Interfacial, and emulsifying properties nexus of green pea protein fractions: Impact of pH and salt

Abstract

In recent years, pea protein isolate has received great attention due to its high nutritional value and multiple functional properties, among which emulsifying properties are one of the most important. However, the application of pea protein in food emulsions is still limited due to insufficient knowledge. As such, the aim of this study was to investigate the impact of environmental pHs (3, 7, 9) and different NaCl concentrations (20 mM, 100 mM) on the physicochemical and interfacial properties of green pea protein individual fractions (globulin, legumin, vicilin, and albumin) at the oil-water interface, and then to research their relationship with emulsifying properties. Results showed that compared to pH 7, samples treated with pH 9 and NaCl had faster initial adsorption (π0), higher final interfacial pressure (π10800) and rearrangement rate (Kr), and better emulsifying ability, while samples treated with pH 3 had the opposite performance. Moreover, pH 9 emulsions were more stable, while NaCl weakened the emulsion, which was reflected in the first increase and then decrease of the interfacial dilatational viscoelasticity (E) induced by NaCl. Regarding the fraction effect, albumin and legumin subunit had the highest and lowest emulsifying ability, respectively. On the other hand, the emulsifying stability of albumin was most easily reduced by NaCl, as evidenced by the dramatically increased droplet size (from 1.62 to 28.92 and 72.00 μm), coalescence index (from 47.60 to 59.86 and 374.30%), and creaming index (from 3.43 to 8.00 and 12.71%). In all, while there is a limited relationship between the emulsifying properties of proteins and their solubility, surface hydrophobicity, secondary structure, and interfacial dilatational viscoelasticity, the interfacial pressure (π) was found to be positively related to the emulsifying ability, and Kr was associated with both emulsifying ability and stability. The results could provide valuable information on the molecular mechanisms of emulsifying properties of pea protein fractions.