Agriculture Reference
In-Depth Information
tolerance to post-harvest heat (50°C hot water) and cold
(0°C storage) treatments than shaded fruit. These
temperatures may be responsible for the variability
observed in post-harvest responses. Thus, it appears that
pre-harvest temperature experienced by avocado fruit
affects their post-harvest behaviour in manners similar to
post-harvest heat treatments (Woolf
et al
. 1999). High
pre-harvest temperatures due to exposure to the sun
dramatically affect a range of post-harvest response in
several avocado cultivars such as 'Ettinger', 'Fuerte',
'Hass', 'Horshim' and 'Pinkerton'. The accumulation of
heat shock proteins in the exposed fruit was an indication
of their response to the stress. The shaded fruit exhibited
more extensive and faster development of inoculated
C. gloeosporioides
than the sun exposed fruit.
Figure 8.2
Avocado washing. Courtesy of Dr Mary
Lu Arpaia, University of California, Riverside, CA.
POST-HARVEST HANDLING
Post-harvest practices are aimed at prolonging fruit storage by
delaying the senescence process and controlling the ripening
of fruit picked at the mature but unripe stage. This can be
achieved by lowering their temperature or changing the gas
composition of the storage environment by decreasing the
oxygen and ethylene concentrations and increasing the CO
2
concentration. Fruit respiration is often used to monitor the
efficiency of these controls (Blanke 1991). Harvesting,
handling and transportation to the packinghouse and all
operations must be done carefully, in order not to cause
mechanical damage. Any injuries can accelerate ripening and
negatively affect the appearance of the peel causing blemishes
and browning during and after storage. Generally, avocados
are very susceptible to bruising during softening (Arpaia
et al
.
1987), and thus should be handled carefully during transport
and display. Any means of minimizing 'squeezing' by
customers will slow quality deterioration. Since quality can
decrease rapidly during softening, it is best to check avocado
ripeness every day and to display or use the ripest fruit first. If
possible, ripe, or near-ripe fruit should be held at lower
temperatures at 1°C to 6°C (Young & Kosiyachinda 1976) to
reduce the proportion of fruit that become over-ripe, with
concomitant increase in rots and other disorders. Avocados
should not receive a water sprinkle or top ice during display.
Figure 8.3
Avocado packing line showing brushes.
Courtesy of Dr Mary Lu Arpaia, University of
California, Riverside, CA.
In the pack house, the boxes are unloaded unto a reception
conveyor that twist them over, and takes the fruit to a clas-
sification machine to separate small avocados. Then the
fruit is cleaned with rotating brushes (Figures 8.2 and 8.3).
The selection and grading can be carried out manually or
with the help of machines, and considering the shape, size
and sanitary characteristics of the fruit, as well as all the
defects caused by insects, rodents, mechanical mishandling
and diseases. The selection criteria also depend on the final
destination of the fruit. Mechanical sizers can be of expand-
ing aperture type or cup weighers. The weighing system
PACKING AND PACKAGING
Fruit are unloaded from the trucks, received and weighed. In
Mexico, fruit arrives in boxes of different colours to identify
its final destination (domestic market, export, organic fruit
etc). Avocados are commonly graded by hand and then
sized by weight devices. Inspection grades are based mainly
on variety characteristics, shape, colour, maturity, trimming
of stems, defects and decay (Nogalingam 1993).
