Longan and Carambola - Tropical and Subtropical Fruits: Postharvest Physiology, Processing and Packaging - page 221

picked fruit without any loss of quality, although peri-
carp browning generally occurs (Wong, 2000; Jiang et al.,
2002). Large longan fruits with moderately thick aril are
preferred for freezing. The fruits should be sorted for
any damage and decay before washing in chlorinated wa-
ter. Besides being frozen in its skin, longan fruit can be
peeled and pitted before freezing. In the production of
frozen longan with pericarp removed, the flesh should be
dipped in a solution of 0.3% citric acid prior to soak-
ing in 7% calcium chloride and 0.5% ascorbic acid so-
lution for 30 min. After that, the flesh is rinsed with wa-
ter and then soaked in a 0.5% sugar solution for 30 min
before drainage. Longan flesh is then packed in thick plas-
tic bags, sealed, and frozen at the temperature of

grade (diameter 20-21 mm), and C grade (diameter 20

mm) (Tapanadilok and Kongkunakul, 2004). Dried longan
aril has great potential in the market due to its superior
quality. The product is ready to eat with no peeling or pit-
ting required. Important markets for dried longan aril are
Japan, Europe, the United States, Taiwan, Hong Kong, and
Singapore. For superior quality, longan aril is usually dried
after removal of the pericarp. After peeling and pitting, the
flesh is washed with water before soaking in potassium
metabisulfite solution for 5 min to prevent browning. The
flesh then is drained by placing on drying rack in a single
layer and dried at 60 ◦ -70 ◦ C for 12-15 hours. Drying tem-
perature higher than 70 ◦ C would result in dark brown to
black product. Final moisture content of the product should
not exceed 18%. Dried longan aril is normally packed in
thick plastic bags tightly sealed or vacuum sealed or flushed
with inert gas before sealing. For longer storage life (longer
than 6 months), finished product should be stored in cold
room, otherwise, darkening of the product would occur un-
der ambient temperature. Normally, to obtain 1 kg of dried
longan aril, 10 kg of fresh longan are required. Dried longan
aril can be classified into A grade and mixed grade. A grade
product is yellowish-gold, with intact flesh and completely
dried. Mixed grade is yellowish-gold but not homogeneous
in size and have some breakages (Tapanadilok and Kongku-
nakul, 2004).

<

40 ◦ C
until the flesh is completely frozen. For extended shelf life
and good eating quality, frozen longan should be kept at
−

−

18 ◦ C with minimal temperature fluctuation during stor-
age and distribution (Tapanadilok and Kongkunakul, 2004).

Drying
A significant number of fresh longan fruits are processed
into dried products every year (OAE, 2010). Longan can
be dried either intact or after removal of the pericarp. The
dried aril is usually brown or black, leathery and smoky
in flavor, and is mainly used for preparing a refreshing
drink that is very popular among the Chinese. A liqueur
can also be made by macerating the longan flesh in alcohol.
Dried longan flesh is also an ingredient in herbal medicine
used for stomachache, insomnia, and as an antidote for poi-
son (Wong, 2000). In Thailand, 'Daw' is a popular cultivar
used for drying due to its large fruit and thin pericarp. Small
and medium longan fruits are usually used for drying. The
fruits should be sorted for decay and graded according to
size. Then they are washed, blanched in boiling water for
5 min, and soaked in potassium metabisulfite solution for
10-15 min to help retain their light color during drying
(Siriphanich et al., 1999). Application of SO 2 gas can also
be used instead of potassium metabisulfite solution. Sun or
tray drying at 55 ◦ C is initially used in the drying process,
and when the fruits start to dry, the temperature is raised to
70 ◦ C, until they are completely dried. The total drying pe-
riod is 19-20 hours (Subhadrabandhu, 1990). Tapanadilok
and Kongkunakul (2004) recommended a drying tempera-
ture of 70 ◦ -80 ◦ C with 40-48 hours drying period for pro-
ducing high-quality dried longan. The dried longan fruits
contain moisture less than 18% and have very high sugar
content of 60 ◦ -65 ◦ Brix. Normally, 3 kg of fresh longan
would yield 1 kg of dried longan (intact). Dried longans
are usually graded into different sizes, including AA grade
(diameter > 25 mm), A grade (diameter 22-25 mm), B

Other products/uses
In addition to the processing described above, a small num-
ber of longans are processed into other products such as
instant longan beverage, longan pickle, and longan pre-
serves. The details of these processings are described in
Tapanadilok and Kongkunakul (2004). Most of the manu-
facturers of these products are small and medium size en-
trepreneurs, not industrial companies. The seed is used as a
shampoo, like soapberries ( Sapindus saponaria L.), due to
its saponin content. Dried leaves, which contain quercetin
and quercitrin, and flowers of longan are also sold as ingre-
dients in Chinese herbal medicine (Wong, 2000).

NUTRITIONAL PROFILE AND
HEALTH BENEFITS
The edible portion of high-quality fruit ranges from 67%
to 78% of the whole fruit. The energy value averages
458 kJ/100 g. Many researchers determined nutritional
composition of longan (Table 12.3). Longan has high car-
bohydrate, mainly due to its high sugar content. The main
sugars presented in the aril are sucrose, fructose, and glu-
cose (Paull and Chen, 1987). The fruit also contributes a
significant amount of vitamin C and phosphorus.