Pickering emulsion gels stabilized by protein and polysaccharide-based particles: A review of stability, synthesis, applications and prospective

Abstract

With a far longer stability than traditional emulsions, Pickering emulsion gels (PKEGs)—stabilized by solid particles—have proven highly efficient in a range of applications during recent years. Particles based on proteins or polysaccharides with distinctive amphiphilic structure are particularly well-suited for the production of PKEGs because of their natural occurrence, low cost, high nutritional content, and potential health advantages. Thus far, it has been shown that plant and animal proteins, as well as their complexes with polysaccharides, effectively stabilize PKEGs. The three main mechanisms that protein-based particles (Pr-Particles) stabilize PKEGs are the formation of a densely packed interfacial layer due to the irreversible adsorption of Pr-Particles, the accumulation of non-adsorbed Pr-Particles at the plateau borders or the formation of a gel-like network in the continuous phase, which decreases drainage, and depletion stabilization. In some applications, each type of Pr-Particles may provide exceptional advantages. This paper summarizes the main functions of PKEGs stabilized by proteins or polysaccharides, looks at the key mechanisms governing gel stability to better understand the complex behavior of PKEGs, and highlights the important scientific, technological advancements being deployed in the food industry using PKEGs. Some important applications of PKEGs in the food and nutraceutical fields are delivery of bioactive compounds, modulation of lipid digestion, fat substitution and design/formulation of novel products including 3D printed foods, which have been covered in the current study.

Highlights

Pickering emulsion gels (PEGs)—stabilized by solid particles—are highly efficient ingredients.

Particles based on proteins or polysaccharides can be applied for production of PEGs.

The key mechanisms governing gel stability in PEGs are described.

The complex behavior of PEGs and their application in different fields is also discussed.

Introduction

A type of food system known as emulsion gel (emulgel) is identified by the way oil droplets are distributed inside a gelled matrix. Its fundamental soft-solid morphological traits have drawn attention from the food industry and medicinal drug release applications [1]. Similarly, solid particles (SOPs) can stabilize Pickering emulsion gels (PKEGs), a kind of emulgel. The benefits of PKEGs over conventional emulgels stabilized by small molecule surfactants include less stabilizer consumption and high storage stability [2]. There are two types of inorganic and organic particles that stabilize PKEGs based on their chemical makeup. PKEGs stop oil droplets from contacting each other by forming a physical barrier at the oil-water interface through the adsorption of SOPs. Destabilizing features such as droplet agglomeration may also be prevented by the formation of an oil-water interfacial layer because this adsorption is usually irreversible [3,4]. At the oil-water interface, adsorbed particles affect the thickness of the interfacial layer and properties such as interfacial tension [[5], [6], [7]]. In turn, these interfacial properties affect the behavior and stability of PKEGs.

The thickness region known as the oil-water interface layer is produced when SOPs adhere to the surfaces of the water and oil phases [8]. This is essential for keeping Pickering emulsions (PEs) stable. Protein-based particles (Pr-Particles) with the amphiphilic structure are especially well-suited for stabilizing PKEGs when compared to other colloidal particles (COPs) because of their many benefits, including high nutritional content, low cost, biocompatibility, natural origin, possible health benefits, and strong surface activity. Furthermore, native proteins can be converted into Pickering particles (PPs) without the need for complicated modifications; for example, by covalent cross-linking, electrostatic complexation, or even basic heat treatment or anti-solvent precipitation (ASP) with other biopolymers, such as polysaccharides, polyphenols, and other surfactants. They also possess useful qualities like gelation and emulsification, which is more significant. The food industry uses milk proteins as emulsifiers because they are amphiphilic [[9], [10], [11]]. Nevertheless, PEs made with separate proteins is not very stable. In PEs generated from whey protein isolate (WPI) alone; for instance, a significant release of free fatty acids (FFAs) was revealed by in vitro simulated digestion [[12], [13], [14], [15], [16]].

Additionally, the stability of PKEGs created from protein-polysaccharide composite particles (Pr/Ps-Particles) are now much more stable, and researchers have extensively documented the study of adding small molecules to increase protein hydrophobicity [8,[17], [18], [19]]. The ability of Pr-Particles or polysaccharide-based particles (Ps-Particles) to modify PKEGs properties primarily depends on their size, shape, concentration, and surface wettability as well as a number of other factors that affect their possible mechanisms, like temperature, light, magnetism, salts, or pH [20]. Depending on their properties, particles can stabilize PKEGs by stabilizing depletion, inhibiting drainage by preventing accumulation at the Plateau borders or the formation of a gel-like network in the continuous phase by non-adsorbed particles, and preventing coalescence or disproportionation by adsorbing and forming a mono- or bilayer at the oil/water interface.

In this work, formation and stabilization of PKEGs by Pr/Ps-Particles is reviewed through an analysis of the pertinent literature. To better understand the complex behavior of PKEGs, the main mechanisms that control their stability are discussed. Finally, we go over the main applications of PKEGs stabilized by proteins or polysaccharides in the food and nutraceutical fields as well as possible future usage, including delivery of bioactive compounds, modulation of lipid digestion, fat substitution and design/formulation of novel products including 3D printed foods, which have been covered in the current study. Theoretical direction for effectively creating PKEGs stabilized by proteins or polysaccharides and additional uses in functional foods is what we hope this review may offer.