Surface phase transitions in foams and emulsions

Foaming properties of the complex of whey protein isolate fibrils and octenyl succinate starch and the application in angel cake

Exploring the functional properties of protein fibrils/polysaccharide complexes has recently attracted significant attention, but their foaming characteristics and potential food applications are still far from being fully understood. This work aimed to enhance the foaming properties of whey protein isolate fibrils (WPIF) through their complexation with amphiphilic octenyl succinate starch (OSS) and assessed the feasibility of utilizing this complex as an egg white alternative in angel cake production. The results showed that at pH 6.0, WPIF/OSS complexes with ratios (r) of 2.0, 4.0, and 10.0 demonstrated equal or superior foaming capacity (up to 1.2) compared to WPIF alone. Low-temperature treatment further augmented both the foaming capacity and foam half-life of the WPIF/OSS complexes. For food application, the complex at pH 6.0 and r = 2.0 was selected. Substituting 12.5 % of the egg white with this complex resulted in cakes with the largest foam volume, lowest foam and batter densities, and reduced cohesiveness and hardness. This was attributed to enlarged pore size, which enhanced product elasticity and resilience. This study used OSS to enhance the WPIF's foaming performance, expanding its applications to the food industry. The improved quality of angel cake with WPIF/OSS highlights its potential as a food formulation ingredient.

Recent Advances in the Properties and Applications of Polyglycerol Fatty Acid Esters

Although polyethylene glycol (PEG)-based surfactants are widely used in various industries due to their wide range of hydrophile-lipophile balance (HLB) values, their possible by-product, 1,4-dioxane, has been listed as a reasonably anticipated human carcinogen, which may limit their applications in fields closely related to the human body. Polyglycerol fatty acid esters (PGFEs), a class of surfactants based on polyglycerol (another polyether), also have a wide range of HLB values that can be adjust by varying the degree of polymerization of the polyglycerol, the length of the fatty acid carbon chain, or the degree of esterification, but do not have the risks caused by 1,4-dioxane. In addition, all the raw materials (glycerol and fatty acids) required for the preparation of PGFEs can be obtained via hydrolysis of renewable vegetable oils. Therefore, PGFEs, as new eco-friendly and biodegradable non-ionic surfactants, have been proposed as potential green alternatives to PEG-based non-ionic surfactants. This review summarizes the properties of PGFEs specifically including their HLB, surface properties, phase behaviors, stabilizing effect on foams and emulsions, and stability, and highlights their potential applications in food, cosmetics, and pharmaceuticals observed in the last decade.

Whipping Creams: Advances in Molecular Composition and Nutritional Chemistry

Whipping cream (WC) is an oil-in-water (O/W) emulsion used in food industry that can be transformed into aerated foam. The cream market has expanded significantly, driven by consumer demands for healthier and higher-quality products, leading to significant scientific research and innovation. This review focuses on formulation challenges related to ingredients such as fats, emulsifiers, and stabilizers, and how these components interact to form a stable emulsion and foam structure. Many studies have aimed to enhance the physicochemical, functional, and nutritional characteristics of WC by fine-tuning formulation parameters. A major focus was to address the health concerns linked to the high saturated fat content in milk fat (MF) by developing healthier alternatives. These include modifying the fat content, developing low-fat formulations, and introducing plant-based substitutes for dairy creams. The participation of additives to improve the properties of whipping cream was also investigated in many recent studies. The use of plant proteins, hydrocolloids, and emulsifiers has been explored, highlighting their effectiveness in enhancing emulsifying and foaming properties. This review summarizes recent advancements in whipping cream formulation, emphasizing the role of additives and alternative ingredients in meeting consumer preferences for healthier, more sustainable whipping cream products with enhanced functional, sensory, and nutritional properties.

