A set of protein-stabilised emulsions at pH 7.0, pH 6.0, and pH 5.0, and their counterpart surfactant emulsions, was designed with near-identical droplet size distribution and phase volume to study the specific contribution of hydrodynamic and pair potential interactions to the interfacial mechanisms of these emulsions systems. In this way, further the interfacial layer of these creaming emulsions to enhance perceived fat content could be manipulated. Creaming behaviour, surface shear, and bulk rheological measurements were performed. This work reflects the great importance of local pair potential in the formation of a highly viscoelastic interfacial film, which could be manipulated changing the surface charge of the protein to develop a well-packed cream layer in the protein-stabilised emulsions.

Pectin and cellulose nanocrystals (CNCs) isolated from banana peels were used to prepare films. The effects of a reinforcing phase (CNCs) and a crosslinker (citric acid, CA) on properties of pectin films were studied. Glycerol-plasticized films were prepared by casting, with different CNC contents (0–10wt%), with or without CA. Overall tensile properties were improved by intermediate CNC contents (around 5wt%). The water resistance and water vapor barrier properties were also enhanced by CNC. Evidences were found from Fourier Transform Infrared (FTIR) spectra supporting the occurrence of crosslinking by CA. Additionally, the tensile strength, water resistance and barrier to water vapor were improved by the presence of CA. The 13C ssNMR spectra indicated that both CA and CNC promoted stiffening of the polymer chains.

Enzymes can be used to enable a specific and controlled approach for structural modifications of protein networks in food technology. Enzymatically induced cross-links between proteins in the continuous phase and/or at interfaces result in better stabilisation and enhanced material properties in foams and emulsions. In this work the interfacial properties of beta-casein and kappa-casein films were investigated with a special focus on the mechanism of transglutaminase (TG) induced cross-linking at the air/water interface. The surface rheology results showed that for the enhanced interfacial strength the order and timing of TG addition matters: TG reaction was most effective when the enzyme was applied during adsorption of proteins to the interface. Differences observed between enzymatic cross-linking of beta-casein and kappa-casein at the air/water interface verified the importance of molecular structure and close packing for formation of an elastic protein network. (c) 2015 Elsevier B.V. All rights reserved.

Enzymes can be used to enable a specific and controlled approach for structural modifications of protein networks in food technology. Enzymatically induced cross-links between proteins in the continuous phase and/or at interfaces result in better stabilisation and enhanced material properties in foams and emulsions. In this work the interfacial properties of β-casein and к-casein films were investigated with a special focus on the mechanism of transglutaminase (TG) induced cross-linking at the air/water interface. The surface rheology results showed that for the enhanced interfacial strength the order and timing of TG addition matters: TG reaction was most effective when the enzyme was applied during adsorption of proteins to the interface. Differences observed between enzymatic cross-linking of β-casein and к-casein at the air/water interface verified the importance of molecular structure and close packing for formation of an elastic protein network.

The digestion of dietary components in the human gastrointestinal (GI) tract is a complex, dynamic, inherently heterogeneous process. A key aspect of the digestion of lipid in the GI tract is the combined action of bile salts, lipase and colipase in hydrolysing and solubilising dispersed lipid. The bile salts are a mixture of steroid acid conjugates with surfactant properties. In order to examine whether the different bile salts have different interfacial properties their dynamic interfacial behaviour was characterised. Differences in the adsorption behaviour to solid hydrophobic surfaces of bile salt species were studied using dual polarisation interferometry and atomic force microscopy (AFM) under physiological conditions. Specifically, the cholates adsorbed more slowly and a significant proportion were irreversibly adsorbed following buffer rinsing; whereas the deoxycholates and chenodeoxycholates adsorbed more rapidly and desorbed to a greater extent following buffer rinsing. The conjugating groups (taurine, glycine) did not influence the behaviour. AFM showed that the interfacial structures that remained following buffer rinsing were also different between these two groups. In addition, the adsorption-desorption behaviour affected the adsorption of colipase to a solid surface. This supports the idea that cooperative adsorption occurs between certain bile salts and colipase to facilitate the adsorption and activity of pancreatic lipase in order to restore lipolytic activity in the presence of bile salts. This study provides insights into how differences in bile salt structure could affect lipase activity and solubilisation of lipolysis products and other lipid-soluble bioactive molecules.

