Emulsion stabilization by tomato seed protein isolate: Influence of pH, ionic strength and thermal treatment

There is a burgeoning interest for plant protein-based emulsifiers owing to their economic benefits and lower environmental impacts. This study investigated the stability of 10.0 wt% oil-in-water emulsions stabilized by 1.0 wt% protein extracted from tomato seeds, a by-product of tomato processing industries. Both water-soluble albumin and salt-soluble globulin fractions of tomato seed protein in the molecular weight range of 48-10 kDa were adsorbed at the oil-water interface, as confirmed by sodium dodecyl sulphate polyacryl amide gel electrophoresis (SDS-PAGE). Tomato seed protein isolate-stabilized emulsions were subjected to environmental stresses such as pH (2-9), ionic strength (0-250 mM NaCl or CaCl2) and thermal treatment (30-90 degrees C, 30 min). Droplet size, droplet charge, microstructure and creaming stability were assessed. Emulsions were stable to droplet aggregation except at pH 2-4, owing to their proximity to isoelectric point. Emulsions showed excellent stability to high NaCl concentrations (250 mM) at pH 6-8 with surface charges above -40 mV. However, extensive droplet flocculation with aggregated optical microstructure and creaming indices was observed in presence of >= 50 mM CaCl2, which was attributed to ion binding and charge screening effects. Droplet aggregation above 80 degrees C was due to the denaturation of the globular protein fractions adsorbed at the interface. These results might have implications for the utilization of tomato seed protein as potential emulsifier for food and beverage applications. (C) 2016 Elsevier Ltd. All rights reserved.