Mechanisms of dissolution and crystallization of amorphous glibenclamide

Amorphous solid dispersions enhance the dissolution and oral bioavailability of poorly water-soluble drugs. However, the link between polymer properties and formulation performance has not been fully clarified yet. We studied the effect of hydroxypropyl cellulose (HPC) polymers molecular weight (Mw) on the storage stability, dissolution kinetics and supersaturation stability of spray-dried amorphous glibenclamide (GLB) formulations. The solid-state stability of amorphous GLB during storage was significantly enhanced by both the 40 kDa (HPC-SSL) and 84 kDa (HPC-L) polymers, regardless of Mw differences. In contrast, HPC-SSL maintained significantly higher aqueous drug concentrations during dissolution, compared to HPC-L (its higher Mw analogue). Dedicated dissolution experiments, in situ optical microscopy and solid-state characterization revealed that aqueous drug concentrations were determined by the interplay between crystallization inhibition, drug ionization, wetting and solubilization effects: (1) HPC prevents surface nucleation, hence inhibiting crystallization, (2) intestinal colloids (bile salts and phospholipids) increase supersaturated drug concentrations via wetting and solubilization effects and (3) pH and drug ionization severely impact the degree of supersaturation. The better performance of the lower Mw HPC-SSL was due to its superior inhibition of surface crystallization during dissolution. These insights into the molecular mechanisms of dissolution and crystallization of amorphous solids provide foundation for rational formulation development.

Propagation of Freezing in Supercooled Water-In-Antifreeze-Oil Emulsions

Water-in-oil (W/O) emulsions, in which water droplets are separated by a continuous oil phase, are frequently used in food and cosmetic products. However, the freezing kinetics of W/O emulsions are not yet well understood. In this study, we find that freezing propagates to individual water droplets that are in direct contact with other frozen droplets. When droplets are not in contact, freezing does not propagate even when the emulsions are cooled to -18 °C. Two measures of the perimeter and the area of the frozen droplets in emulsions are defined to evaluate the propagation velocity of freezing using a simple mathematical model. The velocity is highest (4 × 102 μm s-1) at -18 °C, which is lower than the freezing velocity of individual droplets at the same temperature (1.2 × 103 μm s-1). Water-oil interfaces, or a thin layer of oil between droplets, act as a barrier to propagation of freezing. The dependence of the freezing velocity on the degree of supercooling is consistent with results from a previous study; however, the absolute value of the freezing velocity is smaller by a factor of 102. The propagation velocity also depends on the degree of supercooling but its dependence is different from that of the freezing velocity. Features of freezing of water droplets immersed in antifreeze oil are discussed.

High-purity 1,2-dimyristoyl-sn-glycero-3-phosphocholine: synthesis and emulsifying performance evaluation

Introduction

1,2-Dimyristoyl-sn-glycero-3-phosphocholine (DMPC) is a promising emulsifier for bioactive delivery systems, but its industrial applications are limited by the lack of cost-effective and scalable synthetic routes. The purpose of this study was to economically produce high-purity DMPC by replacing commonly used column chromatography methods and to evaluate the emulsifying performance.

Methods

DMPC was synthesized from sn-glycero-3-phosphocholine using Steglich esterification followed by sequential recrystallization from ethyl acetate and acetone. The structure of DMPC was identified and its purity was confirmed using various spectroscopy and chromatography techniques. The emulsifying performance was evaluated by examining the effects of storage on the properties of o/w emulsions prepared using soybean oil with (i) soy PC, (ii) soy PC + DMPC (1:1, w/w), and (iii) DMPC as emulsifiers.

Results

The chemical impurities formed during the synthesis of DMPC was removed, and its final purity was 96%, and the melt transition temperature was 37.6°C. No visible difference between the three emulsions (soy PC, soy PC+DMPC, and DMPC) was observed during two-week storage, and the DMPC-based emulsion was more stable than soy PC emulsion, showing smaller particle size distribution during 6 months.

Discussion

The highly pure DMPC was synthesized by an economical method, and DMPC-based emulsions demonstrated physicochemical stable, highlighting its potential for food and pharmaceutical industry-related applications. Our findings suggest that DMPC holds promise as an emulsifier with broad applications in the food industry.

