High internal phase water-in-oil emulsions stabilized by food-grade starch.

Water in oil emulsions would be prepared by silicones (SO), modified silicones (DC8500) and a food-grade stabilizer (starch 1). With increasing water contents, the emulsions turned from a liquid-like to gel-like behaviors with enhancing storage and loss modulus. When DC8500/SO was 1/17 with 10 wt% starch 1, a high internal phase emulsion can be obtained with 95 wt% water content. DC8500 and SO worked as efficient emulsifiers and possessed amphiphilic property to form emulsions with water in different ratios. A food-grade starch 1 was supplied as a stabilizer which can enhance both water content and strength of emulsion when added in a low concentration. Besides, it is indicated that the food-grade starches provided potential benefit on stabilizing emulsions in very low concentration.

Carotene location in processed food samples measured by cryo In-SEM Raman.

Cryo In-SEM Raman has been used for the first time to localise carotene compounds in a food matrix. Raman spectra of lycopene and ß-carotene have been obtained from sampling oil droplets and plant cell structures visualised with cryo-SEM in tomato and carrot based emulsions containing 5% oil. It was possible to identify the carotenoids in both the oil droplets and the cell walls. Furthermore our results gave some indication that the carotenoids were in the non-crystalline state. It has been suggested that a higher amount of carotenes solubilised into the oil phase of the food matrix would lead to a higher bioaccessibility, thus understanding the effect of processing conditions on micronutrients distribution in a food matrix might help the design of plant based food products with a better nutritional quality. This shows improved structural characterisation of the cryo-SEM with the molecular sensitivity of Raman spectroscopy as a promising approach for complex biological problems.

Rheology and microstructure of carrot and tomato emulsions as a result of high-pressure homogenization conditions.

High-pressure homogenization, as a way to further mechanically disrupt plant cells and cell walls compared to conventional blending, has been applied to thermally treated and comminuted carrot and tomato material in the presence of 5% olive oil. Mixes of both vegetables in a 1:1 ratio were also included. Both the effect of homogenization pressure and the effect of multiple process cycles were studied. The different microstructures generated were linked to different rheological properties analyzed by oscillatory and steady state measurements. The results showed that while carrot tissue requires a high shear input to be disrupted into cells and cell fragments, tomato cells were broken across the cell walls already at moderate shear input, and the nature of the tomato particles changed to amorphous aggregates, probably composed of cell contents and cell wall polymers. All the plant stabilized emulsions generated were stable against creaming under centrifugation. While for tomato a low-pressure multiple cycle and a high-pressure single-cycle process led to comparable microstructures and rheological properties, carrot showed different rheological properties after these treatments linked to differences in particle morphology. Mixes of carrot and tomato showed similar rheological properties after homogenizing in a single or in a split-stream process. Practical Application: Following consumers' demand, the food industry has shown a growing interest in manufacturing products free of gums and stabilizers, which are often perceived as artificial. By tailored processing, fresh plant material could be used to structure food products in a more natural way while increasing their nutritional quality.

Effect of mechanical and thermal treatments on the microstructure and rheological properties of carrot, broccoli and tomato dispersions.

BACKGROUND: The food industry has shown an increased interest in the manufacture of healthier and more natural food products. By tailored processing fruit and vegetables can be used as structurants thus reducing artificial gums and stabilisers. The effect of different thermal and mechanical treatments, including high-pressure homogenisation, on the microstructural and rheological properties of carrot, broccoli and tomato dispersions was studied. As part of the rheological characterisation small oscillatory deformation as well as shear flow measurements were performed. RESULTS: Carrot and broccoli showed a different behaviour from tomato under the conditions studied. Changing the order of thermal and mechanical treatment led to microstructures with different flow properties. The resulting microstructures differed in the manner of cell wall separation: either breaking across the cell walls or through the middle lamella. High-pressure homogenisation decreased the viscosity of carrot and broccoli dispersions, while it increased the viscosity of tomato. Cryo-scanning electron microscopy showed that the cell walls of carrot and broccoli remained as compact structures after homogenisation whereas tomato cell walls were considerably swollen. CONCLUSIONS: Based on the type of vegetable, the different processes applied led to microstructures with different rheological properties. This study shows that particle size distribution, morphology and phase volume are important parameters to explain the complex relationship between rheology and microstructure for these types of systems.

