Agriculture Reference
In-Depth Information
concentrations of less than 1% may cause off-flavours, and
more than 7% CO
2
leads to internal flesh breakdown
(Crisosto
et al
. 2002; Rushing 1997). Controlled atmos-
pheres must be established within two days of harvest for
maximum benefit (Crisosto
et al
. 2002). Exclusion of
ethylene is again important, such that movement of fruits
around warehouses and stores should be done using
electrically powered vehicles rather than ones with internal
combustion engines that produce small amounts of the
gas (Cheah & Irving 1997).
More recent advances in the protection of minimally
processed kiwifruit involved argon and other noble gasses,
and nitrous oxide, which has been allowed for food use
in the EU. Argon mixtures were less effective than 90%
N
2
O, 5% O
2
and 5% CO
2
in colour retention, firmness and
soluble solids of sliced kiwifruit (Rocculi
et al
. 2005).
In the United States, kiwifruits may be packed in trays,
with up to three trays per wooden or cardboard carton.
Alternatively, bagged fruits are placed in master cartons,
perhaps twenty, 0.5 kg bags per carton. Cartons for volume
filling, typically 10.4 kg, or count filling are also used.
Larger, wooden bins holding 56 kg of fruits may be
employed - carton size or configuration is immaterial as
long as the box is labelled adequately. At retail, kiwifruit
are sold individually or in bags containing 6-10 fruits per
bag (Rushing 2002). Cold tables are recommended when
retailing ripe fruit and warm tables for fruit that is mature
but unripe (Crisosto & Kader 1999).
Table 12.2
Rate of kiwifruit softening
after ethylene exposure at 20°C.
Rate of softening
(kg/day)
Temperature (°C)
0
0.5
5 0.6
7.5 0.9
20 1.5-1.7
Adapted from Crisosto 1997.
Conditioning
Guidelines produced in California suggest that kiwifruit be
marketed as ready to eat to maximise retail returns. To
achieve this requires careful management of ripening,
achieved through temperature (see Table 12.2) or ethylene
treatments (10-100 ppm per 6 h), using firmness as a
measurement. At harvest kiwifruit firmness varies from
5.5-8.2 kg. This falls during ripening to 0.9-1.4 kg, at
which point the fruit is considered ripe and ready to eat.
In general, fruit that has not been pre-conditioned that
has been in store for less than four weeks, or has a firmness
level of 3.6-4.5 kg, should receive further treatment using
ethylene. Conversely, kiwifruit stored for more than four
weeks, or with flesh firmness below 3.6 kg, can be ripened
by temperature modification (Crisosto 1997).
Firmness of the fruit should be measured on intake at
the warehouse and then the appropriate ethylene and/or
temperature regime used to ensure that the required retail
firmness coincides with the anticipated consumption
schedule (Crisosto 1997).
Ethylene
Kiwifruit is the most ethylene-sensitive fruit, even at low
temperatures, with ethylene concentrations of less than
50 ppb at 0°C enhancing softening (Crisosto
et al
. 2002;
Kader 2000a). The post-harvest softening of kiwifruit
occurs in two distinct stages, with an initial slow rate for
about 24 h followed by a period of more rapid decline
(Chen
et al
. 1999). Application of acetylsalicylic acid
reduced the rate of softening, possibly by its conversion to
salicylic acid that inhibits ethylene synthesis (Zhang
et al
.
2003). Similarly, 1-methylcyclopropene (1-MCP) binds to
ethylene receptors and thus inhibits ethylene, and so it has
also been used to modify ethylene response and production
to limit post-harvest physiological changes. Thus, at 20°C
1-MCP decreased or delayed ethylene production, respira-
tion, colour changes, glycosidase activity and softening but
at 0°C ethylene production and softening were unaffected,
as were soluble solids and titratable acidity. 1-MCP had no
effect on superoxide dismutase and peroxidases (Colleli &
Amodio 2003; Boquete
et al
. 2004; Ding
et al
. 2003;
Fan & Zhang 2001; Kim
et al
. 2001; Neves
et al
. 2003).
Processing
Kiwifruit are retailed as whole fruits, or as slices more usually
to the catering trade. Fresh-cut fruits do not keep well, though
calcium treatment and modified atmosphere storage have
been reported as maintaining quality for 9-12 days (Agar
et al
. 1999). Handling at 0-2°C, 90-95% relative humidity
with O
2
from 2-4% and CO
2
at 5-10% is necessary.
Production of off-flavours is a consideration if kiwifruit
slices are exposed to oxygen or carbon dioxide values outside
these optimum ranges (Crisosto & Kader 1999).
Storage
Good-quality kiwifruit entering the store will keep for
four to six months if maintained at 0°C, >95% relative
humidity and <0.01 ppm ethylene. However, using con-
trolled atmospheres can increase the storage time to eight
months, at 3-8% CO
2
and 1-2% O
2
, again at 0°C. Oxygen
