Influence of environmental pH on the interaction properties of WP‐EGCG non‐covalent nanocomplexes

Abstract

AbstractBACKGROUNDWhey protein‐epigallocatechin gallate (WP‐EGCG) covalent conjugates and non‐covalent nanocomplexes were prepared and compared using Fourier‐transform infrared spectra. The effect of pH (at 2.6, 6.2, 7.1, and 8.2) on the non‐covalent nanocomplexes' functional properties and the WP‐EGCG interactions were investigated by studying antioxidant activity, emulsification, fluorescence quenching, and molecular docking, respectively.RESULTSWith the formation of non‐covalent and covalent complexes, the amide band decreased; the ‐OH peak disappeared; the antioxidant activity of WP‐EGCG non‐covalent complexes was 2.59‐ and 2.61‐times stronger than WP‐EGCG covalent conjugates for 1‐diphenyl‐2‐picryl‐hydrazyl (DPPH) and ferric reducing ability of plasma (FRAP), respectively (particle size: 137 versus 370 nm). The antioxidant activity (DPPH 27.48–44.32%, FRAP 0.47–0.63) was stronger at pH 6.2–7.1 than at pH 2.6 and pH 8.2 (DPPH 19.50% and 26.36%, FRAP 0.39 and 0.41). Emulsification was highest (emulsifying activity index 181 m2 g−1, emulsifying stability index 107%) at pH 7.1. The interaction between whey protein (WP) and EGCG was stronger under neutral and weakly acidic conditions: KSV (5.11–8.95 × 102 L mol−1) and Kq (5.11–8.95 × 1010 L mol s−1) at pH 6.2–7.1. Binding constants (pH 6.2 and pH 7.1) increased with increasing temperature. Molecular docking suggested that hydrophobic interactions played key roles at pH 6.2 and pH 7.1 (∆H > 0, ∆S > 0). Hydrogen bonding was the dominant force at pH 2.6 and pH 8.2 (∆H < 0, ∆S < 0).CONCLUSIONEnvironmental pH impacted the binding forces of WP‐EGCG nanocomplexes. The interaction between WP and EGCG was stronger under neutral and weakly acidic conditions. Neutral and weakly acidic conditions are preferable for WP‐EGCG non‐covalent nanocomplex formation. © 2023 Society of Chemical Industry.