| Abstract
| - The interaction between four flavonoids (catechin, epicatechin, rutin, and quercetin) and bovine serumalbumin (BSA) was investigated using tryptophan fluorescence quenching. Quenching constants weredetermined using the Stern−Volmer equation to provide a measure of the binding affinity betweenthe flavonoids and BSA. The binding affinity was strongest for quercetin and ranked in the orderquercetin > rutin > epicatechin = catechin. The pH in the range of 5−7.4 does not affect significantly(p< 0.05) the association of rutin, epicatechin, and catechin with BSA, but quercetin exhibited astronger affinity at pH 7.4 than at lower pH (p< 0.05). Quercetin has a total quenching effect onBSA tryptophan fluorescence at a molar ratio of 10:1 and rutin at approximately 25:1. However,epicatechin and catechin did not fully quench tryptophan fluorescence over the concentration rangestudied. Furthermore, the data suggested that the association between flavonoids and BSA did notchange molecular conformation of BSA and that hydrogen bonding, ionic, and hydrophobic interactionare equally important driving forces for protein−flavonoid association. Keywords: Flavonoid; polyphenol; protein; albumin; tryptophan fluorescence quenching; spectroscopy
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