Chi H. Fong

Biosynthesis of limonoid glucosides in navel orange

Abstract Using radioactive tracers, nomilin was converted to nomilin 17-β- d -glucopyranoside in the mature albedo tissue of a navel orange. The reaction utilized UDP-glucose as a substrate. Application of 2-chloroethylphosphonic acid to small green navel oranges initiated the formation of limonoid glucosides in the fruit. Nomilin glucoside was not metabolized in the mature albedo tissue. The formation of limonoid glucosides represent a natural pathway for the debittering of citrus juices.

Thin-layer and high-performance liquid chromatographic analyses of limonoids and limonoid glucosides in Citrus seeds

Abstract A routine method for the analysis of limonoids and limonoid glucosides in citrus seeds, which utilizes thin-layer chromatography (TLC) and high-performance liquid chromatography (HPLC), is described. Seed meals were washed with n-hexane to remove oily materials, after which limonoids and limonoid glucosides were extracted with acetone and then methanol. The methanol extract contains the remainder of the limonoid aglycones and all limonoid glucosides. After the methanol was evaporated off, the residue was extracted with methylene chloride-water (1:1). The limonoids of both the acetone and methylene chloride fractions were separated and quantified by HPLC. The total limonoid glucoside content of the water fraction was determined by silica gel TLC. Each of the limonoid glucosides was then eluted from the reversed-phase HPLC column by a linear gradient system starting at 15% acetonitrile in 3 mM phosphoric acid and ending with 26% acetonitrile after 35 min, and quantitated by spectrophotometric detection at 210 nm. The limonoid aglycones and limonoid glucosides in two kinds of citrus seeds, Shiikuwasha (Citrus depressa) and Iyo (Citrus iyo), were determined. The content of limonoid glucosides in Shiikuwasha was found to be approximately two-fold higher than that of Iyo.

Limonoid biosynthesis in the stem of Citrus limon

Abstract Using radioactive tracer techniques, the phloem region of Citrus limon stems was shown to be the site of limonoid biosynthesis from acetate. The cortex and inner core regions were found incapable of biosynthesizing limonoids from acetate. However, all the regions were capable of biosynthesizing other limonoids starting from nomilin.

Ichangensin glucoside in citrus junos, citrus sudachi and citrus sphaerocarpa

Abstract Ichangensin 17-β- d -glucopyranoside, a new limonoid glucoside, was isolated from seeds of Yuzu (Citrus junos). This glucoside was also present in seeds of Sudachi (Citrus sudachi) and Kabosu (Citrus sphaerocarpa). The 17-β- d -glucopyranosides of deacetylnomilin, nomilin, nomilinic acid, obacunone, limonin and deacetylnomilinic acid were also present in seeds of these species of citrus. Like Sudachi and Yuzu, Kabosu also contained ichangensin aglycone. The presence of ichangensin and ichangensin glucoside supports the previous suggestions that these species are related to Ichang Chie (Citrus ichangensis).