In Situ Detection and Identification of Hesperidin Crystals in Satsuma Mandarin (Citrus unshiu) Peel Cells

IntroductionHesperidin, a flavonoid known to have important pharmacological effects, accumulates particularly in the peels of satsuma mandarin (Citrus unshiu). Although histochemical studies have suggested that hesperidin forms crystals in some tissues of the Rutaceae and Umbelliferae, there has been no rigorous in situ detection or identification of hesperidin crystals in C. unshiu. ObjectiveTo characterise the chemical component of the crystals found in C. unshiu peels using Raman microscopy. MethodsSections of C. unshiu peels were made. The distribution and morphology of crystals in the sections were analysed microscopically. Raman microscopy was used to detect hesperidin in the sections directly. ResultsThe crystals were more abundant in immature peel and were observed particularly in areas surrounding vascular bundles, around the border between the flavedo and albedo layers and just below the epidermal cells. In the morphological analysis by scanning electron microscopy, needle-shaped crystals aggregated and formed clusters of spherical crystals. Spectra obtained by Raman microscopy of the crystals in the peel sections were consistent with those of the hesperidin standard. ConclusionThis study showed the detailed distribution of crystals in C. unshiu peels and their main component was identified using Raman microscopy to be hesperidin for the first time. Copyright (c) 2014 John Wiley & Sons, Ltd. Flavonoids produced by plants have various derivatives and the accumulation pattern of them is different with each species. Hesperidin is one of the main flavonoids accumulated in Citrus species and has been focused on its pharmacological effects. In this study, we observed numerous needle-shaped crystals in the peel cells of satsuma mandarin (Citrus unshiu) and identified the main component of the crystals to be hesperidin by in situ detection using Raman microscopy for the first time.