Effect of pH and NaCl on rheological and textural properties of lupin protein emulsions

The effect of pH on textural and rheological properties of lupin protein o/w emulsions at various protein contents (2, 3, 4, 5 and 6% wt) was studied. Five emulsions with different pH values ranging from 3 to 8 were prepared at each protein content. The NaCl concentration effect was also investigated on 4.5% wt protein emulsions with salt contents ranging from 0.3 to 5% wt. In both cases, the sunflower oil content was 65% wt. From the results of this work it was observed that for all protein concentrations tested, the textural and rheological properties reach a minimum at a pH value around the protein isoeletric point (pH ca. 4.5), and the oil droplet size given by d(32), shows a maximum at this pH value, indicating low emulsion stability. In the study of the effect of salt, at pH 2.5 the addition of salt reduces emulsion stability, at pH 4.5 the emulsion physical properties are independent of salt concentration and at pH 6.5 the salt addition enhances structure, texture and stability of the emulsions.