Physiological properties of fresh-cut watermelon (Citrullus lanatus) in response to 1-methylcyclopropene and post-processing calcium applications

Seedless watermelon (Citrullus lanatus Thunb. Mansfeld, cv. Millionaire) fruit were exposed to 10 mu L L-1 1-methylcyclopropene (1-MCP) or air for 18h. Afterward, the fruit were processed into placental-tissue pieces, treated with calcium dips (20g kg(-1) CaCl2) or deionized water, and stored in vented containers for 7 days at 10 degrees C. At intervals during storage, fresh-cut placental tissue was monitored for respiration, ethylene production, firmness, electrolyte leakage, total soluble solids, titratable acidity and microbial growth. Ethylene production was below detection in fresh-cut placental tissue, consistent with the low ethylene production in intact watermelon fruit. Respiration rates were significantly enhanced in response to tissue processing, and continued to increase throughout the 7 days of storage. Tissue derived from 1-MCP-treated fruit showed enhanced 1-aminocyclopropane-1-carboxylate synthase (ACS, EC 4.4.1.14) activity, suppressed respiratory rates and undetectable levels of 1-aminocyclopropane-1-carboxylate oxidase (ACO) activity during storage. Post-processing calcium dips (CaCl2) had little influence on ACS activity relative to tissue not receiving calcium, but significantly enhanced ACO activity and maintained firmness of fresh-cut tissue throughout storage. The data collectively support the conclusion that 1-methylcyclopropene treatment of intact watermelon fruit is alone unlikely to benefit the storage duration of fresh-cut watermelon. (c) 2005 Society of Chemical Industry.