POSTHARVEST HANDLING, COOLING AND MARKETING OF LYCHEES

SCIENTIFIC NAME: Litchi chinensis
FAMILY: Sapindaceae

For maximum market and consumer appeal, the essential postharvest handling requirements for lychee fruit are:
1. Harvest only ripe, fully coloured fruit. Immature unripe fruit have low market acceptance and poor eating quality. Increase the harvest of high quality sound fruit by recommended crop management practices, pre-harvest insecticidal and fungicidal spray schedules, and use of tree netting.

2. Dip the fruit carefully in a fungicidal solution (0.5 g/L active benomyl1 at 52°C for 2 minutes), then air-dry and cool to ambient temperature before packing. Departure from these dip conditions may result in ineffective fungicidal control or loss of bright skin colour. This treatment is particularly important for fruit marketed under non-refrigerated conditions.

3. Select only sound, fully-coloured ripe fruit for the wholesale market. Marketable culled fruit should be sold through local outlets.

Methods are now available for packing lychee fruit in bulk and in punnets.

Most lychee fruit are currently packed in volume-filled, bulk packs. The common package is the AUF 9 litre fibreboard carton2. Fruit in bulk packs are susceptible to rapid browning through moisture loss. This can be controlled by:
1. Use of a plastic film liner down the long sides and under and over the fruit. "Crispywrap" PY7 anti fog film sheets on a roll are available from W.R. Grace.

2. Use of 2 x 2.5 kg PY7 "Crispywrap" bags, available from W.R. Grace.

Punnet Pack
Displaying lychee fruit to the consumer without excessive browning can be easily achieved with punnet packs. Packaging procedures are:
1. Pack 12 to 15 fruit promptly in a clear plastic punnet with stem ends down on the top layer, to yield 250 g nett in each punnet. Each punnet should be generously filled.

2. Overwrap each entire punnet completely with a clear PVC cling-wrap film. The film must allow some gas and moisture transmission, but retain sufficient humidity to inhibit loss of bright ripe skin colour without condensation clouding the film. Suitable films, available as dispenser packs, are Goodyear Vitafilm, W.R. Grace URAP or Cryovac® caterer's film.

3. Pack individual punnets in a fibreboard tray with internal spacers3.

The punnet pack provides protection of fresh fruit quality for up to one week at ordinary temperatures and the tray provides protection during transport as well as a convenient method of market and retail display.

COOLING AND STORING LYCHEE
Forced-air cooling and cool storage are used on many horticultural crops to protect fresh quality. Cooling, together with the use of plastic film packaging, will extend the postharvest life of lychee fruit.

Bulk Pack
The AUF 9 litre carton with vented ends is suitable for forced-air cooling. Each package should be lined with a plastic film (PY7 "Crispywrap" antifog sheet) down the long sides and under and over the fruit to form a sleeve around the fruit. Opposite vented ends of the carton are not lined; this allows air to flow through the carton during forced-air cooling.

Palletised lychee fruit can be forced-air cooled to 5°C in about 4 hours. Weight loss during cooling is less than 1%.

Forced-air cooling is suitable for medium-to-large handling operations. Recent trials have shown that individual cartons can be cooled in about 1 hour by using a conveyor cooling system.

The conveyor is a length of unpowered rollers long enough to hold the number of packages packed in an hour. An equal length of air duct is fitted above, and in line with, the conveyor. The simplest duct is a length of polyethylene tubing closed at one end and fitted over a fan shroud at the other end. The duct has a series of holes on the underside located to direct cold air down into each package. The conveyor, duct and fan are located inside the coolstore.

The plastic liner of each package is folded away from the top of the fruit to allow cold air to jet directly down into the fruit from above. After cooling (i.e. when each package reaches the end of the conveyor), the liner is closed over the fruit and the carton is lidded.

The advantage of this system is that the cooled fruit are fully enclosed in plastic film, so that fruit at the ends of the carton are protected against moisture loss and browning during storage.

Conveyor cooling would suit smaller handling operations.

Punnet Pack
Overwrapped punnets can be forced-air cooled or conveyor cooled in about 5 hours providing the package holding the punnets is designed for rapid cooling. A suitable package will have end venting and less than full depth partitions parallel to the vented ends to allow air to flow through the package.

Lychee fruit, properly packaged and rapidly precooled, can be stored at 5°C for up to 4 weeks with minimal loss of fresh quality. The coolroom should be appropriately designed for rapid cooling, refrigeration capacity and storage area.

The main problem with lychee fruit stored under refrigerated conditions is protection against moisture loss and browning. With careful quality control, precooling and cool storage, product monitoring and correct marketing, the postharvest fungicidal dip treatment, necessary for fruit under non-refrigerated conditions, should not be required.

TRANSPORT AND MARKETING
Non-refrigerated packages should be sent promptly to the wholesale market for rapid distribution to retail outlets. Cool-stored packages which are block-stowed can be sent to the market by covered non-refrigerated transport. Individual packages should then be marketed rapidly.

Lychee fruit in bulk packs are difficult to display without excessive browning occurring. Punnet packing provides the best method of delivering lychees of an acceptable quality to consumers.

1 Benlate ® (DuPont) contains 500g/kg benomyl. This treatment is registered for commercial use in Queensland and New South Wales.

2 AUF 9 litre fibreboard carton, external base dimensions 380 x 285 mm which stacks 12 to the layer on the Australian standard pallet.

3 Alternatives are:
1. "Strawberry" type fibreboard 12-punnet package, open-top or lidded, containing standard square clear plastic "strawberry" punnets. This carton is unsuitable for palletization.

2. AUF punnet package, external base dimensions 570 x 480 mm, containing 16 x 250 g rectangular clear plastic punnets, which stacks 6 to the layer on the Australian standard pallet. This carton is designed for retail display.

B.I. Brown and J.B. Watkins
Qld. Department of Primary Industries

DATE: November 1987

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