The anthocyanins were determined using high-performance liquid chromatography (HPLC) as previously described (Qi et al., 2013 (link)). For extraction of other flavonoids, freeze-dried flowers were finely ground and 50mg was extracted in 500 μl of MeOH for 48h at 4 °C in darkness. After samples were centrifuged, the supernatants were transferred to fresh tubes and the pellet was resuspended and incubated in 500 μl of 1% MeOH at 4 °C for 24h, and then the supernatant was combined for further HPLC analysis. HPLC was performed as previously described (Qi et al., 2013 (link)). Cyanidin, Cyanidin-galactoside, dihydroquercetin, dihydrokaempferol, (+)-catechin, (–)-epicatechin, luteolin, naringenin, and quercetin were obtained from Sigma-Aldrich China (Shanghai). Standards of afzelechin, (–)-epiafzelechin, (+)-gallocatechin, and (–)-epigallocatechin were purchased from BioBioPha (Yunnan, China). The delphinidin chloride (ChromaDex, Santa Ana, CA, USA), petunidin chloride (ChromaDex), and other flavonoids such as dihydromyricetin (YiFang S&T, Tianjin, China) equivalents were used as standards for quantification. Mean values and SDs were obtained from three biological replicates.
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