Identification of the Key Astringent Compounds in Spinach (Spinacia oleracea) by Means of the Taste Dilution Analysis

Application of sequential solvent extraction and reverse phase high-performance liquid chromatography separation in combination with the taste dilution analysis, followed by liquid chromatography-mass spectroscopy and 1D/2D nuclear magnetic resonance experiments revealed 11 flavon-3-ol-O-glycosides as the key astringent and mouth-drying compounds in blanched leaves of spinach (Spinacia oleracea). Among these, in particular, 3',5-dihydroxy-3-methoxy-6: 7-methylendioxy-flavon-4'-O-beta-D-glucuronide (3), 5-hydroxy-3,3'-dimethoxy-6: 7-methylendioxy-flavon-4'-O-beta-D-glucuronide (11), and patuletin-3-O-beta-D-glucopyranosyl(1 -> 6)-beta-D-glucopyranoside (5) were found with the highest taste dilution factors. By means of the half-tongue test, the human taste thresholds of these astringent molecules were determined to be between 3.0 and 69.0 mu mol/l (in water) with the lowest threshold found for the mouth-drying glucuronide (11). Although the glucuronides exhibited rather different taste thresholds, they showed rather similar human dose/ response functions.