Colloidal destabilisation mechanisms in protein-stabilised emulsions

Advancing gelatin/cinnamaldehyde O/W emulsions electrospinability: Role of soybean lecithin in core-shell nanofiber fabrication

The main objective of this study is to investigate the impact and mechanism of soy lecithin incorporation into the gelatin-cinnamaldehyde emulsion, focusing on how it influences emulsion stability during the electrospinning process. In this work, a cinnamaldehyde/gelatin/soy lecithin (CGS) fiber membrane with excellent antibacterial properties was successfully created. The addition of soy lecithin improves the stability of the emulsion and improves the loading performance and fiber morphology of the CGS fiber membrane. Fourier Transform infrared spectroscopy (FTIR) and urea addition confirmed that soy lecithin may strengthen the interface structure of gelatin in the oil and water phases through hydrogen bonds, thus enhancing the stability of the emulsion in electrospinning. The application tests also revealed that the CGS fiber membrane effectively preserved the sensory quality of beef. This study indicates that the vector construction method can extend the utilization of cinnamaldehyde in food industry.

Static stability of partially crystalline emulsions: Impacts of carrageenan and its blends with xanthan gum and/or guar gum

In the present study, four different combinations of gums, including carrageenan (CG), its binary blends with xanthan gum (XG) or guar gum (GG) in equal ratios, and its ternary blends with XG and GG in three equal ratios, were involved into making partially crystalline emulsions (PCEs), respectively. The freshly prepared emulsions were systematically characterized by rheological property, particle size distribution, microscopic morphology, interfacial property, and intermolecular interactions, and their emulsion stabilities were further evaluated using multiple light scattering technique and storage test. All PCEs stabilized by gum blends (CG + XG, CG + GG, and CG + XG + GG) obtained decreased apparent viscosities at 0.01 s^-1 (10.12-25.32 Pa·s), particle sizes (3.12-4.06 μm), as well as interfacial protein concentrations (22.60-27.01 mg/m²), which were much lower than those with single CG (35.98 Pa·s, 6.72 μm, and 47.74 mg/m², respectively). The microscopic morphology showed that blending CG with XG and/or GG contributed to formation of firmer three-dimensional matrix, thereby preventing the aggregation of fat droplets. Inclusion of XG and/or GG also significantly reduced contribution of hydrophobic interactions from 0.72 to 0.24-0.44 mg/mL. Both multiple light scattering and storage test revealed that emulsion instabilities were mainly manifested as a clarification at the bottom and an agglomeration at the top. PCE-CG + XG + GG exhibited superior stability with low creaming index (6.20 %) and viscosity (1180.0 mPa·s) after three months of storage. The research aims to evaluate the effects of CG and its blends with XG and GG on stability of PCEs, and the results potentially provide valuable information for manufacture of stable PCE foods.

Influence of Proteins on the Absorption of Lipophilic Vitamins, Carotenoids and Curcumin - A Review

While proteins have been widely used to encapsulate, protect, and regulate the release of bioactive food compounds, little is known about the influence of co-consumed proteins on the absorption of lipophilic constituents following digestion, such as vitamins (A, D, E, K), carotenoids, and curcumin. Their bioavailability is often low and very variable, depending on the food matrix and host factors. Some proteins can act as emulsifiers during digestion. Their liberated peptides have amphiphilic properties that can facilitate the absorption of microconstituents, by improving their transition from lipid droplets into mixed micelles. Contrarily, the less well digested proteins could negatively impinge on enzymatic accessibility to the lipid droplets, slowing down their processing into mixed micelles and entrapping apolar food compounds. Interactions with mixed micelles and proteins are also plausible, as shown earlier for drugs. This review focuses on the ability of proteins to act as effective emulsifiers of lipophilic vitamins, carotenoids, and curcumin during digestion. The functional properties of proteins, their chemical interactions with enzymes and food constituents during gastro-intestinal digestion, potentials and limitations for their use as emulsifiers are emphasized and data from human, animal, and in vitro trials are summarized.

Turbulence-induced formation of emulsion gels

Emulsion gels have a wide range of applications. We report on a facile and versatile method to produce stable emulsion gels with tunable rheological properties. Gel formation is triggered by subjecting a mixture containing aqueous colloidal particle (CP) suspensions and water-immiscible liquids to intense turbulence, generated by low frequency (20 kHz) ultrasound or high-pressure homogenization. Through systematic investigations, requisite gel formation criteria are established with respect to both formulation and processing, including ratio/type of liquid pairs, CP properties, and turbulence conditions. Based on the emulsion microstructure and rheological properties, inter-droplet bridging and CP void-filling are proposed as universal stabilization mechanisms. These mechanisms are further linked to droplet-size scaling and sphere close-packing theory, distinctive from existing gel-conferring models. The study thereby provides the foundation for advancing the production of emulsion gels that can be tailored to a wide range of current and emerging applications in the formulation and processing of food, cosmetics or pharmaceutical gels, and in material science.

