Structure regulation mechanisms and interfacial properties of soy protein isolate with pH and heat treatment

Protein structural features determine distinct molecular interfacial properties. • Molten globule transitions enhance protein solubility, interfacial adsorption, and stabilisation capacity. • SPF formation is strongly correlated with disulfide bond reconstruction. • Well-organised transitions in protein structure enhance their interfacial properties. • pH changes and aggregates conformational transitions exert inconsistent effects on protein interfacial properties. This study investigated the assembly mechanisms, interfacial properties, and structure-function relationships of soybean protein isolate (SPI) via the synergistic effects of pH regulation and heat treatment. Two molten globular (SPG), three aggregated (SPA), and one fibrous (SPF) SPI conformations were successfully prepared. SPG had reduced random coil content; among them, SPG-12 showed the highest solubility (71.6%) and lowest surface hydrophobicity (5025), thus exhibiting optimal emulsifying and foaming properties. Heat induction and pH cycling enhanced SPI solubility and promoted the formation of nanoparticles smaller than 200 nm, while isoelectric point-induced aggregation inhibited ordered structures (e.g., SPA-2 with particle size over 500 nm). SPF formed through three steps: unfolding, then hydrolysis, and finally aggregation; during this process, disulfide bond content first dropped from 63.4% to 32.2% and then recovered to 64.1%, and SPF had improved foaming capacity but reduced stability. This work provides theoretical support for developing plant-based emulsifiers and foaming agents. Download: Download high-res image (244KB) Download: Download full-size image