Essener Brot - Herstellung und Verwendung von Keimlingen in der Bäckerei

Der Leitfaden wendet sich in erster Linie an Bäcker, die Keimlinge in der Bäckerei, zum Beispiel zur Herstellung von Keimlingsbroten oder Essener Broten, verwenden wollen, und gibt darüber hinaus auch Einblicke, inwiefern Keimlinge als technologische Zutat eingesetzt werden können. Weiterhin kann dieser Leitfaden auch als Instrument für Berater im Bäckereiwesen verwendet werden. Der Leitfaden ist wie eine „Betriebsanleitung“ zu lesen und dient zur Erläuterung praktischer Vorgehensweisen. Reflexionen zu theoretischen Hintergründen finden eingeschränkt und nur soweit statt, wie diese der Erläuterung der praktischen Vorgehensweisen dienen. Ziel eines jeden Bäckers ist es, „gutes Brot“ zu backen. Um dies beim Backen mit Keimlingen zu erreichen, müssen bestimmte Parameter berücksichtigt werden. Der Einsatz von Keimlingen bedeutet letztlich den Einsatz von Auswuchsgetreide, weil durch das Keimen der Getreidekörner auch Stärke abbauende Enzyme aktiviert werden. Für eine gleichbleibende Brotqualität sollten die Keimlinge eine konstante Nährstoffzusammensetzung und eine möglichst niedrige Belastung mit Mikroorganismen aufweisen. Die Qualität der Keimlinge kann durch den Keimprozess beeinflusst werden. Beeinflussende Faktoren sind die Schichthöhe, die Keimdauer, die Feuchtigkeit und die Temperatur der Keime. Dazu gibt der Leitfaden konkrete Hinweise. Er gibt aber nicht nur eine Handlungsanweisung für das optimale Keimen von Getreide, sondern auch für ein bestmögliches Verbacken

Keimlinge als neuartige multifunktionelle Zutat in ökologischen Backwaren - Optimierung der Herstellung und Verwendung

Im Rahmen des Projektes „Keimlinge als neuartige multifunktionelle Zutat in ökologischen Backwaren - Optimierung der Herstellung und Verwendung“ wurde die sichere betriebseigene Herstellung von Keimlingen, der Einsatz von Keimlingen in Sprossenbroten und der Einsatz zu technologischen Zwecken entwickelt und optimiert. Diese allgemeinen Handlungsempfehlungen wurden in einem Leitfaden für handwerkliche Bäckereien festgehalten. Um gleichmäßige Backergebnisse zu erhalten, werden Keimlinge mit konstanter Qualität benötigt. Qualitätsbestimmende Faktoren sind die mikrobiologische Belastung, die wertgebenden Inhaltsstoffe und die Enzymatik. Das Keimergebnis lässt sich im Keimprozess durch die Keimtemperatur, die Schichthöhe und die Keimdauer beeinflussen und steuern. Die Einflüsse dieser Faktoren auf die qualitätsbestimmenden Eigenschaften wurden im Projekt untersucht. Aus den Ergebnissen konnte die Faustzahl „15:15:30“ abgeleitet werden. Bei einer Schichthöhe von 15 cm, einer Keimtemperatur von maximal 15 °C und einer Keimdauer von 30 Stunden lassen sich gute Keimlingsergebnisse erzielen. Die Herstellung von Essener Broten stellt besondere Anforderungen an die Teigführung. Durch die Keimung kommt es zu einer deutlichen Vermehrung der Enzymaktivität im Keimgut. Diese Enzymaktivität ist insbesondere für Roggenteige technologisch hoch relevant. Es empfiehlt sich, die Keimlinge möglichst spät und eher grob zerkleinert dem gut gesäuerten Teig hinzu zu geben. Unter Einhaltung der im Leitfaden beschriebenen Bedingungen gelingt es, ein Essener Brot ausschließlich aus Keimlingen herzustellen. Je niedriger die Keimtemperatur, desto fester die Krumenbeschaffenheit und desto weniger klebrig ist die Krume. Die Backergebnisse sind durch die Temperatur bei der Keimung beeinflussbar und die Krumenfestigkeit bzw. die Krumenklebrigkeit kann gesteuert werden. Das so genannte Essener Brot wird typischerweise eher bei niedrigeren Temperaturen über eine verlängerte Backzeit gebacken. Die Keimlinge oder auch das so gewonnene aktive Malz kann zu Steuerung der Enzymatik bei der Teigführung eingesetzt werden. Der Einsatz von Roggenkeimlingen als Zutat bei Weizenbrot kann sehr positive Ergebnisse zeigen. Der Zerkleinerungsgrad der Keimlinge hat entscheidenden Einfluss auf die Qualität der hergestellten Weizengebäcke. Insgesamt konnten das Volumen, die Krumenelastizität und die Krumenfestigkeit verbessert werden

