Interaction of β-casein with (−)-epigallocatechin-3-gallate assayed by fluorescence quenching: effect of thermal processing temperature

Summary The interactions between the flavan-3-ol (−)-epigallocatechin-3-gallate (EGCG) and bovine β-casein in phosphate-buffered saline (PBS) of pH 6.5 subjected to thermal processing at various temperatures (25–100 °C) were investigated using fluorescence quenching. The results indicated that different temperatures had different effects on the structural changes and EGCG-binding ability of β-casein. At temperatures below 60 °C, the β-casein–EGCG interaction changed little (P > 0.05) with increasing temperature. At temperatures above 80 °C, native assemblies of β-casein in solution dissociated into individual β-casein molecules and unfolded, as demonstrated by a red shift of the maximum fluorescence emission wavelength (λmax) of up to 8.8 nm. The highest quenching constant (Kq) and the number of binding sites (n) were 0.92 (±0.01) × 1013 m−1 s−1 and 0.73 (±0.02) (100 °C), respectively. These results provide insight into the potential of interactions between β-casein–EGCG that may modulate bioactivity or bioavailability to be altered during thermal process.