Recent advances in studying crystallisation of mono- and di-glycerides at oil-water interfaces

This review focuses on the current understanding regarding lipid crystallisation at oil-water interfaces. The main aspects of crystallisation in bulk lipids will be introduced, allowing for a more comprehensive overview of the crystallisation processes within emulsions. Additionally, the properties of an emulsion and the impact of lipid crystallisation on emulsion stability will be discussed. The effect of different emulsifiers on lipid crystallisation at oil-water interfaces will also be reviewed, however, this will be limited to their impact on the interfacial crystallisation of monoglycerides and diglycerides. The final part of the review highlights the recent methodologies used to study crystallisation at oil-water interfaces.

Macroscopic Nematic Orientation Dictated by an Orientationally Frustrated Random-Field Surface: Equilibrium Structure and Kinetics

Liquid crystals subjected to frustrated surfaces with mixed anchoring conditions demonstrate a rich variety of orientational patterns. Particularly, it would trigger either continuous or discontinuous variation of the bulk orientation, i.e., a phenomenon known as the anchoring or orientational transition. Despite its prime importance in developing novel optoelectronic devices, how the surface anchoring patterns dedicate the energy landscape of a system, thus the equilibrium state, still needs to be understood. Here, we designed a simulation to model boundary substrates with two randomly mixed anchoring domains in space, which exhibit planar and homeotropic preferences. We numerically obtain general bulk orientational state diagrams under various surface and electric field conditions, which reveal the roles of each domain's size and surface fraction and anchoring strength on the bulk orientational state. Furthermore, we examine how the external electric field modifies the orientational state diagram and uncovers a field-assisted anchoring transition. We discuss the observed bistability and compare it to experimental evidence.

Impact of Saturation of Fatty Acids of Phosphatidylcholine and Oil Phase on Properties of β-Lactoglobulin at the Oil/Water Interface

Oil in water emulsions are commonly stabilized by emulsifying constituents like proteins and/or low molecular weight emulsifiers. The emulsifying constituents can compete or coexist at the interface. Interfacial properties thus depend on molecular structure of the emulsifying constituents and the oil phase and the resulting molecular interactions. The present study systematically analyzed the impact of fatty acid saturation of triacylglycerides and phosphatidylcholine on the interfacial properties of a β-lactoglobulin-stabilized interface. The long-term adsorption behaviour and the viscoelasticity of β-lactoglobulin-films were analyzed with or without addition of phosphatidylcholine via drop tensiometry and dilatational rheology. Results from the present study showed that increasing similarity in fatty acid saturation and thus interaction of phosphatidylcholine and oil phase increased the interfacial tension for the phosphatidylcholine alone or in combination with β-lactoglobulin. The characteristics and stability of interfacial films with β-lactoglobulin-phosphatidylcholine are further affected by interfacial adsorption during changes in interfacial area and crystallization events of low molecular weight emulsifiers. This knowledge gives guidance for improving physical stability of protein-based emulsions in foods and related areas.

Graphic abstract

Essential Factor of Perfluoroalkyl Surfactants Contributing to Efficacy in Firefighting Foams

Two simple model aqueous foams, one made from a perfluoroalkyl surfactant and one from a silicone polyether surfactant, are compared with regard to their stability in contact with heptane as a model fuel oil. The observed foam stabilities are explained in terms of the equilibrium phase behavior of the system water-surfactant-heptane. It is demonstrated that the fundamental enabling factor that makes perfluoroalkyl surfactant perform exceedingly well in stabilizing foams on hydrocarbon fuel oil is its oleophobicity. For hydrocarbon or silicone surfactants, the propensity for the surfactant phase to solubilize hydrocarbon oil and be solubilized in the oil destabilizes the foam. This is particularly so if the surfactant's phase inversion by temperature (PIT) range falls within the application temperature range.

Rotator phases in hexadecane emulsion drops revealed by X-ray synchrotron techniques

HYPOTHESIS

Micrometer sized alkane-in-water emulsion drops, stabilized by appropriate long-chain surfactants, spontaneously break symmetry upon cooling and transform consecutively into series of regular shapes (Denkov et al., Nature 2015, 528, 392). Two mechanisms were proposed to explain this phenomenon of drop "self-shaping". One of these mechanisms assumes that thin layers of plastic rotator phase form at the drop surface around the freezing temperature of the oil. This mechanism has been supported by several indirect experimental findings but direct structural characterization has not been reported so far.

