Stephen Euston
Heriot-Watt University, Lfe Science, Faculty Member
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Research Interests: Chemistry, Chromatography, Kinetics, Protein Aggregation, Thermal Stability, and 11 moreFood Sciences, Food Additive, Water soluble polymers, Molecular weight, Whey Protein, Water Soluble Fertilizers, Food Hydrocolloids, Laser Light Scattering, Pulmonary Surfactant, Low molecular weight, and Whey protein concentrate
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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... more
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.
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Bovine milk has been an important source of food for human beings for thousands of years. Not only is milk a very nutritious food in its own right, but it is also a very versatile starting point for many other dairy products. Milk is a... more
Bovine milk has been an important source of food for human beings for thousands of years. Not only is milk a very nutritious food in its own right, but it is also a very versatile starting point for many other dairy products. Milk is a complex food emulsion and colloidal sol. Table 7.1 gives the composition of whole cow’s milk. The emulsion is composed of fat droplets dispersed in an aqueous phase containing protein. The protein is in the form of both casein micelles, which are themselves colloidal particles, and free in solution as whey protein. A considerable reserve of knowledge has been assembled on the structure and properties of milk proteins (Swaisgood, 1992). The fat droplets are stabilized by an adsorbed layer of protein and phospholipid called the ‘milk fat globule membrane’ (MFGM), which is distinct from the aqueous phase protein (Walstra & Jenness, 1984). The average composition of the MFGM has been estimated to be about 48% protein, 33% phospholipid, and 11% water, with the remainder made up of other minor lipid components (Walstra & Jenness, 1984). The phospholipid fraction of the membrane is composed of lecithin, phosphatidyl ethanolamine, phosphatidyl serine, phosphatidyl inositide, plasmalogens and sphingomyelin. Phospholipids are important food emulsifiers in their own right. The contribution that they make to the stability of the milk fat globule is not well understood, but their use as food-grade emulsifiers has been the subject of extensive fundamental research (Courthaudon et al., 1991; Dickinson et al., 1993a; Dickinson & Iveson, 1993). To control the structure and stability of these products, the manufacturer can add a range of permitted additives that can be either naturally occurring or artificial. One of the most versatile of these additives are the low molecular weight emulsifiers. In the following pages, the major emulsifier-containing dairy and imitation dairy products will be reviewed. A brief description of their production will be given where relevant, with emphasis on the role that emulsifiers play in the formation and stability of the product.
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ABSTRACT A three-dimensional Monte Carlo model of a system of particles and polymer chains is used to simulate bridging flocculation of colloidal particles by adsorbing polymer molecules. Polymer chains are modelled as freely jointed... more
ABSTRACT A three-dimensional Monte Carlo model of a system of particles and polymer chains is used to simulate bridging flocculation of colloidal particles by adsorbing polymer molecules. Polymer chains are modelled as freely jointed off-lattice excluded-volume random chains of 50 segments. The polymer–particle interaction is described in terms of a single well-depth parameter expressing the strength of the segment–particle attraction in terms of a square-well pair potential. Numerical data are presented for the effect of the well depth on the configurations of the polymer chains and the structure of the resulting flocs. We observe that the simulated aggregates have a fractal-type structure with little short-range liquid-like order. There is a trend towards more compact flocs with closer particle–particle separations on increasing the adsorption strength. The large flocs rarely contain particles bridged by long dangling chains. The bridges mainly resemble a sort of polymeric ‘glue’ between particle surfaces separated by no more than a few segment diameters.
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ABSTRACT The adsorption behaviour of NaC and NaDC at the decane-water interface was investigated using molecular dynamics simulation. Both NaC and NaDC adsorbed in a conformation where the sterol ring sits in the decane phase, with on... more
ABSTRACT The adsorption behaviour of NaC and NaDC at the decane-water interface was investigated using molecular dynamics simulation. Both NaC and NaDC adsorbed in a conformation where the sterol ring sits in the decane phase, with on average a tilt angle of 49 degrees to the normal of the interface for both bile salts. This is contrary to previous studies for bile salt adsorption to the phospholipid-water interface where the bile salts adopt a flat conformation parallel to the surface. This is explained by the highly ordered nature of the acyl chains in phospholipid layers. Penetration of the less hydrophobic bile salts into a phospholipid layer would lead to disordering of the structure which is unfavourable. In contrast, the decane phase of a decane-water interface is disordered compared to phospholipids. This allows the bile salt sterol ring to penetrate into it without a significant entropy penalty. The free energy of adsorption calculated using umbrella sampling is greater for NaDC (104 kJ mol(-1)) than for NaC (80 kJ mol(-1)), reflecting the higher hydrophobicity of NaDC. NaC and NaDC also have a tendency to form clusters at the interface, possibly reverse micelles in the decane phase which are stabilised by hydrogen bonds formed between the hydroxyl groups on the sterol ring. The higher free energy of adsorption for NaDC is expected to lead to differentiation between the surface properties of NaDC compared to NaC, including their ability to compete for interfacial area with other molecules. To confirm this, the ability of NaC and NaDC to displace whey protein from the oil-water emulsion droplet interface was investigated experimentally. As expected it was found that NaDC displaces more protein for a given protein: bile salt molar ratio than does NaC.
