Air nanobubbles induced reversible self-assembly of 7S globulins isolated from pea (Pisum Sativum L.)

Abstract

The interplay of food proteins and macro or microscopic bubbles at the air-water interface that shaped the ultimate structures of proteins is well-known, yet knowledge was blank on the interactions between food proteins and nanoscopic bubbles (i.e., nanobubbles). In this study, bulk air nanobubbles were successfully fabricated in the aqueous solutions following a facile “cyclic compression-expansion” method. Subsequently, the effects of generated air nanobubbles and various factors including pH, protein concentration, nanobubble concentration, and ionic strength on the self-assembly behavior of 7S globulins isolated from pea proteins were investigated. It was revealed that air nanobubbles acted as soft templates to trigger 7S globulins self-assembly into core-shell nanospheres adjacent to the protein isoelectric point (∼pH 5). An enhancement of ionic strength from 0 to 0.4 mol L −1 led to increased particle size, whereas attenuating interactions between 7S globulins and air nanobubbles. The particle size of nanoparticles was also demonstrated to be protein and nanobubble concentration-dependent. Protein secondary structures were modified by air nanobubbles with apparently increased contents in random coils and decreased contents in α-helix. Changes in protein tertiary structures demonstrated that 7S globulins are exposed to a more hydrophobic microenvironment with reduced surface hydrophobicity, after complexing with air nanobubbles through electrostatic and hydrophobic interactions. The nanoparticles at pH 6 slightly shrunk during the 30-day refrigeration at 4 °C compared to those at pH 4, and the original nanostructures could revive after replenishing with fresh air nanobubble suspensions, indicating their high stability for future potential applications in food structure design innovation. • Air nanobubbles were generated using a “cyclic compression and expansion” method. • Interplay of 7S globulins and nanobubbles was impacted by extrinsic factors. • Nanobubbles induced reversible protein self-assembly to core-shell nanoparticles. • Air nanobubbles modified secondary and tertiary structures of 7S globulins. • Protein self-assembly behavior were driven by ionic and hydrophobic interactions.