High pressure homogenization increases the in vitro bioaccessibility of α- and ß-carotene in carrot emulsions but not of lycopene in tomato emulsions.

UNLABELLED: The correlation between food microstructure and in vitro bioaccessibility of carotenes was evaluated for tomato and carrot emulsions (5% olive oil) subjected to high pressure homogenization (HPH) at varying degrees of intensity. The aim was to investigate whether additional mechanical disruption of the food matrix could be utilized to further increase the carotene bioaccessibility of an already pre-processed material. The carotene bioaccessibility of the samples was measured after simulated in vitro digestion, carotene release to the oil phase was estimated by Confocal Raman spectroscopy and, to measure active uptake of carotenes, Caco-2 cells were incubated with the digesta of selected samples. HPH did not notably affect the retention of carotenes or ascorbic acid but significantly increased both the release and micellar incorporation of α- and ß-carotene in carrot emulsions 1.5- to 1.6-fold. On the other hand, in vitro bioaccessibility of lycopene from tomato was not increased by HPH under any of the conditions investigated. Instead, the results suggested that lycopene bioaccessibility was limited by a combination of the low solubility of lycopene in dietary lipids and entrapment in the cellular network. Carotene uptake by Caco-2 cells appeared to be mainly dependent upon the carotene concentration of the digesta, but cis-trans isomerization had a significant impact on the micellarization efficiency of carotenes. We therefore conclude that HPH is an interesting option for increasing the bioaccessibility of carotenes from fruits and vegetables while maintaining a high nutrient content, but that the results will depend on both food source and type of carotene. PRACTICAL APPLICATION: A better understanding of the correlation between the processing of fruits and vegetables, microstructure and nutrient bioaccessibility can be directly applied in the production of food products with an increased nutritional value.

Self-assembly of trehalose molecules on a lysozyme surface: the broken glass hypothesis.

To help understand how sugar interactions with proteins stabilise biomolecular structures, we compare the three main hypotheses for the phenomenon with the results of long molecular dynamics simulations on lysozyme in aqueous trehalose solution (0.75 M). We show that the water replacement and water entrapment hypotheses need not be mutually exclusive, because the trehalose molecules assemble in distinctive clusters on the surface of the protein. The flexibility of the protein backbone is reduced under the sugar patches supporting earlier findings that link reduced flexibility of the protein with its higher stability. The results explain the apparent contradiction between different experimental and theoretical results for trehalose effects on proteins.

To switch or not to switch: the effects of potassium and sodium ions on alpha-poly-L-glutamate conformations in aqueous solutions.

Molecular dynamics simulations demonstrate that differences in the interaction of sodium and potassium with the carboxylate side chains of alpha-poly-L-glutamate (alpha-PGA) have a dramatic effect on the conformational properties of the polypeptide. Potassium ions cluster mainly in the second and third solvation shells of alpha-PGA because their low charge density makes the electrostatic interactions between them and alpha-PGA too weak for K(+) to compete with water for the first solvation shell of the alpha-PGA glutamic acid residuals. Unlike sodium ions, they do not switch the conformation of alpha-PGA from extended to alpha-helical. Potentials of mean force for pure water, sodium ion solutions, and potassium ion solutions show marked differences in ion association behavior. This supports the idea that Hofmeister effects depend upon direct ion-macromolecule interactions as well as interactions with water molecules in the first solvation shell rather than bulk water structuring.

The effect of sodium chloride on poly-l-glutamate conformation.

A large-scale fully-atomistic molecular dynamics simulation of poly-l-glutamate demonstrates that a small amount of sodium chloride switches the preferred conformation from an extended conformation to a compact alpha-helix.

Solvent effects and hydration of a tripeptide in sodium halide aqueous solutions: an in silico study.

In this work we are trying to gain insight into the mechanisms of ion-protein interactions in aqueous media at the molecular scale through fully atomistic molecular dynamics simulations. We present a systematic molecular simulation study of interactions of sodium and halide ions with a trialanine peptide in aqueous sodium halide solutions with different salts concentrations (0.20, 0.50, 1.0 and 2.0 M). Each simulation covers more than fifty nanoseconds to ensure the convergence of the results and to enable a proper determination of the tripeptide-ion interactions through the potentials of mean force. Changes in ion densities in the vicinity of different peptide groups are analysed and implications for the tripeptide conformations are discussed.

