Critical Guidelines: #
Sunlight and humidity:
- Light is needed for the development of the red pigment, anthocyanin, which colours the fruit
skin, but excessive sunlight and low humidity can break down this pigment.
- On farm trials indicate that litchis grown under shade netting develop better colour and more
uniform colouration between individual fruit. In addition to improving fruit colour, shade
netting produces a more humid environment. Shade netting may either be permanent or
white drape nets placed over the trees as soon as the flower panicles start bending
- It is important that there is sufficient light penetration in the orchard; inter-tree shading may
result in poorer fruit colour development.
- Research in India has shown that the use of overhead micro-jet sprinklers effectively increased
relative humidity in the orchard aiding in fruit colouration.
- Trees with high N levels (>1.6% leaf N) tend to have more green fruit, especially in young trees.
- Apply the majority of N fertiliser after harvest to build the tree’s reserves to support flowering
and fruit set. Limit N application after fruit set.
- Foliar application of Magnesium chloride may aid in biosynthesis of anthocyanins and thus
fruit colour development.
- A 2% mono potassium phosphate (MKP) application on the developing fruit at the 10 g stage
(2 cm x 3 cm) aids colour development in ‘Fay Zee Siu’ but not ‘Mauritius’.
Degree of fruit development
- Fruit maturity varies between fruit on a tree and between trees in an orchard. Some fruits
develop more quickly and colour up sooner than others. Strip picking results in a range of fruit
maturities, different sizes and different degrees of colouration. To optimise fruit size and
colour, a few rounds of selective picking are advised. Selective picking will result in a higher
proportion of well-coloured fruit and fewer smaller fruit on the packline, as fruit left on the
tree to colour up will, in most cases, also grow bigger.
Packhouse acid bath treatment
- Litchi fruit colouration does not develop further after harvest.
- Post-harvest treatments cannot enhance the degree of colouration present at harvest.
- SO2 fumigation bleaches the fruit, but some red colouration returns as the SO2 levels in the
fruit skin dissipate.
- Acid dips in the packhouse post SO2 fumigation speed up restoration of some of the original
- In unsulphured litchis (exported by airfreight) modified atmosphere / modified humidity bags
play a very important role in reducing fruit moisture loss, hence maintaining red colouration
- There are different types of bags for different fruit types. All of these bags are perforated or
micro-perforated to be semi permeable to water vapour, O2 and CO2.
- StePac XTEND bags are commonly used (Stone fruit combination)- see the Services tab on
- Litchis destined to be exported unsulphured should be picked early in the morning to reach
the packhouse before 9 am to be packed and cooled to 10 °C as soon as possible before
shipping to the airport in refrigerated transport. The fruit is then held at 10 °C in the export
agent’s cold stores until loading into the aircraft. Approximately 80% of litchis exported by air
freight are shipped in the lower deck (cargo hold) of passenger flights which is maintained at
cabin temperature (18- 22 °C). Pallet caps help reduce the degree to which the fruit warms up
during the flight.
- In wet, humid seasons, free water can form in the bottom of modified atmosphere bags.
Solutions to this problem e.g. absorbent pads in the bags or bags with higher degree of water
vapour permeability or a mechanism to elevate fruit above where water would develop,
should be considered and incorporated into packaging where possible.
Litchis on the branch / ‘bouquets’
- Litchis exported unsulphured on the branch or in ‘bouquets’ fetch good prices. These fruits
are also exported in modified atmosphere bags and may be more susceptible to water forming
in the bag as they cannot currently be dried on traditional packlines.
- Litchis exported in this format should not be picked when it is raining, and wet litchis should
not be sent to the packhouse. However, damp litchis (no free water on surface) can be sent
to the packhouse.
- Packhouses should investigate modifying drying equipment to dry litchis on the branch.
- Litchis exported by sea freight should be shipped in controlled atmosphere (CA) containers.
- CA settings: 4% O2 and 8-10% CO2.
- CA does not influence litchi colouration per se but reduces mould development.
Supportive Documents: #