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

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 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 wet-heating 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 24 h 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. 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.