Effects of organic acids on the physico-chemical and functional characteristics of mung bean globulin amyloid fibrils

Amyloid fibers have valuable physicochemical properties for food and biomaterial applications, but research on their aggregation and fibrillation in different acidic environments is limited. This study integrated spectroscopic techniques, visual imaging, and molecular dynamic (MD) simulations to investigate the effect of different acidic environments on the structural transformation and fibrillation of mung bean globulin (MBG). The results indicated that acidic environments significantly affect the hydrolysis, self-assembly, and functional properties of MBG. Among them, mung bean protein amyloid fibrils (MBGF) formed from HCl exhibited the strongest fibrillation ability, with thioflavin T (ThT) fluorescence intensity 6 times higher than that induced by organic acids (lactic acid (LA), malic acid (MA), and citric acid (CA)). Transmission electron microscopy revealed that HCl-MBGF formed compact and uniform fibrils (∼5 nm in diameter), while organic acid-induced MBGF formed entangled fibrils with gel-like networks (∼20 nm in diameter). Functional analysis further showed that HCl-MBGF had the highest emulsifying activity index (EAI) of 17.25 ± 0.13 m²/g, an increase of about 260 % compared to MBG (4.79 ± 0.23 m²/g), and enhanced rheological properties. In contrast, MBGF formed from organic acids exhibited weaker fibrillation abilities, but a rapid gelation process was promoted. MD simulations revealed that HCl disrupted the secondary structure of the protein, promoting the formation of β-sheets, which were crucial for fibrillation. In contrast, organic acids (especially MA) facilitated protein unfolding and increased protein flexibility. This study highlights the impact of acidic conditions on MBG fibrillation and provides insights into its structural-functional design in food systems.