Agriculture Reference
In-Depth Information
develop good flavour, have low brix and are more prone to
chilling injury (Rohrbach & Paull 1982). Fully ripe, yellow
fruit are also unsuitable for transporting to distant markets,
therefore slightly less mature fruit are selected for this
purpose (Akamine 1963; Cancel 1974). Being a non-
climacteric fruit, only a few compositional changes such as
decrease in acidity and de-greening may occur after harvest.
Fruits harvested very early will not develop the characteris-
tic flavour and shell colour.
Pineapples for the fresh market are hand harvested, with
pickers being directed as to stage or stages (shell colour) of
ripeness required (Rohrbach & Schmitt 1994). Fruit is
either packed in the field or at a central packing shed. In
Hawaii, pickers walk in the space between rows and place
the fruit on a conveyer belt, which transfers the fruit to a
truck field bin. Fruits are also harvested by pickers carrying
large baskets on their backs. When the fruits arrive at the
packing shed, it is unloaded by hand, by submerging the
bin in water or by sliding the fruit out of the field bin into
water. Fruit with high translucency are separated at this
step (Rohrbach & Schmitt 1994).
Fruits are best harvested between first light and 8.00
a.m. Fruits harvested at midday or mid-afternoon have
poor keeping quality. Harvesting is done by cutting the
stalk with the help of a sharp knife leaving the stalk about
6-8 inches long. The stalk must not be separated from the
stem end of the fruit to prevent entry of spoilage organisms
into the fruit during storage or transit. Harvested fruits
must not be exposed to sun, but instead they should be
collected in a shady place.
Harvested fruits must be carefully cleaned with a soft
brush to remove any insects and debris. Stalks must be
trimmed to about 1.0-1.5 inches. Knives used for
harvesting and stalk trimming must be cleaned at regular
intervals by dipping the knife blade in a disinfectant
solution. The cut end of the stalks should be dipped in a
suitable fungicide solution to prevent any fungal infection.
A wax treatment may be included at this stage to reduce
physiological disorders and improve visual quality. Rough
handling must be avoided at all stages of harvest, collection,
packing and transport.
Pineapples are graded by the degree of skin colouration,
size (weight), absence of defects and disease, and uniformity
of these characteristics before packing. Other characteristics
include maturity, firmness, nice shape, flat eyes and well-
cured broken stem (peduncle). Crown size is a crucial grade
component, with a minimum size, and ratio of crown:fruit
length (0.33 to 1.5) for higher grades. Crowns developed
during the summer tend to be larger and may require gouging
(removal of the crown center) at harvest to meet the standard.
Nondestructive methods for assessing
pineapple quality
Guthrie and Walsh (1997) have developed a non-invasive
method for measurement of pineapple fruit quality based on
near-infrared (NIR) spectroscopy. A remote reflectance
fibre optic probe, placed in contact with the fruit skin sur-
face in a light-proof box, was used to deliver monochromic
light to the fruit, and to collect NIR reflectance spectra
(760-2500 nm). The NIR spectral attributes were correlated
with pineapple juice Brix (Guthrie & Walsh 1997). Resonant
frequency, firmness and soluble solids were evaluated for
pineapple classification using artificial neutral networks
(ANNs) as the analytical tool. A sample of 149 pineapples
was classified based on their internal qualities into five
classes: unripe, partially ripe, ripe, partially overripe and
completely overripe. The developed ANN model
successfully classified pineapples into merely three classes
as unripe, ripe and completely overripe. The classification
accuracy was more than 83% for all three classes.
Acoustic methods using “tapping” on the fruit showed
100% accuracy in sorting good quality of Smooth Cayenne
pineapple cv. '
Pattavia
'. Fresh fruit is graded based on
eating quality of the flesh, the flavour score and TSS/acid
ratio and this correlated well with “tapping” sound. X-ray
computed tomography (CT) has been used to produce a
precise internal image of the fruit electronically
(Sornsrivichai
et al
. 2000) and the intensity of X-ray CT
images and CT numbers show significant correlation with
the ripeness and translucency of flesh which reflects the
taste quality. The technique could identify other internal
defects such as bruise damage and porosity as well as
identify the inferior fruit with nonsymmetrical shape. Thus,
X-ray CT can be an effective nondestructive tool for internal
quality evaluation and following the internal change of each
fruit during storage (Sornsrivichai
et al
. 2000).
Storage conditions for whole and cut fruit
Temperatures of 7°C to 12°C are recommended for storage
of pineapples for 14 to 20 days, provided fruit are at the
colour break stage (Paull 1993). A relative humidity (RH)
of 85-95% is recommended; a high RH significantly
reduces water loss. Ripe fruit can be held at 7.2°C for about
7 to 10 days. Pineapples may be stored at 0-4°C for weeks,
but upon removal, fruit fail to continue ripening and show
severe chilling injury. Quarter-yellow fruit at harvest gain
about one additional week of storage for every 6°C
decrease in storage temperature (Dull 1971). The maxi-
mum storage life at 7°C is about 4 weeks (Paull & Rohrbach
1985). However, when removed, chilling injury-induced
internal browning develops within 2 to 3 days.