Journal of the American Oil Chemists' Society, Jul 29, 2022
Oleogels based on sterols such as β‐sitosterol blended with the sterol ester γ‐oryzanol are a ver... 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.
Bovine milk has been an important source of food for human beings for thousands of years. Not onl... 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.
Journal of the Chemical Society, Faraday Transactions, 1991
ABSTRACT A three-dimensional Monte Carlo model of a system of particles and polymer chains is use... 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.
ABSTRACT The adsorption behaviour of NaC and NaDC at the decane-water interface was investigated ... 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.
Journal of the American Oil Chemists' Society, Jul 29, 2022
Oleogels based on sterols such as β‐sitosterol blended with the sterol ester γ‐oryzanol are a ver... 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.
Bovine milk has been an important source of food for human beings for thousands of years. Not onl... 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.
Journal of the Chemical Society, Faraday Transactions, 1991
ABSTRACT A three-dimensional Monte Carlo model of a system of particles and polymer chains is use... 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.
ABSTRACT The adsorption behaviour of NaC and NaDC at the decane-water interface was investigated ... 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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