Agriculture Reference
In-Depth Information
from fruits on the outside layers can be minimised if the
baskets are lined or covered by a tarpaulin. Larger com-
mercial operations may carry their fruit in cardboard
boxes or plastic trays that reduce water loss. Dipping fruit
in cold water or covering in ice is also done (Huang 2002)
but this may leave the fruit open to chilling damage, and
free water on the fruit encourages the growth of pathogens
(Menzel 2002).
In Asia, rough roads, lack of refrigeration and poor truck
maintenance damage all fresh produce. Harm from these
sources can be alleviated to some extent if baskets are not
overfilled and are packed firmly so that movement during
the journey is restricted. Exposure to warm air can dry out
the fruit very quickly, so transport during the warmer part
of the day is best avoided, to avoid exposure to warm dry air.
A covering will go some way to addressing this problem
(Menzel 2002).
Lychee shipped by air from Madagascar to France may
be packed in 6 kg loads, cushioned with leaves from the
traveller's palm (
Ravenala madagascariensis
Sonn.). Sea
freighted fruits are hydrocooled at 0-5°C, packed in sealed
polyethylene bags, carried to the port at −20 to −25°C and
containerised at 0-2°C (Morton 1987).
In Australia, lychee is shipped in crispywrap bags in 9 l
cartons that contain 5 kg of fruit, packed in two, 2.5 kg
polybags. Conversely, fruit may be shipped in 250 g
punnets under cling wrap (Menzel & McConchie 1998). In
the United States fibreboard boxes with polyethylene liners,
holding 2.25 or 4.5 kg of fruits, are used. Lychee is also
packed into 0.12 l styrene containers (Paull
et al
. 2002).
Containerised lychee have a post-harvest life of 21-35
days when kept at 1.7-10°C, with 15 cfm fresh air
exchange. Acceptable receiving temperature is 1.1 to 10°C
(APL undated).
harvesting at an inappropriate time could produce a
substantial loss in the fresh weight of fruit. By the time
10% of the harvested fresh weight has been lost through
desiccation, browning of the pericarp takes place, and
the period before browning will be reduced if lychee is
harvested at less than optimal times. However, Olesen
et al
. (2003) showed that there was potential to rehydrate
fruit after harvest. Nonetheless, given that the capacity to
rehydrate fruit reduced during the first hour following
harvest, they were uncertain whether rehydration could
be used commercially as the time from harvest to deliv-
ery at the packhouse may be greater than one hour.
Olesen
et al
. (2003) were also concerned that the risk of
contamination should be addressed since the rehydration
mechanism was not clear.
Controlled atmospheres
Use of controlled atmospheres such as 3-5% CO
2
and
3-5% O
2
(at 5-7°C) reduces water loss, skin browning,
polyphenol oxidase activity, ascorbic acid loss, acidity and
soluble solids. However, exposure to O
2
at less than 1%, or
CO
2
above 15% may give rise to off flavours and a dull
grey appearance (Kader 2000b). Browning and decay in
cv. Mauritius were slowed in an atmosphere of 4% O
2
,
5-7.5% CO
2
, balance nitrogen, at 90% relative humidity
and 5°C (Pornchaloempeng
et al
. 1998). Jiang and Fu
(1999) reported a 75% reduction in water loss in lychee
stored under 3-5% CO
2
and 3-5% O
2
for 30 days at 1°C.
However, the mechanism of the response was not clear and
it has been suggested that this type of gassing may affect
the metabolism of the fruit as well as the pathogens
(Menzel 2002). Modified atmosphere packaging has
been tried in sealed polythene bags, with and without SO
2
but is not widely used (Kader 2000b). Deterioration during
MAP storage can be enhanced if lychee is kept for extended
periods on the trees during the harvest period, when
fermentation that begins on the tree continues during MAP
storage (Pesis
et al
. 2002).
Water losses
Lychee has a very short shelf life as quality is lost within a
couple of days of picking. Skin browning and subsequent
rotting result from loss of membrane integrity. It has been
suggested that structural calcium plays a role in senescence
of lychee through its role in cell wall integrity. However,
pre-harvest spraying of calcium chloride at 40 mmol l
−1
did not increase amounts of structural calcium within the
pericarp, nor was senescence delayed (Huang
et al
. 2005).
In Australia, lychee should be harvested prior to the
extremes of temperature that occur around late morning
and early afternoon. Using fruit water potential, Olesen
et al
. (2003) showed that turgor was rapidly lost at about
8 am, with a recovery at about 4 pm, and that the loss of
turgor could be equivalent to 3-5% of fruit weight. Thus
Temperature
Menzel (2002) suggested that the optimum storage
temperature for lychee seemed to depend on the method of
assessment, ranging from 5°C (Huang & Wang 1990) to
10°C (Olesen & Wiltshire 2000). Kader (2000b) suggested
5°C as optimum, with a range from 1.5 to 10°C, depending
on the cultivar and length of storage period. The higher
temperature presents less of a risk of condensation in the
pack. Lychee should store successfully at 2-5°C and
90-95% relative humidity for three to five weeks (Paull &
Chen 1987), or at 5-10°C and 95% relative humidity for
