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

摘要

BACKGROUNDWhey 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 m(2) 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: K-SV (5.11-8.95 x 10(2) L mol(-1)) and K-q (5.11-8.95 x 10(10) 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 ( increment H > 0, increment S > 0). Hydrogen bonding was the dominant force at pH 2.6 and pH 8.2 ( increment H < 0, increment 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. (c) 2023 Society of Chemical Industry.