Postharvest biology and handling of longan fruit (Dimocarpus longan Lour.)

The mature longan fruit (Diniocarpus longan Lour.) is small (ca. 1.5-2 cm diameter), conical, heart-shaped or spherical in shape and light brown in colour. It has a thin, leathery and indehiscent pericarp surrounding a succulent, edible white aril. The aril contains a relatively large dark brown seed. Maturity can be determined on the basis of fruit weight, skin colour, flesh sugar concentration, flesh acid concentration, sugar:acid ratio, flavour and/or days from anthesis. Longan fruit are non-climacteric with little change in soluble solids concentration (SSC) or titratable acidity (TA) after harvest. Longan fruit deteriorate rapidly unless proper handling techniques are employed. The major factors reducing the storage life and marketability of longan fruit are microbial decay and pericarp browning. Low temperature storage at 1-5 degreesC is used to reduce pathological decay, but has a only limited role in reducing pericarp browning. Moreover, the, fruit deteriorate rapidly when removed from cold storage. Under refrigeration, longan fruit have a storage life of approximately 30 days. Pulp quality and disease development are generally stable during cold storage until such time as fruit become visually unacceptable from pericarp browning. Sulfur dioxide fumigation has been the most effective postharvest treatment for control of pericarp browning in longan fruit, and is used extensively in commercial situations at present. However, there is increasing consumer and regulatory resistance to the use of this chemical. Insect disinfestation has become increasingly important with the expanding export market. Irradiation and heat treatments for insect disinfestation of longan fruit have been found to be alternatives to treatment with insecticides. Recent research has focused on reducing these major postharvest problems in order to produce light-coloured, chemical-free fruit without disease or insect infestation. (C) 2002 Elsevier Science B.V. All rights reserved.