Characterization of flavonols in plants used for textile dyeing and the significance of flavonol conjugates

Although yellow, flavonol-based dyes were widely used in pre-modern times, this class of natural dyes presents special problems because flavonols (3-hydroxyflavones) readily undergo photo-oxidation, resulting in fading or discoloration. However, if the 3-hydroxy group is substituted, e.g., with a glycosyl group, the flavonol derivative is relatively stable. We analyzed representatives of eight plant genera, Delphinium, Flaveria, Pistachia, Prangos, Rhamnus, Sophora, Tamarix and Vitis, with the aim of identifying the flavonol components present. In all cases, the principal colorants were flavonol 3-O-glycosides (or, in one case, 3-O-sulfates), although some plants also contained the light-labile flavonol aglycones. We discuss some strategies that can be and may have been used to reduce the concentration of flavonol aglycones. In addition the identification of specific flavonol glycosides, or their high performance liquid chromatography elution patterns, is useful in identifying the plants used to dye ancient textiles, for which historical records are absent. (C) 2013 Elsevier Ltd. All rights reserved.