Optimization of the emulsifying and encapsulating properties of gum acacia

Gum acacia, a natural hydrocolloid, is extensively used as emulsifier/stabilizer of beverage emulsions as well as encapsulation agent for flavor delivery. Beverage emulsions are consumed in a highly diluted form rather than in their original concentrated form. The stability of the former is a chronic problem in the beverage industry. A number of factors that potentially affect the emulsifying and rheological properties of gum acacia in beverage emulsions were considered. Protein content of the gum was not related to emulsion stability, whereas indigenous minerals decreased stability due to an electrostatic screening effect. Pasteurization and demineralization of the gum favored stability by promoting protein unfolding and eliminating the screening effect, respectively. Adjusting pH of the dilute emulsion to 2.5 significantly decreased stability with respect to pH levels around the isoelectric point of the gum protein, because of the screening effect from added cations. Viscosity of concentrate was decreased by pasteurization and increased by demineralization.; Time-temperature treatments of the gum, ranging between pasteurization and protein denaturation, were optimized by response surface methodology. Emulsion stability was moderately improved although viscosity of the concentrate was not sensibly affected.; Mechanisms of destabilization and shelf-life of dilute emulsions were investigated at six different temperatures. Ostwald ripening was more significant than coalescence. Close fit of the Arrhenius equation to experimental data indicated the occurrence of similar mechanisms throughout the temperature range and validated using increased temperature as an accelerated shelf-life test.; Rheology of emulsion concentrates was modeled according to selected theoretical equations. Best fit corresponded to the Einstein equation for samples that behaved consistently Newtonian. Oil droplets in the concentrates were assumed to be semi-fluid spherical particles subjected to colloidal interaction of limited range.; A mixture experiment was applied to assess possible replacements of gum acacia as an encapsulation agent via spray drying with modified starch and/or maltodextrin. Combinations richer in starch yielded lighter and drier powders than those richer in gum acacia, with greater oil recovery, lesser surface oil, longer shelf-life but also lower emulsion stability. Combinations richer than 25% maltodextrin showed a dramatic drop in oil recovery and an exponential increase in surface oil.