How hybrid excitons suppress charge separation: ultrafast, but delayed

Inorganic/organic hybrid systems offer great technological potential for novel solar cell design due to the combination of high charge carrier mobilities in the inorganic semiconductor with the chemical tuneability of organic chromophore absorption properties. While ZnO basically exhibits all necessary properties for a successful application in light-harvesting, it was clearly outpaced by TiO$_2$ in terms of charge separation efficiency. The physical origin of this deficiency is still under debate. Here, we use a combination of femtosecond time-resolved photoelectron spectroscopy with many-body ab initio calculations to demonstrate that optical excitation of the chromophore is followed by (1) ultrafast electron transfer into the ZnO bulk (350 fs), (2) electron relaxation, and (3) delayed (100 ps) recapture of the electrons at a 1 nm distance from the interface in (4) a strongly bound (0.7 eV) hybrid exciton state with a lifetime exceeding 5 $\mu$s that is analysed by taking into account pump-probe delay-dependent photostationary population dynamics. Beyond this identification and quantification of all elementary steps leading to the suppression of charge separation at ZnO interfaces, our key finding is the substantially delayed hybrid exciton formation. It opens up a sufficiently large time window for counter-measures with the potential to finally successfully implement ZnO in light-harvesting or optoelectronic devices without significant efficiency losses.Comment: main: 11 pages, 3 figures supporting: 6 pages, 3 figure

Electrical tunability of terahertz nonlinearity in graphene

Graphene is conceivably the most nonlinear optoelectronic material we know. Its nonlinear optical coefficients in the terahertz frequency range surpass those of other materials by many orders of magnitude. Here, we show that the terahertz nonlinearity of graphene, both for ultrashort single-cycle and quasi-monochromatic multicycle input terahertz signals, can be efficiently controlled using electrical gating, with gating voltages as low as a few volts. For example, optimal electrical gating enhances the power conversion efficiency in terahertz third-harmonic generation in graphene by about two orders of magnitude. Our experimental results are in quantitative agreement with a physical model of the graphene nonlinearity, describing the time-dependent thermodynamic balance maintained within the electronic population of graphene during interaction with ultrafast electric fields. Our results can serve as a basis for straightforward and accurate design of devices and applications for efficient electronic signal processing in graphene at ultrahigh frequencies.D.T. and H.A.H. acknowledge funding from the European Union’s Horizon 2020 Framework Programme under grant agreement no. 964735 (EXTREME-IR). M.G. and B.G. acknowledge support from the European Cluster of Advanced Laser Light Sources (EUCALL) project that has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement no. 654220. K.-J.T. acknowledges funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement no. 804349 (ERC StG CUHL) and financial support through the MAINZ Visiting Professorship. ICN2 was supported by the Severo Ochoa program from Spanish MINECO (grant no. SEV-2017-0706). Parts of this research were carried out at ELBE at the Helmholtz-Zentrum Dresden-Rossendorf e.V., a member of the Helmholtz Association. F.H.L.K. acknowledges support from the Government of Spain (FIS2016-81044; Severo Ochoa CEX2019-000910-S), Fundació Cellex, Fundació Mir-Puig, and Generalitat de Catalunya (CERCA, AGAUR, and SGR 1656). Furthermore, the research leading to these results has received funding from the European Union’s Horizon 2020 under grant agreement no. 881603 (Graphene Flagship Core 3)

