Background: The dispersed phase volume fraction plays key role in oil-in-water emulsion stability by different mechanisms like partial flocculation, depletion flocculation and bridging flocculation. Since the mentioned mechanism is affected by emulsifier concentration presented in system, the major aim of this study was to investigate the effect of dispersed phase volume fraction on physical stability of oil-in-water emulsion in the presence of gum tragacanth.
Methods: The effect of oil concentration on the stability of oil-in-water emulsion systems containing 0.5% w/w gum tragacanth is investigated by considering rheological properties and droplet size distribution. Emulsion stability was monitored by measuring the extent of gravitational phase separation. Rheological properties and droplet size distribution were measured by rheometer and static laser diffraction immediately after preparation at 25 ºC. All treatments were performed three times and the data were analyzed using SPSS 16.0.
Results: Oil concentration enhancement from 10% to 30% w/w decreased emulsion stability. Increasing the oil concentration enhances consistency coefficient from 2.01 to 5.73 pa.sⁿ but decreases flow behavior index. Considering the particle size distribution revealed that number mean diameter increase significantly by oil concentration addition.
Conclusion: Emulsion stability index decreased by increasing dispersed phase volume fraction. Considering rheological properties and droplet size distribution, it seems that oil concentration addition however, makes the system more structured but it is unable to create a stable system since the emulsifier is insufficient to protect oil droplets from aggregation.