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

Authors: CHOE, UYORY - North Dakota State University; LIUYI, CHANG - North Dakota State University; Ohm, Jae-Bom; CHEN, BINGCAN - North Dakota State University; RAO, JIAJIA - North Dakota State University

Submitted to: Food Hydrocolloids
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/19/2022
Publication Date: 7/30/2022
Citation: Choe, U., Liuyi, C., Ohm, J., Chen, B., Rao, J. 2022. Structure modification, functionality and interfacial properties of kidney bean (Phaseolus vulgaris L.) protein concentrate as affected by post-extraction treatments. Food Hydrocolloids. 133. Article 108000. https://doi.org/10.1016/j.foodhyd.2022.108000.
DOI: https://doi.org/10.1016/j.foodhyd.2022.108000

Interpretive Summary: Kidney beans are a widely cultivated common bean crop, and they usually have a high protein content (20–30%). However, kidney beans have not been popularly utilized as a source for plant protein in the food industry because of their compact protein structure and the limited functionality of their proteins. The process of exposing proteins in an alkaline solution is known to modify structure of proteins and improve their functionality. This research is an investigation into the influence of this alkaline process on the structure and functionality of kidney bean proteins. In addition, the alkaline process experiment was conducted in combination with heating or sonication experiments. The results demonstrated that the treatment combination of the traditional alkaline process and heat treatment changed the protein structure and improved protein functionality by increasing solubility and dispersibility in solution. These findings may be of great importance in providing valuable information to improve functionality of kidney bean protein concentrates and increase their utilization in the food industry.

Technical Abstract: In this study, in-house extracted kidney bean protein concentrate (KPC) was treated with three treatments: pH-shift (pH-S), pH-shift combined with ultrasound (pH-SU) or heat (pH-SH). The structural, functional, and interfacial properties of the modified KPC were then comprehensively evaluated. Upon treatments, the increase of KPC surface hydrophobicity (H0) 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 H0. 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 m2/g), and pH-S, pH-SU, and pH-SH showed EAI values of 20.9, 19.0, 23.9 m2/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 with 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.