Lychee (Litchi) - Tropical and Subtropical Fruits: Postharvest Physiology, Processing and Packaging - page 239

MINIMALLY OR FRESH-CUT PRODUCTS
There is limited information on minimally processed or
fresh-cut products of lychee fruit. The major minimally pro-
cessed or fresh-cut products of lychee fruit are the fresh arils
with vacuum packing (Shah and Nath, 2006, 2008; Bolanos
et al., 2010) or frozen fruit packaged with polyethylene bags
(Jiang et al., 2004a).
As substantial quantities of lychee fruit are rejected easily
by the market due to discoloration of pericarp even though
the edible arils remain in excellent condition, the fruits are
minimally processed as lychee arils which provide fresh
like fruits with simplicity in use and convenience (Shah
and Nath, 2006). Furthermore, lychee arils can be stored
frozen for 1 year without a significant change in color. With
increasing yield of lychee in the world, the production of
the frozen arils will increase steadily to meet consumers'
demand.

(Shah and Nath, 2008). Application of antibrowning agents,
firming agents, osmo-vacuum dehydration, and packing un-
der moderate vacuum significantly extend the shelf life of
lychee arils. To better control pathogens, sanitizers, such as
NaClO or ClO 2 , could be applied additionally.

Quality attributes: physical, chemical,
and sensory
In practice, quality attributes of lychee arils are largely
based on consumer acceptance in terms of aroma, taste,
overall appearance, color, size, freshness, and safety
(residue levels and food-borne pathogens). Some indexes
such as pH, TSS, sugars, TA, ascorbic acid, total pheno-
lics, protein, phospholipids, firmness, and color are used
to evaluate the quality attributes of lychee arils (Shah and
Nath, 2008). Thus internationally accepted official quality
standards need to be established for lychee arils.

Pretreatments and sanitizer use
Lychee fruit is destalked, sorted, packed in boxes, and trans-
ferred to a cold storage chamber prior to minimal process-
ing. In preparation for arils, lychee fruit requires to be
peeled carefully. Special care must be taken to cause mini-
mum damage to aril portion. In China, a machine to separate
pericarp, pulp, and stone of lychee fruit was developed for
commercial use (Zhang et al., 2005). Washing with ster-
ile water is also used to remove dirt and reduce surface
microflora to better control pathogens; 5% H 2 O 2 ,0.1%
NaClO, or ClO 2 solution as sanitizers is used addition-
ally. Application of antibrowning agents (0.5% cysteine,
2% ascorbic acid, and 0.01% 4-hexyl resorcinol) and firm-
ing agents (0.02% calcium lactate) can extend the shelf life
of lychee arils (Shah and Nath, 2006, 2008). Future work
should be concerned with checking the loss of firmness of
delicate lychee arils during storage.

PROCESSING AND PROCESSED PRODUCTS
Processing of lychee fruit is done in different forms. Al-
though most of the fresh lychee fruit is dried as nuts, other
lychee-based food products are also produced in China and
Thailand. The current processings of lychee fruit is for
producing juice and canned or dry fruit. In addition, pulp
of lychee is aseptically packed and stored at 2 ◦ -3 ◦ Cfor
preparing lychee processed products.

Preparation operations
The preparation operations of lychee fruit include grading,
cleaning/washing, cutting, blanching, and so on.

Grading
The general criteria for fruit grading is large, well-colored
fruit with sweet flesh and small seeds (Jiang et al., 2006b).
In practice, lychee fruits are graded on the basis of their di-
ameter or weight. In China, 'Nomici' fruit ranging from 25
to 30 g are considered top grade. To maintain fruit quality, it
is suggested to transport fresh lychee fruit to the processing
plant within 24 hours of harvest. After the grading, small
fruit or fruit with browning, soft rot, or broken skin surfaces
should be removed.

Packaging of minimally processed products
There is limited published information on packaging of ly-
chee arils. Shah and Nath (2008) reported the packing of
lychee arils in polypropylene bags under vacuum. Packing
in a moderate vacuum along with osmo-vacuum dehydra-
tion is found to be highly effective in preserving the product
against microbial proliferation and chemical changes. Fur-
ther investigation into other gas combinations is needed for
packaging.

Cleaning/washing
Fruit is washed with clean water, then soaked for 5 min
in 0.1% potassium permanganate solution as a disinfectant
treatment, and are finally rinsed with flowing, clean water
for 5 min. Immersion operations should be done carefully
to prevent fruit burst.

Microbiological issues/food safety aspects
The visible signs of mold growth of lychee arils after 1 week
during refrigerated storage seriously affect their shelf life