Effect of gamma irradiation and insect proof bagging on postharvest quality of sulfur dioxide fumigated litchi fruit (‘Mauritius’)

Abstract

The South African litchi industry has to sulfur fumigate and irradiate export fruit as quarantine treatment for the US market. However, the SO2 residue levels must be ≤10 ppm in the aril when fruit reaches the USA during shipment or air freight. Furthermore, litchi fruit has to be gamma irradiated as an additional quarantine requirement against insect pest. Therefore, the aim of the experiment was to investigate the potential of SO2 fumigation, insect proof bagging plus gamma irradiation as quarantine requirement for US market. In addition, evaluate the effect of gamma irradiation on internal quality parameters of litchi fruit after storage. Litchi fruit ('Mauritius') were SO2 fumigated and gamma irradiated (0 kGy with or with insect bagging; 0.6, 0.8, 1.0 and 1.2 kGy), afterwards stored at 12°C for up to 16 days. Thereafter, fruits were evaluated for insect damage, fungal infection, aril SO2, total soluble solids and titratable acids. All irradiation doses reduced insect infestation and fungal infection compared with control fruit. Furthermore, all irradiation doses showed SO2 residue levels below 10 ppm as required by the USA market. In addition, irradiation did not negatively affected internal quality (total soluble solids, titratable acids and Brix) of litchi fruit.