Photophysical properties of ruthenium(II) polyazaaromatic compounds: a theoretical insight.

Quantum-chemical methods are applied to study the nature of the excited states relevant in the photophysical processes (absorption and emission) of a series of polyazaaromatic-ligand-based ruthenium(II) complexes. The electronic and optical properties of the free polyazaaromatic ligands and their corresponding ruthenium(II) complexes are determined on the basis of correlated Hartree-Fock semiempirical approaches. While the emission of complexes containing small-size ligands, such as 1,10-phenanthroline or 2,2'-bipyridine, arises from a manifold of metal-to-ligand charge-transfer triplet states ((3)MLCTs), an additional ligand-centered triplet state ((3)L) is identified in the triplet manifold of complexes containing a pi-extended ligand such as dipyrido[3,2-a:2',3'-c]phenazine, tetrapyrido[3,2-a:2',3'-c:3'',2''-h:2''',3'''-j]phenazine, and 1,10-phenanthrolino[5,6-b]-1,4,5,8,9,12-hexaazatriphenylene. Recent experimental data are interpreted in light of these theoretical results; namely, the origin for the abnormal solvent- and temperature-dependent emission measured in pi-extended Ru complexes is revisited.

Determination of DNA guanine sites forming photo-adducts with Ru(II)-labeled oligonucleotides; DNA polymerase inhibition by the resulting photo-crosslinking.

The influence of the distance between the anchoring site of the tethered [Ru(TAP)(2)dip](2+) complex (TAP=1,4,5,8-tetraazaphenanthrene; dip=4,7-diphenyl-1,10-phenanthroline) on a probe sequence and the guanines of the complementary target strand was studied by (1) the luminescence quenching of the complex (by electron transfer) and (2) the oligodeoxyribonucleotide adduct (ODN adduct) formation which results in photo-crosslinking of the two strands. Moving the guanine moieties away from the complex induces an important decrease of the efficiency of both processes, but clearly affects the ODN adduct formation more specifically than the quenching process. From these results, we determined the positions of the guanine bases in the duplex ODN that are able to form a photo-adduct with the tethered complex. We also examined the possible competition between a long-range hole migration in the duplex ODN and the formation of a photo-adduct by using a sequence labeled with the complex at the 5'-phosphate end. Such a hole migration appears to be inefficient as compared to the ODN adduct formation. Finally, we studied the influence of the photo-crosslinking on the function of two different DNA polymerases. A 17-mer Ru(II)-labeled ODN was hybridized to its complementary sequence located on the 5'-side of a 40-mer matrix. After illumination, the elongation of a 13-mer DNA primer hybridized to the 3'-extremity of the same matrix was stopped at a position corresponding to the formation of the ODN adduct.

Synthesis and characterization of optically active and racemic forms of cyclometalated Rh(III) complexes. An experimental and theoretical emission study.

The optically active cyclometalated Rh(III) complexes, delta[Rh(thpy4,5p(R,R)py)(2)TAP]Cl, lambda[Rh(thpy4,5p(S,S)py)(2)TAP]Cl, and delta[Rh(phpy4,5p(R,R)py)(2)TAP]Cl (where TAP = 1,4,5,8-tetraazaphenanthrene, thpy4,5p(R,R)py = (8R,10R)-2-(2'-thienyl)-4,5-pinenopyridine and phpy4,5p(R,R)py = (8R,10R)-2-(2'-phenyl)-4,5-pinenopyridine) have been prepared and characterized. Their photophysics has been examined in parallel with that of rac[Rh(thpy)(2)TAP]Cl and rac[Rh(phpy)(2)TAP]Cl. Their behaviors have been rationalized from results of TD-DFT calculations. The complexes with thienylpyridine (thpy) as cyclometalating ligands exhibit (3)CT (from thpy to TAP) and (3)LC(pi-pi) (centered on thpy) emissions in a solvent matrix at 77 K and one (3)CT luminescence at room temperature. In contrast, with phenylpyridine (phpy), the complexes show only one (3)CT emission (from phpy to TAP) at both temperatures.