Abstract: In this study, docosahexenoic acid (DHA)-rich emulsions were prepared and further microencapsulated. The effect of emulsifiers, pH and metal ions on the stability, interfacial film strength, particle size distribution and zeta potential of emulsions was investigated. The results showed that the mixed emulsifier of Span 80 and Tween 60 with hydrophile-lipophile balance (HLB) value of 11.19 had the strongest effect in improving the emulsion stability. Compared with the HLB value, the type of emulsifier had a more significant effect on the stability of emulsions, and the underlying mechanism was closely related to the interfacial film strength. The interfacial film strength and the emulsion stability increased with increasing total amount of the 58:42 mixture of Tween 20 and monoglyceride up to 1.2%, and then leveled off at higher addition levels. In addition, the emulsion stability was significantly affected by pH and metal ions. Higher pH resulted in stronger electrostatic repulsion force and consequently led to higher emulsion stability. The emulsion stability was improved by low concentrations of metal ions. In contrast, high concentrations of metal ions, especially high-valence metal ions, could significantly reduce the emulsion stability. High concentrations of Fe3+ could destroy the emulsions through the oxidation of DHA, even resulting in the formation of an insoluble suspension. This study can provide a reference for improving the stability of DHA-rich microalgae oil emulsion and developing high-quality microcapsule.

Key words: emulsion stability; docosahexenoic acid-rich microalgae oil; emulsifier; pH; metal ion