Effects of Storage Temperatures and Individual Packaging on the Occurrence of "Kohansho" of Hassaku Fruit

Abstract

The effects of storage temperature and polyethylene bagging on the occurrence of "Kohansho", a physiological disorder of Hassaku (Citrus hassaku hort. ex Tanaka) fruit were investigated. After a postharvest storage at 5°C for a period, the fruit were transferred to a rooms held at 10, 15, 20, 25, 30 and 35°C. Subsequently, they were evaluated for the occurrence of "Kohansho." The fruit kept at 5°C and at 35°C, the disorder did not appear, but kept at between 15 to 25°C numerous fruit came down with the disorder. The "Kohansho" disorder appeared earlier at 25°C than at 15°C. The disorder manifested itself 24 to 48 hr after fruit were transferred from 5 to 20°C, but the symptoms were not observed between 48 to 96 hr. Placing fruit in a polyethylene bag reduced seriousness of the disorder, especially, if done immediately after the harvest. When fruit stored at 20°C were taken out of the polyethylene bag, symptoms of the disorder appeared after 5 hr, but the fruit remained sound if kept in the bag for 32 hr at 20°C. The appearance of "Kohansho" symptoms is attributed to the increase in CO2 concentration in a polyethylene bag to a maximum level during storage at 5°C. In bagged fruit, the respiration which accumulate CO2 in the fruit tissue, such as flavedo or in the stomatal cavity, eventually emerge, increasing the CO2 concentration within the bag. Concurrently, the relative humidity within the bag increased from 30% to above 90%. Fruit weight decreased slightly accompanied by a reduction in abscisic acid (ABA) content in the peel. The number of stomata per fruit was estimated to be 800, 000 ; microscopic examination revealed that the stomata in the affected area remained open.