Agriculture Reference
In-Depth Information
'Gwen' and 19% for 'Zutano' (Rainey
et al.
,
1992). This method is rapid and
less time-consuming and does not involve oil determination.
Fruits are harvested by cutting or snapping of the stem at the base of
the fruit, with about 12 mm of the stem attached. Aluminium picking poles
are usually equipped with a cutter and a bag to catch the fruit. Large trees
on suitable terrain can be partially mechanized by the use of a three- or four-
wheeled, self-propelled, hydraulically powered platform, from which pickers
can use short poles. Pallets or bins should be placed under the shade of trees
while waiting to be picked up for transport to the packing plant. This prevents
overheating of fruit, as precooling is not generally practised.
Postharvest treatments
Most packing houses are automated, with all debris removed automatically
and fruit cleaned with roller brushes. Cleaned fruits pass through graders,
where all diseased, injured and defective fruits are removed and fruits are
separated into size lots for packing. Sizing is done by use of drop-roll (diameter)
sizers or by weight sizers. Each producing country has its own grading
standards and size classes. The major quality criteria are size; skin colour;
freedom from wounds, blemishes, insect damage and spray residues, and
absence of disease, physiological disorders and bruising. Standards for Europe
allow for three classes of avocado, based on appearance, defects, tolerances,
uniformity, packaging and marketing. The minimum mass is 125 g and a
range of size from 125 to 1220 g in 14 ranges is used in all classes (Anon.,
1995). Fruits with lower quality go to processing or are used for local sales.
Sizes of packing cartons dif er in various countries. They are usually
corrugated paperboard cartons for single- or double-layer packing, ventilated
for good air circulation. Pads or styrofoam trays with cup impressions may
be used to prevent bruising. Prepacked consumer units in 'clam shells'
(polyethylene containers) and mesh bags are also used. Fruit may be waxed or
wrapped and packed by hand. All fruit in a specifi c size container must weigh
between a specifi ed minimum and maximum range. Cartons are labelled
with fruit number and size range. In California, packed cartons are cooled at
5-15°C, depending on cultivar, before loading into transport vehicles. 'Hass'
can be stored at 5°C for 3-4 weeks. Longer storage leads to greyish-brown
internal fl esh discoloration and irregular blackening of the skin.
Storage temperature for delaying ripening varies with the cultivar
temperatures of 12.5, 8 and 5°C are used for West Indian, Guatemalan
and Mexican cultivars, respectively. A relative humidity of 80-90% is
recommended. Other storage methods, such as controlled atmosphere (CA)
and hypobaric (low-pressure) storage, have been evaluated. With CA storage
at 2-5% oxygen (O
2
) and up to 10% carbon dioxide (CO
2
) at 5°C and 98-100%
