In situ detection and identification of hesperidin crystals in satsuma mandarin (Citrus unshiu) peel cells.
BACKGROUND
Hesperidin, 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.


OBJECTIVE
To characterise the chemical component of the crystals found in C. unshiu peels using Raman microscopy.


METHODS
Sections 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.


RESULTS
The 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.


CONCLUSIONS
This 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.
Division of Environmental Science and Technology, Graduate School of Agriculture, Kyoto University, Kitashirakawa Oiwake-cho, Sakyo-ku, Kyoto, 606-8502, Japan.
Tsuyoshi
T
Inoue
Arata
A
Yoshinaga
Keiji
K
Takabe
Terutaka
T
Yoshioka
Kazunori
K
Ogawa
Masahiro
M
Sakamoto
Jun-ichi
J
Azuma
Yoichi
Y
Honda
D002957:Citrus / Q000737:chemistry* / Q000648:ultrastructure; D005638:Fruit / Q000737:chemistry / Q000648:ultrastructure; D006569:Hesperidin / Q000737:chemistry / Q000302:isolation & purification*; D008855:Microscopy, Electron, Scanning; D010936:Plant Extracts / Q000737:chemistry / Q000302:isolation & purification*
D010936:Plant Extracts; D006569:Hesperidin
Citrus unshiu; In situ detection; Raman microscopy; albedo; flavedo; flavonoid; fruit peel; hesperidin; organic crystals; scanning electron microscopy