Kiwifruit - Tropical and Subtropical Fruits: Postharvest Physiology, Processing and Packaging - page 473

into products such as fruit juices, jams, wines, and spirits
(Ferguson and Stanley, 2003).

Kiwifruits (>80%
ripeness, dia. >3 cm)

Canning
Canning as a preservation method offer long shelf life.
Kiwifruits are canned as peeled whole kiwifruit, sliced,
halves, dices, or crushed. Solid and firm-ripe fruit should
be used for canning. Kiwifruit may be canned in medium to
heavy syrup or even without sugar. However, owing to its
high acidity (1.5%) and low pH (3.1-3.8), sugar is added
to improve the flavor of kiwifruit. Addition of sweetener
and citric acid can affect the perceived quality of canned ki-
wifruit, but the type of sweetener has little effect (Wildman
and Luh, 1981). The disadvantages of canning are that the
degradation of chlorophyll (90%) and pectin content dur-
ing retorting results in change of color and pigment pattern,
producing a commercial product with a yellow brown ap-
pearance which is different from that of the fresh kiwifruit
(Cano and Marın, 1992). Kiwifruits also develop hard core
after canning, which is more prevalent in overmature fruits
(Dawes, 1972). A typical processing flow chart is presented
in Fig. 25.4.

Washing

Hot causc peeling
(soak in boiling 12-15%
NaOH soluon, 2 min.)

Peeling with water
rinsing

Soak in acid (0.1% HCl,
10 min)

Rinsing with water

Soak in 1% NaCl, 3 min.

Freezing
The correct selection of the fruit variety to be processed
has considerable importance to obtain a frozen product
with good color, flavor, and texture (Cano et al., 1993a).
The advantages of frozen kiwifruit slices are very similar
to fresh fruit in terms of its appearance and flavor, and
the freezing process does not cause large compositional
changes.
The general sequence of steps commonly used in frozen
kiwifruit slices is as follows: Fresh kiwifruit → Peeling →
Slicing

Soak in boiling 0.2%
citric acid, 3 min.

Cool down

Add sugar
soluon 28% &
citric acid 0.13%

Packaging with vacuum
sealing (>75 o C)

Figure 25.4. Diagram depicts the processing steps
for a canned kiwifruit in syrup (drawn based on
information from Li, 1991).

→ → →

Blanching Sugar pretreatment Cooling

→ Frozen storage.

The effect of sugar pretreatment (maltose vacuum infu-
sion) and freezing condition (slow or quick freezing) on
the quality of frozen kiwifruit slices has been investigated
by Li et al. (2008). Maltose pretreatment is the main factor
affecting the water content of kiwifruit slices, followed by
the factor of storage temperature; however, freezing rate
has no significant effect. Different processing options for
the production of frozen kiwifruit products are presented in
Table 25.3.

Packaging → Freezing →

1998). Drying time and temperature greatly influence the
color and visual appearance of kiwifruit (Luh and Wang,
1984). The disadvantage of drying for kiwifruits is loss of
flavor, green color, and vitamin C (Ferguson and Stanley,
2003). Different processing options for the production of
dried kiwifruit products are presented in Table 25.4.

Drying
Drying regulates the product stability by reducing its water
activity to prevent product deterioration (Youn and Choi,

Juice, concentrate, and juice blends
The general processing sequence commonly used in the
production of kiwifruit juices (Balasingham and Clement,