In the present paper we have investigated the impact of microbial transglutaminase on thermally treated ovalbumin. In fact, ovalbumin was modified by microbial transglutaminase following heat treatment for 1 h at 80 degrees C. The protein was both intra- and inter-molecularly crosslinked as shown by the formation of high molecular weight polymers and a monomer having similar molecular weight but higher electrophoretic mobility when compared to unmodified ovalbumin. Analysis of simulated digestion under physiological conditions has demonstrated that the biopolymers obtained after transglutaminase treatment were more resistant to both gastric and duodenal digestion. Whilst they started gradually being digested after 5 min of incubation with pepsin, some of them were still present even after 60 min incubation with the duodenal enzymes, trypsin and chymotrypsin. Furthermore, incubation of 1.5% (w/v) ovalbumin gel in the presence of transglutaminase led to the formation of a well-developed viscoelastic gel network with higher modulus and lower phase angle values. These results suggest a possible use of transglutaminase-modified ovalbumin in the food industry as a potential ingredient to enhance both the functional properties of many food-based products, such as digestibility, and mechanical properties, such as viscoelasticity and gel strength. (C) 2011 Elsevier Ltd. All rights reserved.

The objective of this study was to investigate the influence of acylglycerol (AG; mono-diglycerides) and acylpropyleneglycol (APG; fatty acid mono-diesters of propylene glycol) lipophilic emulsifiers, as well as their mixtures, on the structural transformations of emulsions, observed during emulsion formation and storage. The investigations aimed to characterize the phenomena that can be encountered during the manufacturing and shelf-life of emulsions prepared with these commonly used emulsifiers. It was found that in the presence of AG or AG–APG mixtures and up to 55–60 wt.% water content (depending on the emulsifiers proportions) continuous emulsification and cooling of the water-in-oil (W/O) emulsion initially formed, led to the local phase inversion and finally formation of an oil-in-water-in-oil (O/W/O) double emulsion with unique structure. The inversion was caused by the temperature-dependent formation of the multilamellar liquid-crystalline structures of monoglyceride in the aqueous phase of emulsion. The self-assembled structures encapsulated oil droplets formed under the dynamic emulsification conditions and immobilized them in a liquid-crystalline gel matrix. The resulting oil-in-water (O/W) emulsion gel was then gradually dispersed in the oil phase, which was not involved in the formation of the internal oil droplets. Finally, double O/W/O-type droplets were produced. Their structure can be described as an O/W-emulsion lamellar-gel core surrounded by the interfacial layer of the crystallized surface-active components of the emulsifiers. Such droplets coexisted in the external oil phase with water droplets. When APG emulsifier was used as a sole stabilizer, no phase inversion was observed. The W/O emulsion produced with this emulsifier underwent crystallization- and shear-induced flocculation and subsequent deflocculation during the emulsification. We also report on the time-dependent structural evolutions of the finally produced emulsions. The outcome of the multiple light scattering experiments and microscopic observations was that emulsions based on the AG emulsifier or the AG-rich AG–APG blends developed with time towards more tightly packed systems due to formation of a fat-crystal network in the continuous oil phase. When the only emulsifier used was APG, the structure of emulsion settled within three weeks, due to formation of crystalline bridges between droplets.

Delivering lipids in a controlled manner is one method of modulating dietary fat intake. Rationally designed emulsion microstructures can be exploited to reduce dietary lipid intake either directly (reduced fat foods), or indirectly by modifying the body's response to the food structure. A critical factor is acceptability, therefore the organoleptic properties must be similar to the full fat counterpart. There are three novel approaches that we are currently investigating: The first is to enhance the sensory perception of fat content of emulsions by manipulating the properties of individual lipid droplets; The second is to physically reduce the fat content in the individual lipid droplets, and finally we will describe an approach where we aim to design interfaces which can alter the rate (but not extent) of lipid digestion in order to suppress appetite. We will describe the micro- and nano-structures we are formulating to achieve these objectives.

The interactions between emulsion droplets containing solid fat are important for the rheology and functionality of the emulsion as a whole, particularly for aerated emulsion systems where partial coalescence plays a role in the overall structure of the product. In this study, the interactions between emulsion droplets appeared to be sensitive to the relative amounts of solid fat and liquid oil, thus changing the rheology of the whole system. Incorporation of air had a major effect on these interactions as it appeared to force the emulsion to adopt a stronger structure by encouraging partial coalescence. The rheological behaviour of a non-aerated emulsion and an aerated emulsion was compared. Non-aerated samples did not show major changes in viscosity with increasing temperature. In contrast, the aerated emulsion seemed to be considerably more temperature sensitive, showing a dramatic increase of viscosity as the temperature was increased above a critical value. The effect of temperature ramp rates was investigated. Higher temperature ramp rates resulted in delayed changes in viscosity. The phase behaviour of the fat is both time and temperature dependent; therefore, a faster temperature ramp means that a higher temperature could be reached before critical phase changes in the fat could take place. The rheological behaviour of the emulsions was also dependent on the shear rate applied during the experiment.

