Role of water soluble and water swellable fractions of gum tragacanth on stability and characteristic of model oil in water emulsion

• The emulsification activities of two types of gum tragacanth (GT) were studied.
• Water soluble fraction of gum acts as a structuring or adsorbing agent.
• The main role of water swellable fraction is rheology modification.
• Better stabilizing property of GT was related to special soluble/swellable ratio.
• The chemical composition of GT types can highly affect the emulsion properties.

The influence of concentration (0.1–0.5% w/w) and type of gum tragacanth (GT) obtained from Astragalus gossypinus (AG gum) and Astragalus fluccosus (AF gum) species on stability and physicochemical properties of oil in water emulsion were investigated by considering the role of water soluble (tragacanthin) and water swellable (bassorin) fractions. Sugar composition determination, particle size distribution, interfacial tension, steady shear and oscillatory rheological measurements were used to characterize the emulsions and obtain more information about the possible stability mechanism. The emulsions were prepared by homogenizing 10 wt% sun flower oil with 90 wt% aqueous gum dispersions and were stored quiescently at 25 °C for two months. The results indicated that AF gum was more effective in reducing interfacial tension; but, effect of AG gum on increasing viscosity and reducing size of droplets was more pronounced. Moreover, except the sample contained Bassorin, with increasing gum concentration, a pronounced decrease in droplet size and polydispersity were observed. According to the results, emulsifying activity of tragacanthin and viscosity enhancement properties of bassorin was responsible for emulsion stabilizing function of AG gum. Better stabilizing property of AG than AF gum was related to their differences in soluble/swellable ratio and chemical composition (methoxylation degree, uronic acid and neural sugar content). This study revealed that AG gum alone could be used as an alternative for mixed biopolymer systems to stabilize oil in water emulsions.

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