Effects of Fruit Position in Standard Place Pack Cartons and Gamma Irradiation on the Postharvest Quality of ‘Barnfield’ Navel Oranges

The objective of this study was to determine if oranges in the top and bottom layers within a Standard Place Pack were impacted differently by irradiation after long-term storage. ‘Barnfield’ Navel oranges were packed in Standard Place Pack cartons and treated with 0, 0.15, or 1 kGy of gamma irradiation. The fruit were stored for 3 weeks at 5 °C and then for 1 week at 20 °C. After storage, the fruit from the top and bottom layers were separately evaluated for quality. The development of stem-end rind breakdown (SERB) was the main cause of quality loss and was greater in irradiated fruit in the top layer. Fruit in the bottom layer showed more physical damage (flattening) but lower incidence of SERB. The changes in individual sugar content were minimal but significant for layer. The content of individual organic acids was consistently lower in irradiated fruit from the bottom layer. Layer type showed a stronger effect on phenolic compounds than irradiation dose. The tristimulus color, total soluble solids, titratable acidity, and firmness of fruit were not influenced by irradiation dose or layer type. The results show that damage in irradiated Navel oranges depends on dose and layer, with the top layers showing greater physiological damage and bottom layers showing more physical damage.