Longan and Carambola - Tropical and Subtropical Fruits: Postharvest Physiology, Processing and Packaging - page 217

Kader (2009b). However, a higher ethylene production rate
of 28.3 μ l/kg/hr was reported to be associated with fruit
decay (Zhou et al., 1997a). Low-temperature storage re-
duces ethylene production. Ethylene production of 'Shixia'
fruit was 0.1 μ l/kg/hr at 0 ◦ C, 0.6 μ l/kg/hr at 4 ◦ C, and 1.1 μ l/
kg/hr at 8 ◦ C (Zhou et al., 1997a). The highest ethylene pro-
duction in 'Fuyan' fruit stored at 4 ◦ and 30 ◦ C was 2.3 and
3.9 μ l/kg/hr, respectively (Pan et al., 1996).

O'Hare and Prasad (1991a) reported that 'Biew Kiew' lon-
gan stored at 5 ◦ C had good eating quality but developed
mild chilling injury. Slight water-soaking or scald spots
in the inner pericarp of 'Shixia' longan were observed af-
ter storage at 0 ◦ C for 14 days (Zhou et al., 1997a). In
1998, McGuire reported that 'Kohala' longan stored at
1.1 ◦ C for 15 days, followed by 3 days at 5 ◦ C, developed
bronze patches on the pericarp. Longans stored at 0 ◦ Cfor
21 days or 1.1 ◦ C for 15 days maintain an acceptable tex-
ture, despite browning of the pericarp (Zhou et al., 1997a;
McGuire, 1998).

Composition changes
During ripening, total soluble solids, total sugars, and ascor-
bic acid contents increase, while TA decreases (Ke et al.,
1992; Huang, 1995; Lin, 2002). After harvest, total soluble
solids and TA of the pulp usually decrease during storage
(Lin et al., 2002b). Increasing of total soluble solids in
later stages of storage could be associated with the degra-
dation of cell wall substances such as pectin, cellulose and
other polysaccharides (Lin et al., 2002b, 2002c). Infection
of pulp by Geotrichum candidum (pulp sour-rot disease)
could result in an increasing of TA during long-term stor-
age at 20 ◦ C (Liu, 1991). As the fruit mature, the activity of
pectin methylesterase (PME) and polygalacturonase (PG)
increases resulting in softening of the pulp. Hardening of
the pulp in overmature fruit could be due to water loss and
lignifications (Lin, 2002; Lu et al., 1992).

Pathological disorders
Decay-inducing fungi, including Lasiodiplodia theobro-
mae, Aspergillus niger, cladosporium sp., and Fusarium
sp., can be controlled by reducing physical injuries and
proper management of temperature and relative humidity
during postharvest handling. Sulfur dioxide treatment may
be used in some countries to prevent skin darkening and
control postharvest diseases of longan (Kader, 2009b).

Precooling
Prior to transportation and storage, longan fruit should
be subjected to precooling to reduce field heat as well as
respiration and transpiration rate. Room cooling, forced-air
cooling, hydrocooling, and vacuum cooling have also been
used as precooling methods for longans in combination
with low-storage temperature to help extend the shelf life of
longan fruits (Lin and Zhang, 1997; Chen and Lin, 2000).
Lin (2002) reported that room cooling is an ineffective pre-
cooling method for 'Wulongling' and 'Youtanben' longan,
with a cooling time of 12 hours for reduction temperatures
from 30 ◦ Cto3 ◦ -5 ◦ C. Forced-air cooling is 3-4 times
faster than room cooling. For rapid cooling, fruits should
be cooled before packing in plastic bags or in fiberboard
cartons. Container venting and stacking should be designed
to facilitate rapid cooling. Hydrocooling has been used
widely with longan (Chen et al., 1998). According to com-
mercial practices in China, the fruits are immersed in cold
water (0 ◦ -6 ◦ C) for 3-5 min, loaded into plastic crates, and
allowed to dry in a cold room before packing (Chen et al.,
1998). In Thailand, longan is usually carried out by immer-
sion of longan baskets into cold water with ice (2 ◦ -5 ◦ C)
for 10-15 min before draining and storage in cold room
(Ratanachinakorn and Sukwiboon, 2004). However, hydro-
cooling of SO 2 -fumigated fruit can result in browning of
the pulp near the fruit stalk. This problem can be prevented
by using forced-air cooling or by holding the fumigated
fruit at room temperature for 1-2 hours prior to hydrocool-
ing. Sanitation of water used for hydrocooling is necessary

Physiological disorders
Wa t e r l o s s
Longans are very susceptible to water loss. Skin changes
from light brown to dark brown as a result of water stress
(desiccation) (Kader, 2009a). Storage in plastic bags ef-
fectively reduced water loss and extended storage life (Lin
et al., 1997, 2001b, 2002a). Using polyethylene (PE) film
bags (0.015 mm) could effectively reduce water loss of
'Fuyan' longan, especially at low-temperature storage (Lin
et al., 2002a, 2002c). Liu (1988) reported that 'Pumingan'
fruit packed in PE (0.010, 0.025, 0.040, or 0.060 mm) bags
and stored at 29 ◦ -33 ◦ C for 10 days lost only 0.5-4.0% of
their fresh weight. However, off flavors could be detected
in bags thicker than 0.025 mm.

Chilling injury
Chilling injury is a serious problem during cold storage
of longan, with typical symptoms including darkening of
the skin color and water-soaked areas on the pericarp (Zhou
et al., 1997a; Kader, 2009b). Chilling injury usually leads to
increased susceptibility to decay and loss of flavor (Kader,
2009b). Injury may occur in fruit stored below 5 ◦ -7 ◦ C
for 20 days (Wang, 1998). Susceptibility of chilling injury
depends on cultivars and planting location (Wang, 1998).