Fig. 1. Aglycones of flavonoids common in foods, with the numbering system shown on the flavanones [11]. Anthocyanidins: cyanidin, R1=OH, R2=H; delphinidin, R1=R2=OH; malvidin, R1=R2=OMe; pelargonidin: R1=R2=H; peonidin: R1=OMe, R2=H. Catechins: (+)-catechin [(+)-Cat], R1=R2=H; R3=OH; (−)-epicatechin [(−)-EC], R1=R3=H, R2=OH; (−)-epicatechin gallate [(−)-ECG], R1=R3=H, R2=OGallate; (−)-epigallocatechin [(−)-EGC], R1=R2=OH, R3=H; (−)-epigallocatechin gallate [(−)-EGCG], R1=OH, R2=OGallate, R3=H. Flavanones: hesperetin, R1=OH, R2=OMe; naringenin, R1=H, R2=OH. Flavones: apigenin, R1=H; luteolin, R1=OH. Flavonols: kaempferol, R1=R2=H; myricetin, R1=R2=OH; quercetin, R1=OH, R2=H.

Fig. 2. Chromatogram of a solution of 17 flavonoid standards monitored at 210 nm. Chromatographic conditions are described in text. See Table 2 for peak identification.

Fig. 3. Chromatogram of a solution of 17 standards monitored at 520 nm. Anthocyanidins are the only flavonoids tested which absorb at 520 nm. Chromatographic conditions are described in text. See Table 2 for peak identification.

Fig. 4. Chromatogram of extract of blueberries at 520 nm. Chromatographic conditions are described in text. Peak identification for peaks 6, 7, and 11 as in Table 2; peak 18 is petunidin.

Fig. 5. Chromatogram of extract of Dragon Well Green Tea at 210 nm. Chromatographic conditions are described in text. Peak identification for peaks 1, 2, 3, 4, and 5 as in Table 2. Peak 19 is gallic acid, peak 20 is theobromine, peak 21 is caffeine, and peak 22 is gallocatechin gallate (GCG).

Table 1. Solvent parameters for the separation of flavonoid aglyconesa^, b

Table 2. Retention times of the flavonoids