Stability of corn and olive oil-in-water emulsions supplemented with ethanol-treated rapeseed meal protein isolate

Rapeseed meal was treated with 70% ethanol to reduce anti-nutrient compounds, and used in the preparation of a protein isolate. The ethanol- treated rapeseed meal protein isolate (ERPI) was produced by alkaline extraction of proteins (pH 12) followed by isoelectric precipitation at pH 4.5. The aim of the present work was to evaluate the potential of ERPI as an emulsifying agent in corn and olive oil-in-water emulsions under slightly acidic conditions (pH 6). A total of nine emulsions for each type of oil were prepared to assess the significant effect of two variables, oil (5, 10, and 15% w/w) and ERPI protein concentrations (0.25, 0.5, and 1.0% w/w), on emulsion stability. The initial stability was evaluated by Gibbs free energy (ΔG) and lipid particle size distribution, while the dynamics of emulsion stability was investigated along 7 d by turbidity measurement. The increase in concentration of both types of oil positively influenced initial stability of the emulsions as indicated by ΔG. At each oil concentration, the three ERPI supplementation levels resulted in significant differences in ΔG. While in all olive oil-in-water emulsions, the highest initial stability was achieved by the addition of 0.25% ERPI; and in corn oil-in-water emulsions, lower ΔG values were achieved by supplementing either with 0.5 or 1.0% ERPI. With a few exceptions, there was an agreement between Gibbs free energy and microstructural characteristics of the emulsions. With a reduction in turbidity not higher than 30% at day 7, all corn oil-in-water emulsions supplemented with 0.5% ERPI demonstrated a better stability than the emulsions prepared with olive oil.