Stabilization mechanisms of oil-in-water emulsions by Saccharomyces cerevisiae

• Emulsions were stabilized by yeast and cell material.
• Washed yeast cells decreased emulsion stability but increased cell adhesion.
• Cells and other cellular materials showed adhesion onto the hexadecane droplets.
• Emulsifying capacity was not lost with cell autoclaving.
• Rheological properties were not affected by different treatments of yeasts.

A multiphase system is commonly formed during the oil production by microbial route, which can lead to stable emulsions hindering product recovery. Thus, this study aimed to investigate the mechanisms of emulsion stabilization by the yeast Saccharomyces cerevisiae in order to contribute with processes development of oil production by fermentation. A model system using hexadecane as oil phase and yeast suspension as aqueous phase was used to prepare O/W emulsions. The yeast was subjected to different treatments as inactivation (autoclaving) and washing before to be resuspended in water. The washing water (water from the first washing) and suspension of commercial yeast (active) were also used as aqueous phase. After 24 h of preparation, the emulsions separated into three phases: top (cream), intermediate, and bottom phase. The top or cream phase was a concentrated emulsion that kept stable during seven days, except for those prepared from washed yeast that were stable only for a short period of time. Emulsions prepared with washed yeast showed higher cell adhesion to the droplets interface, which implied in a higher amount of yeast into the cream phase in comparison to other formulations. Therefore, yeast cells adhesion plays a role on emulsion stability, but the greater contribution was provided by cell material dispersed into the aqueous phase, regardless of cell viability.

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