Cellulose nanocrystals from ultrasound process stabilizing O/W Pickering emulsion.

Cellulose nanocrystals (CNC) are bio-based solid particles arisen as promising stabilizers for Pickering emulsions in food, pharmaceutical and cosmetics industries. This study aimed to understand the stabilization mechanism of oil-in-water emulsion using CNC as stabilizing particles. CNC were obtained from cellulose microcrystalline after acid hydrolysis, dialysis, ultrasound treatment and vacuum filtration. Atomic force microscopy (AFM) showed needle-shaped CNC. The CNC presented good stability against agglomeration due to the high electrostatic repulsion between particles, making them feasible to be used in O/W emulsions. O/W emulsions were stabilized by CNC and prepared using rotor-stator and ultrasound as mechanical processes. Emulsions stabilized by CNC were opaque, homogeneous and kinetically stable during few days. Small droplets generated during the ultrasound process, could be covered by cellulose nanoparticles that acted as an effective mechanical barrier against droplets coalescence in a Pickering mechanism. The mechanism of droplets stabilization was associated with electrostatic and steric repulsion between droplets. Emulsions were evaluated varying the proportion between flaxseed oil and cellulose nanocrystals (CNC). Emulsions with a lower proportion of CNC showed better kinetic stability compared to emulsions with higher CNC proportion. After 7 days of storage, the viscosity of emulsions with a higher proportion of CNC particles decreased, which was associated to the emulsion destabilization. Our results improved the understanding of the relationship between the proportions of oil and particles for emulsion properties by evaluating the potential application of CNC as a food emulsifier.

The stabilizing effect of cellulose crystals in O/W emulsions obtained by ultrasound process.

The encapsulation of lipophilic bioactive compounds, such as flaxseed oil, is usually done using O/W emulsions as carrier matrix. The aim of this study was to understand the stabilization mechanism of micro-nano cellulose crystals produced from acid hydrolysis in O/W emulsion. Effects of emulsification process conditions using ultrasound on the cellulose particles properties were evaluated varying the proportion of oil-cellulose particles in the emulsion formulation. Cellulose structure did not change using different conditions of emulsification and X-ray diffraction showed major presence of cellulose I. Particle size distribution of cellulose was bimodal and mean particle size reduced after hydrolysis. Emulsions stabilized by cellulose were opaque, homogeneous and showed good kinetic stability. The largest microcrystals were displayed between the oil droplets, preventing the flocculation of the droplets while smaller particles were adsorbed on the oil-water interface. The mechanism of droplets stabilization was not associated to the reduction of interfacial tension. Stabilization was associated to significant effect of electrostatic repulsion and increase in viscosity. Moreover, the flaxseed oil droplets were completely surrounded by cellulose nanocrystals, showing also Pickering-type stabilization. Therefore, emulsions with cellulose crystals were stabilized by different mechanisms and have interesting properties and characteristics for the protection of lipophilic compounds that could be applied in food and cosmetics products.

The role of Saccharomyces cerevisiae in stabilizing emulsions of hexadecane in aqueous media.

During downstream operations involved in the purification of hydrophobic biofuels produced by microorganisms, undesired stable emulsions may be formed. Understanding the mechanisms behind this stability is a pre-requisite for designing cost-effective strategies to break these emulsions. In this work, we aimed at increasing our knowledge on the mechanisms responsible for stabilizing yeast-containing oil-in-water emulsions. For this purpose, emulsions containing hexadecane and different yeast-based aqueous phases were prepared and analyzed for phase separation, surface charge density, particle size, and rheology. First, we observed that compounds present in fresh tablet baker's yeast contribute to emulsion stability. In order to eliminate this effect, we generated stocks with this yeast in the laboratory, and compared its performance with an industrial fuel ethanol strain, namely Saccharomyces cerevisiae PE-2. We confirmed that the presence of yeast cells enhances emulsion stability. The cultivation medium (complex or defined) in which cells are grown, as well as the physiological state of the cells (pre- or post-diauxic), prior to emulsion preparation, influenced emulsion stability. The smaller cell size of tablet yeast probably also contributes to more stable emulsions, when compared to those prepared with yeast cells grown in the laboratory. Baker's and fuel ethanol yeast cells in post-diauxic phase promote the formation of more stable emulsions than those with cells in the pre-diauxic physiological state. Finally, we propose a mechanism to explain the enhanced emulsion stability due to the presence of yeast cells, with electrostatic repulsion between emulsion droplets having the prevailing effect.