Emulsions have applications as wide ranging as food, pharmaceuticals, oil production, printing, agrochemicals and photography. They are incorporated into a broad range of food products, and it is estimated that over 40% of processed foods contain emulsified oils or fats. The emulsified fat is includ...

We have quantified observed differences in the microstructure and rheology of creaming emulsions stabilized by protein and low molecular weight surfactants. In this study, we made two sets of emulsions from a single parent emulsion, which differed only in their interfacial composition (i.e., either protein or surfactant). The protein studied was whey protein isolate. The zeta potential of the surfactant-stabilized emulsion was controlled by mixing anionic (SDS) and nonionic (Brij 35) surfactants to match the zeta potential of the protein-stabilized emulsion. Despite this, ultrasonic creaming measurements and confocal microscopy showed that the structures within the cream layers were different between the two sets of emulsions. The protein-stabilized emulsions appeared to slow or arrest the packing within the cream, leading to a lower density network of emulsion droplets, whereas the surfactant emulsion droplets rearranged more quickly into a well-packed, concentrated cream layer. Rheological analysis of the creams showed that despite the protein-stabilized emulsions having a lower dispersed phase volume fraction, their elastic modulus was approximately 30 times greater than that of a comparable surfactant-stabilized emulsion. These differences were caused by the ability of the protein to form a highly viscoelastic interfacial network around the droplets which may include intermolecular covalent cross-links. At close range the adhesive nature of the interaction between the layers contributes to the microstructure and rheology of concentrated emulsions. This is the first time that such well-defined emulsion systems have been studied in detail both noninvasively to look at the impact on creaming and also invasively to look at the impact on bulk rheological properties.

Atomic force microscopy has been used to visualise the internal structures of sectioned, encased starch granules isolated from near-isogenic pea starch mutants (rug3-a, rug4-b, rug5-a, and lam-c). A mutation at the locus rug4 was found to have little effect on the granule ultrastructure. However, mutations at rug3 and lam, which give rise to low-amylose starches, led to granules that showed banding (growth rings) in which individual blocklets could not easily be seen. High-amylose (rug5) mutants formed granules ranging in shape from simple ellipsoids through to quite complex, convoluted structures. The internal granule structure was found to be heterogeneous. In some regions, normal banding was visible and the underlying ‘hard’ blocklets were embedded in a ‘soft’ matrix. In other regions of the granule, the banding structure was absent and the matrix in which the blocklets are embedded contained a fine hard network structure. It is proposed that this fine, hard structure is due to the presence of a crystalline amylose network.

The adsorption of dilute mixtures of beta-casein/beta-lactoglobulin to the air-water interface was investigated using surface dilatation and surface shear rheology. The data were fitted to simple rheological models to try to gain further information regarding the composition and nature of the interface. The dilatational measurements suggested that the composition of the interface could be determined using these models and that the surface concentration was dominated by the beta-casein in the early stages of adsorption but that high levels of beta-lactoglobulin were present in the final stages. Surface shear rheological measurements showed a similar trend. However, the shear measurements appeared to be more sensitive to the strength of the network than to the composition of the interface. Fluorescence microscopy supported the findings and demonstrated that any "phase separation" capable of affecting the surface rheological measurements occurred at the sub-micrometer scale. The results also demonstrated that the heterogeneity of the interface, once formed, is kinetically trapped, and no further phase separation occurs over the time span of the experiments.

Rheological studies have confirmed that the bacterial polysaccharide P2, a genetically modified variant of the Acetobacter xylinum polysaccharide acetan, undergoes synergistic gelation with either of the plant polysaccharides carob or konjac mannan. Xray fibre diffraction data shows that P2 can form a 5-fold helical structure of pitch 4.7nm and an axial rise per disaccharide repeat of 0.92 nm. Optical rotation data demonstrate that P2 undergoes a coil-helix transition in solution and that deacylation enhances the stability of the helical structure in solution. Studies made on mixtures prepared at different temperatures and ionic strengths suggest that denaturation of the P2 helix favours interaction and gelation. Deacetylation of P2 enhances gelation. X-ray diffraction data for oriented fibres prepared from deacetylated P2-konjac mannan mixed films reveal a 6-fold helical structure of pitch 5.54nm with an axial rise per disaccharide repeat also of 0.92 nm. This mixed helix provides direct evidence for binding between the two polysaccharides. P2 contains two sites of acetylation: one on the backbone and one on the sidechain. The former site of acetylation inhibits helix formation for P2. It is suggested that this site of acetylation also inhibits formation of the mixed helix, explaining the enhanced gelation of mixtures on deacetylation. (C) 2004 Elsevier Ltd. All rights reserved.