Interaction of milk protein and black tea aroma compounds: selectivity, binding mechanism, and theaflavin effect

Milk tea, a cultural convention in parts of the United Kingdom, India, Sri Lanka and China, modulates polyphenol-induced astringency and bitterness while improving flavor. Previous studies have mainly focused on the health impacts of milk protein-tea polyphenol interactions, with less attention paid to 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, was particularly obvious. Multi-spectroscopic analyses combined with molecular docking revealed that volatile compounds, such as benzaldehyde, could 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 thus 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.