Dispersion characteristics of pregelatinized waxy rice starch and its performance as an emulsifier for oil-in-water emulsions: Effect of gelatinization temperature and starch concentration

The dispersion characteristics and the emulsifier performance of pregelatinized waxy rice starch gelatinized at different temperatures (65, 75, and 85 degrees C abbreviated as PWRS 65, 75, and 85, respectively) and various concentrations (3, 5, 7, and 9 wt%) were studied. The varying degree of gelatinization resulted in different characteristics for both PWRS dispersions and emulsions. The rheological parameters of the PWRS 65 dispersion and emulsions were strongly affected by concentration; the yield stress, consistency coefficient, pseudoplasticity, and apparent viscosity increased with an increase in PWRS 65 concentration. The remaining granules resulting from an incomplete gelatinization process were able to prevent creaming at PWRS 65 concentrations of more than 5 wt% but were unable to protect against oil droplet coalescence. Consequently, a change in droplet size distribution occurred in the emulsions with PWRS 65, even at high concentrations. The higher gelatinization temperature generates a higher density polymer network, created by expanded starch during gelatinization, in the dispersion. Gelatinization at 75 and 85 degrees C produced a dispersion structure that was sensitive to shear stress and generated shear-thinning behavior in the emulsions with unnoticed yield stress. The better ability of PWRS in maintaining droplet size resulting from a higher temperature indicates the melted starch polymer during gelatinization provides better protection against droplet coalescence than the starch polymer in a crystalline state. PWRS 85 can be considered for further development as a food grade emulsifier because it can produce a stable emulsion.