Exchanging the substrate specificities of pyruvate decarboxylase from Zymomonas mobilis and benzoylformate decarboxylase from Pseudomonas putida

Pyruvate decarboxylase from Zymomonas mobilis (PDC) and benzoylformate decarboxylase from Pseudomonas putida (BFD) are thiamine diphosphate-dependent enzymes that decarboxylate 2-keto acids. Although they share a common homotetrameric structure they have relatively low sequence similarity and different substrate spectra. PDC prefers short aliphatic substrates whereas BFD favours aromatic 2-keto acids. These preferences are also reflected in their carboligation reactions. PDC catalyses the conversion of benzaldehyde and acetaldehyde to (R)-phenylacetylcarbinol and predominantly (S)-acetoin, whereas (R)-benzoin and mainly (S)-2-hydroxypropiophenone are the products of BFD catalysis. Comparison of the X-ray structures of both enzymes identified two residues in each that were likely to be involved in determining substrate specificity. Site-directed mutagenesis was used to interchange these residues in both BFD and PDC. The substrate range and kinetic parameters for the decarboxylation reaction were studied for each variant. The most successful variants, PDCI472A and BFDA460I, catalysed the decarboxylation of benzoylformate and pyruvate, respectively, although both variants now preferred the long-chain aliphatic substrates, 2-ketopentanoic and 2-ketohexanoic acid. With respect to the carboligase activity, PDCI472A proved to be a real chimera between PDC and BFD whereas BFDA460I/F464I provided the most interesting result with an almost complete reversal of the stereochemistry of its 2-hydroxypropiophenone product.     

Impact of Different Hop Compounds on the Overfoaming Volume of Beer Caused by Primary Gushing

When weather conditions favour the growth of moulds on barley, beers brewed from the resulting malts often tend to gush. Certain Fusarium species (e.g., F. graminearum and F. culmorum) may cause this problem. Supersaturated with CO₂, a primary gushing beer contains an overcritical concentration of microbubbles; these are reputed to be stabilised by Fusarium‐derived hydrophobins. Research with varying brewhouse parameters has been performed to investigate the factors of primary gushing. As hops are known to contribute to a wide range of both gushing positive and negative substances in beer, the hopping regime has emerged as an important aspect. This paper examines the impact of different hop varieties on gushing. Hop oils and unsaturated fatty acids are reputed to be gushing‐suppressors. Compounds such as dehydrated humulinic acid can intensify the effect. Hop pellets, with a prevalent range of conductometric values (5–10% α‐acid), commonly employed in breweries to adjust bitterness and aroma were selected. By working with the same “gushing malt”, the spectrum of compounds in the finished beer only differed through the hop product used. The overfoaming volumes of different samples were determined according to MEBAK guidelines. Respective hop oil and fatty acid concentrations (by GC) and iso‐α‐acid contents (by HPLC) were compared and a chronological sequence of the changing percentages of beer loss is shown.     

Optimisation of the Mashing Procedure for 100% Malted Proso Millet (Panicum miliaceum L.) as a Raw Material for Gluten‐free Beverages and Beers

Proso millet is a gluten‐free cereal and is therefore considered a suitable raw material for the manufacturing of foods and beverages for people suffering from celiac disease. The objective of this study was to develop an optimal mashing procedure for 100% proso millet malt with a specific emphasis on high amylolytic activity. Therefore, the influence of temperature and pH on the amylolytic enzyme activity during mashing was investigated. Size exclusion chromatography was used to extract different amylolytic enzyme fractions from proso millet malt. These enzymes were added into a pH‐adjusted, cold water extract of proso millet malt and an isothermal mashing procedure was applied. The temperatures and pH optima for amylolytic enzyme activities were determined. The α‐amylase enzyme showed highest activity at a temperature of 60°C and at pH 5.0, whereas the β‐amylase activity was optimum at 40°C and pH 5.3. The limit dextrinase enzyme reached maximum activity at 50°C and pH 5.3. In the subsequent mashing regimen, the mash was separated and 40% was held for 10 min at 68°C to achieve gelatinisation. The next step in the mashing procedure was the mixture of the part mashes. The combined mash was then subjected to an infusion mashing regimen, taking the temperature optima of the various amylolytic enzymes into account. It was possible to obtain full saccharification of the wort with this mashing regimen. The analytical data obtained with the optimised proso millet mash were comparable to barley wort, which served as a control.     

