Application of Kluyveromyces marxianus, Lactobacillus delbrueckii ssp. bulgaricus and L. helveticus for sourdough bread making

The application of Kluyveromyces marxianus (IFO 288), Lactobacillus delbrueckii ssp. bulgaricus (ATCC 11842) and Lactobacillus helveticus (ATCC 15009) as starter cultures for sourdough bread making was examined. Production of lactic and acetic acids, bread rising, volatile composition, shelf-life and organoleptic quality of the sourdough breads were evaluated. The amount of starter culture added to the flour, the dough fermentation temperature and the amount of sourdough used were examined in order to optimise the bread making process. The use of mixed cultures led to higher total titratable acidities and lactic acid concentrations compared to traditionally made breads. Highest acidity (3.41 g lactic acid/kg of bread) and highest resistance to mould spoilage were observed when bread was made using 50% sourdough containing 1% K. marxianus and 4% L. delbrueckii ssp. bulgaricus. The use of these cultures also improved the aroma of sourdough breads, as shown by sensory evaluations and as revealed by GC–MS analysis.     

Fractionation of green tea extracts: correlation of antimutagenic effect with flavanol content

The present study was undertaken to evaluate the role of individual flavanols in the antimutagenic potential of green tea. Aqueous extracts of green tea were fractionated into four fractions, each of which was fully defined with respect to its content of (-)-epigallocatechin gallate, (-)-epicatechin gallate, (-)-epigallocatechin, (-)-epicatechin and gallic acid. The ability of each fraction to antagonize the mutagenicity of four model mutagens, namely N-nitrosopyrrolidine, benzo(a)pyrene, 2-aminoanthracene and Glu-P-1 (2-amino-6-methyldipyrido[1,2-a: 3,2-d]imidazole), was investigated in the Ames test. No correlation could be established between any of the flavanols and antimutagenic potential. Similarly, no correlation was evident between the flavanol content of each fraction and its ability to inhibit CYP1A, as exemplified by the O-dealkylations of methoxy- and ethoxy-resorufin. Furthermore, no relationship could be established between CYP2B activity, as exemplified by the O-depentylation of pentoxyresorufin and the antimutagenic potential of green tea. Using a modified Ames test procedure, the ability of each tea fraction to scavenge the metabolically generated reactive intermediates of the model mutagens was investigated, this being an additional mechanism of the antimutagenic potential of green tea. Generally, fractions with high flavanol content were more effective scavengers. It is concluded that the contribution of flavanols to the antimutagenic activity of green tea is, at best, limited. ©1997 SCI     

The remarkable effect of oxygen on the N2 selectivity of water catalytic denitrification by hydrogen

The selective catalytic reduction of nitrates (NO3-) in pure water toward N2 formation by the use of gaseous H2 and in the presence of O2 (air) at 1 atm total pressure and 25 degrees C has been investigated over Pd-Cu supported on various mixed metal oxides, x wt % MO(x(/gamma-Al2O3 (MO(x) = CeO2, SrO, Mn2O3, Cr2O3, Y2O3, and TiO2). It is demonstrated for the firsttime that a remarkable improvement in N2 reaction selectivity (by 80 percentage units) can be achieved when oxygen is present in the reducing feed gas stream. In particular, significantly lower reaction selectivities toward NH4+ and NO2- can be obtained, whereas the rate of NO3- conversion is not significantly affected. Moreover, it was shown thatthe same effect is obtained over the Pd-Cu-supported catalysts irrespective to the chemical composition of support and the initial concentration of nitrates in water used. The Pd-Cu clusters supported on 4.8 wt%TiO2/gamma-Al2O3 resulted in a solid with the best catalytic behavior compared with the rest of supports examined, both in the presence and in the absence of oxygen in the reducing feed gas stream. DRIFTS studies performed following catalytic reduction by H2 of NO3- in water revealed that the presence of TiO2 in the Pd-Cu/TiO2-Al2O3 system enhanced the reactivity of adsorbed bidentate nitrate species toward H2. Nitrosyl species adsorbed on the alumina and titania support surfaces are considered as active intermediate species of the selective catalytic reduction of NO3- by H2 in water. Pd-Cu/TiO2-Al2O3 appears to be the most selective catalyst ever reported in the literature for the reduction of nitrates present in pure water into N2 by a reducing gas mixture of H2/air.     

A study of the transport phenomena in a wall-coated micro steam-methanol reformer

Microreactors have important advantages due to the increased heat and mass transfer resulting from the small dimensions of the system. This results in enhanced performance and efficiency. Microreformers with wall-coated or suspended catalytic layer configurations have been studied due to their lower transport resistances compared to packed-bed microreformers. In the present work, a theoretical study of the reacting flow in a wall-coated microreformer is carried out. The theoretical results for the conversions and carbon monoxide concentration of wall-coated reformers are compared with the reported experimental data. The effects of important parameters for wall-coated reformers such as the catalyst layer thickness, wall temperature, and the flow velocity of the reactants are studied. Recommendations for the design of micro wall-coated reformers are provided.     

