Lychee (Litchi) - Tropical and Subtropical Fruits: Postharvest Physiology, Processing and Packaging - page 241

for seconds then cooled rapidly with cold water and finally
soaked with 0.1% (w/v) citric acid solution (unpublished
data). Precooling at about 0 ◦ C as a preprocessing step is
necessary to reduce cracking of the frozen fruit. Applica-
tion of a polyethylene bag acts as inner packaging, while
a paper box or plastic box acts as the outside packaging.
Generally, lychee fruits are packaged, then precooled, and
finally frozen.
Lychee arils can also be frozen well (Dong et al., 2004).
After the fruits are peeled while fruit stones are removed,
the pulp is collected. The pulp is cleaned with flow clean
water then dried to lose the surface water and finally dipped
into a solution containing 0.3% (w/v) citric acid, 0.2% (w/v)
ascorbic acid, and 40% (w/v) sucrose (unpublished data).
The treated arils are then packaged in polyethylene bags,
frozen, and stored at

stage, fruits are usually stored for 3-5 days. (3) The final
drying is at a temperature of 45 ◦ -50 ◦ Cfor8

10 hours. It
is to be noted that the dried fruit with top quality should ex-
hibit easily breakable skin and succulent and smooth flesh.
In addition, special attention should be paid to packaging
and storage of dried fruit because of insects, hot tempera-
ture, high moisture, and external damage. In recent years,
electric oven drying at a controlled temperature has been
used commercially. Florida researchers have demonstrated
the feasibility of drying lychee at 48.8 ◦ C with free-stream
airflow. In China, the best-quality fruit with pale-colored
flesh instead of dark brown is achieved by first blanching
in boiling water for 3

−

−

5 min then immersing in a solution
of 2% potassium metabisulfite for 24 hours and finally dip-
ping in about 4% citric acid for 5

− 10 min before drying

0 ◦ C for 1 year. Thus the quick freez-
ing technology of lychee arils exhibits an advantage over
the whole fruit to avoid skin browning and reduce fruit
cracking.

< (unpublished data).

Juice, concentrate, and juice blends
Lychee juice has large amounts of sugars, acids, vitamins,
minerals and aroma compounds (Zeng et al., 2008; Li et al.,
2009). For thoroughly matured lychee fruit, its sugar con-
tent can reach up to 160 g/liter, and the organic acid is
usually around 2-3 g/liter. The lychee juice is widely pro-
duced in some countries. The production of lychee juice is
similar to that of sweet cane, but it uses a lower sugar (about
14%). Good, fresh lychee juice should be sweet flavor, with
12-15% of TSS and 0.2-0.25% of total acidity.

Drying/dehydration
Dried products of lychee fruit are considered to be impor-
tant sources of essential vitamins and minerals for humans
(Janjai et al., 2010). Osmotic dehydration is the most re-
ported pretreatment used prior to air drying and has received
considerable attention due to low temperature and reduced
energy requirements. Osmotic dehydration by sugar solu-
tion has been used extensively in fruit preservation because
the browning is reduced, the volatile retention is increased,
and the sweet taste is reinforced. Drying pretreatments are
necessary to avoid damage to tissue structures. Mahayothee
et al. (2009) reported the effect of osmotic pretreatment
with combined antibrowning agents (acid, glycerol, and/or
trehalose) on the color characteristics of dried lychee af-
ter drying and during 5 months of storage compared to
samples without pretreatment and then found that the pre-
treatment with glycerol showed the best potential browning
in the dried lychee fruit, followed by glycerol combined
with trehalose and trehalose, respectively. In practice, the
production of dried lychee fruit in China is described as
follows: fruit selection

Indigenous processed products
and new products
Although most of fresh lychees are dried as nuts, lychee-
related foods such as lychee wine, health tonic solution, and
glue are produced. In addition, functional foods from the
fruits in relation to their beneficial effects against gastralgia,
tumors, and enlargements of the glands of consumers are
being developed.

Standards of quality
Quality standards for lychee processed products have not
been established. The general quality standard of lychee
processed fruit is based on sensory evaluation. In practice,
quality standards of lychee processed products are evalu-
ated on appearance, color, texture, flavor, taste, and overall
acceptance in combination with the contents of TSS, total
acidity, vitamins, and minerals.

→ washing → grading → baking

→ storage. It is important to choose an ap-

propriate cultivar with large and round shape fruits with
thick and even skin and high dry matter content and sweet
taste but low astringency. Lychee drying is a three-stage
process: (1) it starts at a high temperature of 65 ◦ -70 ◦ C,
with turning the fruits every 2-3 hours. After 24 hours
at this temperature, fruits are bagged and stored for
2-3 days at room temperature. (2) The second stage of
drying is at a temperature of 55 ◦ -65 ◦ C for 10-12 hours,
with turning the fruits every 2-3 hours. After the second

packaging →

Food safety of processed products
Microbiological contamination is the major safety issues
of lychee processed products (Li, 2008). Micro-organisms
present in processed products can cause food-borne ill-
nesses or spoilage and thus the decontamination can