Lubrication properties of model dairy beverages: Effect of the characteristics of protein dispersions and emulsions

Physiochemical characteristics, morphology, and lubricating properties of size-specific whey protein particles by acid or ion aggregation

To investigate the influence of particle characteristics on their lubricating capacity, microparticles of controlled size (~300, ~700, and ~1900 nm) were prepared from whey proteins using two different approaches: reducing the pH and increasing the calcium ion concentration. The physiochemical, morphological, and tribological properties of the two types of particles were determined. Both treatments pronouncedly decreased the absolute value of zeta-potential and surface hydrophobicity of whey proteins, with calcium ions showing a more severe effect on zeta-potential. The viscosity of the particle suspensions increased with particle size, and ion-induced samples showed higher viscosity than acid-induced ones. Morphology investigation revealed that particle aggregation and irregularity increased with particle size increase. Distinct lubricating behaviors were observed for the two particle types within different size ranges. Viscosity played a more important role in lubrication when the particle size was small, while particle characteristics became more dominant for large particles.

Promising application of probiotic microorganisms as Pickering emulsions stabilizers

The purpose of this work was to study the ability of nineteen food-grade microorganisms as Pickering emulsion (PE) stabilizers. Medium-chain triacylglycerol (MCT) oil-in-water (50:50) PEs were fabricated by 10 wt% or 15 wt% of thermally-inactivated yeast, cocci, Bacillus spp. and lactobacilli cells. The characteristics of microorganisms related to "Pickering stabilization" including morphology, surface charge, interfacial tension, and "contact angle" were firstly studied. After that, the cells-stabilized PEs were characterized from both kinetic and thermodynamic viewpoints, microstructure and rheological properties. The interfacial tension and "contact angle" values of various microorganisms ranged from 16.33 to 38.31 mN/m, and from 15° to 106°, respectively. The mean droplet size of PEs ranged from 11.51 to 57.69 µm. Generally, the physical stability of cell-stabilized PEs followed this order: lactobacilli > Bacillus spp. > cocci > yeast. These variations were attributed to the morphology and cell wall composition. Increasing the microorganism concentration significantly increased the physical stability of PEs from a maximum of 12 days at 10 wt% to 35 days at 15 wt% as a result of better interface coverage. Shear-thinning and dominant elastic behaviors were observed in PEs. Physical stability was affected by the free energy of detachment. Therefore, food-grade microorganisms are suggested for stabilizing PEs.