Interactions of Phenolic Acids and β-Glucan: Studies of Adsorption Isotherms and Thermodynamics

Interactions between polyphenols and dietary fiber might play an important role in polyphenol bioactivities. These interactions can be studied through adsorption processes. The aim of this study was to investigate the adsorption of phenolic acids (p-coumaric acid, caffeic acid, chlorogenic acid) onto dietary fiber – β-glucan. Adsorption was carried out at different temperatures (25, 37, and 45 °C) and pH values (1.5, 5.5, and 10). Non-linear isotherm adsorption models (Langmuir, Freundlich, Dubinin-Radushkevich, Temkin, Hill) were applied to analyze the data. Experimentally determined adsorption capacities showed some fluctuations with temperature and pH. Adsorption isotherms modelled the experimentally determined adsorption capacities well. According to isotherm parameters, it can be suggested that the adsorption was a physical process with non-covalent bonding at all temperatures and pH. Thermodynamic parameters showed that the adsorption was spontaneous (except for chlorogenic acid) and exothermic. Adsorption isotherms and thermodynamics gave useful information about phenolic acid – β-glucan interactions. This work is licensed under a Creative Commons Attribution 4.0 International License

Effects of pH on the Adsorption and Desorption of Naringin onto Zymosan A in Aqueous Systems

This study aimed to investigate the interactions between naringin and dietary fiber from yeast (zymosan A) through adsorption and desorption processes. The effects of different solution pH conditions (pH 3.0, pH 7.0, and pure water at pH 5.5), as well as varying initial concentrations of zymosan A and naringin, on their interaction were examined. The adsorption capacity of naringin onto zymosan A was higher at pH 7.0 (12 to 275 mg g–1), lower in water (6 to 83 mg g–1) and lowest at pH 3.0 (0 to 55 mg g–1). The desorption ratio was lowest in pH 3.0 solution, followed by water and pH 7.0 solution. UV-Vis and FTIR spectral analyses confirmed the binding of naringin onto zymosan A. The antiradical activity for naringin was highest at pH 3, followed by pH 7 and pure water. For the naringin-zymosan A complex, antiradical activity was highest at pH 3, with similar but lower values at pH 7 in pure water. This work is licensed under a Creative Commons Attribution 4.0 International License

Scalar brane backgrounds in higher order curvature gravity

We investigate maximally symmetric brane world solutions with a scalar field. Five-dimensional bulk gravity is described by a general lagrangian which yields field equations containing no higher than second order derivatives. This includes the Gauss-Bonnet combination for the graviton. Stability and gravitational properties of such solutions are considered, and we particularily emphasise the modifications induced by the higher order terms. In particular it is shown that higher curvature corrections to Einstein theory can give rise to instabilities in brane world solutions. A method for analytically obtaining the general solution for such actions is outlined. Genericaly, the requirement of a finite volume element together with the absence of a naked singularity in the bulk imposes fine-tuning of the brane tension. A model with a moduli scalar field is analysed in detail and we address questions of instability and non-singular self-tuning solutions. In particular, we discuss a case with a normalisable zero mode but infinite volume element.Comment: published versio

Gene duplication, modularity and adaptation in the evolution of the aflatoxin gene cluster

