Physiological Studies of Chilling Injury in Citrus Fruits

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Abstract
The physiological responses of citrus fruits to chilling injury were evaluated by determining the rate of CO2 evolution, the rate of O2 uptake, internal atmosphere, and total CO2 content of chilled and non-chilled citrus fruits at 20[degree] C. A pronounced increase in the rate of CO2 evolution was associated with the chilling treatments. There was a cumulative time-temperature influence of chilling exposure upon the degree of stimulation in CO2 evolution. An increase in the rate of O2 uptake at 20[degree] C of immature orange, lemon, and lime fruits was observed after exposure to 0[degree] and 10[degree] C. Determinations of the composition of the internal atmosphere and total CO2 content of orange fruits conclusively show that physical processes, such as the release of dissolved CO2 as the fruits warmed, cannot account for the increased amount of CO2 involved after a chilling exposure. It is suggested that the stimulated respiratory rate of chilled fruits may arise from changes in the relative amounts of certain metabolites which are rapidly oxidized at the non-chilling temperature.