Fabrication of a Macroporous Microwell Array for Surface‐Enhanced Raman Scattering

Here, a colloidal templating procedure for generating high‐density arrays of gold macroporous microwells, which act as discrete sites for surface‐enhanced Raman scattering (SERS), is reported. Development of such a novel array with discrete macroporous sites requires multiple fabrication steps. First, selective wet‐chemical etching of the distal face of a coherent optical fiber bundle produces a microwell array. The microwells are then selectively filled with a macroporous structure by electroless template synthesis using self‐assembled nanospheres. The fabricated arrays are structured at both the micrometer and nanometer scale on etched imaging bundles. Confocal Raman microscopy is used to detect a benzenethiol monolayer adsorbed on the macroporous gold and to map the spatial distribution of the SERS signal. The Raman enhancement factor of the modified wells is investigated and an average enhancement factor of 4 × 10⁴ is measured. This demonstrates that such nanostructured wells can enhance the local electromagnetic field and lead to a platform of ordered SERS‐active micrometer‐sized spots defined by the initial shape of the etched optical fibers. Since the fabrication steps keep the initial architecture of the optical fiber bundle, such ordered SERS‐active platforms fabricated onto an imaging waveguide open new applications in remote SERS imaging, plasmonic devices, and integrated electro‐optical sensor arrays.     

Physical properties of burnt timber, with special focus on the drying performance

Burnt wood has been found to perform different from sound (green) wood when dried together, but also with regards to other physical and mechanical properties. In this study the drying performance of wood burnt to different degrees in recent plantation fires was investigated, and the physical, chemical and wood anatomical properties of these different wood types were determined. Different cell structure and chemical composition due to thermal degradation could be observed as well as different drying performance and variation in mechanical properties. An explanation for the deviant drying performance was attempted with the observed structural changes.     

Improved Adhesion, Growth and Maturation of Vascular Smooth Muscle Cells on Polyethylene Grafted with Bioactive Molecules and Carbon Particles

High-density polyethylene (PE) foils were modified by an Ar⁺ plasma discharge and subsequent grafting with biomolecules, namely glycine (Gly), polyethylene glycol (PEG), bovine serum albumin (BSA), colloidal carbon particles (C) or BSA and C (BSA + C). As revealed by atomic force microscopy (AFM), goniometry and Rutherford Backscattering Spectroscopy (RBS), the surface chemical structure and surface morphology of PE changed dramatically after plasma treatment. The contact angle decreased for the samples treated by plasma, mainly in relation to the formation of oxygen structures during plasma irradiation. A further decrease in the contact angle was obvious after glycine and PEG grafting. The increase in oxygen concentration after glycine and PEG grafting proved that the two molecules were chemically linked to the plasma-activated surface. Plasma treatment led to ablation of the PE surface layer, thus the surface morphology was changed and the surface roughness was increased. The materials were then seeded with vascular smooth muscle cells (VSMC) derived from rat aorta and incubated in a DMEM medium with fetal bovine serum. Generally, the cells adhered and grew better on modified rather than on unmodified PE samples. Immunofluorescence showed that focal adhesion plaques containing talin, vinculin and paxillin were most apparent in cells on PE grafted with PEG or BSA + C, and the fibres containing α-actin, β-actin or SM1 and SM2 myosins were thicker, more numerous and more brightly stained in the cells on all modified PE samples than on pristine PE. An enzyme-linked immunosorbent assay (ELISA) revealed increased concentrations of focal adhesion proteins talin and vinculin and also a cytoskeletal protein β-actin in cells on PE modified with BSA + C. A contractile protein α-actin was increased in cells on PE grafted with PEG or Gly. These results showed that PE activated with plasma and subsequently grafted with bioactive molecules and colloidal C particles, especially with PEG and BSA + C, promotes the adhesion, proliferation and phenotypic maturation of VSMC.     

