The Effect of Phytosanitary Irradiation on the Quality of Chandler Pummelo [Citrus maxima (Burm.) Merr.]

Phytosanitary treatments prohibit the introduction of pests such as fruit flies into pest free zones, and are often required for international trade. Irradiation is increasingly being considered as an alternative to chemical phytosanitary treatments, such as methyl bromide. While 400 Gy is the generic dose for all insects except the adults and pupae of Lepidoptera, 150 Gy is sufficient to control most species of Bacterocera and 1000 Gy is the upper limit of treatment for fresh produce.  In this study, we evaluated the chemical and physiological effect of low-dose gamma irradiation on the post-harvest quality of Chandler Pummelos (Citrus maxima (Burm.) Merr.), an emerging crop of interest in the U.S. Chandler pummelos from a local grower in California were irradiated at target doses of 150 Gy and 1000 Gy. Irradiated and untreated pummelos were stored at 12 °C for 3 weeks and at 20 °C for the 4thweek to reflect 3 weeks of sea shipment at the ideal temperature for storage of pummelos and an additional week of retail under ambient conditions. Color, titratable acidity, total sugars, juice content, weight loss and concentrations of organic acids were not different for the irradiated fruit in comparison to the untreated pummelos. Irradiation reduced hardness of the pummelo rind and firmness of the flesh. Rind hardness continued to decrease during the 3 weeks of storage at 12 °C, however, during storage at 20 °C for 1 week, hardness increased, most likely due to moisture loss from the surface of the fruit. Although, a decrease in the firmness of the pummelo flesh was observed immediately following irradiation, storage did not lead to additional softening. The external appearance of pummelos was negatively impacted by higher irradiation dose, longer storage time and higher temperatures as pitting and mold growth were evident on pummelos treated at 1000 Gy and following storage at 20 °C. When stored at ideal temperature, pummelos irradiated at 150 Gy appeared to maintain similar quality as untreated pummelos. The results suggest that Chandler pummelo quality is compromised at 20 °C and 1000 Gy treatment but irradiation with 150 Gy can serve as a potential phytosanitary treatment for Chandler pummelos.