Uncovering the (un-)occupied electronic structure of a buried hybrid interface

The energy level alignment at organic/inorganic (o/i) semiconductor interfaces is crucial for any light-emitting or -harvesting functionality. Essential is the access to both occupied and unoccupied electronic states directly at the interface, which is often deeply buried underneath thick organic films and challenging to characterize. We use several complementary experimental techniques to determine the electronic structure of p -quinquephenyl pyridine (5P-Py) adsorbed on ZnO(1 0   −1 0). The parent anchoring group, pyridine, significantly lowers the work function by up to 2.9 eV and causes an occupied in-gap state (IGS) directly below the Fermi level EF. Adsorption of upright-standing 5P-Py also leads to a strong work function reduction of up to 2.1 eV and to a similar IGS. The latter is then used as an initial state for the transient population of three normally unoccupied molecular levels through optical excitation and, due to its localization right at the o/i interface, provides interfacial sensitivity, even for thick 5P-Py films. We observe two final states above the vacuum level and one bound state at around 2 eV above EF, which we attribute to the 5P-Py LUMO. By the separate study of anchoring group and organic dye combined with the exploitation of the occupied IGS for selective interfacial photoexcitation, this work provides a new pathway for characterizing the electronic structure at buried o/i interfaces.Deutsche Forschungsgemeinschafthttps://doi.org/10.13039/501100001659Peer Reviewe

Ultrafast Tunable Terahertz-to-Visible Light Conversion through Thermal Radiation from Graphene Metamaterials

Several technologies, including photodetection, imaging, and data communication, could greatly benefit from the availability of fast and controllable conversion of terahertz (THz) light to visible light. Here, we demonstrate that the exceptional properties and dynamics of electronic heat in graphene allow for a THz-to-visible conversion, which is switchable at a sub-nanosecond time scale. We show a tunable on/off ratio of more than 30 for the emitted visible light, achieved through electrical gating using a gate voltage on the order of 1 V. We also demonstrate that a grating-graphene metamaterial leads to an increase in THz-induced emitted power in the visible range by 2 orders of magnitude. The experimental results are in agreement with a thermodynamic model that describes blackbody radiation from the electron system heated through intraband Drude absorption of THz light. These results provide a promising route toward novel functionalities of optoelectronic technologies in the THz regime

Tunable room temperature nonlinear Hall effect from the surfaces of elementary bismuth thin films

The nonlinear Hall effect (NLHE) with time-reversal symmetry constitutes the appearance of a transverse voltage quadratic in the applied electric field. It is a second-order electronic transport phenomenon that induces frequency doubling and occurs in non-centrosymmetric crystals with large Berry curvature -- an emergent magnetic field encoding the geometric properties of electronic wavefunctions. The design of (opto)electronic devices based on the NLHE is however hindered by the fact that this nonlinear effect typically appears at low temperatures and in complex compounds characterized by Dirac or Weyl electrons. Here, we show a strong room temperature NLHE in the centrosymmetric elemental material bismuth synthesized in the form of technologically relevant polycrystalline thin films. The ($1\,1\,1$) surface electrons of this material are equipped with a Berry curvature triple that activates side jumps and skew scatterings generating nonlinear transverse currents. We also report a boost of the zero field nonlinear transverse voltage in arc-shaped bismuth stripes due to an extrinsic geometric classical counterpart of the NLHE. This electrical frequency doubling in curved geometries is then extended to optical second harmonic generation in the terahertz (THz) spectral range. The strong nonlinear electrodynamical responses of the surface states are further demonstrated by a concomitant highly efficient THz third harmonic generation which we achieve in a broad range of frequencies in Bi and Bi-based heterostructures. Combined with the possibility of growth on CMOS-compatible and mechanically flexible substrates, these results highlight the potential of Bi thin films for THz (opto)electronic applications.Comment: 44 pages, 21 figure