Free-standing graphene on microstructured silicon vertices for enhanced field emission properties

Controlled deposition of graphene in different orientations relative to the substrate is challenging and majority of existing deposition methods lead to sheets that lay flat on the substrate surface, limiting the potential applications in which the exposed sheet surface area and the atomically thin edges of graphene are exploited. Here we describe a simple and general solution-based methodology for the fabrication of random arrays of free-standing few-layer graphene (FLG) flakes on micro-spikes engraved on Si substrates. This should greatly benefit applications using free-standing graphene, such as in energy storage/conversion devices and bright electron sources. As a proof of concept, it is shown that the FLG sheets protruding on the top of micro-spikes are good electron emitters with turn-on fields as low as 2.3 V μm(-1) and field enhancement of few thousands. The emission performance and long-term stability achieved by this hierarchical deposition process are superior to that of planar graphene sheets and demonstrate promise for applications. Mechanisms leading to formation of free-standing FLG flakes are discussed.     

Field studies on the formation of sinking CO2 particles for ocean carbon sequestration: effects of injector geometry on particle density and dissolution rate and model simulation of plume behavior

We have carried out the second phase of field studies to determine the effectiveness of a coflow injector which mixes liquid CO2 and ambient seawater to produce a hydrate slurry as a possible CO2 delivery method for ocean carbon sequestration. The experiments were carried out at ocean depths of 1000-1300 m in Monterey Bay, CA, using a larger injector than that initially employed under remotely operated vehicle control and imaging of the product. Solidlike composite particles comprised of water, solid CO2 hydrate, and liquid CO2 were produced in both studies. In the recent injections, the particles consistently sank at rates of approximately 5 cm s(-1). The density of the sinking particles suggested that approximately 40% of the injected CO2 was converted to hydrate, while image analysis of the particle shrinking rate indicated a CO2 dissolution rate of 0.76-1.29 micromol cm(-2) s(-1). Plume modeling of the hydrate composite particles suggests that while discrete particles may sink 10-70 m, injections with CO2 mass fluxes of 1-1000 kg s(-1) would result in sinking plumes 120-1000 m belowthe injection point.     

Molecular Dissection of Escherichia coli CpdB: Roles of the N Domain in Catalysis and Phosphate Inhibition,and of the C Domain in Substrate Specificity and Adenosine Inhibition

CpdB is a 3′-nucleotidase/2′3′-cyclic nucleotide phosphodiesterase, active also with reasonable efficiency on cyclic dinucleotides like c-di-AMP (3′,5′-cyclic diadenosine monophosphate) and c-di-GMP (3′,5′-cyclic diadenosine monophosphate). These are regulators of bacterial physiology, but are also pathogen-associated molecular patterns recognized by STING to induce IFN-β response in infected hosts. The cpdB gene of Gram-negative and its homologs of gram-positive bacteria are virulence factors. Their protein products are extracytoplasmic enzymes (either periplasmic or cell–wall anchored) and can hydrolyze extracellular cyclic dinucleotides, thus reducing the innate immune responses of infected hosts. This makes CpdB(-like) enzymes potential targets for novel therapeutic strategies in infectious diseases, bringing about the necessity to gain insight into the molecular bases of their catalytic behavior. We have dissected the two-domain structure of Escherichia coli CpdB to study the role of its N-terminal and C-terminal domains (CpdB_Ndom and CpdB_Cdom). The specificity, kinetics and inhibitor sensitivity of point mutants of CpdB, and truncated proteins CpdB_Ndom and CpdB_Cdom were investigated. CpdB_Ndom contains the catalytic site, is inhibited by phosphate but not by adenosine, while CpdB_Cdom is inactive but contains a substrate-binding site that determines substrate specificity and adenosine inhibition of CpdB. Among CpdB substrates, 3′-AMP, cyclic dinucleotides and linear dinucleotides are strongly dependent on the CpdB_Cdom binding site for activity, as the isolated CpdB_Ndom showed much-diminished activity on them. In contrast, 2′,3′-cyclic mononucleotides and bis-4-nitrophenylphosphate were actively hydrolyzed by CpdB_Ndom, indicating that they are rather independent of the CpdB_Cdom binding site.     

Amphiphilic polymer co‐networks: 32 years old and growing stronger – a perspective

This brief perspective overviews amphiphilic polymer co‐networks (APCNs), polymeric chemically crosslinked hydrogels also covalently hosting a hydrophobic segment, conferring upon these materials the important property of internal self‐organization in aqueous environments. APCN synthesis is most conveniently accomplished via the random crosslinking copolymerization of a hydrophilic monomer with a hydrophobic macro‐crosslinker, whereas better structures are attained via the end‐linking of amphiphilic linear ABA triblock copolymers or amphiphilic star diblock copolymers. Microphase‐separated morphologies, translucency‐to‐transparency, biocompatibility, low to moderate aqueous swelling, fair mechanical strength and possible stimulus‐responsiveness constitute the main physicochemical properties of APCNs, with their major commercial application being in silicone hydrogel soft contact lenses. Modeling the swelling, morphological and mechanical behavior of these intriguing materials is an area where more progress is necessary in order to improve our understanding of these networks and facilitate the design of next‐generation APCNs. © 2020 Society of Industrial Chemistry