Search

Oleogels based on sterols such as β-sitosterol blended with the sterol ester γ-oryzanol are a very interesting class of systems, but there are aspects of their formation and structure that remain elusive. It has previously been shown that a methyl group on the C30 position of the sterol-ester plays an important role in gelation. This work explored the effect that having C30 methyl groups on both the sterol and the sterol-ester had on the gelation process and subsequent gel structure. Lanosterol and saponified γ-oryzanol (which was synthesized as part of this study) were identified as materials of interest, as both feature a methyl group on the C30 position of their steroidal cores. It was observed that both sterols formed gels when blended with γ-oryzanol, and also that lanosterol gelled sunflower oil without the addition of γ-oryzanol. All of these gels were significantly weaker than that formed by β-sitosterol blended with γ-oryzanol. To explore why, molecular docking simulations along with AFM and SAXS were used to examine these gels on a broad range of length scales. The results suggest that saponified γ-oryzanol-γ-oryzanol gels have a very similar structure to that of β-sitosterol-γ-oryzanol gels. Lanosterol-γ-oryzanol gels and pure lanosterol gel, however, form with a totally different structure facilitated by the head-to-tail stacking motif exhibited by lanosterol. These results give further evidence that relatively slight changes to the molecular structure of gelators can result in significant differences in subsequent gel properties.

C13-dipeptides that did not gel on their own were found to form hydrogels when combined with mixtures (coassembly). At pH = 4.6, by mixing negatively charged C13-WD (C13-WD2- and/or C13-WD-) with C13-KW or C13-YK, where the side chain of K carried positive charge, two composite hydrogels with different mechanical properties were formed. The gels exhibited various fiber structures that would account for their individual functionalities. According to molecular dynamics computer simulations, the composite systems formed spherical micelles through hydrophobic interactions that further aggregate to form gels through electrostatic interactions. The electrostatic repulsions between C13-WD molecules were interfered by insertions of C13-KW or C13-YK molecules, which result in gel formation in the composite systems. The results of computer simulations well explained the experimental observations, which provided new insights into the design and selection strategies for peptide gelators.

Abstract This study assessed the impact of sonication on the structure and properties of a functional extract (retentate 100 or R100) from the Quorn fermentation co-product (centrate). In a previous study, we reported that the R100 fraction displayed good foaming, emulsifying and rheological properties. Sonication of a R100 solution led to the breakdown of the large hyphal structures characteristic of this extract into smaller fragments. Foams prepared with sonicated R100 displayed a higher foaming ability than with untreated R100 and a high foam stability but lower than untreated R100 ones. Oil-in-water emulsions prepared with sonicated R100 displayed smaller oil droplet size distributions than with untreated R100. Confocal micrographs suggested that small fungal fragments contributed to the stabilisation of oil droplets. 50% oil-reduced R100 emulsions were prepared by mixing R100 emulsions (untreated or sonicated) with a sonicated R100 solution at a 1:1 ratio. Smaller oil droplet size distributions were reported for the oil-reduced emulsions. These results showed that the addition of small hyphal fragments or surface-active molecules and molecular aggregates released during sonication contributed to the formation and stabilisation of smaller oil droplets. This study highlighted the potential to modulate the structure, emulsifying and foaming properties of functional extracts from the Quorn fermentation co-product by sonication and the potential of these extracts as oil-lowering agents in emulsion-based products through the reduction of oil droplet size and their stabilisation. Graphical abstract

This study provides the first mapping of mycoprotein functionality, composition and structure throughout the Quorn fermentation process. The fermentation broth, RNA-reduced broth (RNA-broth), centrate and their centrifugation deposits and supernatants were characterised. The broth, RNA-broth and their deposits displayed high concentrations of fungal filaments, which contributed to their high gelling properties (with a 5,320 Pa elastic modulus reported for RNA-broth deposits gels). Foams prepared with RNA-broth and centrate supernatants via frothing exhibited high stability (380 min), with high concentrations of a foam-positive cerato-platanin reported in these samples. Emulsions prepared with the broth and broth supernatant showed high emulsifying activity and stability indexes (12.80 m2/g and 15.84 mins for the broth supernatant) and low oil droplet sizes (18.09 µm for the broth). This study identified previously unreported gelling, foaming and/or emulsifying properties for the different Quorn streams, highlighting opportunities to develop novel sustainable alternatives to animal-derived functional ingredients using mycoprotein material.

