This review is a survey of studies on protein-stabilized foams and emulsions in relatively simple, well-defined systems (rather than in food products per se). The emphasis is on the extent of basic understanding developed, particularly in terms of the physicochemical properties involved. The stability of the system, its formation, and its rheology are covered. Unfortunately, much work is of limited fundamental value because of poorly designed experimental approaches and the failure to measure key parameters. Reasonable generalization can be made concerning the effects of a number of variables, particularly protein solubility, pH, protein structure and the presence of small molecule surfactants. However, several possible explanations of these effects in terms of surface properties remain tenable. A number of observations can fairly confidently be ascribed to the influence of rheology on flow processes within foams and emulsions.

Protein‐stabilized foams and emulsions

Exploring the specific features of interfacial enzymology based on lipase studies.

Microbiological contaminants (e.g., bacteria, protozoa, and viruses) pose one of the greatest risks in water resources. About 70% of the waterborne microbial illness outbreaks in the United States has been associated with groundwater. Although viruses are not the only pathogens known to contaminate groundwater, they are much smaller in size than bacteria or protozoan cysts and are not filtered out to the same extent in the porous soil matrix. Knowledge of the factors that influence the fate and transport of viruses in soil and aquifers is critical to making accurate determinations of groundwater vulnerability and to developing regulations that are protective of public health. In this paper, we review the current state of knowledge on fate and transport of viruses in porous media which include (i) mechanisms and modeling of virus sorption, (ii) virus survival and factors affecting virus inactivation in the natural environment, and (iii) mechanisms of virus transport in porous media and available modeling approaches. Because viruses are surrounded by a protein capsid and are expected to behave similarly to proteins, an overview on the mechanisms of protein sorption and denaturation is also provided. Factors such as solution chemistry, virus properties, soil properties, temperature, association with solid particles, and water content have been found to influence virus sorption, survival, and transport in porous media. A review of protein literature provides some insights as to what mechanism might be involved in virus sorption that have so far not been studied. Some needs for future research are suggested.

Fate and Transport of Viruses in Porous Media

Batch sorption experiments were carried out with the bacteriophages MS2 and φX174. Two types of reactor vessels, polypropylene and glass, were used. Consistently lower concentrations of MS2 were found in the liquid phase in the absence of soil (control blanks) than in the presence of soil after mixing. High levels of MS2 inactivation (∼99.9%) were observed in control tubes made of polypropylene (PP), with comparatively little loss of virus seen in PP tubes when soil was present. Minimal inactivation of MS2 was observed when the air-water interface was completely eliminated from PP control blanks during mixing. All batch experiments performed with reactor tubes made of glass demonstrated no substantial inactivation of MS2. In similar experiments, bacteriophage φX174 did not undergo inactivation in either PP or glass control blanks, implying that this virus is not affected by the same factors which led to inactivation of MS2 in the PP control tubes. When possible, phage adsorption to soil was calculated by the Freundlich isotherm. Our data suggest that forces associated with the air-water-solid interface (where the solid is a hydrophobic surface) are responsible for inactivation of MS2 in the PP control tubes. The influence of air-water interfacial forces should be carefully considered when batch sorption experiments are conducted with certain viruses.

https://aem.asm.org/content/aem/64/1/304.full.pdf

Role of the Air-Water-Solid Interface in Bacteriophage Sorption Experiments

Measurements of the surface dilational elasticity close to equilibrium did not indicate significant distinctions in the surface conformation of different forms of bovine serum albumin (BSA) in a broad pH range. At the same time, the protein denaturation in the surface layer under the influence of guanidine hydrochloride led to strong changes in the kinetic dependencies of the dynamic surface elasticity if the denaturant concentration exceeded a critical value. It was shown that the BSA unfolding at the solution surface occurred at lower denaturant concentrations than in the bulk phase. In the former case, the unfolding resulted in the formation of loops and tails at surface pressures above 12 mN/m. The maximal values of the dynamic surface elasticity almost coincided with the corresponding data for the recently investigated solutions of β-lactoglobulin, thereby indicating a similar unfolding mechanism.

Leroy G. Augenstein

Papers

Adsorption of Enzymes at Interfaces: Film Formation and the Effect on Activity