Characterization of the Fluorescent Spectra and Intensities of Various Lignans: Application to HPLC Analysis with...

There is considerable interest in dietary lignans since they have been shown to have antioxidant, estrogenic and lipid-lowering activity in humans. In this study, the fluorescent excitation and emission spectra of seven lignans were characterized and their relative fluorescent intensities compared. The lignans were found to have similar excitation (286.6 ± 2.5 nm, X ± SD) and emission (320.1 ± 6.4 nm) maxima; however, their fluorescence intensities on a molar basis decreased in the following order: asarinin, sesamin, sesamolin, seco-isolariciresinol, seco-isolariciresinol diglucoside and matairesinol. Enterolactone, a mammalian lignan conversion product, and sesamol, an antioxidant found in sesame oil, also exhibited significant fluorescence excitation and emission intensities. A high-performance liquid chromatographic method using photodiode array (PDA) and fluorescent detection was developed for the analysis of the individual lignans. Analysis was performed on a reversed phase C-18 column with methanol-water (70:30, v/v) as the mobile phase. With fluorescent detection, the limits of quantitation (LOQ) was 0.1 ng or 2.82 nmol for sesamin and asarinin, 2.70 nmol for sesamolin, 2.76 nmol for seco-isolariciresinol, 1.45 nmol for seco-isolariciresinol diglucoside, 2.79 nmol for matairesinol and 0.5 ng or 1.67 nmol for enterolactone. With PDA detection, the LOQ was a 1000-fold less sensitive than with fluorescent detection.