Recent developments in food foams

The scientific literature from 2015 onwards with respect to foams and thin films in the context of foods has been reviewed. Proteins are the dominant foaming agents in foods, and investigations of the classic, meringue-forming egg white protein still dominate the literature because the unique properties of this system are still not properly understood. The current drive of many studies is to find suitable replacers of egg proteins, driven by consumer trends for more plant-based alternatives. This has led to investigations of the stabilizing properties of various protein aggregates, ‘nanoparticles’ and microgel particles as Pickering-type stabilizers of foams (Pickering foams). At the same time, other work has sought to manipulate the surface properties of biopolymer- and nonbiopolymer–based particles by chemical means, to make the particles adsorb more strongly. Few, truly novel foam stabilizers have emerged, but two include saponin aggregates and bacteria as particle-type stabilizers

Pickering emulsions for food and drinks

The scientific literature from 2016 onwards on aspects of Pickering emulsions relevant to food and drink has been reviewed. Ongoing unsolved issues surrounding the general Pickering stabilization mechanism are discussed, such as contact angles of microscopic, irregularly size particles; adsorption and desorption barriers; and competition and complex formation with other surface-active species. The main types of emulsion that have been studied are surveyed: oil-in-water (O/W), water-in-oil (W/O), water-in-water (W/W) and multiple emulsions. There is still a lack of food-grade particle types suitable for W/O and therefore multiple emulsions. Finally, work on different types of Pickering emulsifiers is discussed, the principal types being organic crystals, prolamins, cellulose, starch and microgel particles. The latter are highlighted as particularly versatile in terms of their properties and the food components from which they can be formed

On the Origin of Seemingly Non-Surface Active Particles Partitioning between Phase Separated Solutions of Incompatible Non-Adsorbing Polymers and Their Adsorption at the Phase Boundary.

We have computed the free energy per unit area (i.e., interfacial tension) between a solid surface and two co-existing polymer solutions, where there is no specific interaction between the particles and either polymer, via self-consistent field calculations. Several different systems have been studied, including those where the two polymers differ in molecular weight (Mw) by a factor of ~ 2, or where the polymers have the same Mw but one set of chains is branched with the other being linear. In the absence of any enthalpic contribution resulting from adsorption on the particle, the differences in free energy per unit area resulting from the polymer depleted regions around the particles in the two co-exiting phases are found to be ~ 1 μN m-1. Although this value may seem rather small, this difference is more than capable of inducing the partitioning of particles of 100 nm in size (or larger) into the phase with the lower interfacial free energy at a solid surface. By examining the density profile variation of the polymers close to the solid surface, we can also infer information about the wettability and contact angle (Θ) of the solid particle at the interface between the two co-existing phases. This leads to the conclusion that for all systems of this type, when the incompatibility between the two polymers is sufficiently large, will be close to 90°

Experimental Modeling of Flavonoid-Biomembrane Interactions

Nonspecific interactions of flavonoids with lipids can alter the membrane's features (e.g., thickness and fluctuations) as well as influence their therapeutic potentials. However, relatively little is known about the details of how flavonoids interact with lipid components. Structure-dependent interactions of a variety of flavonoids with phospholipid monolayers on a mercury (Hg) film electrode were established by rapid cyclic voltammetry (RCV). The data revealed that flavonoids adopting a planar configuration altered the membrane properties more significantly than nonplanar flavonoids. Quercetin, rutin, and tiliroside were selected for follow-up experiments with Langmuir monolayers, Brewster angle microscopy (BAM), and small-angle X-ray scattering (SAXS). Relaxation phenomena in DOPC monolayers and visualization of the surface with BAM revealed a pronounced monolayer stabilization effect with both quercetin and tiliroside, whereas rutin disrupted the monolayer structure rendering the surface entirely smooth. SAXS showed a monotonous membrane thinning for all compounds studied associated with an increase in the mean fluctuations of the membrane. Rutin, quercetin, and tiliroside decreased the bilayer thickness of DOPC by ∼0.45, 0.8, and 1.1 Å at 6 mol %, respectively. In addition to the novelty of using lipid monolayers to systematically characterize the structure-activity relationship (SAR) of a variety of flavonoids, this is the first report investigating the effect of tiliroside with biomimetic membrane models. All the flavonoids studied are believed to be localized in the lipid/water interface region. Both this localization and the membrane perturbations have implications for their therapeutic activity

