Chlorophyll Fluorescence Imaging Allows Early Detection and Localization of Lemon Rind Injury following Hot Water Treatment

Abstract

Green lemons (Citrus limon (L.) Burm.) were imaged for chlorophyll fluorescence (CF) 30 minutes after immersion of the fruit into 55 °C water for 5 minutes to determine if CF could be used to identify areas of hot water-induced rind injury before the appearance of visible symptoms. Fluorescence was variable in intensity over the surface of the rind with defined areas of enhanced fluorescence being present that corresponded in shape and location with visible injury that later developed during 24 hours of storage. Images showing minimum fluorescence (F0) and maximal fluorescence (Fm) provided the best image contrast between injured and noninjured areas of the rind. Total F0 present in the image was closely correlated (r2 = 0.87) with the area of rind injury present following storage. Holding the fruit under conditions of low humidity for 24 h before hot water treatment prevented both the formation of areas of enhanced fluorescence and the corresponding rind injury. Imaging of CF has potential as a means to identify areas of incipient rind injury in citrus to facilitate study of the causal mechanisms of postharvest rind disorders.