Influence of temperature on the beginning of degreening in lemon peel

Abstract

The loss of greenness (degreening) in citrus fruit during ripening is associated with autumnal falls in temperature, and there is a close correlation between the color of the fruit measured in the HunterLab space (colorimetric coordinate a) and the mean daily minimum temperatures recorded for the 7 and 21 days prior to the measurement being made. The term colorimetric coordinate a expresses the variation from green to yellow during lemon fruit ripening.

In this work we attempt to determine the temperature below which degreening begins in three varieties of lemon fruit on the tree: Eureka, Lisbon and Fino. Only the results for Eureka are described since all three varieties showed the same behavior. The colorimetric coordinate a was measured weekly in the peel of previously marked and identified lemon fruit over a period of 7 years, and the temperature was recorded in a weather station situated on the same farm.

The results show that degreening begins when the minimum temperatures fall below 10.5 °C for 2 days (not necessarily consecutive). In our experiment the mean daily minimum temperature recorded for the previous 7 and 21 days were 12.14 °C and 13.64 °C, respectively.

This implies that a knowledge of autumn temperatures should enable growers to know when it is best to harvest the fruit – when degreening has just begun (with a shortened artificial degreening period) or when more time has elapsed, although this may mean that the commercial opportunity associated with early fruit may be lost.