Texture-modified foods (TMFs) and thickened fluids have been used as a therapeutic strategy in the management of food intake in the elderly and people with dysphagia. Despite recent advances in describing rheological features of TMFs for dysphagia management, there is still paucity of research regarding the sensory attributes, therapeutic thickness levels and swallowing safety of these foods. Additionally, the relationship between mechanical and structural properties of TMFs throughout the oral processing is not yet fully understood. The present review discusses several properties of food boluses that are important during oral processing to allow for safe swallowing. Dynamic changes that occur during oral processing of TMFs will be reviewed. The use of hydrocolloids to improve the cohesiveness of TMFs and how this impacts the sensory properties of TMFs will be also discussed. Additionally, this review will suggest potential new research directions to improve textural and sensory properties of TMFs.

Computational and experimental methods were applied to investigate the self-assembly and gelation of C13-dipeptides. A modified aggregation propensity (APS) was introduced to correlate the effects ...

Abstract The production of mycoprotein biomass by Marlow Foods for use in their meat alternative brand Quorn is a potential source of sustainable alternatives to functional ingredients of animal origin for the food industry. The conversion of this viscoelastic biomass into the Quorn meat-like texture relies on functional synergy with egg white (EW), effectively forming a fibre gel composite. In a previous study, we reported that an extract (retentate 100 or R100) obtained from the Quorn fermentation co-product (centrate) via ultrafiltration displayed good foaming, emulsifying, and rheological properties. This current study investigated if a possible similar synergy between EW and R100 could be exploited to partially replace EW as foaming and/or gelling ingredient. The large hyphal structures characteristic of R100 solutions were observed in EW–R100 mixtures, while EW–R100 gels showed dense networks of entangled hyphal aggregates and filaments. R100 foams prepared by frothing proved less stable than EW ones; however, a 75/25 w/w EW–R100 mixture displayed a similar foam stability to EW. Simlarly, R100 hydrogels proved less viscoelastic than EW ones; however, the viscoelasticity of gels prepared with 50/50 w/w and 75/25 w/w EW–R100 proved similar to those of EW gels, while 75/25 w/w EW–R100 gels displayed similar hardness to EW ones. Both results highlighted a functional synergy between the R100 material and EW proteins. In parallel tensiometry measurements highlighted the presence of surface-active material in EW–R100 mixtures contributing to their high foaming properties. These results highlighted the potential of functional extracts from the Quorn fermentation process for partial EW replacement as foaming and gelling agent, and the complex nature of the functional profile of EW–R100 mixtures, with contributions reported for both hyphal structures and surface-active material. Graphic abstract

Emulsion-based formulations are widely exploited in medicine, food and cosmetics, where surfactants and emulsifiers play contrasting, but equally important roles. Both are able to adsorb at the oil and water interface enabling dispersion of droplets of one phase in the second. The main function of surfactants is lowering the interfacial tension, while emulsifiers, adsorb more slowly to the droplet surface and give longer-term stability. High toxicity and high ecological impact of many synthetic surfactants/emulsifiers have led to interest in other, natural molecules such as biosurfactants and bioemulsifiers. These bio-based surface-active agents are interesting for the main industries linked to human health – pharmaceuticals, food and cosmetics, with several having been discovered and already widely applied. However, the commercialisation of the production of bio-surfactants/emulsifiers is often limited by optimisation difficulties, high purification costs and low yields, all of which have an impact on their wider application. Therefore, much effort is required to find stable and cost effective methods to produce bio-surfactants/emulsifiers on a large scale. This review focuses on the main properties of bio-emulsifiers and bio-surfactants, followed by an overview of their current use in consumer product formulations. Finally, the potential of bio-surfactants/emulsifiers to replace the currently used counterparts will be assessed.

