375 1-Methylcyclopropene (1-MCP) and Heat Treatment Affected Weight Loss and Ethylene Biosynthesis of ‘Sekaki’ Papaya Stored at Low Temperature M. Razali a Horticulture Research Centre MARDI Headquarters Persiaran MARDI-UPM 43400 Serdang Selangor Darul Ehsan Malaysia Z.M. Ali and R. Othman School of Bioscience and Biotechnology Faculty of Science and Technology Universiti Kebangsaan Malaysia (UKM) 43000 Bangi Selangor Darul Ehsan Malaysia Keywords: synthetic cyclopropene, physical treatment, physical changes, ripening, storage Abstract The effects of 1-methylcyclopropene (1-MCP) and heat treatments on weight loss and ethylene biosynthesis on ‘Sekaki’ papaya fruits stored for 28 days at 10°C and after being held at ambient temperature (28°C) for up to five days were investigated. The weight loss of fruits in all treatments increased very slowly during storage at 10°C and increased at faster rates during holding period at ambient following 28 days of low temperature storage. The trends in weight loss, ethylene production, 1-aminocycloprpane-1-carboxylic acid (ACC), ACC synthase (ACS) and ACC oxidase (ACO) activities were similar in all treatments although significant differences were observed between the treatments on the respective holding periods at ambient. Generally, a combination of heat treatment and 1-MCP was found to be effective in inhibiting the ethylene biosynthesis and reduced percentage of weight loss of ‘Sekaki’ papaya stored for 4 weeks at 10°C and also after being held at ambient temperature until the fruit reached a complete ripening. INTRODUCTION The quality of fresh fruits can be maintained by storage at low temperatures. Low temperatures are capable in slowing down the ripening processes in fruits. The ripening process can also be slowed down using ethylene action inhibitor 1-methylcyclopropene (1-MCP). This approach has been used to maintain the quality and extend the storage life of many types of fruits including bananas, plums, avocados and mandarins (Blankenship and Dole, 2003). However, most tropical fruits are very sensitive to low temperatures, which can lead to the occurrence of physiological disorders especially chilling injury (CI). Chilling injury occurs when fruits are exposed to temperatures below the optimum temperature for long periods (Serrano et al., 1997). In papaya, the level and symptoms of chilling injury are influenced by the cultivar and storage type. According to Ali et al. (1993) tropical fruit, especially papaya will suffer from CI when they are exposed to temperatures below 10-12°C. Heat treatment has been widely used in postharvest handling to overcome the problems of insect infestations, control of decay, delay the ripening process and control CI (Paull and Chen, 2000). Heat treatment can minimize chilling injuries on avocado and mango fruits (Florissen et al., 1996). Heat treatment can also decrease ethylene production and control degradation of cell walls, through gene expression and protein synthesis (Lurie, 1998). The ethylene biosynthesis will recover when the fruits are transferred to ambient temperature following low temperature storage as have been reported on avocado and muskmelon (Dunlap et al., 1990). Chilling injury can also be reduced by 1-MCP treatment as has been reported on many fruits including avocado a razally@mardi.gov.my Proc. 7 th International Postharvest Symposium Eds.: H. Abdullah and M.N. Latifah Acta Hort. 1012, ISHS 2013