Modification of black bean (Phaseolus vulgaris L.) protein isolate by high-intensity ultrasound: Effect on the rheological structure, amino acid composition, and nutritional profiling

Abstract High-intensity ultrasound (HIU), a promising ‘green’ technology, can potentially improve the functionality of biomolecules, particularly proteins and peptides. The current research aimed to evaluate the influence of HIU (40% amplitude for 5, 10, 20, 30, and 40 min) on black bean protein isolate (BBPs), which was assessed with nutritional profile, structural and rheological properties, and digestion behavior. The results showed that HIU treatment improved the molecular flexibility of proteins from 0.31 to 0.39 by disrupting non-covalent interactions and promoting partial unfolding. The in vitro digestibility of HIU-treated BBPs increased to 44.76%, compared to 34.95% in the control sample, indicating improved protein structure for better enzymatic hydrolysis and bioavailability. HIU treatment alters the pattern of BBPs by modifying their crystalline structure, increasing amorphous regions. The circular dichroism spectroscopy showed that the β-sheet of HIU-treated BBPs increased, whereas the random coil and α-helix decreased. During the temperature sweep evaluation, HIU-treated BBPs exhibited a higher storage modulus (G′) throughout the temperature profile while improving their viscosity properties in the frequency sweep analysis. HIU treatment (30 min) enhanced hydrophobic amino acid content, resulting in a higher total amino acid content than the control sample. Therefore, HIU treatment significantly improved black bean protein isolate properties with promising applications in food supplements.