Interactions of salivary mucins and saliva with food proteins: a review

Mucins are long glycoprotein molecules responsible for the gel nature of the mucous layer that covers epithelial surfaces throughout the body. Mucins, as the major salivary proteins, are also important proteins for the food oral processing and digestion. The interactions of salivary mucins and saliva with several food proteins and food protein emulsions, as well as their functional properties related to the food oral processing were reviewed in this paper. The target food proteins of focus were whey proteins (lactoferrin and beta-lactoglobulin) and non-whey proteins (casein, gelatin, galectin/lectin, and proline-rich proteins). Most of the studies suggest that electrostatic attraction (between positively charged food proteins with negatively charged moieties of mucin mainly on glycosylated region of mucin) is the major mode of interaction between them. On the other hand, casein attracts the salivary proteins only via non-covalent interactions due to its naturally self-assembled micellar structure. Moreover, recent studies related to β-lactoglobulin (BLG)-mucin interactions have clarified the importance of hydrophobic as well as hydrophilic interactions, such as hydrogen bonding. Furthermore, in vitro studies between protein emulsions and saliva observed a strong aggregating effect of saliva on caseinate and whey proteins as well as on surfactant-stabilized emulsions. Besides, the sign and the density of the charge on the surface of the protein emulsion droplets contribute significantly to the behavior of the emulsion when mixed with saliva. Other studies also suggested that the interactions between saliva and whey proteins depends on the pH in addition to the flow rate of the saliva. Overall, the role of interactions of food proteins and food protein emulsions with mucin/saliva-proteins in the oral perception, as well as the physicochemical and structural changes of proteins were discussed.

Lubrication of chocolate during oral processing

The structure of chocolate is drastically transformed during oral processing from a composite solid to an oil/water fluid emulsion. Using two commercial dark chocolates varying in cocoa solids content, this study develops a method to identify the factors that govern lubrication in molten chocolate and saliva's contribution to lubrication following oral processing. In addition to chocolate and its individual components, simulated boluses (molten chocolate and phosphate buffered saline), in vitro boluses (molten chocolate and whole human saliva) and ex vivo boluses (chocolate expectorated after chewing till the point of swallow) were tested. The results reveal that the lubrication of molten chocolate is strongly influenced by the presence of solid sugar particles and cocoa solids. The entrainment of particles into the contact zone between the interacting surfaces reduces friction such that the maximum friction coefficient measured for chocolate boluses is much lower than those for single-phase Newtonian fluids. The addition of whole human saliva or a substitute aqueous phase (PBS) to molten chocolate dissolves sugar and decreases the viscosity of molten chocolate so that thinner films are achieved. However, saliva is more lubricating than PBS, which results in lower friction coefficients for chocolate-saliva mixtures when compared to chocolate-PBS mixtures. A comparison of ex vivo and in vitro boluses also suggests that the quantity of saliva added and uniformity of mixing during oral processing affect bolus structure, which leads to differences in measured friction. It is hypothesized that inhomogeneous mixing in the mouth introduces large air bubbles and regions of non-emulsified fat into the ex vivo boluses, which enhance wetting and lubrication.

Fabrication of a nutrient delivery system of docosahexaenoic acid nanoemulsions via high energy techniques

A high energy nanoemulsification technique has been developed to encapsulate docosahexaenoic acid (DHA), with the major objective of enhancing its chemical and kinetic stability for a substantial storage period.

New insights into binding interaction of novel ester-functionalized m-E2-m gemini surfactants with lysozyme: a detailed multidimensional study

Different binding patterns of m-E2-m (12-E2-12 and 14-E2-14) surfactants to HEWL.

Perspective of surface active agents in baking industry: an overview

Different researchers have previously used surfactants for improving bread qualities and revealed that these compounds result in improving the quality of dough and bread by influencing dough strength, tolerance, uniform crumb cell size, and improve slicing characteristics and gas retention. The objective of this review is to highlight the areas where surfactants are most widely used particularly in the bread industries, their role and mechanism of interaction and their contribution to the quality characteristics of the dough and bread. This review reveals some aspects of surface-active agents regarding its role physiochemical properties of dough that in turn affect the bread characteristics by improving its sensory quality and storage stability.

