Make a direct treatment of the plant source with a hot polar solvent, usually methanol or ethanol. A pre-treatment of the sample with water can be also made. Then, the methanolic extract can be directly analyzed or concentrated and diluted with water. Methanol-water solution is further fractionated with hexane to remove non-polar compounds including lipids, terpenes and chlorophylls and subsequently extracted with chloroform, dichloromethane or ethyl acetate to obtain a ligan enriched fraction. The methodology using 95% ethanol proved better for extracting the lignans from plant leaves.
Flavonoids are virtually universal plant pigments. When they are not directly visible, they contribute to colour by acting as co-pigments. All flavonoids have a common biosynthetic origin and, therefore, possess the same basic structural elements, namely the 2-phenylchromane skeleton (3-phenylchromane skeleton for the isoflavonoids). The glycosidic form of flavonoids are water-soluble, accumulate in vacuoles and depending on the species, are either concentrated in the epidermis of the leaves or spread in both the epidermis and the mesophyll. In flowers, they are concentrated in epidermal cells. Whenever flavonoids are present in the leaf cuticle, they are always free aglycones, made even more lipophilic by the partial or total methylation of their hydroxyl groups (Harborne, 1967; Harborne et al, 1975; Harborne and Mabry, 1982; Markham, 1982; Harborne, 1988; Harborne, 1994).
As a general rule, glycosides are water-soluble and soluble in alcohols, however, only a fair number are sparingly soluble (rutin, hesperidin). Aglycones are, for the most part, soluble in apolar organic solvents. When they have at least one free phenolic group, they dissolve in alkaline solutions.
5.1 Total Extraction of Flavonoids without Previous Tissue Hydrolysis
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