245-2004 [CODEX
Standard for Oranges 1999] and CODEX STAN 214-1999
[CODEX Standard for Grapefruit 1999]).
Packaging
Corrugated full-telescoping fibreboard cartons with vent
holes are the primary containers used for the packaging
and transport of citrus fruit. This is to protect fruit from
mechanical damage during transport and should also pro-
vide a suitable micro-environment to retain fruit quality.
Fruit is also packed into polyethylene mesh or transparent
perforated polyethylene consumer packs in fibreboard car-
tons. The design of carton and the arrangement of cartons
in unitized stacks are important to allow proper fruit tem-
peratures and ventilation (Timmer & Duncan 1999). Film
with the correct perforation is required to prevent the accu-
mulation of excess moisture and high CO
2
levels. Fruit
packed in mesh bags should be maintained under high rela-
tive humidity to prevent excessive moisture loss and shriv-
elling. Cartons should be stacked on wooden pallets,
wrapped with mesh, tape or plastic, and protected with cor-
ner boards to provide maximum protection during long
transit times.
Drying
Fruit drying can occur at various sections of the packing
line, but large drying tunnels are required after waxing.
Efficient drying is achieved by running high velocities of
air over the fruit. Driers often consist of wide-open convey-
ors with vertical fans mounted above fruit flow. Heater fans
are spaced in the drying, but their use is dependent on
ambient conditions. The drying process is time, tempera-
ture and humidity dependant, with at least 2-3 minutes
generally required to dry waxed fruit. In Australia, drying
tunnels are commonly heated up to 50°C. In certain
countries with dry hot summers, heating is seldom required
(Tugwell 1999). Fruit should not roll continuously, but
should turn once in the drying tunnel to ensure even drying.
Storage
Citrus fruit are held in cool rooms and distributed in refrig-
erated road transport to maximise shelf life. However,
there is no ideal temperature for the storage of citrus but
some recommendations for different cultivars are used in
some countries (Tables 4.5 and 4.6). Recommended stor-
age and carriage temperatures are a compromise between
the temperature below which cold-induced rind blemish
will develop, and the desire to minimise loss of quality due
to shrinkage, loss of flavour and the development of mould
wastage. The sensitivity of citrus to chilling injury varies
according to cultivar, growing region and seasonal condi-
tions. Often fruit is stored at low temperatures to maintain
freshness and then quickly marketed before the expression
of rind blemish. It is recommended to rapidly pre-cool cit-
rus (to below 10°C) prior to loading into refrigerated con-
tainers. Container and road transport refrigeration units are
not designed for pre-cooling and slow cooling of hot fruit
Sorting
Sorting is necessary to remove blemishes and damaged
fruit and grading is done according to market specifica-
tions. Electronic sorting equipment is usually placed at the
start of a packing line to remove a proportion of blemished
fruit. Some blemishes are difficult to sort electronically,
and hand sorting is still required after waxing. Grading
areas need to be comfortable with good lighting. The flow
of fruit is usually diverted into narrow lanes (30 cm wide),
and one sorter is responsible for each lane.
Sizing
Citrus fruit must be sized accurately to enable packages to
be correctly filled and uniformly presented in the market
place. Citrus fruit can be sized using electronic optical
sizers or weight sizing equipment. Electronic volumetric
sizing is more accurate and less damaging to fruit than
