Physicochemical properties and formation mechanism of electrostatic complexes based on ε-polylysine and whey protein: Experimental and molecular dynamics simulations study

ε‑Polylysine (ε-PL) is a new natural food-grade antimicrobial that has been widely applied in the food and beverage industry. This study characterized the physicochemical properties of an electrostatic complex of the ε-PL and whey protein at different whey protein-to-ε-PL mass ratios, pH, and ionic strength by using the turbidity measurements, size and zeta potential measurements. The interaction and formation mechanism of the electrostatic complexes are explored by analysis of the hydrogen bonds and ion pairs, hydrophobic and hydrophilic solvent assessable surface area and secondary structure using molecular dynamics simulations. The experimental results showed that the ε-PL bound to the surface of whey protein forming an electrostatic complex which could be either soluble or insoluble depending on the whey protein-to-ε-PL mass ratios, pH, and ionic strength. The molecular dynamics simulations results showed that conformational rearrangements of α‑lactalbumin and bridging effect of β‑lactoglobulin occurred. The interaction was mostly driven by the hydrogen bonds and ion pairs, which mainly occurred in the hydrophilic part of the whey protein surface. This study provides the theoretical basis that will facilitate more rational application of ε-PL in the food matrix.