Lychee

Maturity & Quality

Maturity Indices

• Red Color (due to anthocyanins in the skin) is a good indicator of maturity along with fruit size (minimum of 25 mm in diameter).
• Reaching the optimum range of sugar: acid ratio for the cultivar.
• Lychees should be harvested fully-ripe because they do not continue to ripen after harvest.

Quality Indices

• Bright red color with no brown discoloration even though it is not an indicator of aril quality.
• Sweet and juicy aril (edible portion); soluble solids: acid ratio of 30 or higher.
• Freedom from defects (such as bird damage, insect damage, physical damage, cracking, and browning) and from decay.
• Lychees are excellent source of vitamin C (40 to 90 mg/100 g fresh weight)

Temperature & Controlled Atmosphere (CA)

Optimum Temperature

5°C (41°F), range: 1.5°C to 10°C (35°F to 50°F) depending on cultivar and intended storage duration.

Optimum Relative Humidity

90-95%
Maintenance of high relative humidity is essential for reduction of water loss and browning, which is the major symptom of deterioration.

Rates of Respiration

To calculate heat production multiply ml CO₂/kg·hr by 440 to get Btu/ton/day or by 122 to get kcal/metric ton/day.

Rates of Ethylene Production

Less than 0.5 µl/kg·hr at 20°C (68°F)
Lychee is a nonclimacteric Fruit

Responses to Ethylene

Ethylene may accelerate deterioration of lychee fruits (aril breakdown and  increased decay).

Special Treatment

Color can be preserved by bleaching with SO₂ fumigation followed by a dip in dilute hydrochloric acid; but this treatment may induce undesirable aftertaste and is not approved for use on lychee marketed in the U.S.A.
Responses to Controlled Atmospheres (CA)

Recommended CA

3-5% O₂ and 3-5% CO₂.
Benefits include reduced skin browning and polyphenoloxidase activity and slower rates of losses of ascorbic acid, acidity, and soluble solids.

Modified atmosphere packaging is used commercially to a limited extent.

Exposure to oxygen levels below 1% and/or carbon dioxide levels above 15% may induce off-flavors and dull gray appearance of the pulp.