Effects of Pre-Drying , Delayed Cooling , and Carbon Dioxide on Skin Blackening Disorder in Asian pear ( Pyrus pyrifolia Nakai ) ‘ Chuhwangbae ’

We examined the effects of pre-drying rates, delayed cooling, and carbon dioxide (CO2) treatment on skin blackening, a major physiological disorder during cold storage in Asian pear (Pyrus pyrifolia Nakai) ‘Chuhwangbae’. Total skin blackening incidence was calculated as the percent disorder index (PDI). PDI significantly decreased with increasing pre-drying rate: the highest PDI was 37.3 for the 1% pre-drying treatment and the lowest PDI was 5.1 for the 4% treatment. Meanwhile, the 5% pre-drying treatment did not show a statistically significant difference from the 4% treatment. A 48-h cooling delay at 20°C was the most effective treatment for preventing skin blackening. PDI after cold storage at 1°C was 6.2, 9.2, and 19.1 for 48-h delay, 24-h delay, and no delay, respectively. In the CO2 treatment, 2% CO2-treated fruit showed rapid disorder symptoms from eight days after cold storage at 1°C, and the PDI increased to 19.6 at 12 days and to 63.2 at 20, which was three times higher than the untreated fruits. A decrease in total phenolic content appeared more pronounced in the tissues treated with 2% CO2, while polyphenol oxidase (PPO) activity in untreated fruits increased with increasing skin blackening incidence. However, there was no increase in PPO activity with the 2% CO2 treatment, skin blackening appeared to be a CO2 injury rather than enzymatic oxidation. Additional key words: CO2 injury, peroxidase, polyphenol oxidase, pre-conditioning, storage