Improving phytosanitary irradiation treatment of mangoes using Monte Carlo simulation

• Ellipsoid shape was used to simulate dose distributions in mangoes.
• For one-sided gamma-ray irradiation, the dose at the outermost segment was quite low.
• Adding plastic wrap or edible coating improved dose distribution significantly.
• The average doses at mangoes decreased with increase of the number of mangoes.

Mango is a popular tropical fruit, comprising approximately half of all tropical fruits produced worldwide. Phytosanitary irradiation is a promising treatment as an alternative to fumigation. Most of the irradiation, however, is done in pallet loads, resulting in non-uniform dose distribution in fruits. Therefore, accurate dose calculation is needed to ensure proper process control to minimize quality changes. Our objective was to evaluate phytosanitary irradiation treatment for mangoes in pallet loads. Mango’s 3D geometry, ellipsoid shape, based on Computed Tomography data, was used to simulate dose distributions in mangoes using radiation transport code (MCNP5). To calculate average doses at different depths, mango flesh was divided into 20 segments from the surface to the seed. Mango was divided into 0.05-cm vertical sections to calculate doses along the major axis. Radiation energy was 1.25 MeV from a Cobalt-60 source. For one-directional irradiation, doses from the surface to the mango seed had a build-up region at the outermost region (up to 0.13 cm) with only 78% of the average dose. An average dose at the outermost segment up to the center of the fruit (0.37 kGy) was significantly less than 0.56 kGy at the middle shell and 0.54 kGy at the innermost shell. Adding 0.1-cm of plastic wrap (PVC) and edible coating to improve dose distribution, the doses at the outermost segment were 0.52 and 0.51 kGy, respectively. These results are crucial since most insects lay eggs just under the produce’s skin. For multiple product arrangement, as the number of mangoes increased, the average doses decreased. However, at both-directional irradiation, even nine mangoes were acceptably irradiated; the dose uniformity ratio was 2.26. Proper control of phytosanitary irradiation treatment is critical to ensure insect elimination while maintaining product quality.