We use coarse-grained molecular dynamics simulations to study the effect of surfactant structure on the ordering of bulk tristearin at an oil-water interface. In the absence of surfactant, tristearin acyl chains are marginally aligned normal to the interface. The surfactant glycerol monooleate (GMO), a common small-molecule monoacylglycerol (MW: 357 g/mol), preferentially adsorbs to the oil-water interface, displacing more of the tristearin as its concentration increases. The tristearin that remains at the interface is closely aligned normal to the interface. Adjacent to the interface, bulk tristearin increasingly aligns with its acyl chains entwined with the GMO acyl chain, which also preferentially aligns normal to the interface. In contrast, polyglycerol polyricinoleate (PGPR), a bulkier, polymeric surfactant (MW: 1398 g/mol for a molecule with five monomers), both displaces tristearin from the interface and reduces the alignment of the molecules that remain. We suggest that the similar fatty acid moieties of GMO (oleic acid) and tristearin (stearic acid) lead to liquid-state association and alignment, the latter of which can then serve as a template onto which tristearin crystals can nucleate. Conversely, by both displacing tristearin from the interface and reducing alignment below that of the surfactant-free system, PGPR eliminates the possibility of tristearin interfacial crystallisation.

The adsorption of proteins at surfaces and interfaces is important in a wide range of industries. Understanding and controlling the conformation of adsorbed proteins at surfaces is critical to stability and function in many technological applications including foods and biomedical testing kits or sensors. Studying adsorbed protein conformation is difficult experimentally and so over the past few decades researchers have turned to computer simulation methods to give information at the atomic level on this important area. In this review we summarize some of the significant simulation work over the past four years at both fluid (liquid–liquid and gas–liquid interfaces) and solid–liquid interfaces. Of particular significance is the work on surfactant proteins such as fungal hydrophobins, ranspumin-2 from the tungara frog and the bacteria protein BslA. These have evolved unique structures impart very high surface-active properties to the molecules. A highlight is the elucidation of the clam-shell unhinging mechanism of ranspumin-2 adsorption to the gas–liquid interface that is responsible for its adsorption to and stabilization of the air bubbles in tungara frog foam nests.

This study assessed the functional profile (foaming, emulsifying and rheological properties), proteomic and metabolomic composition of a naturally foaming and currently unexploited co-product (centrate) from the Quorn fermentation process. Due to the low environmental footprint of this process the centrate is a potential source of sustainable functional ingredients for the food industry. A range of fractions were isolated from the centrate via successive ultrafiltration steps. The retentate 100 (R100) fraction, which was obtained following a 100 kDa ultrafiltration, displayed good foaming, emulsifying and rheological properties. R100 solutions and oil-in-water emulsions displayed high viscosity, while R100 solutions and hydrogels showed high viscoelasticity. R100 foams displayed high stability while oil-in-water R100 emulsions showed small and stable oil droplet size distributions. Large mycelial aggregates were reported in R100 solutions and gels, correlating with their high viscosity and viscoelasticity. A dense mycelial network was observed in R100 foams and contributing to their stability. In parallel tensiometry measurements highlighted the presence of interfacially-active molecules in R100 which formed a rigid film stabilising the oil/water interface. A number of functional metabolites and proteins were identified in the centrate, including a cerato-platanin protein, cell membrane constituents (phospholipids, sterols, glycosphingolipids, sphingomyelins), cell wall constituents (chitin, chitosan, proteins), guanine and guanine-based nucleosides and nucleotides. This study highlighted the potential of functional extracts from the Quorn fermentation process as novel ingredients for the preparation of sustainable food products and the complex and specific nature of the centrate’s functional profile, with contributions reported for both mycelial structures and interfacially-active molecules.

