Evaluation of the emulsifying properties of cottonseed protein isolates

Cotton is mainly cultivated for fiber production, but its seed is also very important as a source of proteins for human and animal consumption. In the present work cottonseed protein isolates (CPI) produced either by isoelectric precipitation (at different pH values) or dialysis through membranes, were evaluated for their emulsifying properties. The respective emulsion stability of the emulsions produced at pH 7.0 and 6.0, as well as the effect of polysaccharides (xanthan and pullulan) and different concentration of NaCl, on these properties, were evaluated. Emulsion stability was greater at continuous phase pH 7.0 than at 6.0. The addition of xanthan gum 0.1% w/v had a positive effect on emulsion stability while pullulan had a smaller positive effect. Addition of NaCl enhances emulsion stability at pH 7.0 and pH 6.0 until the concentration of 0.2M by increasing the solubility of proteins, which declined at higher concentrations. The physicochemical parameters used in the model systems (e.g. methods for CPI preparation, pHs of the continuous phase, values of the interfacial pressure, etc.) and viscoelastic parameters give us a picture (not always clear) for the conditions which should be used in order to increase the stability, against coalescence of the emulsion systems. A close parallelism was observed between emulsifying properties and the rheological characteristics of the absorbed films.