Interaction of β-lactoglobulin with (−)-epigallocatechin-3-gallate under different processing conditions of pH and temperature by the fluorescence quenching method

The binding interactions between (−)-epigallocatechin-3-gallate (EGCG) and bovine β-lactoglobulin (β-LG) during food processing under different temperatures (25–100 °C) and pH levels (3.2–7.4) were investigated using the fluorescence quenching method. The results indicated that temperature and pH had different effects on the structure and EGCG-binding ability of β-LG. At a higher pH (≥6.4) and temperature (≥80 °C), the structure and conformation of β-LG were more open than those of its native state due to the heat-induced denaturation and unfolding of protein, which increased its binding affinity with EGCG through hydrophobic interactions and hydrogen bonds, which in turn promoted its further unfolding. The highest binding constant (KA) and the binding site numbers (n) were 12.50 (±0.60) × 105 M−1 (pH 6.4, 80 °C), and 0.62 (±0.02)~0.97 (±0.16), respectively. However, at 100 °C and a neutral pH, the oxidative loss of EGCG during thermal processing probably led to a decrease in β-LG–EGCG interactions. These results would be helpful to better understand the relevance of the β-LG–EGCG interaction to the bioactivity and bioavailability of EGCG during food processing, and to maintain the health benefits of this type of functional products in the food industry.