Oral tribology of dairy protein-rich emulsions and emulsion-filled gels affected by colloidal processing and composition

Designing nutritious food for the elderly population often requires significant quantities of leucine-rich whey proteins to combat malnutrition, yet high-protein formulations can cause mouth dryness and increased oral friction. This study investigated how various colloidal processing methods and compositions impact the in vitro oral tribological properties of protein-rich emulsions and emulsion-filled gels. Oil-in-water emulsions with oil fractions from 1 wt% to 20 wt% were prepared, alongside emulsion-filled gels containing whey protein isolate (WPI), hydrolysed whey protein (HWP), or a blend of both (10 wt% protein content). Two processing approaches were employed: creating emulsions with an initial 10 w% protein content (M1) and initially forming emulsions with 0.1 wt% protein content, then enriching to a final 10 wt% concentration (M2). The hypothesis was that formulations with HWP or method 2 (M2) would offer lubrication benefits by inducing droplet coalescence, aiding in the formation of a lubricating boundary tribofilm. Surprisingly, the tribological behavior of high-protein emulsions showed minimal dependence on oil droplet volume fraction. However, both HWP-based emulsions and those processed with M2 for WPI exhibited significant friction reduction, which may be attributed to the presence of coalesced oil droplets, supporting our hypothesis. Substituting 50 wt% of WPI with HWP in emulsion-filled gel boli resulted in very low friction coefficients in the boundary lubrication regime, suggesting oil droplet release from the gel matrix. These findings provide insights into designing high-protein foods with improved mouthfeel for the elderly population, necessitating further validation through sensory studies

Flaxseed oleosomes: Responsiveness to physicochemical stresses, tribological shear and storage

This study aimed to extract oleosomes (OLs) from flaxseeds and assess their response to environmental conditions during storage (pH and ionic strengths), shear and tribological stresses. Our hypothesis was that a shear-induced instability will enable OLs to exhibit favourable lubrication performance. During storage, OLs exhibited resistance to droplet aggregation for up to 6 weeks owing to the proteins (3.5–152.8 kDa molecular weights) stabilizing the OL droplets. However, presence of divalent (Ca2+) ions induced destabilization with marked increase in droplet size (p < 0.05). OLs demonstrated shear thinning behaviour, displaying an order of magnitude higher viscosity than flaxseed oil (FSO) at low shear rates (<10 s−1). Strikingly, OLs mirrored the frictional profile of FSO regardless of entrainment speeds, due to droplet coalescence, validating the hypothesis. Such kinetic stability with shear-induced coalescing feature of OLs hold strong potential for future plant-based food development, particularly in achieving desired mouthfeel characteristics

Pickering Water‐in‐Oil Emulsions Stabilized Solely by Fat Crystals

Water-in-oil (W/O) emulsions have attracted heightened attention because of the ever-increasing interest in using non-calorific water to replace calorie-dense fat in food. However, designing clean-label and ultra-stable W/O emulsions is a longstanding challenge in colloid science. Herein, a novel, facile approach is introduced to designing cocoa butter (CB)-based crystals to stabilize Pickering W/O emulsions. Results using a combination of small- and wide-angle X-ray scattering and microscopy across length scales reveal that the fat crystals formed in an oleogel of CB with vegetable oil offer high stability to water droplets (up to 60% (v/v)) against coalescence and phase inversion, over storage for 7 months. Such extraordinary stability is attributed to the nanoplatelet-like CB crystals of βV polymorph located at the water–oil interface and to the inter-droplet fat crystal network formation, interlocking the water droplets. The increment in water volume fraction endows gel-like properties with the water droplets acting as “active fillers.” These newly designed Pickering W/O emulsions stabilized solely by fat crystals with unusual rigidity offer great promise for fabricating advanced functional materials in food, pharmaceutics, and cosmetic applications, where long-term stabilization of water droplets using sustainable particles is a necessity

Pickering emulsion stabilized by protein nanogel particles for delivery of curcumin: Effects of pH and ionic strength on curcumin retention

This study aimed to design whey protein nanogel particles (WPN)-stabilized Pickering emulsion as a delivery vehicle for curcumin (CUR). Firstly, the effectiveness of WPN to stabilize medium chain triglyceride (MCT) oil was assessed using droplet sizing, microscopy across scales, surface coverage calculations and interfacial viscosity measurements. Then, the ability of this delivery vehicle to encapsulate CUR and the effects of pH and ionic strengths on the retention of CUR were investigated in an in vitro release model at 37 ○C. Results demonstrate that 1.0 wt% WPN was sufficient to create a monolayer of particles at the droplet surface resulting in ultra-stable droplets that were resistant to coalescence over a year. Addition of 500 μg/ mL of CUR did not result in any change in the droplet size of the Pickering emulsion droplets. The CUR was fully retained within the Pickering emulsions, which might be attributed to the nanometric size of the gaps (≅30 nm) at the interface that did not allow CUR to diffuse out into the release media. The partitioning of CUR to the dispersed phase was influenced by pH of the media. Increased binding affinities between CUR and WPN at the interface (binding affinity constant, Ka = 1 × 104 M−1) existed at pH 3.0 as compared to that at pH 7.0 (Ka = 6.67 × 101 M−1) owing to the electrostatic interactions between CUR and interfacial WPN in the former. Such binding affinities between CUR and interfacial WPN at pH 7.0 was further influenced by presence of ions

