Response of Lychee Fruit to Cold and Gamma Irradiation Treatments for Quarantine Eradication of Exotic Pests

In separate treatments, fruit of Litchi chinensis Sonn. were subjected to 15 days at 1.1 °C or to gamma irradiation from a 60Co source at dosages of 100, 200, or 300 Gy. Cold-treated `Mauritius' fruit lost some color intensity externally and internally, and the pale flesh had a greener hue. The pericarp of `Brewster' fruit was injured to a greater extent by cold treatment than that of `Mauritius', and the pulp of treated fruit had lower concentrations of acids and soluble solids. Cold treatment increased decay susceptibility of both cultivars. `Mauritius' fruit were also more susceptible to decay following irradiation at 300 Gy and 6 days of storage at 5 °C. Both cultivars lost firmness after this treatment. The pericarp of irradiated `Mauritius' fruit became more orange, whereas the flesh of both cultivars became greener. Irradiated `Brewster' fruit were less acidic and contained less soluble solids, but sensory evaluations could not differentiate between irradiated and nontreated fruit regardless of cultivar. Loss of quality was minimal with either cold or irradiation treatment, and both should be acceptable for lychees requiring quarantine treatment for eradication of exotic pests.