Surface active agents (SAAs), currently used in modern industry, are synthetic chemicals produced from non-renewable sources, with potential toxic impacts on humans and the environment. Thus, there is an increased interest for the identification and utilization of natural derived SAAs. As such, the marine environment is considered a promising source of biosurfactants with low toxicity, environmental compatibility, and biodegradation compared to their synthetic counterparts. MARISURF is a Horizon 2020 EU-funded project aiming to identify and functionally characterize SAAs, derived from a unique marine bacterial collection, towards commercial exploitation. Specifically, rhamnolipids produced by Marinobacter MCTG107b and Pseudomonas MCTG214(3b1) strains were previously identified and characterized while currently their toxicity profile was assessed by utilizing well-established methodologies. Our results showed a lack of cytotoxicity in in vitro models of human skin and liver as indicated by alamar blue and propidium iodide assays. Additionally, the use of the single gel electrophoresis assay, under oxidative stress conditions, revealed absence of any significant mutagenic/anti-mutagenic potential. Finally, both 2,2’-azino-bis (3-ethylbenzothiazoline-6-sulphonicacid) (ABTS) and 2,2-diphenyl-1-picrylhydrazyl radical (DPPH) cell-free assays, revealed no significant anti-oxidant capacity for neither of the tested compounds. Consequently, the absence of significant cytotoxicity and/or mutagenicity justifies their commercial exploitation and potential development into industrial end-user applications as natural and environmentally friendly biosurfactants.

The interaction between proteins and polyphenols is known to modify both the bioavailability and bioactivity of dietary polyphenols. Understanding these interactions can facilitate the design of delivery systems for polyphenols in the digestive tract. Molecular modelling of protein–polyphenol and protein–ligand interactions in general has long been used as a way to identify small molecule binding sites on proteins. However, these are often used without a careful consideration of the assumptions used and limitations of these methods, and how this affects the accuracy of the predictions. In this paper, two common methods for predicting binding site location and binding energy, molecular dynamics simulation and molecular docking, will be discussed. The simplifications and assumptions implicit in these approaches, as well as ways to improve their predictions will be covered.

Hypothesis Molecular dynamics simulation can be used to differentiate between the adsorption properties of rhamnolipid congeners at a vacuum-water interface. Experiments Adsorption of five congeners with differing alkyl chains (two C10 chains, two C14 chains or mixed C14C10 and C10C14), number of rhamnose rings (mono- or di-) and carboxyl group charge (non-ionic or anionic) are simulated at the vacuum-water interface. Findings All rhamnolipids adsorb in the interfacial region with rhamnose and carboxyl groups closer to the water phase, and alkyl chains closer to the vacuum phase, but with differing adsorbed conformations. Headgroups of uncharged congeners show two preferred conformations, closed and partially open. Di-rhamnolipid has a low proportion of closed conformation, due to the steric constraints of the second pyranose ring. Charged congeners show strong preference for closed headgroup conformations. For rhamnolipids with equal alkyl chains lengths (C10C10, C14C14) the distribution of alkyl chain tilt angles is similar for both. Where chain lengths are unequal (C14C10, C10C14) one chain has a greater tendency to tilt towards the water phase (>90°). The order parameter of the alkyl chains shows they are disordered at the interface. Together, these results show congener-dependent adsorbed conformation differences suggesting they will have differing surface-active properties at vacuum-water and oil-water interfaces.

In this work, we have employed docking and atomistic molecular dynamics (MD) simulations supported by complementary experiments using atomic force microscopy, rheology and spectroscopy to investigate the self-assembled structure of β-sitosterol and γ-oryzanol molecules into cylindrical tubules in a non-aqueous solvent. Docking models of several phytosterols, including sitosterol, with oryzanol and other sterol-esters demonstrate that for systems to form tubules, the phytosterol sterane group must be stacked in a wedge shape with the esters sterane group, and a hydrogen bond must form between the hydroxyl group of the phytosterol and the carbonyl group of the ester. Molecular dynamics of the self-assembled structure were initiated with the molecules in a roughly cylindrical configuration, as suggested from previous experimental studies, and the configurations were found to be stable during 50 ns simulations. We performed MD simulations of two tubules in proximity to better understand the aggregation of these fibrils and how the fibrils interact in order to stick together. We found that an interfibril network of non-covalent bonds, in particular van der Waals and π-π contacts, which is formed between the ferulic acid groups of oryzanol through the hydroxyl, methoxy and aromatic groups, is responsible for the surface-to-surface interactions between fibrils; an observation supported by molecular spectroscopy. We believe these interactions are of primary importance in creating a strong organogel network.

