Agriculture Reference
In-Depth Information
Table 8.6
Post-harvest Life of Some Avocado Cultivars at Optimum
Temperature and Relative Humidity (RH).
Cultivar
Temperature (°C)
RH (%)
Post harvest life (wks)
'Hass'
3-7
85-90
2-4
'Fuerte'
3-7
85-90
2-4
'Fuchs'
13
85-90
2
'Pollock'
13
85-90
2
'Lula'
4
90-95
4-8
'Booth 1'
4
90-95
4-8
of ripening depends on temperature of storage (Eaks 1978).
The response of avocado to storage temperatures varies
according to temperature range and fruit type (race), vari-
ety, growing conditions, time in the season, maturity stage
and length of storage required. Recommended optimum
storage conditions vary according to the avocado variety
(Table 8.6). All West Indian cultivars are chilling sensitive
and stored best at 12.8-13°C for a maximum period of
2 weeks, and Guatemalan and Mexican cultivars are
commonly maintained at 4°C and 8°C, respectively (Hatton
et al
. 1965; Zauberman
et al
. 1973). Chilling tolerant
cultivars such as 'Lula', 'Booth 8' and 'Taylor' are stored
best at 4.4°C; while a few cultivars such as 'Fuerte', 'Hass'
and 'Booth 7' are intermediate in sensitivity to CI and store
best at 7.2°C. Optimum storage temperatures for 'Hass'
are 5°C to 7°C for early season fruit and 4°C to 5.5°C for
late season fruit. After 3 to 4 weeks storage, 'Hass' fruit
quality is reduced, and storing fruit for >6 weeks remains a
challenge. Storage temperature should be maintained with
a maximum variation of 1°C. It is important to avoid
temperature fluctuations during transport and storage.
Optimum relative humidity is 85% to 95% RH.
Temperatures above 30°C cause adverse effects on avocado
quality and ripening (Erickson & Takaake 1964; Zauberman
et al
. 1977). From 10°C to 25°C the avocado fruit
commonly softens faster as storage temperature increases.
From 5°C to 8°C softening is usually controlled, but will
occur if the fruit is transferred to higher temperatures.
From 0°C to 4°C, softening at these temperatures is limited
by time, due to the risk of CI. 'Step-down' temperatures
(Vorster
et al
. 1987), where temperatures are typically
decreased 1°C to 2°C each week during shipping, with the
final temperature not <3.5°C, with progressively lower
initial temperatures as fruit maturity increases, are
temperature regimes that have been developed and have
resulted in a protocol for each cultivar for differing times in
the season and growing region.
PRE-STORAGE TREATMENTS
Some pre-storage treatments have been reported to delay
ripening and prolong storage life of avocado fruit. Waxing
can be regarded as a cosmetic treatment, as it imparts
glossiness, but it also has pronounced physiological
effects, especially on the internal atmosphere and weight
loss of the fruit (Durand
et al
. 1984). A gain of 1 or 2 days
of shelf-life may be achieved, but in some cases at the
expense of development of some fruit rots. Waxing was
found to cause a considerable reduction in moisture loss, in
addition to modify the internal atmosphere of the fruit tis-
sue, decreasing the internal oxygen and increasing carbon
dioxide concentrations (Durand
et al
. 1984). Acclimation
(temperature management) is being used successfully in
South Africa, where temperature is reduced gradually
(Vorster
et al
. 1990). Low-oxygen atmosphere pre-storage
treatments (3% oxygen and 97% nitrogen) for 24 h reduced
CI symptoms and softening in 'Fuerte' avocado fruit after
3 weeks of storage at 2°C (Pesis
et al
. 1994). Carbon
dioxide shock pre-treatment (25% in air, for 3 days) was
reported as a promising treatment (Bower
et al
. 1989).
Prusky et al. (1995) suggested that a post-harvest dip or
spray of avocado fruit with the antioxidant butylated
hydroxyanisol might reduce post-harvest decay in avocado
by modulating the natural fruit resistance.
MODIFIED (MA) AND CONTROLLED
ATMOSPHERES (CA)
Optimum MA and CA (2-5% O
2
and 3-10% CO
2
) delay
softening and skin colour changes and reduce respiration,
ethylene production rates, and CI of avocado fruit (Yahia
1998). Mature-green 'Hass' avocado can be kept at 5-7°C in
2% O
2
and 3-5% CO
2
for 9 weeks, then ripen in air at 20°C
to good quality. Exclusion and/or removal of ethylene from
CA storage are recommended. Elevated (>10%) CO
2
levels
may increase skin and flesh discoloration and off-flavour
development, especially when O
2
is <1% (Table 8.7).
