Effect of pH on the inter-relationships between the physicochemical, interfacial and emulsifying properties for pea, soy, lentil and canola protein isolates

• Proteins with high charge and low hydrophobicity associated best to the interface.
• Proteins of high charge and hydrophobicity formed strong interfacial films.
• Lentil protein isolate may be an effective alternative to soy, as an emulsifier.

The inter-relationships between the physicochemical, interfacial and emulsifying properties for pea, soy, lentil and canola protein isolates as a function of pHs (3.0, 5.0, and 7.0) were investigated. Surface charge, hydrophobicity, solubility, interfacial tension, rheology, droplet size and emulsion stability were all studied. Conditions that favored the protein to have a high charge, low hydrophobicity and high solubility (pH 7.0) were better able to associate with the oil–water interface to lower interfacial tension. However, conditions that fostered the protein to have a high charge, high hydrophobicity and high solubility (pH 3.0) led to stronger interfacial viscoelastic films. Findings suggest that a balance of the surface active properties is most ideal for using plant protein emulsifiers in a food application. Overall, findings from this study indicated that all proteins could form stable emulsions away from its isoelectric point (pH 3.0 or pH 7.0), although the ones formed at pH 3.0 displayed much better interfacial rheology. Of the protein-types studied, the most promising alternative to soy protein isolate as an emulsifier was lentil protein isolate because it had high charge, solubility and hydrophobicity at pH 3.0. The low solubility of pea protein at acidic pH could cause sedimentation issues in products, whereas allergen concerns are still associated with the napin protein from canola.