Partially denatured whey protein products (PDWPC's) can be classified based on the viscoelastic properties of their solutions. Strain sweeps show that PDWPC-A and –B and microparticulated WPC (MPWPC) with compact, spherical aggregated particles exhibit a strong strain overshoot. PDWPC-C and –D, on the other hand, which have open, elongated porous particles show a weak strain overshoot. The concentration dependence of the elastic modulus G′ in the linear viscoelastic region has a biphasic power law dependence with concentration for all protein products studied, except for WPC where G′ is independent of protein concentration. Frequency sweeps suggest that MPWC solutions form a strong physical gel at all concentrations above 14% (w/w). PDWPC-A and –B form weak gels over the same concentration range. PDWPC-C and –D also form weak gels at 14% protein (w/w) but strong physical gels at higher concentrations. The frequency dependence of G′ and G″ for all aggregated proteins show a power law dependence indicating fractal type structures. For all solutions above a critical concentration, the fractal dimensions span the range 1.6–2.3, indicating a range of gel network structures from open and diffuse to compact and dense. Adherence to the empirical Cox-Merz rule was observed in PDWPC-A, -C and –D at concentrations of 14 and 16% (w/w) protein, suggesting liquid-like behaviour. At higher protein concentrations the deviations from the Cox-Merz rule suggest more pronounced elasticity in the structure. For PDWPC-B, the behaviour is complex, with deviation from the Cox-Merz rule at low frequencies/shear rates, but correspondence at higher frequencies/shear rates at all concentrations. This indicates a frequency-dependent change from liquid-like behaviour over long timescale deformations, to a solid-like behaviour at short timescale deformations. MPWPC solutions of all concentrations do not follow the Cox-Merz rule, suggesting solid-like behaviour. The PDWPCs exhibit a complex rheological behaviour which suggests they could be versatile thickening, texturizing and fat replacement ingredients that will offer food manufacturers greater control over the texture of formulated fluid foods.

Rheology and atomic force microscopy (AFM) were employed to examine the microstructure of β-sitosterol:γ-oryzanol organogels in sunflower oil. Using time-resolved rheology, we followed gel formation, paying specific attention to the fibril aggregation process, which had not been studied in detail previously for this system. Using AFM, we observed gel structures directly and obtained detailed information on the gel structure, far exceeding previous studies. Our analysis suggests that though gels are formed by the self-assembly and aggregation of one-dimensional fibrils, the manner in which these fibrils aggregate into ribbons results in complex structures of higher dimensionality. We emphasize that it is a surprise to find ribbons and not twisted strands. Comparing AFM images of 10% w/w and 20% w/w gelator systems, we observed differences in the degree of branching which are consistent with the rheology. We also observed the individual self-assembled fibrils which make up these gels with much greater clarity than in previous microscopy studies, and the fibril diameters of ∼9.8 nm we measured agree excellently with those obtained from existing small-angle neutron scattering data. These results provide new insight into the structure and formation kinetics of this important organogel system.

The application of molecular modelling, and in particular all-atom and coarse grained molecular dynamics simulation, to the study of low molecular weight surfactants with relevance to food systems is reviewed. Two key aspects of surfactant behaviour — their ability to form micelles and their tendency to adsorb to fluid–fluid interfaces (air–water and oil–water) are covered. Since the modelling literature on synthetic amphiphilic surfactants is vast, and much of it not directly relevant to foods, the review concentrates on biosurfactants. Two particular topics are covered in detail: the behaviour of bile salts because of the importance of these in understanding food digestion; the behaviour of novel glycolipid and lipopeptide surfactants derived from microorganisms (bacteria and yeast) due to their increasing importance as functional ingredients in consumer products including foods.

