Longan and Carambola - Tropical and Subtropical Fruits: Postharvest Physiology, Processing and Packaging - page 220

(McGuire, 1998). Lin et al. (2001b) reported that longan
can deteriorate rapidly when removed from the cold treat-
ment.
Hot-water immersion for 20 min at 49 ◦ Cusedtocon-
trol fruit flies in longan is also effective against nut borers,
Cryptophlebia spp. (Follett and Sanxter, 2001). Hot-water
treatment of 49 ◦ C for 15 min killed Chinese fly species
without affecting the quality of longans (Lu et al., 1992).
A dip in hot water at about 100 ◦ C for 30-40 sec followed
by keeping at ambient temperature for 6-8 days was effec-
tive in controlling longan fruit decay and fruit fly without
adversely affecting eating quality (Peng and Cheng, 1999).
Longan exported to Japan is required to be heat treated un-
til the center of the fruit reaches 46.2 ◦ C and is maintained
there for 20 min, followed by cooling until the fruit finally
reaches 2 ◦ C, where it is held for 42 hours (Armstrong,
1994). However, longan fruit can develop peel browning
after this quarantine treatment and may not be acceptable
for marketing (Jiang et al., 2002).
McGuire (1998) reported that 100-300 Gy of CO 60
(cobalt) irradiation was a successful quarantine treatment,
which helped maintained better quality of fresh longan than
those undergoing cold quarantine treatment.

Figure 12.2. Processed longan products sold in
Thailand (canned longan, longan beverage, instant
longan beverage, and dried longan). For color
detail, please see color plate section.

Canned longan is a highly acceptable product due to its bet-
ter retention of individual flavor when compared to lychee
and rambutan. Suitable cultivars for canning are varied, de-
pending on the location. Lower sugar content cultivars are
preferred in China, while those with large fruit and small
seed with whiter flesh are preferred in Thailand (Huang,
1995; Wong, 2000). The preferred cultivars for canning in
Thailand include 'Biew Khiew' and 'Daw' (Wong, 2000).
Processing of canned longan begins with peeling and
pitting of fresh longan. Then the aril (flesh) is soaked in
0.1% of calcium chloride and 0.2% of citric acid for 15-
20 min. After that, the longan flesh is rinsed with water two
to three times and drained. Longan is usually packed in a
tinplate can approximately 250 g/can and hot-filled with
syrup (23 ◦ -25 ◦ Brix) or its own juice, leaving headspace of
approximately 1 cm. Exhausting is a necessary procedure
to get rid of air before seaming. The temperature before
seaming should be at least 85 ◦ C. Heat treatment is usually
carried out at 100 ◦ C for 22 min with a cooling time of
20-30 min. The can is then dried, sampled for a quality
check, and labeled before being packed into a corrugated
box (Tapanadilok and Kongkunakul, 2004).

MINIMALLY OR FRESH-CUT PRODUCTS
Consumption of fresh-cut products has increased in the last
few years, mainly due to demand for quality, convenience,
and safety. However, information on fresh-cut longan is
very limited. Zhao and Li (2010) investigated the effects of
ultrahigh pressure (UHP) on the quality of fresh-cut longan
fruits and found that the UHP treatment of 600 MPa for
10 min could result in microbial destruction and product
stabilization without affecting the sensory characteristics,
when stored at 4 ◦ C for 9 days. Thus, UHP could be an
alternative potential nonthermal preservation method for
pasteurization of fresh-cut longan fruit.
PROCESSING AND PROCESSED
PRODUCTS
Besides being eaten fresh, longan can be processed into
various products. In Thailand, the longan fruits have been
processed into canned longan, dried longan, frozen longan,
longan beverage, longan nectar, and instant longan bever-
age. Examples of processed longan products are shown in
Fig. 12.2.

Freezing
According to the Office of Agricultural Economics (OAE,
2010), a small number of longans are commercially pro-
cessed into frozen products when compared to dried and
canned products (Table 12.2). Longan fruit can be frozen
in its skin and packaged in airtight containers. On thaw-
ing, the fruit aril can be used in similar manner as freshly

Canning
Thailand and Taiwan are leaders in canned longan pro-
duction. The export amount of canned longan in Thailand
has significantly increased approximately 3.5 times from
12,669 tons in 2005 to 43,160 tons in 2009 (Table 12.2).