Recent advances in emulsion-based delivery approaches for curcumin: From encapsulation to bioaccessibility

Background Curcumin has been widely acknowledged for its health-promoting effects. However, its application is often limited by its poor water solubility and biochemical/structural degradation during physiological transit that restricts its bioavailability. Emulsion based approaches have attracted the most research attention to encapsulate curcumin and improve its stability, bioaccessibility and bioavailability. Scope and approach This review summarizes the recent advances in application of different oil-in-water emulsion-based approaches, such as, conventional emulsions (surfactants-, protein- and protein-polysaccharide-stabilized emulsions), nanoemulsions, and Pickering emulsions that have been specifically used to deliver curcumin. Particular emphasis is given to factors affecting curcumin solubility, change in crystalline structure of curcumin upon dispersion and encapsulation efficiency. Changes in the droplet size and emulsion stability during in vitro oral-to-gastrointestinal digestion are discussed, with clear focus on the bioaccessibility of the encapsulated curcumin. Key findings and conclusions Key factors that influence curcumin delivery include emulsion droplet size, oil composition, volume fraction, dispersion conditions of curcumin in the oil phase and the type of interfacial materials. Nanoemulsions have been the preferred choice for delivery of curcumin up to now. Although scarce in literature, emulsions stabilized by edible Pickering particles as shown by recent evidence are effective in protecting curcumin in an in vitro gastrointestinal setting due to their high coalescence stability. Further studies with emulsions stabilized by food-grade particles and accurate tracking of the physiological fate (in vitro to human trials) of different emulsion-based delivery vehicles are essential for rational designing of curcumin-rich functional foods with high bioaccessibility

Recent advances in design and stability of double emulsions: Trends in Pickering stabilization

There is an increased pressure on food manufacturers to design low calorie and low fat foods to address the global obesity crisis. Designing double emulsions (DEs) is a microstructural approach to incorporate water that appears as promising fat replacement strategy. However, these complex microstructures are thermodynamically unstable and a thorough understanding of the factors that determine the stability of DEs are required to tailor their functionality. This review provides an update on the main strategies used to stabilize DEs, focusing on the developments in the last five years. Emphasis is placed on the recent use of surfactants, combination of surfactants with gelling agents, particles, fat crystals, and/or coatings. Novel processing techniques were also reviewed, and one-step processing methodologies were particularly examined. We also briefly reviewed the rheological and tribological performance of DEs. Properties and stability of the DEs depend strongly on the formulation and fabrication technique (homogenization, phase inversion, microfluidics, 3D Printing etc). Fat crystal forming a shell around the droplets offers a promising strategy to prevent diffusion of the internal phase in DEs. Pickering stabilization has captured significant research attention, though DEs fabricated solely using particle-laden interfaces are limited. A combined approach of Pickering and bulk stabilization by gelling the aqueous phase appears as a promising strategy to improve stability of DE, which needs research attention. Future studies should focus on characterizing rheological and tribological performance of DEs and link them with mouthfeel perception to accelerate their use in food applications

Can tribology be a tool to help tailor food for elderly population?

The rapidly ageing population requires food products that meet their specific physiological needs and have pleasurable sensory characteristics. Conventionally, rheology is used as a food formulation design tool that allow food bolus to be swallowed safely. Nevertheless, in the last few decades, there has been increased understanding of soft-tribology of thickeners and fabrication of biologically-relevant tribological set-ups. We discuss how this knowledge can offer a solid baseline to employ tribology as a design tool to tailor foods for the elderly population with various oral insufficiencies. In depth characterization of oral conditions of the elderly population is a necessary undertaking to fabricate tribology apparatus that better emulate in vivo conditions, to allow rational design of food products for this growing population

Conjugate microgel-stabilized Pickering emulsions: Role in delaying gastric digestion