The structure of foods is a complex amalgam of different biomolecules that are structurally diverse and that exhibit heterogeneity within their own biomolecule type. The interactions among these components control the structure and texture of foods, in addition to indirectly influencing other properties such as colour, flavour, and aroma. Molecular modelling has been used increasingly over the past few decades to help understand the interactions that control food structure and, as modelling techniques and hardware improve, will become an ever more important tool for food scientists. In this chapter, we will review aspects of food structure formation that are highly amenable to the modelling approach. The review will concentrate on the modelling of biomolecule self-association and gel formation and how this contributes to food structure and texture. Modelling the development of gelling agents into 3D fibrillar structures is a very important and challenging task and can provide significant insights to food chemists and biologists. This chapter gives an overview of recent studies focusing on how modelling and computer simulations can be used to investigate the relationship between the microscopic and macroscopic properties of different building blocks, such as oleogelators, polysaccharides, or proteins, that are commonly used for formulating food products.

Many drugs and phytochemicals are bitter, leading to noncompliance with prescriptions and avoidance of healthy foods and a need to suppress their taste. The goal of this study was to investigate the binding of bitterants (quinine and caffeine) by whey protein isolate (WPI) and the effect on perceived bitterness. Caffeine interacted minimally with WPI, while the proportion of unbound quinine decreased exponentially with protein concentration. Molecular modeling was used to show the energy of the quinine-Β-lactoglubulin interaction was an order of magnitude greater than the caffeine-Β-lactoglobulin interaction. Untrained assessors were used to assess the bitterness of caffeine (1.8, 5.7, and 18 mM) and quinine (0.056, 0.10, and 0.18 mM) solutions with 0% or 1% WPI. There was no significant effect of protein on the bitterness of caffeine solutions, but WPI decreased the bitterness of quinine relative to the same concentration in water. This is generally consistent with our hypothesis that higher binding results in lower bitterness; however the magnitude of reduction was not large and the bitterness of the protein-quinine solutions was greater than would be expected for the unbound quinine present.

We demonstrate that by mixing the phytosterol-ester oryzanol with lecithin in an organic solvent, both components may be dispersed at much higher concentrations than they may be individually. Dynamic light scattering and molecular dynamics simulations show that the mechanism for this is the formation of r ∼ 4 nm mixed micelles. Infrared spectroscopy and simulations suggest that these micelles are formed due in part to hydrogen bonding of the phosphate of the lecithin head-group, and the phenol group of the oryzanol. Rheology shows that by mixing these materials at an equimolar ratio, highly viscous suspensions are created. Furthermore, by adding water to these samples, a solid-like gel may be formed which offers mechanical properties close to those desired for a margarine type spread, whilst still solubilizing the oryzanol.

Partial denaturation of whey protein concentrates has been used to make protein powders with differing viscosity properties. PDWPC particles have been manufactured to have a range of aggregate sizes (3.3–17 μm) and structures (compact particle gel to open fibrillar gel). In solution the PDWPC samples show complex viscosity behaviour dependant on the size and morphology of the PDWPC aggregate particles. For the same protein content the compact particles have a lower viscosity than open, fibrillar particles. The viscosity also appears to depend on the surface structure of the particles, with particles of a similar size, but having a rougher surface giving higher viscosity than similar smooth particles. The viscosity of the WPC, MPWPC and PDWPC solutions are explained in terms of the postulated interactions between the protein aggregates in solution.

This chapter gives an overview of the use of plant proteins to fortify breads. It furthermore investigates the sensory acceptability and textural properties of leavened wheat bread fortified with cow protein isolates that had been denatured and glycated by thermal treatment. Defatted cowpea flour was prepared from cowpea beans, and the protein isolate was prepared as cowpea protein isolate (CPI) and thermally denatured cowpea protein isolate (DCPI). To prepare glycated cowpea protein isolate (GCPI), the cowpea flour slurry was heat-treated before the protein was isolated. CPI was more susceptible to thermal denaturation than GCPI, as determined by turbidity and sulfydryl groups, resulting in greater loss of solubility. This is attributed to the higher glycation degree and higher carbohydrate content of GCPI, as demonstrated by glycoprotein staining of sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) gel. Water absorption of bread dough was significantly enhanced by DCPI, and to a larger extent by GCPI compared to the control, resulting in softer texture. CPI resulted in significantly increased crumb hardness in baked bread than the control, whereas DCPI or GCPI resulted in significantly softer crumbs. Bread fortified with 4% DCPI or GCPI was similar to the control with regard to sensory and textural properties, whereas 4% CPI was significantly different, limiting its inclusion level to 2%. There was a trend for higher sensory acceptability scores for GCPI-containing bread compared to DCPI. Whole egg was replaced by 20% by GCPI (3.5%) in sponge cake without affecting the sensory acceptability, whereas CPI- and DCPI-supplemented cakes were significantly different from the control.