EXPERIMENTS

We combine small- and wide-angle X-ray scattering (SAXS/WAXS) with optical microscopy and DSC measurements of self-shaping drops in emulsions.

FINDINGS

In the emulsions exhibiting drop self-shaping, the scattering spectra reveal the formation of intermediate, metastable rotator phases in the alkane drops before their crystallization. In addition, shells of rotator phase were observed to form in hexadecane drops, stabilized by C₁₆EO₁₀ surfactant. This rotator phase melts at ca. 16.6 °C which is significantly lower than the melting temperature of crystalline hexadecane, 18 °C. The scattering results are in a very good agreement with the complementary optical observations and DSC measurements.

Surface science of cosmetic substrates, cleansing actives and formulations

The development of shampoo and cleansing formulations in cosmetics is at a crossroads due to consumer demands for better performing, more natural products and also the strong commitment of cosmetic companies to improve the sustainability of cosmetic products. In order to go beyond traditional formulations, it is of great importance to clearly establish the science behind cleansing technologies and appreciate the specificity of cleansing biological surfaces such as hair and skin. In this review, we present recent advances in our knowledge of the physicochemical properties of the hair surface from both an experimental and a theoretical point of view. We discuss the opportunities and challenges that newer, sustainable formulations bring compared to petroleum-based ingredients. The inevitable evolution towards more bio-based, eco-friendly ingredients and sustainable formulations requires a complete rethink of many well-known physicochemical principles. The pivotal role of digital sciences and modelling in the understanding and conception of new ingredients and formulations is discussed. We describe recent numerical approaches that take into account the specificities of the hair surface in terms of structuration, different methods that study the adsorption of formulation ingredients and finally the success of new data-driven approaches. We conclude with practical examples on current formulation efforts incorporating bio-surfactants, controlling foaming and searching for new rheological properties.

Nucleation of melt: From fundamentals to dispersed systems

The most evident aspects of a first order transition of a system from an old to a new phase, are the presence of a discontinuity at the interface between both phases and the thermal effects related to the latent heat exchanged with the surrounding environment. These effects are the result of a sequence of events promoted by thermodynamic conditions persisting over the equilibrium in a metastable state. The breakdown of metastability is promoted by infinitesimal energy fluctuations resulting in the germination of clusters of the new phase that can grow to a critical size (nucleus) and then develop or vanish. Examples of these sequences are common in various technological fields such as combustion, food processing, pharmaceutical manufacturing, condensation, and phase change heat transfer, etc. This work aims to highlight a logical path that leads the readers from the fundamental phenomenology to the most intricated aspects of the nucleation within dispersed systems such as oil-in-water emulsions. Differences between the homogeneous and heterogeneous mechanisms are, under the light of the Classical Nucleation Theory (CNT), presented in bulk and confined systems until defining a minimum confinement size. By collecting insights coming from a rich scientific literature mostly focused on the stability of emulsified systems, the discussion is then on the aspects related to the surface related mechanisms. Two main aspects are then considered: a) the wettability of the nucleating cluster by the surrounding melt; b) the affinity between the adsorbed layer, where a surfactant is located, and the oil melt phase (mainly n-alkanes and triacylglycerols with different moieties). In cases where nucleation is dominating over the dewetting of the nucleus, the contact angle can be considered as a constant value. The affinity in terms of molecular features between the surfactant and the oil phase can promote the template effect. Several factors seem to play a role in this interaction such as the thermal characteristics of the surfactant and comparable dimensions between the molecule (or fractions) of the dispersed compound and the tail of the surfactant.

