Water-soluble fraction of pea protein isolate is critical for the functionality of protein-glucose conjugates obtained via wet-heating Maillard reaction

Authors: GAO, KUN - North Dakota State University; CHANG, LIUYI - North Dakota State University; Xu, Yixiang; RAO, JIAJIA - North Dakota State University; CHEN, BINGCAN - North Dakota State University

Submitted to: Food Research International
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/22/2023
Publication Date: 9/23/2023
Citation: Gao, K., Chang, L., Xu, Y., Rao, J., Chen, B. 2023. Water-soluble fraction of pea protein isolate is critical for the functionality of protein-glucose conjugates obtained via wet-heating Maillard reaction. Food Research International. 174. Article 113503. https://doi.org/10.1016/j.foodres.2023.113503.
DOI: https://doi.org/10.1016/j.foodres.2023.113503

Interpretive Summary: Dry pea is a major leguminous grain accounting for about 34% of global pulse production in 2020, while pea protein isolate (PPI) is now one of the most popular plant proteins in terms of satisfying market expectations. However, low water solubility and the associated functionalities including emulsifying and foaming properties have limited applications for PPI in food systems. Maillard reaction (MR), a glycation reaction originated from natural cooking process, is a practical method to improve the functional properties of protein. High intensity ultrasound (HIUS), a green and efficient technique to modify protein structure and functionality, has been found to accelerate MR. In this study, PPI pretreated with HIUS ultrasonic was centrifuged to obtain the soluble fraction (supernatant). The supernatant was then glycated with glucose via MR. Structural and functional properties of the glycated PPI were determined to explore the mechanism of HIUS pretreatment in combination with MR. The results showed the proportion of soluble protein in PPI is critical to its wet-heating MR-based conjugation with glucose and the solubility of the conjugates.

Technical Abstract: Wet-heating Maillard reaction (MR) has been applied to improve the function of proteins by conjugating with soluble carbohydrates. However, the impact of soluble solutes particularly in plant protein on the degree of MR and the properties of the corresponding conjugates has yet to be discussed. In this study, high-intensity ultrasound (HIUS) was utilized to pretreat commercial pea protein isolate (PPI) in order to improve its solubility. Two different fractions including soluble fraction (SUPPI) and whole solution (UPPI) of HIUS treated PPI were conjugated with glucose (G) to prepare SUPPI-G and UPPI-G, respectively, over a course of 24 h at 80 °C. Conjugation was confirmed by the degree of glycation, SDS-PAGE, FTIR, and intrinsic fluorescence analysis. Color change and glucose content analysis showed that the degree of MR was greater when using SUPPI rather than UPPI. The solubility of SUPPI-G was further improved by 24h of MR while it remained unchanged for UPPI-G. The emulsifying activity index and foaming capability of SUPPI-G were similar to those of UPPI-G. Interfacial properties determined by dynamic adsorption and dilatational rheology at both oil-water and air-water interface suggested that insoluble fraction of UPPI is essential to make stable emulsions and foams. It also suggested that the amount and the particle size had an influence on the interfacial behavior of PPI. In conclusion, the proportion of soluble protein in PPI is critical to its wet-heating MR based conjugation with glucose and the solubility of the conjugates.