Predicting the impact of irradiation on mango quality

Abstract

Predicting the impact of irradiation on mango quality is important to enable exporters to gauge the potential for and to manage the risk associated with using irradiation as a treatment protocol. There are a suite of variables affecting the likelihood of damage from irradiation including where and how the fruit are grown, the environmental conditions leading up to and at harvest, the post treatment storage conditions as well as the mango variety itself. The trial undertook detailed dose mapping of a commercial sized pallet using Mod12 trays suitable for cost effective export, to better understand the likely variation in dose anticipated in pallets of fruit exposed to irradiation. This trial also examined the effect of irradiating pre-ripening Kensington Pride mangoes using two post irradiation storage regimes, three irradiation level treatments (plus a control). Combined this was designed to give an exporter a reasonable expectation of what potential damage will occur, when and where in the pallet of commercially pre-ripened Kensington Pride mangoes.
Dosimetry illustrated that the irradiation service provider’s process of using pallet density to define the length of exposure to reach a desired minimum irradiation dose, worked well. However it also reinforced the risk that the dose required to ensure the minimum dose (400Gy) to all fruit can result in some fruit receiving more than 850Gy. This equates to a Dose Uniformity Ratio (DUR) of well over 2.0. This can pose risk of the fruit being damaged, depending on the variables mentioned above. The dose mapping and quality assessment suggests that the fruit at greatest risk of quality loss are those in trays at the front or back (rather than in the middle) of the pallet. These trays should be targeted during export market quality inspections at arrival.
Not surprisingly, the use of 12°C storage for the first seven days (then 20°C for the remaining 11 days of assessment) post irradiation held back the ripening of the fruit by 2 and 5 days as indicated by fruit firmness and skin colour, respectively when compared with fruit held at 20°C for the entire 18 day assessment period. The cooler storage condition also delayed the expression of lenticel spotting and skin browning by about 3 days.
The irradiation dose did not have a significant effect on fruit ripening for this pre-ripened fruit, but all three irradiation doses (440Gy, 640Gy and 840Gy) resulted in higher (but similar) lenticel spotting than the control treatment (0Gy). Fruit receiving 640Gy and 840Gy did show a greater level of skin browning than those receiving 440Gy or 0Gy. Cool storage delayed the start of visible skin browning by 3 days (from 7 to 10 days after irradiation) for the 640Gy and 840Gy treatments, while skin browning in the 440Gy treatment did not start to express until day 14 after irradiation.