Exploration of the natural waxes-tuned crystallization behavior, droplet shape and rheology properties of O/W emulsions

Lipid crystallization in O/W emulsions is essential to control the release of nutrients and to food structuring. While few information is involved in adjusting and controlling the performance of emulsions by adjusting oil phase crystallization behavior. We herein developed a novel strategy for designing lipid crystallization inside oil droplets by natural waxes to modify the O/W emulsion properties. Natural waxes, the bio-based and sustainable materials, displayed a high efficiency in modifying the crystallization behavior, droplet surface and shape, as well as the overall performance of emulsions. Specifically, waxes induced the formation of a new hydrocarbon chain distances of 3.70 and 4.15 Å and slightly decreased the lamellar distance (d₀₀₁) of the single crystallites, thus forming the large and rigid crystals in droplets. Interestingly, these large and rigid crystals in droplets tended to penetrate the interface film, forming the crystal bumps on the droplet surface and facilitating non-spherical shape transformation. The presence of rice bran wax (RW) and carnauba wax (CW) induced the droplet shape into ellipsoid and polyhedron shape, respectively. Furthermore, the uneven interface and non-spherical shape transformation promoted the crystalline droplet-droplet interaction, fabricating a three-dimensional network structure in O/W emulsions. Finally, both linear and nonlinear rheology strongly supported that waxes enhanced the crystalline droplet-droplet interaction and strengthened the network in O/W emulsions. Our findings give a clear insight into the effects of adding natural waxes into oil phase on the crystalline and physical behavior of emulsions, which provides a direction for the design and control of emulsion performance.

Thinning and thickening transitions of foam film induced by 2D liquid-solid phase transitions in surfactant-alkane mixed adsorbed films

Mixed adsorbed film of cationic surfactant and linear alkane at the air-water interface shows two-dimensional phase transition from surface liquid to surface frozen states upon cooling. This surface phase transition is accompanying with the compression of electrical double layer due to the enhancement of counterion adsorption onto the adsorbed surfactant cation and therefore induces the thinning of the foam film at fixed disjoining pressures. However, by increasing the disjoining pressure, surfactant ions desorb from the surface to reduce the electric repulsion between the adsorbed films on the both sides of the foam film. As a result, the foam film stabilized by the surfactant-alkane mixed adsorbed films showed unique thickening transition on the disjoining pressure isotherm due to the back reaction to the surface liquid films. In this review, we will summarize all these features based on the previously published papers and newly obtained results.

Surface activity and foaming properties of saponin-rich plants extracts

Saponins are amphiphilic glycosidic secondary metabolites produced by numerous plants. So far only few of them have been thoroughly analyzed and even less have found industrial applications as biosurfactants. In this contribution we screen 45 plants from different families, reported to be rich in saponins, for their surface activity and foaming properties. For this purpose, the room-temperature aqueous extracts (macerates) from the alleged saponin-rich plant organs were prepared and spray-dried under the same conditions, in presence of sodium benzoate and potassium sorbate as preservatives and drying aids. For 15 selected plants, the extraction was also performed using hot water (decoction for 15 min) but high temperature in most cases deteriorated surface activity of the extracts. To our knowledge, for most of the extracts this is the first quantitative report on their surface activity. Among the tested plants, only 3 showed the ability to reduce surface tension of their solutions by more than 20 mN/m at 1% dry extract mass content. The adsorption layers forming spontaneously on the surface of these extracts showed a broad range of surface dilational rheology responses - from null to very high, with surface dilational elasticity modulus, E' in excess of 100 mN/m for 5 plants. In all cases the surface dilational response was dominated by the elastic contribution, typical for saponins and other biosurfactants. Almost all extracts showed the ability to froth, but only 32 could sustain the foam for more than 1 min (for 11 extracts the foams were stable during at least 10 min). In general, the ability to lower surface tension and to produce adsorbed layers with high surface elasticity did not correlate well with the ability to form and sustain the foam. Based on the overall characteristics, Saponaria officinalis L. (soapwort), Avena sativa L. (oat), Aesculus hippocastanum L. (horse chestnut), Chenopodium quinoa Willd. (quinoa), Vaccaria hispanica (Mill.) Rauschert (cowherb) and Glycine max (L.) Merr. (soybean) are proposed as the best potential sources of saponins for surfactant applications in natural cosmetic and household products.