Phytosanitary irradiation employs ionizing radiation to sterilize or kill quarantine pests such as fruit flies, which are detrimental to fresh produce during international trade. This method utilizes the destructive impact of ionizing radiation on the DNA of these pests, causing lethal mutations or reproductive sterilization, thereby preventing their spread and establishment in new environments.
The sources of ionizing radiation are varied:
Gamma Rays: Produced spontaneously by the radioactive decay of substances such as cobalt-60, gamma rays possess deep penetration power, making them effective for treating large quantities of horticultural produce even when packed in bulk on pallets. The continuous nature of gamma emission means facilities often operate round the clock to maximize the use of the radioactive material.
X-rays: These are generated when high-energy electrons hit a metal target, such as tantalum or tungsten, converting kinetic energy into X-rays. The advantage of X-ray technology in phytosanitary treatment is its ability to be switched off after use, thus addressing safety concerns associated with continuous radiation sources like gamma rays. X-rays also have the benefit of high penetration depth, similar to gamma rays.
Electron Beams (e-beams): Produced by accelerating electrons to high energies, e-beams provide high-energy electrons capable of treating surface contaminants. However, due to their relatively low penetration depth—limited to a few centimeters—they are less suitable for bulk treatments and are typically used for surface treatments or for products packaged in thin layers.
The effects of irradiation are not only limited to pests but can also influence the fresh produce’s quality. At the cellular level, direct exposure to high levels of radiation can cause DNA strand breaks, impairing critical cellular functions such as transcription and replication. Indirect effects, largely stemming from the radiolysis of water, result in reactive oxygen species (ROS). These ROS can cause oxidative stress, damaging cellular membranes, enzymes, and DNA. However, the use of low-dose irradiation minimizes these risks, exploiting the natural radio tolerance of many fruits and vegetables while activating their stress response mechanisms, which can mitigate the damage.