The interaction of milk protein and black tea aroma compounds: Selectivity, binding mechanism, and theaflavins’ effect

Abstract

Milk tea, a cultural convention in part regions of the United Kingdom, India, Sri Lanka and China, modulates polyphenol-induced astringency and bitterness while improves flavor. Existing studies mainly focused on the health impacts of milk protein-tea polyphenol interaction, with less attention on the flavor modulation. The present study systematically investigated the impact of milk proteins on aroma compound release in black tea infusions. After adding milk, the release of volatile compounds in the black tea infusion was significantly suppressed, among which the release of aroma compounds such as benzaldehyde is particularly obvious. Multi-spectroscopic analyses combined with molecular docking revealed that volatile compounds, such as benzaldehyde would bind to the hydrophobic regions of casein and be stabilized by hydrogen bonds, which induced static quenching of casein fluorescence. Furthermore, competitive binding assays demonstrated that theaflavins occupied the binding sites of benzaldehyde and (E,E)-2,4-heptadienal, facilitated the aggregation of milk protein and thereby promoted the release of aroma substances. The experimental results provided a theoretical basis for the mechanism of milk tea aroma and established a framework for the preservation of milk tea flavor.