Study of emulsions and foams stabilized with Phaseolus vulgaris or Phaseolus coccineus with the addition of xanthan gum or NaCI

The properties of oil-water emulsions stabilized with 1% w-v common bean (Phaseolus vulgaris L.) or scarlet runner bean (P. coccineus L.) proteins, extracted by isoelectric precipitation or ultrafiltration, at pH 7.0 and 5.5 were studied. The stability of emulsions, evaluated on the basis of droplet size, creaming, viscosity and protein adsorption measurements, is increased by the addition of xanthan (0.1 and 0.25% w-v). This is probably due to the increase in the continuous phase viscosity and the creation of a network, which prevents the oil droplets from coalescing. Also, the ability and stability of 1 or 2% w-v foams was studied. Xanthan (0.25% w-v) does not enhance foam formation, but promotes foam stability, possibly owing to the increased viscosity of the aqueous phase, making it more difficult for air to enter the system and create a satisfactory foam volume. The addition of NaCI destabilizes emulsions by lowering the energy barrier and therefore increasing the tendency of the oil droplets to aggregate. However, NaCI at a certain concentration seems to promote the emulsion stability and foaming ability and foam stability. This could be attributed to the alteration of the protein molecule configuration leading to the building of a rigid and viscoelastic protein film around the droplet. [PUBLICATION ABSTRACT]