Water-In-Oil Pickering Emulsions Stabilized by Water-Insoluble Polyphenol Crystals

In recent years, there has been a resurgence of interest in Pickering emulsions because of the recognition of the unique high steric stabilization provided by particles at interfaces. This interest is particularly keen for water-in-oil (W/O) emulsions because of the limited range of suitable Pickering stabilizers available. We demonstrate for the first time that W/O emulsions can be stabilized by using crystals from naturally occurring polyphenols (curcumin and quercetin particles). These particles were assessed based on their size, microstructure, contact angle, interfacial tension, and ζ-potential measurements in an attempt to predict the way that they act as Pickering stabilizers. Static light-scattering results and microstructural analysis at various length scales [optical microscopy, confocal laser scanning microscopy (CLSM), and scanning electron microscopy (SEM)] confirmed that the quercetin particles has a nearly perfect crystalline rod shape with a high aspect ratio; that is, the ratio of length to diameter (L/D) was ca. 2.5:1–7:1. On the other hand, the curcumin particles (d₃,₂ = 0.2 μm) had a polyhedral shape. Droplet sizing and CLSM revealed that there was an optimum concentration (0.14 and 0.25 wt % for quercetin and curcumin, respectively) where smaller water droplets were formed (d₃,₂ ≈ 6 μm). Interfacial shear viscosity (ηi) measurements confirmed that a stronger film was formed at the interface with quercetin particles (ηi ≈ 25 N s m⁻¹) rather than with curcumin particles (ηi ≈ 1.2 N s m⁻¹) possibly because of the difference in the shape and size of the two crystals. This study provides new insights into the creation of Pickering W/O emulsions with polyphenol crystals and may lead to various soft matter applications where Pickering stabilization using biocompatible particles is a necessity

Effect of Oil on Cellulose Dissolution in the Ionic Liquid 1-Butyl-3-methyl Imidazolium Acetate

While ionic liquids (ILs) are well known to be excellent solvents for cellulose, the exact mechanism of dissolution has been a much disputed topic in recent years and is still not completely clear. In this work, we add to the current understanding and highlight the importance of hydrophobic interactions, through studying cellulose dissolution in mixtures of 1-butyl-3-methyl imidazolium acetate (BmimAc) and medium-chain triglyceride (MCT) oil. We demonstrate that the order in which constituents are mixed together plays a key role, through nuclear magnetic resonance (NMR) spectroscopic analysis. When small quantities of MCT oil (0.25–1 wt %) were introduced to BmimAc before cellulose, the effect on BmimAc chemical shift values was much more significant compared to when the cellulose was dissolved first, followed by oil addition. Rheological analysis also showed small differences in the viscosities of oil–cellulose–BmimAc solutions, depending on the order the constituents were added. On the other hand, no such order effect on the NMR results was observed when cellulose was replaced with cellobiose, suggesting that this observation is unique to the macromolecule. We propose that a cellulose–oil interaction develops but only when the cellulose structure has a sufficient degree of order and not when the cellulose is molecularly dispersed, since the hydrophobic cellulose plane is no longer intact. In all cases, cellulose–BmimAc–oil solutions were stable for at least 4 months. To our knowledge, this is the first work that investigates the effect of oil addition on the dissolving capacity of BmimAc and highlights the need for further re-evaluation of accepted mechanisms for cellulose dissolution in ILs

Comparison of blueberry powder produced via foam‐mat freeze‐drying versus spray‐drying: evaluation of foam and powder properties