苏黎士西门子餐厅

本案位于西门子公司瑞士总部,虽然也对公众开放,但主要是面向其1500名员工。此栋建筑包括了三个餐厅,它们分别叫做“运动”、“放松”和“第一”餐厅,另外还有一个名为“点”的咖啡屋,总计700个座位。咖啡屋全天开放,户内户外共有150个座位。名为“运动”的主餐厅共有350个座位且提供自助服务。     

Non-thermal pasteurization of fruit juices by combining high-intensity pulsed electric fields with natural antimicrobials

The effect of high-intensity pulsed electric fields (HIPEF) on the Salmonella Enteritidis and Escherichia coli O157:H7 populations inoculated in apple, pear, orange and strawberry juices as influenced by treatment time and pulse frequency was investigated. Combinations of HIPEF (35 kV/cm, 4 μs pulse length in bipolar mode without exceeding 40 °C) with citric acid or cinnamon bark oil against these pathogenic microorganisms in fruit juices were also evaluated. Treatment time was the more influential factor on the microbial reduction in all the fruit juices analyzed. S. Enteritidis and E. coli O157:H7 were reduced by more than 5.0 log₁₀ units in orange juice treated by only HIPEF; whereas strawberry, apple and pear juices were pasteurized when HIPEF was combined with citric acid at 0.5, 1.5, 1.5%, respectively, or cinnamon bark oil at 0.05, 0.1 and 0.1%, respectively. Synergistic and additive killing effects against S. Enteritidis and E. coli O157:H7 in fruit juices by combining treatments were observed.

Industrial relevance

The use of high-intensity pulsed electric fields treatment as a non-thermal pasteurization method in combination with organic acids or essential oils is an effective process for eliminating S. Enteritidis and E. coli O157:H7 populations in fruit juices upper 5.0 log₁₀ reductions. Therefore, combinations of those treatments may help to ensure the microbiological safety in juice products, and to reduce the risk of food-borne illness caused by the consumption of these kinds of foods.     

Structural studies on Ca3Al4MgO10 (C3A2M)—A ternary phase in the system CaO–Al2O3–MgO

In a sequence of temperature-dependent solid-state reactions in the system CaO–Al₂O₃–MgO the formation of the ternary phase Ca₃Al₄MgO₁₀ or C₃A₂M has been studied. Whereas the compound could not be prepared at 1200°C, a yield of 85 wt.-% of Ca₃Al₄MgO₁₀ was obtained at 1320°C (incongruent melting point: 1330°C). Powder diffraction data compare well with results of previous investigations from the 1960s. Single crystals of Ca₃Al₄MgO₁₀ could be retrieved from the sinter-pellets. Basic crystallographic data are as follows: orthorhombic symmetry, space group Pbcm, a = 5.14073(8), b = 16.7576(2), c = 10.70977(16) Å, V = 922.61(2) ų, Z = 4. Using synchrotron diffraction data it was possible to solve the crystal structure. Least-squares refinements resulted in a residual of R(|F|) = 0.021 for 1000 independent observed reflections with I > 2σ(I) and 97 parameters. The structure contains [TO₄]-tetrahedra (T=Al,Mg) forming a three-dimensional (3-D) framework whose topological characteristics have been determined. Al-Mg distributions on the different T-sites have been studied. The calcium cations are located in voids of the network. More than 50 years after its first observation our investigation clarifies the crystal structure of a compound belonging to a system that is of relevance for several fields of materials science.     

Fiber formation and properties of polyester/lignin blends

Thermotropic liquid crystalline polyesters with varied chemical structure are synthesized by melt transesterification polycondensation. They are employed as matrix for blends with lignin materials to obtain melt-spinnable precursors for carbon fibers. The lignin samples are carefully purified by fractionation, enzymatic removal of reducing sugars, and subsequent modification of the terminal OH groups. Effective melt blending is achieved with liquid-crystalline aromatic–aliphatic polyesters having melting ranges that match the softening temperature of the lignin fractions, which is necessary to prevent thermal decomposition of the lignin. Polyester/lignin blends are partially compatibilized, phase-separated materials. The polyester/lignin materials are melt-spun successfully. The fiber properties depend on the lignin purification process. X-ray scattering reveals that orientation in lignin-containing fibers is maintained. First experiments show that the fibers can be converted successfully to carbon fibers by thermal annealing procedures. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48257.