L-Histidine improves solubility and emulsifying properties of soy proteins under various ionic strengths

Abstract

Soy protein is a commonly used functional ingredient. Despite its versatility, modifications of soy proteins could further enhance its functionalities. The objective of this study is to investigate the effect of l-histidine on physicochemical and functional properties of soy protein isolate (SPI) in the presence of 0, 0.1, and 0.6 M NaCl. The incorporation of l-histidine improved SPI solubility and decreased turbidity regardless of the salt concentrations. Notably, at 0.1 M NaCl, the incorporation of 0.3% l-histidine more than doubled the SPI solubility. Reactive sulfhydryl groups and surface hydrophobicity of the SPI decreased up to 24.2% and 38.6%, respectively, by the l-histidine treatment. The SPI-histidine interactions facilitated exposure of tryptophan residues in the absence of salt while mitigated salt-induced protein unfolding. With no salt, 0.3% l-histidine improved the emulsifying activity and stability of the SPI by 11.5% and 9.2%, respectively. At 0.1 M NaCl, 0.3% l-histidine did not improve the emulsifying activity but increased the emulsion stability by 30.1%. At 0.6 M NaCl, 0.3% l-histidine induced a 25.4% increase in emulsifying activity while no change in emulsion stability. In conclusion, l-histidine can be used as a functional ingredient to enhance the performance of SPI in various food formulations.