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Research Interests: Chemistry, Molecular Dynamics Simulation, Molecular Dynamics, Transition, Temperature, and 14 moreAggregation, Molten Globule, Secondary Structure, Protein Secondary Structure, Denaturation, IR Spectroscopy, Emulsions, Food Sciences, Beta Lactoglobulin Gene, Food Hydrocolloids, Music Information Dynamics, smooth Particle Mesh Ewald Method, Milk Protein, and Emulsifying Properties
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Major recent advancesThe continued application of computer simulation techniques to the study of protein conformation promises to throw light on their role as functional ingredients in food systems. This review concentrates on three areas... more
Major recent advancesThe continued application of computer simulation techniques to the study of protein conformation promises to throw light on their role as functional ingredients in food systems. This review concentrates on three areas where protein structure impacts on functionality in food systems, namely protein adsorption at a surface, gelation and self-association. Recent studies have demonstrated that adsorbed proteins do not take up a unique conformation at an interface, but can access a range of conformations that are close to the global energy minimum. More detailed simulations have also highlighted the changes in secondary structure that may occur on adsorption, particularly the possibility of intra-molecular β-sheet formation. Studies have also investigated the importance of intra-molecular β-sheet in the formation of amyloid fibrils, a process that may be relevant to the formation of fine-stranded whey protein food gels. Significant progress has also been made in the simulation of micellization and mesophase formation in blocks copolymer solutions, and the application of these methods to the study of milk casein self-association. Ultimately, it is believed this will give insight into the structure and formation of the casein micelle.
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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... more
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.
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Publisher Summary An important functional property of food polymers is in the stabilization of food colloids. The two main types of food polymers found in oil-in-water emulsions are proteins and polysaccharides and some food emulsion... more
Publisher Summary An important functional property of food polymers is in the stabilization of food colloids. The two main types of food polymers found in oil-in-water emulsions are proteins and polysaccharides and some food emulsion products contain both types of macromolecule. This chapter discusses the way in which the nature of the protein-polysaccharide interaction affects the behavior of such colloidal systems. The traditional view is that proteins make good emulsifying agents because of their substantial hydrophobicity and molecular flexibility, which allows rapid adsorption and rearrangement at the interface to give a coherent macromolecular protective layer. Polysaccharides make good stabilizing agents because of their hydrophilicity, high molecular weight, and gelation behavior, which lead to the formation of a macromolecular barrier in the aqueous medium between dispersed droplets. The chapter presents a paper that illustrates the stability of model food emulsions containing both protein and polysaccharide by the experiments carried out at Leeds on three types of macromolecular systems: (a) gum arabic (natural protein polysaccharide hybrid), (b) milk protein + propylene glycol alginate (strong protein-polysaccharide complex), and (c) milk protein + “non-interacting” polysaccharide (weak complex or no association).
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... Awade and Efstathiou, 1999 and Takeuchi et al., 1992), electrophoretic separations (Galyean and Cotterill, 1979, Kitabake et al., 1988, Lush, 1961, Mine et al., 1990 and Parkinson, 1972) and some high-performance techniques (Beeley,... more
... Awade and Efstathiou, 1999 and Takeuchi et al., 1992), electrophoretic separations (Galyean and Cotterill, 1979, Kitabake et al., 1988, Lush, 1961, Mine et al., 1990 and Parkinson, 1972) and some high-performance techniques (Beeley, 1971, Beeley and McCairns, 1972 and ...
Research Interests: Chemistry, Chromatography, Mass Spectrometry, Food Chemistry, Multidisciplinary, and 15 moreProteomic, Maldi Tof, Identification, Ms, Dimensional, High Resolution, Egg, Proteome analysis, Rpm, Gel electrophoresis, Chemical Composition, SDS PAGE, Two dimensional Gel Electrophoresis, Physicochemical Properties, and Ief
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Research Interests: Chemistry, Antioxidant, Hydrolysate, DPPH, Sodium, and 5 moreWhey Protein, ABTS, Egg White, Hydrolysis, and Sustainability
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Research Interests: Chemical Engineering, Chemistry, Food, Adsorption, Soybean, and 3 moreFood Sciences, Emulsion, and Soybean Oil
Bovine milk has been an important source of food for human beings for thousands of years. Not only is milk a very nutritious food in its own right, but it is also a very versatile starting point for many other dairy products. Milk is a... more
Bovine milk has been an important source of food for human beings for thousands of years. Not only is milk a very nutritious food in its own right, but it is also a very versatile starting point for many other dairy products. Milk is a complex food emulsion and colloidal sol. Table 7.1 gives the composition of whole cow’s milk. The emulsion is composed of fat droplets dispersed in an aqueous phase containing protein. The protein is in the form of both casein micelles, which are themselves colloidal particles, and free in solution as whey protein. A considerable reserve of knowledge has been assembled on the structure and properties of milk proteins (Swaisgood, 1992). The fat droplets are stabilized by an adsorbed layer of protein and phospholipid called the ‘milk fat globule membrane’ (MFGM), which is distinct from the aqueous phase protein (Walstra & Jenness, 1984). The average composition of the MFGM has been estimated to be about 48% protein, 33% phospholipid, and 11% water, with the remainder made up of other minor lipid components (Walstra & Jenness, 1984). The phospholipid fraction of the membrane is composed of lecithin, phosphatidyl ethanolamine, phosphatidyl serine, phosphatidyl inositide, plasmalogens and sphingomyelin. Phospholipids are important food emulsifiers in their own right. The contribution that they make to the stability of the milk fat globule is not well understood, but their use as food-grade emulsifiers has been the subject of extensive fundamental research (Courthaudon et al., 1991; Dickinson et al., 1993a; Dickinson & Iveson, 1993). To control the structure and stability of these products, the manufacturer can add a range of permitted additives that can be either naturally occurring or artificial. One of the most versatile of these additives are the low molecular weight emulsifiers. In the following pages, the major emulsifier-containing dairy and imitation dairy products will be reviewed. A brief description of their production will be given where relevant, with emphasis on the role that emulsifiers play in the formation and stability of the product.
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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... more
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 dist...
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SummaryTexture‐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... more
SummaryTexture‐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 sens...
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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... more
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 stab...
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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... more
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 × 10 Pa even with ∼30% w/w glycerol dispersed throughout the matrix. ...