Abstract: The objective of this study was to use ultrasound treatment to improve the emulsion stability of pre-emulsified soybean oil with sodium caseinate. The effect of ultrasound irradiation at 20 kHz and 450 W for different times (0, 3, 6, 9 and 12 min) on pH, conductivity, creaming index, mean droplet diameters and size distribution and viscosity of preemulsified soybean oil was investigated. Our results illustrated that there was no significant difference in pH or conductivity among all treatment groups (P > 0.05). All treatment groups showed no significant difference in terms of creaming index at 0 h of storage (P > 0.05); however, they were significantly lower than the control at 12, 24 and 36 h (P < 0.05). With prolonged ultrasound irradiation, D4,3, D3,2 and D50 of soybean oil emulsion droplets decreased, and viscosity at a shear rate of 0.1 s-1 increased significantly (P < 0.05). These findings showed that the application of ultrasound treatment to pre-emulsified soybean oil with sodium caseinate could extend the storage period, reduce the particle size, increase the viscosity, and thus improve the emulsion stability.

Key words: ultrasound, pre-emulsified, emulsion stability, size distribution