Effect of pH and salt on the structure and thermal properties of pea legumin and vicilin

As an increasingly important ingredient in sustainable foods, an understanding of the structure and functionality of pea protein is critical for the improvement of its use. This study investigated the structural and functional differences between pea legumin and vicilin by examining the effects of pH and salt on the thermal properties, solubility, and secondary structure change before and after heating (95°C for 1 h). Pea proteins were extracted using 0.4 M NaCl at pH 7, and legumin and vicilin were further fractionated using size exclusion chromatography. Both fractions were most soluble at pH 8.5. At pH 3.5, they formed soluble aggregates, which dissociated upon heating. At neutral or alkaline pH, the presence of 0.4 M sodium salt did not affect their solubility before heating, but caused extensive precipitation of vicilin after heating. Synchrotron radiation CD spectroscopy was employed to measure structural changes for legumin and vicilin fractions. The presence of 0.4 M sodium salt had little effect on their secondary structure before heating. However, it influenced their heat denaturation behaviors. Salt slightly stabilized the heat-induced structural change of legumin, whereas it promoted the unfolding of vicilin with heating. NanoDSC results indicated that 0.4 M NaCl resulted in a shift to higher denaturation temperatures and increased enthalpy for both fractions, with this effect more pronounced for vicilin. These findings highlight key structural and functional differences between legumin and vicilin, which were purified under mild conditions, providing fundamental insights on how to modulate their techno-functional properties. • Protein solubility of legumin and vicilin was not influenced by 0.4 M sodium salt. • Both proteins at pH 8.5 and 7 remained soluble after extensive heating at low ionic strength. • Vicilin solubility significantly decreased after extensive heating with 0.4 M sodium salt. • Both proteins had the highest solubility at pH 8.5 and the lowest at pH 3.5 with heating significantly improving solubility at pH 3.5. • Salt enhanced heat stability and promoted protein unfolding with vicilin being more prone to unfolding than legumin.