Factors affecting the emulsifying and rheological properties of gum acacia in beverage emulsions

Gum acacia, a natural hydrocolloid, is extensively used as an emulsifier/stabilizer in beverage emulsions. Factors that may affect emulsion formation, emulsion stability and viscosity of the emulsion concentrate were studied to assess their significance, including proximal composition of the gum (protein content and mineral content), gum processing prior to emulsion preparation (pasteurization and demineralization), and pH of the dilute emulsion. Protein content was not related to emulsion stability, whereas minerals decreased stability presumably due to an electrostatic screening effect. Both pasteurization and demineralization favored stability, most likely by promoting protein unfolding and eliminating the screening effect, respectively. Emulsions were less stable at pH = 2.5 than at higher pH levels (4.5 and 5.5). There was a significant difference between the two gum species studied (Senegal and Seyal) in their sensitivity to these treatments. The viscosity of the emulsion concentrate was decreased by pasteurization and increased by demineralization. Protein load at the O/W interface and thickness of the adsorbed layer of emulsifier were not related to emulsion stability. The most important colloidal interactions in dilute beverage emulsions are van der Waals, electrostatic and polymeric steric.