Breaking oil-in-water emulsions stabilized by yeast

Abstract

Several biotechnological processes can show an undesirable formation of emulsions making difficult phase separation and product recovery. The breakup of oil-in-water emulsions stabilized by yeast was studied using different physical and chemical methods. These emulsions were composed by deionized water, hexadecane and commercial yeast (Saccharomyces cerevisiae). The stability of the emulsions was evaluated varying the yeast concentration from 7.47 to 22.11% (w/w) and the phases obtained after gravity separation were evaluated on chemical composition, droplet size distribution, rheological behavior and optical microscopy. The cream phase showed kinetic stability attributed to mechanisms as electrostatic repulsion between the droplets, a possible Pickering-type stabilization and the viscoelastic properties of the concentrated emulsion. Oil recovery from cream phase was performed using gravity separation, centrifugation, heating and addition of demulsifier agents (alcohols and magnetic nanoparticles). Long centrifugation time and high centrifugal forces (2 h/150,000×g) were necessary to obtain a complete oil recovery. The heat treatment (60°C) was not enough to promote a satisfactory oil separation. Addition of alcohols followed by centrifugation enhanced oil recovery: butanol addition allowed almost complete phase separation of the emulsion while ethanol addition resulted in 84% of oil recovery. Implementation of this method, however, would require additional steps for solvent separation. Addition of charged magnetic nanoparticles was effective by interacting electrostatically with the interface, resulting in emulsion destabilization under a magnetic field. This method reached almost 96% of oil recovery and it was potentially advantageous since no additional steps might be necessary for further purifying the recovered oil.

Optimization of Settling Behavior for an Efficient Solvent‐Extraction Process for Biobased Components

“…This explains both the hindered coalescence and faster sedimentation. An additional treatment, such as a shift in temperature; the addition of an alcohol or of magnetic nanoparticles; and other additives, such as surfactants or enzymes can enhance phase separation in cell‐containing systems with stabilized emulsions , .…”

“…The microorganisms behave like surface‐active particles to hinder coalescence and stabilize the interface , which is partly based on cell adhesion . Apart from the mechanism of stabilization, the reduction of these effects by adjusting the composition of the system or variation of process conditions, such as temperature, are measures that can be applied to improve the process , . The analysis of diamine extraction as the chosen model component from aqueous media focused only on phase equilibrium, but not on phase separation , .…”

Fermentation broth components influence droplet coalescence and hinder advanced biofuel recovery during fermentation

“…For Pickering stabilization, the particles (cells in this case) need to attach to the oil/water (O/W) interface, which depends on their surface properties. Yeast cells are reported to have a low affinity for O/W interfaces (23%) [16] and even cells with an O/W interface affinity of 50% are not capable of adequately stabilizing the O/W interface to form emulsions [17]. Therefore, droplet stabilization by the cells is not considered in this paper; instead, we focus on components that are either initially present in the fermentation broth, or are excreted into it.…”

Stability of polyethylenimine solution‐in‐liquid paraffin emulsion for preparing polyamine microspheres with potential adsorption for ionic dyes

“…For evaluating the stability of emulsion, various methods has been used, such as changes of temperature, pH and salinity, centrifugation application and the addition of chemical de‐emulsifier . In this study, the stability of the PEI emulsion was evaluated by addition of ethanol to separate the emulsion mixture . The addition of ethanol reduces the polarity difference between the oil phase and the water phase of emulsion, and increases the solubility of surfactants in the two phases resulting in the breakdown of emulsion …”