Emulsions with unique properties from proteins as emulsifiers

Many proteins are surface active molecules and form stable emulsions. In these emulsions, the protein covered oil droplets behave as sticky droplets even when they are ionically charged. As a result of the stickiness of the droplets the emulsions have gel-like properties. The stickiness is due to the multipolar nature of the proteins in contrast to the bipolar nature of surfactants or other amphiphilic compounds that form emulsions with repulsive droplets. Stable emulsions are also formed from particles like clays to which proteins are adsorbed. These hybrid compounds form even more stable emulsions with stronger elastic properties than clays and proteins on their own. These so called pickering emulsions have paste-like properties and do not flow. The scaffolding network of the crosslinked protein bilayers on the droplets is so strong that both the water and the oil can be removed from the emulsions by freeze drying without collapse of the scaffold. The resulting sponge can be used again for the uptake of both water and oil. Emulsions which are prepared from different proteins differ mainly in their elastic properties.

Protein concentration and protein-exposed hydrophobicity as dominant parameters determining the flocculation of protein-stabilized oil-in-water emulsions

DLVO theory is often considered to be applicable to the description of flocculation of protein-stabilized oil-in-water emulsions. To test this, emulsions made with different globular proteins (β-lactoglobulin, ovalbumin, patatin, and two variants of ovalbumin) were compared under different conditions (pH and electrolyte concentration). As expected, flocculation was observed under conditions in which the zeta potential is decreased (around the isoelectric point and at high ionic strength). However, the extent of flocculation at higher ionic strength (>50 mM NaCl) decreased with increasing protein-exposed hydrophobicity. A higher exposed hydrophobicity resulted in a higher zeta potential of the emulsion droplets and consequently increased stability against flocculation. Furthermore, the addition of excess protein strongly increased the stability against salt-induced flocculation, which is not described by DLVO theory. In the protein-poor regime, emulsions showed flocculation at high ionic strength (>100 mM NaCl), whereas emulsions were stable against flocculation if excess protein was present. This research shows that the exposed hydrophobicity of the proteins and the presence of excess protein affect the flocculation behavior.

Food proteins: a review on their emulsifying properties using a structure-function approach

Proteins are of great interest due to their amphiphilic nature, which allows them to reduce the interfacial tension at the oil-water interface. The incorporation of proteins at the oil-water interface has allowed scientists to utilise them to form emulsions (O/W or W/O), which may be used in food formulations, drug and nutrient delivery. The systematic study of the proteins at the interface and the factors that affect their stability (i.e., conformation, pH, solvent conditions, and thermal treatment) has allowed for a broader use of these emulsions tailored for various applications. In this review, the factors affecting the stability of emulsions using food proteins will be discussed. The use of polysaccharides to complex with proteins will also be explored in relation to enhancing emulsion stability.

Factors affecting the stability of O/W emulsion in BSA solution: Stabilization by electrically neutral protein at high ionic strength

Bovine serum albumin (BSA) was used as an emulsifier to disperse corn oil in aqueous media with various protein concentration, pH, and ionic strength. Quantitative estimation was made on the homogenizing activity of BSA and dispersion stability of oil particles by measuring particle size, turbidity, and creaming rate. Dispersion stability strongly depended on pH and became a minimum around pH 5.0 which was the isoelectric point of BSA. The interfacial tension between BSA solution and corn oil was minimized at pH 5.0. Interesting results were obtained concerning the ionic-strength dependence of stability. When the ionic strength was set below 30 mM, the emulsions became more stable with the increase of BSA concentration at pH 6.7 but the opposite behavior (enhanced destabilization) was confirmed at pH 5.0 with the BSA content. In high ionic strength conditions (ca. > or = 80 mM NaCl), however, BSA-stabilized emulsions became fairly stable even at pH 5.0. These results suggested that BSA molecules having no net charge induced some attractive interactions (e.g., bridging or depletion) in low ionic strength but steric stabilization in high ionic strength, respectively.

