Kiwifruit - Tropical and Subtropical Fruits: Postharvest Physiology, Processing and Packaging - page 468

acidity) (MacRae et al., 1989; Marsh et al., 2004) stored at
0 ◦ C and ripened after removal from cool storage compared
with the fruits stored at higher temperatures (Lallu et al.,
1999). The storage life of kiwifruit at 0 ◦ C can be enhanced
without negative impact when the compositions of 3% O 2
and 3-5% CO 2 are used (Arpaia et al., 1994).
The use of appropriate packaging (polyethylene film,
200 gauge with 0.5% ventilation) can create an optimal
microclimate for the storage of the 'Hayward' variety
(Bhushan et al., 2002). The quality of the fruits under this
system have been rated better at the end of 8 weeks' stor-
age owing to the development of an optimum MA in these
packages.
The application of ethylene blockers to delay ripening
and improve the storage life of kiwifruit is commonly used.
Treatment of kiwifruit with 1 μl/liter 1-MCP for 20 hours
at room temperature can result in better appearance scores
(no effect on texture, sweetness, acidity, flavor) compared
to untreated fruit (Antunes et al., 2010). While there was
no clear effect on antioxidants, higher citric acid content
and less initial levels of oxalic acid and fructose have been
found with 1-MCP treated samples. Also, better color is
found in the treated fruits due to the inhibitory effect of
1-MCP on chlorophyllase activity, preventing pheophytin
formation and discoloration of the flesh on cutting.

ducing the pathogen load and inhibiting pathogens through
the induction of defense mechanisms in the outer layers
of the epicarp) and biochemical properties of the tissue
(e.g. inhibition of polyphenol oxidase and activation of
pectin methylesterase, promoting deesterification of pectin
molecules, thus increasing the number of calcium binding
sites, resulting in strengthening of the cell wall). Incuba-
tion of kiwifruit at 40 ◦ C (Antunes and Sfakiotakis, 2000)
or hot water treated at 45 ◦ C for 25 min can increase the
firmness of the fruit and prevent the softening of fruit slices
due to the activation of pectin methylesterase (Beirao-da-
Costa et al., 2006, 2008a, 2008b). A positive effect of mild
heat treatment depends on the fruit maturity stage with best
quality of minimally processed kiwifruit slices being pro-
duced from early maturity stage (Beirao-da-Costa et al.,
2006).

Chemical treatment
The physiological implications of calcium concentration
in kiwifruits during storage have been reported in several
publications. High concentration of calcium is associated
with lower incidences of premature fruit softening (Benge,
1999), less physiological pitting (Thorp et al., 2003), and
development of bruising and water-soaked patches during
storage (Davie, 1997). Therefore pre- and postharvest use
of calcium salts (chloride, lactate, caseinate, chelate) either
to maintain quality of the whole fruit or freshly cut fruit
(either directly or as pretreatment) have been widely inves-
tigated (Conway, 1987; Hopkirk et al., 1990; Souty et al.,
1995; Agar et al., 1999; Xie et al., 2003; Gerasopoulos
and Drogoudi, 2005; Martın-Diana et al., 2007; Beirao-da-
Costa et al., 2008a, 2008b; Fisk et al., 2008; Franco et al.,
2008; Antunes et al., 2010).
Pre- and postharvest application of calcium salts reduce
loss of firmness and slow down the ripening process (Souty
et al., 1995; Franco et al., 2008) by decreasing the rate
of CO 2 and ethylene production (Conway, 1987). Calcium
also induces lower rates of color change (Conway, 1987;
Vial et al., 1991; Antunes et al., 2010) and increases ascor-
bic acid content (Franco et al., 2008; Antunes et al., 2010).
Up to 12 days of shelf life has been reported using calcium
application in combination with MA storage (Agar et al.,
1999) compared with storage for 4 days of nontreated ki-
wifruit slices. The studies above have employed different
combination of treatments and parameters (pre- vs. posthar-
vest; concentration of calcium; different calcium salts; the
temperature of application; fruit maturity; the use of ethy-
lene blockers and under different atmosphere conditions),
which results in a plethora of different optimum conditions,
indicating the need to optimize the use of this technology

MINIMALLY OR FRESH-CUT PRODUCTS
Wounds, whether unintentionally caused during handling of
the kiwifruit or intentionally caused through peeling, slicing
and other size reduction systems, such as those employed
during minimal processing of kiwifruit, can lead to consid-
erable damage to the quality of the fruit (excessive soften-
ing, loss of mass, decrease in the flavor intensity, and the
production of ethylene) (Varoquaux et al., 1990; O'Connor-
Shaw et al., 1994; Agar et al., 1999). The firmness of peeled
and sliced kiwifruit decreases very rapidly during storage
in temperature-dependent fashion (Agar et al., 1999) with
increased production of ethylene and CO 2 production that
propagates the deterioration of the product. Therefore sev-
eral chemical, thermal, and physical processing options
have been suggested to minimize the changes in the qual-
ity of processed kiwifruit. Most of the available product
reports discuss the extension of peeled kiwifruit, kiwifruit
slices, and cubes either alone or combined with other fruits.

Pretreatments and sanitizer use
Thermal treatments
Mild heat treatment of the whole kiwifruit can improve the
storage quality due to changes in physiological (e.g., re-