Interfacial and Emulsifying Characteristics of Acid-treated Pea Protein

This work presents equilibrium and dynamic aspects for the adsorption at the oil-water interface of pea (Pisum sativum L.) protein isolate (PPI). Dynamic interfacial tension, gamma, and surface viscoelasticity modulus, epsilon, were determined using pendant-drop method. Adsorption kinetics studies revealed that pea proteins adsorb faster at pH 7.0 than at acidic pH (pH 2.4). On the other hand, the measured epsilon is lower at pH 7.0. This is probably due to fast adsorption, leading to the formation of inhomogeneous film structures. In fact, compared with pHs above the isoelectric point (pI similar to 4.3), acidic conditions slow down the adsorption, but the modulus is increased. Pea-protein-stabilized emulsions are more stable to creaming at acidic pH and their particle-size distributions are more homogeneous in these conditions. Effect of pH on interfacial properties and on properties of oil-in-water emulsions stabilized by PPI was interpreted in terms of pea protein solubility, globulin dissociation, and oil-droplet surface electrostatic charge. We propose that at acidic conditions, adsorbed dissociated globulins form stronger and denser viscoelastic networks when adsorbed at oil-water interface. Consequently, the pH-dependence of pea-globulin-stabilized emulsions properties could be of great interest to tune barrier properties of oil/water interfacial membranes for several applications such as encapsulation and controlled release of lipophilic bioactive components within the food, medical, and pharmaceutical industries.