Lychee (Litchi) - Tropical and Subtropical Fruits: Postharvest Physiology, Processing and Packaging - page 237

of taste, overall appearance, color, size, and freshness and
safety (i.e., residue levels and food-borne pathogens).

affects the hue value of the lychee pericarp, which turned
yellowish red during long-term low-temperature storage.
Furthermore, a negative impact on fruit quality can be en-
countered when the fruit in MA packaging is subjected to
temperature fluctuations during shipping and handling or
in the retail display. Thus application of GRAS compounds
in the current storage and shipping practices need to be
assessed further.

Innovative postharvest technologies
Fumigation with SO 2 has been used commercially to con-
trol pericarp browning, but SO 2 fumigation leaves unde-
sirable residues and alters the fruit taste (Sivakumar et al.,
2010). The strict standards enforced by the European com-
munity on fruit, allowing maximum sulfur residue levels of
only 10 μ g/g in the fresh edible portion of the fruit, have
necessitated the development of an alternative postharvest
technology to maintain overall fruit quality during storage
and transportation (Paull et al., 1998; Jiang et al., 2006b).
New attempts have been made to reduce postharvest fruit
browning and rotting during storage and transportation. In-
novative postharvest technologies include application of
biocontrol agents or generally regarded as safe (GRAS)
compounds, preharvest bagging and short-term N 2 treat-
ments, and hydrogen chloride dip plus storage closer to
freezing temperature.

Bagging and short-term N 2 treatment
Bagging fruit 3 days before normal harvest delayed skin
browning and reduced rotting of harvested lychees during
storage (Jiang et al., 2005), whereas a prestorage treatment
in N 2 for 3 or 6 hours extended the shelf life of the fruit
compared with the untreated fruit (Jiang et al., 2004b). Fur-
thermore, prestorage anoxia treatment maintains membrane
integrity of pericarp tissues, with high ATP and ADP con-
centrations and high adenylate energy charge levels (Liu
et al., 2007) (Fig. 13.3). Thus bagging fruit prior to harvest
and a short N 2 treatment appear to show some promise to
maintain physical quality and extend storage life of lychee
fruit, but they require commercial development.

Biocontrol agents
Postharvest decay control in lychee fruit recently became
more focused on the use of naturally occurring non-
pathogenic bacteria or yeasts as antagonists. The biocontrol
agent Bacillus subtilis was found to be effective in control-
ling postharvest decay in 'Madras' and 'Huaizhi' lychee
cultivars (Jiang et al., 2001; Sivakumar et al., 2007) when
stored at 5 ◦ C. The mode of action of this antagonist was re-
ported as the antibiotic action of a cyclic polypeptide, iturin
A (Jiang et al., 2001). Treatment with a cell-free suspen-
sion (extract) of the antagonist was effective in controlling
fruit decay for a storage period of 30 days at 5 ◦ C. Al-
though application of the antagonist did not alter the eating
quality significantly, it caused moderate browning on the
pericarp. The environment, therefore, still needs to be opti-
mized to favor both antagonist survival and retention of fruit
quality. More research is needed on new biocontrol agents
and their application as alternatives to chemical treatments
in the lychee industry to maintain a protective barrier that
does not allow fungal infection without compromising fruit
integrity.

Hydrogen chloride dips
Hydrogen chloride dips are very effective in controlling
the pericarp browning of lychee fruit during storage (Jiang
et al., 2004a) but result in increased infection with fungi
in the absence of fungicides. Storage at above freezing
temperatures can effectively control lychee fruit rotting (Hu
et al., 2005). It is suggested that dipping the fruit in 2% (v/v)
HCl solution for 6-8 min following storage at − 0.5 ◦ to 0 ◦ C
could be an alternative to the postharvest sulfur handling
used currently.

Other technologies
Stern et al. (2006) reported that application of the cytokinin
N-(2-chloro-4-pyridyl)-N -phenylurea extends storage life
of 'Mauritius' fruit. Zheng and Tian (2006) reported that
exogenous treatment with oxalic acid effectively reduced
lychee fruit pericarp browning during storage. This effect
by oxalic acid could be due to induced inhibition of degra-
dation and oxidation of anthocyanins and also to the main-
tenance of relatively low POD activity. The commercial use
of oxalic acid merits further evaluation.

GRAS compounds
GRAS compounds such as ethylenediaminetetraacetic acid
(EDTA), 4-hexylresorcinol or phosphoric acid are tested
in combination with different film types (Sivakumar et al.,
2005; Sun et al., 2010). EDTA and 4-hexylresorcinol in-
hibited the PPO-induced browning in lychee fruit (Shah
and Nath, 2006). However, the EDTA or 4-hexylresorcinol

Shelf life extension and quality maintenance
The current handling slows the loss of quality and extends
shelf life of lychee fruit. Storage in sealed polyethylene
bags or plastic containers delays loss in lychee fruit qual-
ity and extends the shelf life (Archibald and Bower, 2008;