Antimicrobial kinetics of nanoemulsions stabilized with protein: pectin electrostatic complexes

Abstract

Pectin is an anionic carbohydrate present in many plant-based materials that can interact with positively charged macromolecules, such as proteins, to form electrostatic complexes with promising applications. The aim of this study was to form and characterize whey protein isolate (WPI):high or low methoxylated pectin (HMP or LMP, respectively) electrostatic complexes. Then, the surface activity of the complexes and their capacity to form and stabilize nanoemulsions was assessed. Finally, the impact of the interfacial composition on the antimicrobial killing kinetics of essential oil nanoemulsions against Escherichia coli was evaluated. First, a stronger complexation was observed at pH below 5, where pectin and protein were negatively and positively charged, respectively. Additionally, LMP led to the formation of stronger complexes in comparison to HMP due to the presence of more ionizable carboxylic groups and therefore it was more negatively charged. Second, protein:pectin complexes were more effective than the biopolymers alone in order to form essential oil nanoemulsions, maintaining their oil droplet size stable during at least 30 days. And third, WPI:LMP complex-stabilized antimicrobial nanoemulsions resulted in a slower and lower Escherichia coli killing kinetics in comparison to WPI:HMP complexes, evidencing that the compactness of the interfacial layer determines the interaction with bacterial cells. Hence, the diffusion of the antimicrobial compounds from the lipid core through the interfacial layer and towards bacteria might be modulated by controlling the interfacial composition using WPI:pectin complexes.