The role of particles in stabilising foams and emulsions

The efficient development and production of high quality emulsion-based products depends on knowledge of their physicochemical properties and stability. A wide variety of different analytical techniques and methodologies have been developed to characterize the properties of food emulsions. The purpose of this review article is to provide a critical overview of the most important properties of emulsions that are of interest to the food industry, the type of analytical techniques that are available to measure these properties, and the experimental protocols that have been developed to characterize the stability of food emulsions. Recommendations are made about the most suitable analytical techniques and experimental protocols needed to characterize the stability and properties of food emulsions.

Critical Review of Techniques and Methodologies for Characterization of Emulsion Stability

More polyunsaturated fats in processed foods and fewer additives are a huge demand of public health agencies and consumers. Consequently, although foods have an enhanced tendency to oxidize, the usage of antioxidants, especially synthetic antioxidants, is restrained. An alternate solution is to better control the localization of reactants inside the food matrix to limit oxidation. This review establishes the state-of-the-art on lipid oxidation in oil-in-water (O/W) emulsions, with an emphasis on the role of the interfacial region, a critical area in the system in that respect. We first provide a summary on the essential basic knowledge regarding (i) the structure of O/W emulsions and interfaces and (ii) the general mechanisms of lipid oxidation. Then, we discuss the factors involved in the development of lipid oxidation in O/W emulsions with a special focus on the role played by the interfacial region. The multiple effects that can be attributed to emulsifiers according to their chemical structure and their location, and the interrelationships between the parameters that define the physicochemistry and structure of emulsions are highlighted. This work sheds new light on the interpretation of reported results that are sometimes ambiguous or contradictory.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/1541-4337.12097

Lipid Oxidation in Oil‐in‐Water Emulsions: Involvement of the Interfacial Layer

Rheology of emulsions.

Oils and mixtures of oils with hydrophobic particles are widely used in various technologies and consumer products to control foaminess and foam stability. The aim of this review is to summarize our current understanding of the mechanisms of foam destruction by such substances, which are usually called antifoams or defoamers. The experimental results show that two types of antifoam can be distinguished (called for brevity "fast" and "slow") which differ in the modes of their action. Fast antifoams are able to rupture the foam films at the early stages of film thinning. As a result, fast antifoams destroy completely the foam in less than a minute, in a typical foam-stability test. Microscopic observations have shown that the fast antifoams rupture the foam films by the so-called "bridging" mechanisms, which involve the formation of oil bridges between the two surfaces of the foam film. The stability/instability of these oil bridges is explained by using the theory of capillarity. In contrast, the oily globules of the slow antifoams are unable to enter the surfaces of the foam films and are first expelled into the Plateau borders (PBs). Only after being compressed by the narrowing walls of the PBs (due to water drainage from the foam), are the globules of the slow antifoams able to enter the solution surface and to destroy the adjacent foam films. Typically, the process of foam destruction by slow antifoams requires much longer time, minutes or tens of minutes, and a residual foam of well-defined height is observed in the foam tests. The experiments show that there is no direct relation between the magnitudes of the entry, E, spreading, S, and bridging, B, coefficients, on one side, and the antifoam efficiency, on the other side. The only requirement for having active antifoam, with respect to the bridging mechanisms, is that B should be positive. On the other hand, the barrier preventing the emergence of pre-emulsified antifoam globules on the solution surface (so-called "entry barrier") is of crucial importance for the mode of foam destruction and for the antifoam efficiency. Measurements of the entry barrier with recently developed film trapping technique (FTT) showed that antifoams possessing low entry barriers act as fast antifoams, whereas high barriers correspond to slow or inactive antifoams, although E, S, and B coefficients could be strongly positive in the latter case. A good agreement between the magnitude of the entry barrier, measured by FTT, and the height of the residual foam, in the presence of slow antifoams, was experimentally established and theoretically explained. The importance of various factors, such as the size of antifoam globules, oil spreading, kinetics of surfactant adsorption, hydrophobicity of solid particles in mixed oil-solid antifoams, and the presence of amphiphilic additives (foam boosters), is discussed from the viewpoint of the mechanisms of antifoaming. The main experimental methods, used for studying the modes of antifoam action, are briefly described.

Mechanisms of foam destruction by oil-based antifoams.

Rheological properties of highly concentrated protein-stabilized emulsions.

In the present paper, we report measurements of the disjoining pressure vs thickness isotherms of emulsion films stabilized by proteins. A novel variant of the Mysels−Bergeron thin liquid film setup was constructed and further employed in the investigation of foam and emulsions films. The films are formed in a porous glass plate immersed in the corresponding oil phase. The disjoining pressure is directly measured by means of a pressure transducer, and the thickness is determined via light interferometry. The disjoining pressure vs thickness isotherms show different features in respect to the stabilizing protein. When the films are stabilized by bovine serum albumin (BSA) and β-lactoglobulin (BLG), a steric-like interaction comes into play being differently pronounced in the two cases. In contrast, the films stabilized with β-casein exhibit classical Derjaguin−Landau−Verwey−Overbeek (DLVO) behavior. The disjoining pressure was converted to force adopting the Derjaguin approximation, and the result is compa...

https://www.lcpe.uni-sofia.bg/publications/2001/2001-28-TDD-TG.pdf

Disjoining Pressure vs Thickness Isotherms of Thin Emulsion Films Stabilized by Proteins

https://www.lcpe.uni-sofia.bg/publications/2004/2004-11-TD-FLC-TG-BC.pdf

Surface forces in model oil-in-water emulsions stabilized by proteins.

We measured forces between tiny emulsion droplets by using the magnetic chaining technique. Force versus distance profiles were obtained for emulsions stabilized by Tween 20, Tween 20 bovine serum albumin (BSA) mixtures and β-casein. For emulsions stabilized with Tween 20 alone, we observed classical Derjaguin-Landau-Verwey-Overbeek (DLVO) behavior. At high Tween 20 concentrations the force profiles clearly deviate from the double-layer repulsion. An interpretation of the data is proposed combining classical DLVO with stericlike additional effective repulsion due to the micellar condensation at the droplet surface. The systems containing both Tween 20 and BSA qualitatively show the same kind of behavior: the purely electrostatic repulsion is progressively transformed into a steric one in the presence of BSA. The emulsions stabilized by β-casein obey a different type of behavior: in that case the depletion attraction is found to be of great importance. The data are interpreted assuming additivity of DLVO forces and depletion attraction. The threshold flocculation force as a function of the ionic strength was determined for these systems.

Fernando Leal-Calderon

Papers

Rheological properties of highly concentrated protein-stabilized emulsions.

Disjoining Pressure vs Thickness Isotherms of Thin Emulsion Films Stabilized by Proteins

Surface forces in model oil-in-water emulsions stabilized by proteins.

Colloid forces in model food-type emulsions