Abstract

Proteins constitute an important fraction of microalgal biomass, with their composition being strongly influenced by cultivation conditions. Extracting these biomolecules while maintaining their native conformation represents a key technical challenge to preserving their functional properties. This study evaluated the stability of emulsions prepared with water-soluble protein extracts from the green microalga Nannochloropsis gaditana, cultured in open raceway ponds in the Atacama Desert (Chile). Single and double emulsions were prepared and evaluated under environmental factors such as pH (4-12), ionic strength (100-500 mM NaCl), and temperature (4-55 degrees C for single emulsions and up to 100 degrees C for double emulsions). The extracted protein, with high water solubility and HLB (>10), acts as a hydrophilic emulsifier favoring oil-in-water (O/W) emulsions. Thermodynamic analyses revealed that stable emulsions (EC 100 %) were achieved at water concentrations above 90 % and oil concentrations below 5 %, requiring at least 2.8 % protein to maintain stability over 24 h. Protein concentration, ionic strength, and pH significantly influenced the emulsifying capacity of single emulsions, with optimal performance at 2-3 % protein, neutral pH, and moderate ionic strength, while temperature showed no significant effect on emulsion stability. In double emulsions, the protein concentration in the external aqueous phase (w2) did not significantly affect emulsifying capacity. These double emulsions maintained high structural stability, with emulsifying capacity above 50 % under pH 5-11, NaCl concentrations of 0-500 mM, and temperatures up to 65 degrees C. They exhibited a typical W/O/W morphology (oil droplets similar to 10 +/- 0.8 mu m encapsulating aqueous droplets similar to 3 +/- 0.5 mu m). Although extended storage reduced stability, the protein's emulsifying performance under these controlled environmental factors supports its potential application in food and cosmetic formulations.