Effects of Heat Treatments on the Ethylene Forming Enzyme System in Papayas

Abstract

Heat inactivation studies were conducted on the ethylene-forming enzyme system (EFE) in papayas. Heat inactivation of the papaya EFE was biphasic and both phases followed first order kinetics. The activation energies E, for the thermal inactivation of the heat resistant (HR) and the heat susceptible (HS) EFEs were 68.3 and 51.2 Kcal/ mole, respectively. The thermodynamic constants for the heat inactivation of both EFEs were; enthalapy, 5 1.2 kcal/mole for HS and 66.7 kcal/mole for HR; free energy, 22.5 kcal/mole for HS and 23.3 kcal/mole for HR; entropy, 87.2 cal/deg-mole for HS and 137.8 calI deg-mole for HR. The heat resistant EFE appeared to compromise about 25% of the total EFE activity. Commercial heat treatments used for quarantine treatments affected mainly the heat susceptible portion which comprised the remaining 75% of the total EFE activity.

Expression of genes associated with ethylene‐signalling pathway in harvested banana fruit in response to temperature and 1‐MCP treatment

“…Ripening of climacteric banana fruit is associated with a sharp increase in ethylene evolution 1. Storage at high temperature (>35 °C) inhibits ripening of many fruits, including pear, avocado, papaya, tomato and kiwifruit 2–6. Failure of these fruits to ripen normally at high temperature has been attributed to a reduction in ethylene biosynthesis at high temperature 3.…”

Temperature and Abscisic Acid Can Be Used to Regulate Survival, Growth, and Differentiation of Cultured Guard Cell Protoplasts of Tree Tobacco

“…A high rate of ethylene production leads to loss of Chl from chloroplasts of cultured cells (chlorosis) and a "cellular senescence" that results in poor cell survival at these temperatures. It is well documented that ACC oxidase is fully inhibited in vitro at temperatures >34°C (Chan, 1986a(Chan, , 1986b. Thus, we further hypothesize that culturing GCP at higher temperatures (>30°C) decreases ethylene production to levels that allow more cells to survive, reducing cellular senescence.…”

ACC Oxidase in Papaya Sections After Heat Treatment

“…They presumed that the rate constants required for the 23ЊC to 42ЊC range could be determined by extrapolation of activation energies given by Chan (1986). Similarly, the first order kinetics of Hayes et al (1987) obtained in fruit fly mortality studies in the 43ЊC to 51ЊC range were presumed to provide mortality data in the 23ЊC to 42ЊC region through extrapolation.…”

“…Discs of exocarp tissue from papayas heated by water immersion were assayed for ACC oxidase activity. Thermal inactivation curves of ACC oxidase between 43-51ЊC were described as first-order reaction decay rates and were described thermodynamically (Chan, 1986). Subsequently whole fruit were heated at 43-49ЊC with hot air and discs excised after treatment exhibited initial increases in ACC oxidase activity prior to eventual enzyme inactivation (Chan and Armstrong, 1990).…”