Functional properties of proteins such as solubility, foaming, and emulsifying properties are essential attributes for food applications. However, plant proteins such as kidney bean proteins have limited functionalities due to their packed structure. Therefore, to improve functional properties and use them in food systems, modification is required. As modification methods, pH-shift combined with ultrasound or heat were applied to kidney bean protein (denoted as pH-SU and pH-SH, respectively) and their structural characteristics, functional properties, as well as interfacial properties were compared to untreated and pH-shift treated kidney bean proteins (denoted as control and pH-S, respectively). At the structural level, all three treatments including pH-shift, pH-shift combined with ultrasound or heat were able to change native trimers found in untreated proteins to monomers. In addition, pH-SH induced aggregates. The total sulfhydryl group contents decrease was observed upon treatment but disulfide bond contents (SS) varied depending on the treatment that the pH-S increased SS (18.60 μmol/g) but decreases were found in pH-SU (17.15 μmol/g) and pH-SH (11.90 μmol/g) compared to the control (17.32 μmol/g). Besides, pH-SH had the highest surface hydrophobicity (H₀) followed by pH-SU, pH-S, and control. In interfacial properties, all treatments increased diffusion rate, but pH-SH showed the fastest diffusion among tested samples. Also, pH-SH had the highest viscoelastic modulus (E), indicating strong viscoelastic film formation. In functional properties, pH-SH had the highest emulsifying activity index (EAI) of 23.9 m²/g followed by pH-S (20.9 m²/g), pH-SU (19.0 m²/g), and control (8.2 m²/g). Moreover, pH-SH showed a significantly higher emulsifying stability index (ESI) of 60.7% compared to control (27.2%), pH-S (22.7%), or pH-SU (22.1%). As results of emulsifying properties indicate, pH-SH had superior emulsifying properties compared to others. This significant improvement has been attributed to structural changes in proteins, enhanced solubility, H₀, fast diffusion rate, as well as improved E. Findings in this study can serve as a basis for understanding the relationship among structural, functional, and interfacial properties of modified plant proteins, along with industrial adaptation.

Uyory Choe

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