Identification of UV-Fluorescence Components for Detecting Peel Defects of Lemon and Yuzu using Machine Vision

Fluorescence imaging has been used to detect peel defects in many citrus varieties, but not in lemon and yuzu. In this study, we extract and identify fluorescent components from the peel of lemon and yuzu. The characteristics of excitation and fluorescence of these extracted components were determined, and their identity clarified using NMR spectroscopy. Extracted fluorescent components for both lemon and yuzu have a coumarin structure. Two coumarins (5-7-dimethoxycoumarin,5-geranyloxy-7-methoxycoumarin) were identified in lemon and one (5-geranyloxycoumarin) in yuzu. Their excitation and fluorescence wavelength were observed at 320–330 nm and 380–400 nm, respectively. Moreover, when a fluorescence imaging system was set-up with UV-A illumination, it was shown that this systemcan detect peel defects in lemon, and to a lesser extent in yuzu.