A Structural Study on Canola Oil-Fermented Microbial Emulsions Using BT1 Strain.

The demand for sustainable bioderived surfactants, such as microbial surfactants, is steadily increasing. While prior studies have mainly focused on developing new production methods for biosurfactants, identifying their chemical identities, or elucidating underlying metabolic mechanisms, research on the structure of emulsions formed by these surfactants and their internal fluid-fluid interfaces remain relatively scarce. In this study, we present a novel microbial emulsion produced by fermenting canola oil with BT1 strain and investigate its detailed structure. The extracted fermentation products exhibited water affinity and water-canola oil interfacial activity, which were characterized using relaxation nuclear magnetic resonance and pendant drop tensiometry, respectively. These fermentation products, functioning as biosurfactants, spontaneously generate water-in-oil-in-water (W/O/W) emulsions during fermentation by facilitating transitional phase inversion, thereby eliminating the need for complex multistep processes. The resulting emulsion droplets displayed intriguing interfacial coloration when observed under a reflective polarized optical microscope (POM). Typically, emulsions exhibiting similar patterns (e.g., Maltese crosses) in POM are classified as "liquid crystal emulsions". However, for the first time in this study, we present counterexamples that exhibit such interfacial patterns without possessing a crystalline structure. We discuss the origins of this phenomenon and emphasize the need for careful interpretation of similar systems. Cryogenic scanning electron microscopy suggests the adsorption of interface-active substances derived from fermentation products at the water-oil interfaces, while others may remain suspended in the aqueous continuous phase. Differential scanning calorimetry demonstrates their influence on the melting and crystallization behaviors of water and canola oil, which is associated with enhanced refrigeration stability of the resulting microbial emulsions.