Kiwifruit - Tropical and Subtropical Fruits: Postharvest Physiology, Processing and Packaging - page 466

Current storage and shipping practices
As mentioned earlier, the kiwifruits soften after harvest un-
less certain interventions to delay the rate of ripening are
taken. The quality of kiwifruit at harvest (harvest maturity)
is normally estimated by the firmness of the fruit and the
soluble sugar content as ◦ Brix (Mitchell, 1990). Kiwifruit
firmness declines from above 60 Newtons (N) at harvest
to about 5-8 N, where it is suitable for eating (Beever and
Hopkirk, 1990). The industry standard in New Zealand is
11.8 N firmness levels as the export threshold (Lallu et al.,
1999). Kiwifruit variety 'Hayward' in California is har-
vested when the fruits reach a ◦ Brix level of at least 6.5
(Crisosto and Crisosto, 2001), whereas in Chile and New
Zealand a minimum of 6.2 ◦ Brix is required (Cheah and
Irving, 1997). The level of soluble sugars content increases
during storage and market processing to about 17 ◦ Brix as
a result of carbohydrate metabolism. The rate of softening
and ripening of kiwifruit depends on several factors (e.g.,
initial maturity at harvest, storage temperature, atmosphere
composition, ethylene availability, and concentration)
(McDonald, 1990). While ripe and sweet kiwifruit is de-
sired by consumers, delay of ripening and maintaining the
fruit firmness is very important for the industry to accom-
modate storage, exports and marketing needs.
The decrease in the firmness of kiwifruit tissue (soften-
ing) is accomplished by a decrease in the fruit starch and
an increase in the soluble sugars content (MacRae et al.,
1992). The migration of moisture during storage seems to
play a crucial role in rapid ripening during storage even at
low storage temperatures (Taglientia et al., 2009).

O 2 levels that do not compromise the product quality) as
well as ethylene blockers (e.g., 1-MCP) can improve the
shelf life greatly. The fruits are shipped in trays (3.5-10 kg
each) in pallets (contain from 96 to 240 trays) (OPG, 2010).
Before distribution to local retails or at distant markets, the
ripening is initiated using ethylene (100 ppm). The treated
fruit will be held up to 5 weeks at 0 ◦ C or they will ripen
within 2-3 days at 20 ◦ C. Given the sensitivity of kiwifruit
to ethylene, vast losses can result from fruit soften pre-
maturely without ripening during storage. Several systems
are available to scavenge ethylene from storage room (e.g.,
simple ventilation systems, potassium permanganate filters,
catalytic converters, ozone generators).

Postharvest storage technologies
The following are postharvest storage technologies.

Ethylene blockers
The use of ethylene blockers is a very active research area
due to their effective control of the ripening process. The
main compounds of interest are 1-methylcyclopropene,
cyclopropene, and 3,3-dimethylcyclopropene due to the
low concentration required for inhibiting ethylene syn-
thesis. Optimization of the required concentrations of
these compounds under different commercial conditions
for kiwifruits and other fruits indicate variable concen-
trations required under different storage conditions (i.e.,
storage temperature, atmosphere composition, maturity
at harvest).

Antimicrobial compounds
Plants' active compounds have been extensively studied
for their use as an agrochemical to specifically target sev-
eral plant pathogens or as a template for new synthetic
fungicides (Ramezani et al., 2002; Rahman et al., 2005).
One of these promising plants as a source of antifungal
compounds is eucalyptus trees, which have been known
to produce several natural substances having antagonis-
tic activities against several pathogenic micro-organisms
(Delaquis et al., 2002; Ramezani et al., 2002; Oh et al.,
2008). The efficacy of compounds isolated from several
eucalyptus trees ( Eucalyptus darlympleana, E. globules,
E. gunnii ,and E. unigera ) was investigated against the fun-
gal pathogens ( B. cinerea, Botryosphaeria dothidea ,and
Diaporthe actinidiae ), which cause kiwifruit soft rot decay
during postharvest storage. Generally, methanolic extracts
of eucalyptus tree exhibit antagonistic activity against the
pathogenic fungi (Oh et al., 2008). Fractionation of the
methanolic extracts revealed the existence of two pheno-
lic compounds (gallic acid and 3,4-dihydroxybenzoic acid)

Industry practice
Kiwifruits should be harvested when the skins are com-
pletely dry to avoid increased risk of storage rots, especially
gray mold caused by B. cinerea when the fruits are collected
wet (Cheah and Irving, 1997). Wet fruit can promote phys-
iological pitting during storage (Clark et al., 2003). Careful
handling and hygiene practice are employed during har-
vest. Curing (holding the fruits at room temperature) is car-
ried out for 2 days before cooling to reduce the incidence
of Botrytis decay (Lallu et al., 1999) and development of
internal breakdown (Lallu, 1997) during subsequent cold
storage. Fruit cleaning, sorting, packaging, and palletizing
are carried in packinghouses. The product after cooling by
forced air is stored in cold rooms. The recommended con-
ditions for commercial storage of kiwifruit are 0 ◦ C with
relative humidity between 90% and 95%. The product un-
der these conditions can have 4-6 months of storage life.
The use of controlled/modified atmosphere (use of CO 2 and