Abstract: W/O emulsions were prepared ultrasonically using Newtonian pseudoplastic chitosan solution as the aqueous phase, palm oil as the oil phase and Span-80 as the emulsifier. The preparation process was optimized using a combination of one-factor-at-a-time method and response surface methodology. The stability of the emulsion prepared under optimized conditions was examined. The results showed that the proportion of inner aqueous phase was a critical factor affecting the mean droplet size, and excessively high ultrasonic power led to an increase in particle size and wider particle size distribution. The optimal preparation conditions were obtained as follows: ultrasonic power 300 W, ultrasonic time 15 min, inner aqueous phase 13%, and Span-80 6%, giving a mean droplet size of (156.1 ± 20.0) nm and a polydispersity index (PDI) of (0.43 ± 0.03). The stability test and the micro-morphology observation indicated that the prepared emulsion was stable at 25 ℃ and showed creaming?index of 0.6%, while the emulsion stability decreased sharply at 50 ℃ and the creaming?index increased up to 7.0%. The increase in particle size and more uneven particle size distribution were detrimental to the emulsion stability, and aggregation was the main cause of the decrease in the emulsion stability.

Key words: ultrasonic emulsification; chitosan; W/O emulsion; polysaccharide; stability