In this study, a new class of microgels called ‘conjugate microgels’ was designed, where whey protein isolate (WPI) was conjugated with dextran (Dx, 500 kDa) (WPI-Dx) via Maillard reaction before fabricating the microgel particles. Such microgel particles were assessed for their abilities to act as Pickering stabilizers for oil-in-water emulsions and also checked if they offered gastric stability to the Pickering emulsions during in vitro digestion against interfacial pepsinolysis. WPI-Dx conjugates were obtained by controlled dry heating (60 °C, 79% RH, 24–48 h incubation). Sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) and ortho-phthaldialdehyde (OPA) profile revealed that the degree of conjugation ranged from 11.6 to 28.1%. The WPI-Dx conjugates were re-dispersed and heat-treated to form heat-set gels with moduli ranging from ∼45 to 250 kPa. Microgel particles (hydrodynamic diameters of 130–150 nm, ζ-potentials of −4.5 to −8.0 mV) were created by controlled shearing of these heat-set gels. Interfacial shear rheology measurements and microscopic examination confirmed that conjugated microgel particles with lower degree of conjugation (WPDx10M) were effective as Pickering stabilizers. When present in an aqueous dispersion, WPDx10M had reduced the degree of gastric proteolysis (120–130 μM free NH2) as compared to non-conjugated counterparts (187–205 μM free NH2). When present at the droplet surface, cross-correlation image analysis revealed that WPDx10M was successful in delaying interfacial gastric proteolysis. Insights from this study suggest that conjugate microgel particles might be useful to design gastric-stable Pickering emulsions in the future for effective delivery of lipophilic compounds to the intestines

Pickering emulsions stabilized by colloidal gel particles complexed or conjugated with biopolymers to enhance bioaccessibility and cellular uptake of curcumin

The aim of this study was to investigate the fate of curcumin (CUR)-loaded Pickering emulsions with complex interfaces during in vitro gastrointestinal transit and test the efficacy of such emulsions on improving the bioaccessibility and cellular uptake of CUR. CUR-loaded Pickering emulsions tested were whey protein nanogel particle-stabilized Pickering emulsions (CUR-EWPN) and emulsions displaying complex interfaces included 1) layer-by-layer dextran sulphate-coated nanogel-stabilized Pickering emulsions (CUR-DxS+EWPN) and 2) protein+dextran-conjugated microgel-stabilized Pickering emulsions (CUR-EWPDxM). The hypothesis was that the presence of complex interfacial material at the droplet surface would provide better protection to the droplets against physiological degradation, particularly under gastric conditions and thus, improve the delivery of CUR to Caco-2 intestinal cells. The emulsions were characterized using droplet sizing, apparent viscosity, confocal and cryo-scanning electron microscopy, zeta-potential, lipid digestion kinetics, bioaccessibility of CUR as well as cell viability and uptake by Caco-2 cells. Emulsion droplets with modified to complex interfacial composition (i.e. CUR-DxS+EWPN and CUR-EWPDxM) provided enhanced kinetic stability to the Pickering emulsion droplets against coalescence in the gastric regime as compared to droplets having unmodified interface (i.e. CUR-EWPN), whereas droplet coalescence occurred in intestinal conditions irrespective of the initial interfacial materials. A similar rate and extent of free fatty acid release occurred in all the emulsions during intestinal digestion (p > 0.05), which correlated with the bioaccessibility of CUR. Striking, CUR-DxS+EWPN and CUR-EWPDxM significantly improved cellular CUR uptake as compared to CUR-EWPN (p < 0.05). These results highlight a promising new strategy of designing gastric-stable Pickering emulsions with complex interfaces to improve the delivery of lipophilic bioactive compounds to the cells for the future design of functional foods

Tuning Lubrication Performance of Phase‐Changing Emulsion‐Filled Gels by Sugar Alcohols

Lubrication by hydrogels is an emerging area in surface science. Although oil‐driven friction reduction is predominant in literature, emulsion gel‐based lubrication has attracted very little attention to date. We hypothesize that an interplay of viscoelasticity and oil volume fraction may modulate the lubricity of emulsion‐filled gels. Herein, phase‐change gelatin‐based emulsion‐filled gels with different sugar alcohols and oil droplet concentrations (0–30 wt%) are tested for their lubrication performance. The rheological and tribological tests are analyzed in conjunction with spectroscopic and structural characterizations to reveal structure–function relationship. Structural characterizations demonstrate that hydrogen bonding is enhanced in pure gelatin gels with the increase of sugar alcohol (glycerol)‐replacement time, which enhance the storage modulus (G′) of the gel networks. Emulsified droplets serve as active fillers further strengthening the G′ and strikingly the presence of glycerol reduced the thermoresponsiveness of the emulsion‐filled gels. Emulsion‐filled gels containing sugar alcohols, irrespective of their type, can greatly reduce the friction coefficients (μ) between hydrophobic surfaces in the boundary and mixed regimes versus the systems without sugar alcohols. In the hydrodynamic regime, the friction coefficient of the system is proportional to the second plateau shear viscosity, regulated by the oil content