The emulsion flocculation stability of protein–carbohydrate diblock copolymers

The effect of the steric layer thickness on the flocculation stability of beta-lactoglobulin-carbohydrate diblock copolymers was assessed. The diblock copolymers were created by conjugating beta-lactoglobulin to maltose or a series of different M(n) maltodextrins using the Maillard reaction. The thickness and spatial arrangement of the interfacial layers were assessed via latex adsorption and selective enzymatic digestion studies. An increase in the molecular weight of the maltodextrin (900, 1900 and 3800 Da) increased the interfacial thickness (1.1, 2.5 and 7.3 nm, respectively). No detectable change to interfacial thickness was observed upon the attachment of maltose. The increase in the interfacial layer thickness scaled with the hydrodynamic size of the carbohydrate. The beta-lactoglobulin-maltodextrin conjugates were found to have a diblock architecture, with the protein anchored at the surface and the carbohydrate protruding into the aqueous continuous phase. The stability of oil-in-water emulsions formed using the conjugates was assessed by exposing them to salt (150 mM NaCl or 0-20 mM CaCl(2)), heat alone or heat in the presence of 150 mM NaCl. Conjugation of a 900 Da maltodextrin provided sufficient steric stabilization to prevent flocculation in high salt environments. The effect of the (number) density of the steric layer was also assessed by controlling the average number of maltodextrins attached per beta-lactoglobulin molecule. The steric layer density at which emulsions became unstable was a function of carbohydrate M(n). Emulsions made from the 900 Da maltodextrin conjugate became unstable below a steric layer density of one tail per 7.5 nm(2), whilst emulsions made from the 1900 Da maltodextrin were unstable below a steric layer density of one tail per 9.5 nm(2). This trend was expected and can be explained by the stronger van der Waals attraction that arises from the closer interdroplet separations that are permissible with the shorter maltodextrins. The excellent flocculation stability of Maillard conjugate emulsions is thought to arise from the combined effects of weak electrostatic repulsion from the screened protein surface charge and steric repulsion from the attached carbohydrate layer. This means that attachment of a relatively thin steric layer is enough to stabilize the emulsions against flocculation. These findings have important implications for the development of commercial processes to manufacture protein-carbohydrate Maillard conjugate emulsifiers. Furthermore the work provides a greater empirical understanding of the relationship between interfacial architecture and colloidal stability, and may provide the means for greater theoretical understanding of biopolymer stabilization of interfaces.

Coalescence stability of emulsions containing globular milk proteins

This review summarizes a large set of related experimental results about protein adsorption and drop coalescence in emulsions, stabilized by globular milk proteins, beta-lactoglobulin (BLG) or whey protein concentrate (WPC). First, we consider the effect of drop coalescence on the mean drop size, d32, during emulsification. Two regimes of emulsification, surfactant-rich (negligible drop coalescence) and surfactant-poor (significant drop coalescence) are observed in all systems studied. In the surfactant-rich regime, d32 does not depend on emulsifier concentration and is determined mainly by the interfacial tension and the power dissipation density in the emulsification chamber, epsilon. In the surfactant-poor regime and suppressed electrostatic repulsion, d32 is a linear function of the inverse initial emulsifier concentration, 1/C(INI), which allows one to determine the threshold emulsifier adsorption needed to stabilize the oil drops during emulsification, Gamma* (the latter depends neither on oil volume fraction nor on epsilon). Second, we study how the BLG adsorption on drop surface changes while varying the protein and electrolyte concentrations, and pH of the aqueous phase. At low electrolyte concentrations, the protein adsorbs in a monolayer. If the pH is away from the isoelectric point (IEP), the electrostatic repulsion keeps the adsorbed BLG molecules separated from each other, which precludes the formation of strong intermolecular bonds during shelf-storage as well as after heating of the emulsion. At higher electrolyte concentration, the adsorption Gamma increases, as a result of suppressed electrostatic repulsion between the protein molecules; monolayer or multilayer is formed, depending on protein concentration and pH. The adsorption passes through a maximum (around the protein IEP) as a function of pH. Third, the effect of various factors on the coalescence stability of "fresh" emulsions (up to several hours after preparation) was studied. Important conclusion from this part of the study is the establishment of three different cases of emulsion stabilization: (1) electrostatically-stabilized emulsions with monolayer adsorption, whose stability is described by the DLVO theory; (2) emulsions stabilized by steric repulsion, created by protein adsorption multilayers - a simple model was adapted to describe the stability of these emulsions; and (3) emulsions stabilized by steric repulsion, created by adsorption monolayers. Fourth, we studied how the emulsion stability changes with storage time and after heating. At high electrolyte concentrations, we find a significant decrease of the coalescence stability of BLG-emulsions after one day of shelf-storage (aging effect). The results suggest that aging is related to conformational changes in the protein adsorption layer, which lead to formation of extensive lateral non-covalent bonds (H-bonds and hydrophobic interactions) between the adsorbed molecules. The heating of BLG emulsions at high electrolyte concentration leads to strong increase of emulsion stability and to disappearance of the aging effect, which is explained by the formation of disulfide bonds between the adsorbed molecules. The emulsion heating at low electrolyte concentration does not affect emulsion stability - this result is explained with the electrostatic repulsion between the adsorbed molecules, which keeps them separated so that no intermolecular disulfide bonds are formed. Parallel experiments with WPC-stabilized emulsions show that these emulsions are less sensitive to variations of pH and thermal treatment; no aging effect is detected up to 30 days of storage. The observed differences between BLG and WPC are explained with the different procedures of preparation of these protein samples (freeze-drying and thermally enhanced spray-drying, respectively). Our data for emulsion coalescence stability are compared with literature results about the flocculation stability of BLG emulsions, and the observed similarities/differences are explained by considering the structure of the protein adsorption layers.