BACKGROUND; Blueberry juice powder was developed via foam‐mat freeze‐drying (FMFD) and spray‐drying (SD) via addition of maltodextrin (MD) and whey protein isolate (WPI) at weight ratios of MD/WPI = 0.4 to 3.2 (with a fixed solids content of 5 wt% for FMFD and 10 wt% for SD). Feed rates of 180 and 360 mL h−1 were tested in SD. The objective was to evaluate the effect of the drying methods and carrier agents on the physical properties of the corresponding blueberry powders and reconstituted products. RESULTS; Ratios of MD/WPI = 0.4, 1.0 and 1.6 produced highly stable foams most suitable for FMFD. FMFD gave high yields and low bulk density powders with flake‐like particles of large size that were also dark purple with high red values. SD gave low powder recoveries. The powders had higher bulk density and faster rehydration times, consisting of smooth, spherical and smaller particles than in FMFD powders. The SD powders were bright purple but less red than FMFD powders. Solubility was greater than 95% for both FMFD and SD powders. CONCLUSION; The FMFD method is a feasible method of producing blueberry juice powder and gives products retaining more characteristics of the original juice than SD

Advances in the use of microgels as emulsion stabilisers and as a strategy for cellulose functionalisation

Microgel particles have recently emerged as an alternative route to emulsion stabilisation. Classed as soft colloidal particles, their ability to swell to differing degrees in certain solvents and to rearrange once attached to an interface makes them highly suitable for systems requiring long-term stabilization, such as formulations in the food, agricultural, cosmetic and pharmaceutical industries. Microgels made with biocompatible polymers such as proteins and polysaccharides in particular offer an environmental advantage and currently form a very active area of research. Cellulose, being a natural, biodegradable polymer, is an attractive ingredient for gels and microgels. However, its use as a functional material is often somewhat hindered by its insolubility in water and most other organic solvents. Furthermore, the surface activity of cellulose has proven difficult to harness and therefore its ability to act as an emulsion stabiliser has been almost exclusively applied to oil-in-water (O/W) emulsions, with very few reports on its water in oil (W/O) activity. This review aims to summarise some of the recent progress made in the microgel field including their ability to act as emulsion stabilisers, with a focus on cellulose microgels (CMGs). A brief overview of cellulose processing is also given, describing the dissolution and reprecipitation routes used to functionalise cellulose without covalent modification and the potential for cellulose particles and CMGs to act as O/W and W/O emulsion stabilisers

Relationship between size and cellulose content of cellulose microgels (CMGs) and their water-in-oil emulsifying capacity

Soluble polysaccharides have been used extensively as gelling/thickening agents in emulsions, but they generally display weak surface activity. Insoluble polysaccharides such as cellulose can be converted to thickening agents and even emulsifiers, but generally only after considerable chemical modification. Here we use the ionic liquid (IL) 1-butyl-3-methyl imidazolium acetate (BmimAc) to dissolve and reprecipitate cellulose in the presence of oil, i.e., a physical process, to tune the cellulose properties. ILs have previously been used in this way to form hydrophobic (‘oily’) cellulose microgels (CMGs), potentially capable of stabilizing water-in-oil (W/O) emulsions. However, these previous CMGs were made via a ‘top-down’ method and were relatively large and polydisperse, giving limited stability to the W/O emulsions formed. Here we demonstrate how the CMG size can be drastically reduced via a ‘bottom-up’ approach and employing high-pressure homogenization (HPH), thus achieving sub-micron CMG particle sizes. This has previously been impossible with other reported IL-cellulose coagulation methods and the corresponding W/O emulsions were more stable. In addition, confocal and cryo-scanning electron microscopy (SEM) revealed that the surface coverage of these CMGs on droplets increased over time, which led to the formation of even thicker interfacial layers and further enhanced emulsion stability (at least 2 months). We also demonstrate unequivocally that the stability of the W/O emulsions is indeed due to the CMGs adsorbing via the Pickering mechanism, rather than forming a stabilizing cellulosic network in the continuous phase, thus providing a novel route to ‘green’ Pickering emulsions