Abstract : After dragon fruits, rambutan, lychee and longan, Vietnamese star apple was officially imported into USA market. Star apples are commonly grown and exclusively exported from Vietnam. Therefore, it has many competitive advantages in the international market. After harvest, star apples normally are infested insect pests and harmful microorganisms that can spread and damage the agricultural production. Especially, Lasiodiplodia theobromae is one of the main causes of rotting and dieback diseases in star apple fruits. Irradiation doses ≥ 1 kGy can control this type of fungal infection but the quality of star apple changed significantly with doses higher than 0.6 kGy. Therefore, the combined treatment with sodium dichloroisocyanurate (NaDCC) 20ppm and irradiation was investigated in this study to reduce the irradiation dose of star apple. The results showed that irradiation in combination with NaDCC 20ppm can reduce D10 from 0.95 kGy to 0.13kGy (Gamma irradiation) and from 1.1 kGy to 0.19 kGy (Electron beam irradiation). The appearance of insects was not detected during the experiment at normal conditions. Gamma irradiation was appropriate for quarantine treatment when the current box size of L38 x W30 x H32 cm is suitable for both types of star apples and the dose uniformity ratio (DUR) is relatively small (1.44). Using the box size of 49 x 32 x 12cm during electron beam irradiation was appropriate for Lo Ren star apples, the small size of the fruits made it easier for the absorbed dose distributed evenly. Meanwhile, the purple star apple box needed an addition of wooden board (1 cm of thickness) to support proportion and reduce the DUR from 2.2 to 1.4. The quality of both types of star apples were tested to have recommendations before using radiation for quarantine treatment by 10MeV electron beam irradiator (UELR-10-15S2) in the commercial scale. The treatment using NaDCC (20 ppm) and EB irradiation (doses of 400-600 Gy) showed more effective in control fungi growth and in extending the shelf life of both kinds of star apples (13 days) than the control (non- treatment, un-irradiation) (6 days).
Keyword: Electron beam, gamma, quarantine treatment, star apple