Higher-harmonic generation in boron-doped silicon from band carriers and bound-dopant photoionization

We investigate ultrafast harmonic generation (HG) in Si:B, driven by intense pump pulses with fields reaching 100 kV/cm and a carrier frequency of 300 GHz, at 4 K and 300 K, both experimentally and theoretically. We report several findings concerning the nonlinear charge carrier dynamics in intense sub-THz fields: (i) Harmonics of order up to n = 9 are observed at room temperature, while at low temperature we can resolve harmonics reaching at least n = 11. The susceptibility per charge carrier at moderate field strength is as high as for charge carriers in graphene, considered to be one of the materials with the strongest sub-THz nonlinear response. (ii) For T = 300 K, where the charge carriers bound to acceptors are fully thermally ionized into the valence subbands, the susceptibility values decrease with increasing field strength. Simulations incorporating multi-valence-band Monte Carlo and finite-difference-time-domain (FDTD) propagation show that here, the HG process becomes increasingly dominated by energy-dependent scattering rates over the contribution from band nonparabolicity, due to the onset of optical-phonon emission, which ultimately leads to the saturation at high fields. (iii) At T = 4 K, where the majority of charges are bound to acceptors, we observe a drastic rise of the HG yields for internal pump fields of 30 kV/cm, as one reaches the threshold for tunnel ionization. We disentangle the HG nonlinear response into contributions associated with the initial photoionization and subsequent motion in the bands, and show that intracycle scattering seriously degrades any contribution to HG emission from coherent recollision of the holes with their parent ions

Terahertz signatures of ultrafast Dirac fermion relaxation at the surface of topological insulators

Topologically protected surface states present rich physics and promising spintronic, optoelectronic, and photonic applications that require a proper understanding of their ultrafast carrier dynamics. Here, we investigate these dynamics in topological insulators (TIs) of the bismuth and antimony chalcogenide family, where we isolate the response of Dirac fermions at the surface from the response of bulk carriers by combining photoexcitation with below-bandgap terahertz (THz) photons and TI samples with varying Fermi level, including one sample with the Fermi level located within the bandgap. We identify distinctly faster relaxation of charge carriers in the topologically protected Dirac surface states (few hundred femtoseconds), compared to bulk carriers (few picoseconds). In agreement with such fast cooling dynamics, we observe THz harmonic generation without any saturation effects for increasing incident fields, unlike graphene which exhibits strong saturation. This opens up promising avenues for increased THz nonlinear conversion efficiencies, and high-bandwidth optoelectronic and spintronic information and communication applications.Parts of this research were carried out at ELBE at the Helmholtz-Zentrum Dresden-Rossendorf e.V., a member of the Helmholtz Association. The films are grown in IRE RAS within the framework of the state task. This work was supported by the RFBR grants Nos. 18-29-20101, 19-02-00598. N.A., S.K., and I.I. acknowledge support from the European Union’s Horizon 2020 research and innovation program under grant agreement No. 737038 (TRANSPIRE). T.V.A.G.O. and L.M.E. acknowledge the support by the Würzburg-Dresden Cluster of Excellence on Complexity and Topology in Quantum Matter (ct.qmat). K.-J.T. acknowledges funding from the European Union’s Horizon 2020 research and innovation program under Grant Agreement No. 804349 (ERC StG CUHL) and financial support through the MAINZ Visiting Professorship. ICN2 was supported by the Severo Ochoa program from Spanish MINECO Grant No. SEV-2017-0706