Agriculture Reference
In-Depth Information
(A)
(B)
(C)
Figure 13.4. Commercial lychee peeler (A), peeled lychee (B), and lychee seed (C). For color detail, please see
color plate section.
Peeling and removing stone
With the mandrel cylinder (big head, 1.5
syrup is poured over, leaving 1/4 inch (
6 mm) headspace.
Syrup should be poured at a temperature not lower than
75 C with the addition of 0.25% citric acid in the syrup
to preserve fruit color. Cans with fruit and syrup are then
passed through an exhaust box (to remove any trapped
gases) maintained at 75 -80 C using steam as a heating
medium. The exhaust operation takes 5-6 min, following
which cans are sealed immediately. Cans are then thermally
processed in a commercial retort at a temperature range
of 116 -121 C for 15-20 min. At the end of the thermal
treatment, cans should be cooled immediately to around
35 C. Process time and temperature are dependent on the
can size used and are typical of those used for canning
similar fruits.
Top-quality canned lychees exhibit white to reddish sur-
face color and red to brown interior tissue color. The firm-
ness is medium-hard, and drained fruit has a 14 -18 Brix
with respect to soluble solids.
1.6cmindiam-
eter, and small head, 1.3
1.4 cm in diameter with a sharp
tip) and a forceps with a sharp knife by the end of cylin-
der, lychee fruits are passed through tube or small head by
slightly turning to obtain a good separation of flesh and
stone. Along with rotation of the rubber wheel, a feeding
wheel pushes fruit to the surface of oriented strips to be
cut by knives, which are fixed on a knife shelf one by one.
Lychee pit is separated from the flesh by a plunger-type
knife and falls into a vibratory disposal chute. Last, an
output wheel for rind takes the rind out of the machine.
For better quality, it is important to maintain the integrity
of the flesh well (Anon, 2011). A typical commercial ly-
chee peeler, peeled lychee, and lychee seed are shown in
Fig. 13.4.
Rinsing
To obtain the top-quality lychee flesh, nuclear debris must
be removed. Furthermore, the flesh should be passed
through a sieve and then rinsed in a clean water flume. The
rinsing should be finished within 10-12 min to minimize
contact with air.
Freezing
As the freezing point of lychee fruit is
3.0 C, while the
maximal crystal forming temperature ranges from
3 Cto
15 C (Hu et al., 2005), the fruit can be frozen well. The
freezing of lychee fruit includes the selection of raw ma-
terial, cleaning, color protection, precooling, quick-frozen,
package, and frozen storage (Jiang et al., 2004a). Special
attention for selection of fresh raw material is requested:
fruit with no rot, insects, or damage and an appropriate
harvest time. In sunny morning of picking, after-harvest
lychee fruit should be transported back to the processing
factory as early as possible. After removing fruits with
pests, damage, and brown spots, or overmatured or imma-
ture fruit, the fruits are blanched generally with hot water
Canning
The major processed product of lychee fruit is “canned
in syrup.” The lychee industry has established production
procedures for canned lychee. According to the quality
standards, cans must be precleaned first either by steam
or boiling water. Sugar syrup of 30 Brix concentration is
prepared in hot water, which is then brought to boiling
temperature kept for 1 min. Peeled lychees are filled into
cans at predetermined weight for the proper can size and hot
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