Ontogenetic and Seasonal Variation in the Flavonoid Composition of Sophora japonica. Cultivated in Bulgaria

Abstract

Quantitative changes in the accumulation of the flavonol glycosides rutin and kaempferol 3-rutinoside and the isoflavone glycosides genistin and sophorabioside have been investigated in flowers and fruits of cultivated in Bulgaria Sophora japonica. during ontogenetic and seasonal development. A method for extraction of flavonoids with good recovery was developed (98% for rutin and 97% for kaempferol 3-rutinoside). The subsequent high-performance liquid chromatography separation of flavonoid glycosides was achieved using Hypersil ODS C18 column and UV detection. The mobile phase comprised methanol and phosphate buffer, pH 3.23, and linear gradient elution mode within 25 min was applied. Accumulation of rutin started with initiation of the flower buds, having the maximal content up to 287 mg/g (dry weight) in mid-July during the earliest stages of flower development and tended to have high levels until mid-August. A further decrease in the amount of rutin up to 44 mg/g was found proportionally with the decline of flavonoids throughout and after the flowering period. Rutin was the predominant glycoside and can account for up to 90% of flavonoid glycoside mixture in young buds, whereas sophorabioside (64.7 mg/g, calculated as rutin equivalent) and kaempferol 3-rutinoside (46.8 mg/g) dominated at later development stages of the fruits. No significant differences in flavonoid quantity between the analysis periods of two successive years were observed. This indicated clearly the ontogenetic dependence of flavonoid formation.