Amino acid composition, foaming, emulsifying properties and surface hydrophobicity of mustard protein isolate as affected by pH and NaCl

Amino acid composition, protein hydrophobicity, foaming and emulsifying properties of mustard protein isolate at pH 3, 5, 7 and in 0.05 and 0.1 m NaCl were studied. Glutamic (19.18 +/- 0.30%) and aspartic (7.49 +/- 0.11%) acids were the dominants. Foaming ability was enhanced by NaCl. Time to reach 75 mL foam was 23% higher in water than in NaCl. Drained volume after 10 min was concentration dependent and was the lowest in 0.05 and 0.1 m NaCl at protein concentration of 2.5% and 5%. The emulsifying properties were pH and concentration dependent, and the best results were obtained at pH 3, corresponding to the highest positive charge density of the protein surface. The highest emulsion stability (90.22 +/- 3.52%) was obtained in 0.05 m NaCl and 5% protein concentration, whereas the lowest (63.00 +/- 1.06%) was in water at all protein concentrations. Protein hydrophobicity was low and depended of pH but not of NaCl.