<p>Abstract</p> <p>Background</p> <p>The biosynthesis of aflatoxin (AF) involves over 20 enzymatic reactions in a complex polyketide pathway that converts acetate and malonate to the intermediates sterigmatocystin (ST) and <it>O</it>-methylsterigmatocystin (OMST), the respective penultimate and ultimate precursors of AF. Although these precursors are chemically and structurally very similar, their accumulation differs at the species level for Aspergilli. Notable examples are <it>A</it>. <it>nidulans </it>that synthesizes only ST, <it>A</it>. <it>flavus </it>that makes predominantly AF, and <it>A</it>. <it>parasiticus </it>that generally produces either AF or OMST. Whether these differences are important in the evolutionary/ecological processes of species adaptation and diversification is unknown. Equally unknown are the specific genomic mechanisms responsible for ordering and clustering of genes in the AF pathway of <it>Aspergillus</it>.</p> <p>Results</p> <p>To elucidate the mechanisms that have driven formation of these clusters, we performed systematic searches of aflatoxin cluster homologs across five <it>Aspergillus </it>genomes. We found a high level of gene duplication and identified seven modules consisting of highly correlated gene pairs (<it>aflA/aflB, aflR/aflS, aflX/aflY</it>, <it>aflF/aflE, aflT/aflQ</it>, <it>aflC/aflW</it>, and <it>aflG/aflL</it>). With the exception of <it>A. nomius</it>, contrasts of mean <it>Ka/Ks </it>values across all cluster genes showed significant differences in selective pressure between section <it>Flavi </it>and non-section <it>Flavi </it>species. <it>A. nomius </it>mean <it>Ka/Ks </it>values were more similar to partial clusters in <it>A. fumigatus </it>and <it>A. terreus</it>. Overall, mean <it>Ka/Ks </it>values were significantly higher for section <it>Flavi </it>than for non-section <it>Flavi </it>species.</p> <p>Conclusion</p> <p>Our results implicate several genomic mechanisms in the evolution of ST, OMST and AF cluster genes. Gene modules may arise from duplications of a single gene, whereby the function of the pre-duplication gene is retained in the copy (<it>aflF</it>/<it>aflE</it>) or the copies may partition the ancestral function (<it>aflA/aflB</it>). In some gene modules, the duplicated copy may simply augment/supplement a specific pathway function (<it>aflR/aflS </it>and <it>aflX/aflY</it>) or the duplicated copy may evolve a completely new function (<it>aflT/aflQ </it>and <it>aflC/aflW</it>). Gene modules that are contiguous in one species and noncontiguous in others point to possible rearrangements of cluster genes in the evolution of these species. Significantly higher mean <it>Ka/Ks </it>values in section <it>Flavi </it>compared to non-section <it>Flavi </it>species indicate increased positive selection acting in the evolution of genes in OMST and AF gene clusters.</p

Restriction fragment length polymorphism evidence for genetic homology within a pathovar of Pseudomonas syringae

Pseudomonas syringae pv. phaseolicola NPS3121 hrp sequences were used as hybridization probes in a restriction fragment length polymorphism (RFLP) analysis of 24 P. syringae pv. tabaci strains as a means to evaluate the genetic and taxonomic relationship of pathovars of P. syringae. Southern blot analyses of genomic restriction digests, with hrpA-S sequences as hybridization probes, and restriction analyses of PCR-amplified DNA of regions within hrpD were conducted. The resulting RFLP patterns were uniform for 23 of the 24 isolates tested, with strain BR2R having a unique pattern. BR2R is a pathogen of bean which was classified as pathovar tabaci because of its ability to produce tabtoxin, but unlike the other 23 tabaci strains in this study, it does not incite disease symptoms on tobacco. When a DNA fragment containing hrpM sequences was used as a hybridization probe, the tabaci isolates could be divided into three groups on the basis of the RFLP patterns : BR2R, Pt11528R and Pt113R, and the remaining strains. For all of the above analyses, BR2R shared identical RFLP patterns with P. syringae pv. phaseolicola NPS3121, also a bean pathogen which does not cause disease on tobacco. However, BR2R AND NPS3121 could be differentiated from each other on the basis of the RFLP patterns from restriction analysis of PCR-amplified DNA of argF, while the remaining tabaci strains had a third pattern. These studies indicate that hrp genes and argF are conserved in strains of P. syringae pathogenic to tobacco, suggesting that P. syringae strains pathogenic to specific hosts may have a high level of genetic similarity. We believe that these analyses have shown that distinct identifiable genetic differences may be correlated with host range and suggest that such information may be useful for assigning pathovar designations.</jats:p