Seasonal Variation of Polyphenols and Pigments in Ginkgo ( L.) Leaves: Focus on 3',8″-Biflavones.

Ginkgo ( L.) is a widely recognized medicinal plant, often grown as an ornamental species in parks around the world. Its leaves change color from green in spring to yellow in autumn. In this study, we collected ginkgo leaves at seven developmental stages from May to November and measured chlorophylls, carotenoids, flavonoids, and antioxidant activity. The total polyphenol content showed a significant increase from May to November, rising from 15.15 ± 0.14 mg GAE g dw to 45.18 ± 0.42 mg GAE g dw. The total flavonoid content reached its peak in August at 5.87 ± 0.18 mg GAE g dw. In contrast, the highest concentrations of total polyphenolic acids (4.13 ± 0.16 mg CAE g dw) and antioxidant activity (306.95 ± 3.47 µmol TE g) were recorded in May. We specifically focused on a less-studied group of dimeric flavonoids or biflavonoids-3',8″-biflavones. We identified five 3',8″-biflavones (amentoflavone, bilobetin, ginkgetin, isoginkgetin, and sciadopitysin) throughout all developmental stages. Sciadopitysin was the most abundant biflavonoid, with its concentration rising from 614.71 ± 5.49 µg g dw in May to 2642.82 ± 47.47 µg g dw in November. Alongside sciadopitysin, the content of other biflavonoids (excluding amentoflavone) generally increased over the same period. This trend is further highlighted by the total biflavonoid content, which grew from 1448.97 ± 6.63 µg g dw in May to 6071.67 ± 97.15 µg g dw in November. We observed a negative correlation between biflavonoid and chlorophyll content, which may indicate their involvement in leaf senescence. However, this hypothesis warrants further investigation.