Structure modification, functionality and interfacial properties of kidney bean (Phaseolus vulgaris L.) protein concentrate as affected by post-extraction treatments

Abstract

In this study, in-house extracted kidney bean protein concentrate (KPC) was treated with pH-shift (pH-S), pH-shift combined with ultrasound (pH-SU) or heat (pH-SH), and the structural, functional, and interfacial properties of the modified KPC were comprehensively evaluated. Upon treatments, the increase of KPC surface hydrophobicity (H 0 ) was observed, and the intensity was in the order of pH-SH > pH-SU > pH-S > control. The intrinsic tryptophan fluorescence of KPC solution had a negatively proportional relationship with their H 0 . All post-extraction treatments also significantly decreased the contents of total and free sulfhydryl groups. But disulfide bonds (SS) showed a different trend that the KPC from pH-S had the highest SS of 18.60 μmol/g followed by the control (17.32 μmol/g), pH-SU (17.15 μmol/g), and pH-SH (11.90 μmol/g). In functional properties, KPC from pH-SH showed significantly improved percentage solubility at pH 6.0 when compared to the others. All treated KPC exhibited a higher emulsifying activity index (EAI) than the control (8.2 m 2 /g), and pH-S, pH-SU, and pH-SH showed EAI values of 20.9, 19.0, 23.9 m 2 /g, respectively. But only KPC from pH-SH showed an improved emulsifying stability index (ESI) of 60.7% when compared to the control (27.2%). Meanwhile, the improved foaming capacity was only found in KPC from pH-SH, but a decrease in foaming stability was observed. The interfacial properties indicated that the improvement in EAI is associated with the fast diffusion rate while a higher ESI found in KPC from pH-SH has been closely related to the formation of a stronger viscoelastic film. Overall this study has established the relationships among structural characteristics of KPC upon various post-extraction treatments, their functional properties and interfacial properties. • Kidney bean protein concentrate (KPC) was modified via post-extraction treatment. • Three treatments include pH-shift (pH-S), pH-shift + ultrasound/heat (pH-SU/pH-SH). • Different structural characteristics were observed in pH-SU and pH-SH modified KPC. • Structural change notably affected interfacial and functional properties of KPC. • KPC with pH-SH treatment showed better emulsifying properties.