Sitosterol–oryzanol organogels are unstable near water, but are shown to be stable in the presence of glycerol., Sitosterol and oryzanol self-assemble to form very firm gels in a range of organic solvents. However, due to the formation of sitosterol hydrate crystals, these gels are unstable in the presence of water, prohibiting the dispersal of water droplets throughout the gel matrix. We demonstrate that by using glycerol as the polar phase rather than water, droplets may be dispersed throughout the oil phase without disrupting the self-assembly of the gel. As increasing volumes of water are added to the glycerol, the G′ values decrease. This can be correlated to both a drop in water activity, and also the stability of the fibrils in the presence of glycerol compared to water, as elucidated by molecular dynamics simulations. We explore how changing the total volume of polar droplets, and changing the water content of these droplets alters the strength of 15% w/w sterol gels. We find that gels exhibit G′ values of ∼1 × 107 Pa even with ∼30% w/w glycerol dispersed throughout the matrix. At higher glycerol loadings, complex multiple emulsion morphologies can form.

Molecular dynamics simulation has been used to model the adsorption of the class II hydrophibin HFBI from Trichoderma reesei at the vacuum–water, DPPC bilayer–water and decane–water interfaces. When two HFBI molecules were simulated in a water-box they self-associated into a dimer with the two hydrophobic patches of the molecule forming the dimer interface. When at the fluid interfaces HFBI adsorbed to both the vacuum–water and decane–water interfaces by adopting a conformation where the hydrophobic patch is parallel to and embedded into the interface. At the DPPC bilayer interface, however, the hydrophobic patch is oriented perpendicular to the interface, although still partially embedded into the bilayer. This difference in adsorbed conformation orientation is most likely due to the presence of the hydrophilic phosphatidyl head groups that are found preferentially at the surface of the bilayer. The degree of tertiary conformational change in the adsorbed HFBI molecules is low at the vacuum–water, slightly greater at the DPPC–water interface, and quite substantial at the decane–water interface. Changes in secondary structure are small, with only HFBI at the decane–water interface showing a significant reduction in beta structure. The effect of the HFBI molecule on the DPPC bilayer is marked, with changes in the ordering of the DPPC molecules being observed not only on the side of the bilayer where the protein is adsorbed, but also on the side opposite to that where the protein adsorbs. The results support the view that hydrophobin molecules behave as rigid janus particles when they adsorb to fluid interfaces.

Defensins are small peptides with anti-microbial properties and potential use as anti-fungal agents in foods. Molecular dynamics simulation elucidated the mechanisms of anti-fungal activity, by following the interaction between mung bean defensin VrD1 peptide and a diphosphatidylcholine (DPPC) bilayer. VrD1 interacts with the bilayer, initially, via electrostatic interaction between cationic amino acid side chains of lysine and arginine and the negatively charged DPPC head group. This initial docking of the VrD1 with the interface is independent of the peptide orientation at first approach, and is similar to the mechanism observed for lysozyme, also a cationic protein. Gradual penetration of the VrD1 peptide into the acyl chain leaflet of the bilayer follows. Some change to the tertiary fold of the protein occurs upon insertion of the peptide into the bilayer, but no significant changes to the secondary structure, with evidence of a stabilization of the VrD1 conformation upon adsorption. The net effect of VrD1 penetration into the bilayer is a disruption of the acyl chain order in the DPPC, which in a cell membrane would lead to disruption of metabolic processes and ultimately to cell death.

