The adsorption-desorption behaviour and structure function relationships of bile salts.

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.

Effect of the interfacial layer composition on the properties of emulsion creams.

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.

3-Dimensional Facial Analysis-Facing Precision Public Health.

Precision public health is a new field driven by technological advances that enable more precise descriptions and analyses of individuals and population groups, with a view to improving the overall health of populations. This promises to lead to more precise clinical and public health practices, across the continuum of prevention, screening, diagnosis, and treatment. A phenotype is the set of observable characteristics of an individual resulting from the interaction of a genotype with the environment. Precision (deep) phenotyping applies innovative technologies to exhaustively and more precisely examine the discrete components of a phenotype and goes beyond the information usually included in medical charts. This form of phenotyping is a critical component of more precise diagnostic capability and 3-dimensional facial analysis (3DFA) is a key technological enabler in this domain. In this paper, we examine the potential of 3DFA as a public health tool, by viewing it against the 10 essential public health services of the "public health wheel," developed by the US Centers for Disease Control. This provides an illustrative framework to gage current and emergent applications of genomic technologies for implementing precision public health.

Bionanocomposite films based on polysaccharides from banana peels.

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.

Interaction of transglutaminase with adsorbed and spread films of ß-casein and к-casein.

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 ß-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 ß-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.

Synergistic interactions between the genetically modified bacterial polysaccharide P2 and carob or konjac mannan.

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. X-ray 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 0.92nm. 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 0.92nm. 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.

Atomic force microscopy of pea starch granules: granule architecture of wild-type parent, r and rb single mutants, and the rrb double mutant.

AFM studies have been made of the internal structure of pea starch granules. The data obtained provides support for the blocklet model of starch granule structure (Carbohydr. Polym. 32 (1997) 177-191). The granules consist of hard blocklets dispersed in a softer matrix material. High-resolution images have yielded new insights into the detailed structure of growth rings within the granules. The blocklet structure is continuous throughout the granule and the growth rings originate from localised defects in blocklet production distributed around the surface of spheroidal shells within the granules. A mutation at the rb locus did not lead to significant changes in granule architecture. However, a mutation at the r locus led to loss of growth rings and changed blocklet structure. For this mutant the blocklets were distributed within a harder matrix material. This novel composite arrangement was used to explain why the granules had internal fissures and also changes in gelatinisation behaviour. It is suggested that the matrix material is the amylose component of the granule and that both amylose and amylopectin are present within the r mutant starch granules in a partially-crystalline form. Intermediate changes in granule architecture have been observed for the double mutant rrb.

Rheology of mixed beta-casein/beta-lactoglobulin films at the air-water interface.

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.

Atomic force microscopy of pea starch: origins of image contrast.

Atomic force microscopy (AFM) has been used to image the internal structure of pea starch granules. Starch granules were encased in a nonpenetrating matrix of rapid-set Araldite. Images were obtained of the internal structure of starch exposed by cutting the face of the block and of starch in sections collected on water. These images have been obtained without staining, or either chemical or enzymatic treatment of the granule. It has been demonstrated that contrast in the AFM images is due to localized absorption of water within specific regions of the exposed fragments of the starch granules. These regions swell, becoming "softer" and higher than surrounding regions. The images obtained confirm the "blocklet model" of starch granule architecture. By using topographic, error signal and force modulation imaging modes on samples of the wild-type pea starch and the high amylose r near-isogenic mutant, it has been possible to demonstrate differing structures within granules of different origin. These architectural changes provide a basis for explaining the changed appearance and functionality of the r mutant. The growth-ring structure of the granule is suggested to arise from localized "defects" in blocklet distribution within the granule. It is proposed that these defects are partially crystalline regions devoid of amylose.