The use of confocal Raman microscopy is applied to the study of whey-protein-stabilized oil-in-water emulsions. The stability of emulsions is an important parameter for many applications and is dependent on several factors including protein content and particle size. Emulsions were prepared with varying particle size ranging from 0.8 to 10.0 µm. Changes in sample volume due to laser-induced heating were monitored and correlated to protein content in samples and to particle diameters. It was found that samples with the lowest protein content and larger particle diameters experienced the largest volume changes. The newly developed approach is of a potential predictive use. Copyright © 2013 John Wiley & Sons, Ltd.

Three molecular dynamics (MD) simulation methods are used to follow the thermal unfolding of bovine β-lactoglobulin (β-lac). The methods used, classical MD simulation at different temperatures in the range 300–500 K, essential dynamics and replica exchange MD, were chosen to give a range of conventional and accelerated methods. At 350 K, just above the experimentally determined denaturation temperature of β-lac only small changes to the tertiary fold and secondary structure were seen during a 110 ns simulation. At 400 K and 450 K more unfolding was observed, but it was not until the temperature was increased to 500 K that substantial disruption to the protein structure was seen. For the time that the heated simulated β-lac molecules occupy the same conformation space, they appear to follow similar unfolding pathways. ED simulations biased along the first 5 eigenvectors (determined at 350 K) give rise to conformations that have a more elongated tertiary fold compared to heated simulations, and do not follow similar unfolding pathways to the heated simulations. The REMD simulation, which is the equivalent of an approximately 0.7 μs simulation at 350 K, shows a small degree of tertiary structure unfolding, but very little secondary structure change. The results are discussed in terms of the structural changes that have been observed to occur experimentally in β-lac.

The emulsion properties, protein adsorption and visco-elastic properties of heat-treated soy protein isolate (SPI) emulsions containing sunflower oil, soy oil and palm stearin were studied at neutral pH. The rheological properties, textural profile and fat adsorption capacity of subsequently induced glucono-δ-lactone (GDL) gels were investigated. At neutral pH the palm stearin emulsions showed higher stability than the sunflower and soy oil emulsions. The former also showed higher protein adsorption, emulsifying activity index and visco-elastic properties than the latter, indicating a higher denaturation degree for SPI at the oil/water interface of palm stearin emulsions at neutral pH. Acidified SPI-palm stearin emulsion gels were significantly harder than the soy and sunflower oil versions as well as the control (SPI without oil), whereas gels containing the two liquid oils were softer than the control. SPI-palm stearin gels also had higher fat adsorption capacity than SPI-sunflower oil/soy oil emulsion gels.

The effects of the reducing sugars (glucose and lactose) and the non-reducing sugar (sucrose), heated in combination with soy protein isolate (SPI) at neutral pH, on the physicochemical and rheological properties of SPI were determined. After formation of gels induced by glucono-δ-lactone (GDL), the textural profile and physicochemical bonds of the non-heated and heated SPI gels were investigated. The gelation of SPI was induced in three stages of processing that is similar to some tofu-making procedures. First, SPI was heated in the presence of sugars at neutral pH above the denaturation temperature of SPI; then gelation was induced by GDL at iso-electric pH and finally the acidic gels were heat treated again. Heat treatment with glucose at neutral pH resulted in SPI with higher glycation degree than with lactose, whereas SPI heat treated in the presence of sucrose was not glycated. GDL-induced gels of SPI glycated with glucose was more soluble in water than gels of SPI reacted with lactose, which in turn was more soluble than the control and gels of SPI heated in the presence of sucrose. This indicates a change in the net charge of proteins caused by the glycation reaction. Glucose and lactose had a protective effect on protein denaturation at neutral pH, albeit less than sucrose, resulting in GDL-induced gels with increased water holding capacity and reduced gel hardness than sucrose. Chemical analysis indicated that disulphide bonds were involved in maintaining the structure of the gels, and solubility profiles of gels in different buffers indicate that other types of covalent bonds besides disulphide bonds were formed in gels of glycated SPI, resulting in reduced gel elasticity.