En kvalitativ undersökning om konsumenters uppfattningar kring surdegsbröd

Surdegsbrödet har förekommit i den mänskliga historien sedan 7000 år tillbaka. Populariteten har varierat men brödet har de senaste åren frekvent synts såväl i media som i bagerier. Brödindustrin har uppmärksammat trenden och resultatet av den dynamiska produktutvecklingen kan ses i livsmedelsbutikernas utbud. Produktutvecklingen är idag konsumentinriktad och endast ett fåtal av nylanserade livsmedelsprodukter överlever på den tuffa marknaden. För att produkten ska sälja är det enligt flera forskare av största vikt att involvera konsumentens tankar och uppfattningar tidigt i produktutvecklingen Ett pågående forskningsprojekt är en del av statens och livsmedelsbranschens storsatsning på livsmedelsforskning. Detta projekt avser att utveckla surdegsbrödet till ett hälsosamt bake-off bröd bakat med energisnåla innovativa tekniker. Denna studie är en del av detta projekt och syftar till att belysa konsumenters tankar och uppfattningar om surdegsbröd för att bidra till produktutvecklingen. För att ta reda på konsumenters tankar och uppfattningar utfördes sju kvalitativa djupintervjuer. Intervjuerna baserades på bilder utifrån en specifik teknik. Resultatet visar att konsumtion av surdegsbröd för respondenterna leder till fysiskt och mentalt välbefinnande. Surdegsbrödet uppfattas som hälsosamt, ska helst vara hem- eller bageribakat samt äts till vardag och fest. Vidare visar resultatet att inte bara produktegenskaper, som knaprig brödskorpa och tuggmotstånd är viktiga, utan också hur brödet är producerat och inhandlat. Industrin anses dra nytta av surdegsbrödet som trend och för att använda en för liten andel surdeg i sina bröd, varpå respondenterna känner sig lurade. Respondenternas känslor till surdegsbröd är således ambivalenta

A Light-Actuated Nanovalve Derived from a Channel Protein

Toward the realization of nanoscale device control, we report a molecular valve embedded in a membrane that can be opened by illumination with long-wavelength ultraviolet (366 nanometers) light and then resealed by visible irradiation. The valve consists of a channel protein, the mechanosensitive channel of large conductance (MscL) from Escherichia coli, modified by attachment of synthetic compounds that undergo light-induced charge separation to reversibly open and close a 3-nanometer pore. The system is compatible with a classical encapsulation system, the liposome, and external photochemical control over transport through the channel is achieved.

Thermodynamic Evidence for Conformational Coupling between the B and C Domains of the Mannitol Transporter of Escherichia coli, Enzyme IImtl

The transport across the cytoplasmic membrane and concomitant phosphorylation of mannitol in Escherichia coli is catalyzed by the mannitol-specific transport protein from the phosphoenolpyruvate-dependent phosphotransferase system, enzyme IImtl. Interactions between the cytoplasmic B and the membrane embedded C domain play an important role in the catalytic cycle of this enzyme, but the nature of this interaction is largely unknown. We have studied the thermodynamics of binding of (i) mannitol to enzyme IImtl, (ii) the substrate analog perseitol to enzyme IImtl, (iii) perseitol to phosphorylated enzyme IImtl, and (iv) mannitol to enzyme IImtl treated with trypsin to eliminate the cytoplasmic domains. Analysis of the heat capacity increment of these reactions showed that approximately 50–60 residues are involved in the binding of mannitol and perseitol, but far less in the phosphorylated state or after removal of the B domain. A model is proposed in which binding of mannitol leads to the formation of a contact interface between the two domains, either by folding of unstructured parts or by docking of preexisting surfaces, thus positioning the incoming mannitol close to the phosphorylation site on the B domain to facilitate the transfer of the phosphoryl group.

Interdomain Interactions between the Hydrophilic Domains of the Mannitol Transporter of Escherichia coli in the Unphosphorylated and Phosphorylated States

Interdomain interactions in the mannitol-specific enzyme II of the phosphoenolpyruvate-dependent phosphotransferase system of Escherichia coli play a key role in the mechanism of mannitol transport across the membrane. In this study, we focus on the interactions between the hydrophilic A and B domains and try to determine those as a function of the phosphorylation state of the enzyme. To this end, unfolding studies on the subcloned domains IIAmtl and IIBmtl, as well as on the binary combination IIBAmtl, were performed, both in the unphosphorylated and in the phosphorylated states, using GuHCl and heat as the denaturant. It is shown that IIAmtl and IIBmtl, as well as P-IIAmtl and P-IIBmtl, unfold according to a two-state mechanism but that IIBAmtl and P2-IIBAmtl do not exhibit such behavior. Two transitions are observed instead, indicating a lack of strong positive cooperative interactions. DSC studies of the unphosphorylated proteins showed a destabilization of the B domain in IIBAmtl with respect to the free IIBmtl as indicated by a lowering of the melting temperature and a lower enthalpy of unfolding. Furthermore, it is shown that phosphorylation has a destabilizing effect on both IIAmtl and IIBAmtl but not on IIBmtl. Possible explanations for this behavior and the biological relevance of the destabilizing forces in IIBAmtl are discussed.

Conductance and selectivity fluctuations in D127 mutants of the bacterial porin OmpF

A recent molecular dynamics study questioned the protonation state and physiological role of aspartate 127 (D127) of E. coli porin OmpF. To address that question we isolated two OmpF mutants with D127 either neutralized (D127N) or replaced by a positively charged lysine (D127K). The charge state of the residue at position 127 has clear effects on both conductance and selectivity. The D127K but not the D127N mutant expresses resilient conductance and selectivity fluctuations. These fluctuations reflect, we think, either changes in the ionization state of K127 and/or transitions between unstable subconformations as induced by the electrostatic repulsion between two positively charged residues, K127 and the nearby R167. Our results slightly favor the view that in WT OmpF residue D127 is deprotonated. As for the role of D127 in OmpF functionality, the gating of both mutants shows very similar sensitivity toward voltage as WT OmpF. Moreover, the current fluctuations of the D127K mutant were observed also in the absence of an applied electric field. We therefore dismiss D127 as a key residue in the control mechanism of the voltage-dependent gating of OmpF

A Biological Porin Engineered into a Molecular, Nanofluidic Diode

We changed the nonrectifying biological porin OmpF into a nanofluidic diode. To that end, we engineered a pore that possesses two spatially separated selectivity filters of opposite charge where either cations or anions accumulate. The observed current inhibition under applied reverse bias voltage reflects, we believe, the creation of a zone depleted of charge carriers, in a sense very similar to what happens at the np junction of a semiconductor device

Slow Cooperative Folding of a Small Globular Protein HPr

The folding of an 85-residue protein, the histidine-containing phosphocarrier protein HPr, has been studied using a variety of techniques including DSC, CD, ANS fluorescence, and NMR spectroscopy. In both kinetic and equilibrium experiments the unfolding of HPr can be adequately described as a two-state process which does not involve the accumulation of intermediates. Thermodynamic characterization of the native and the transition states has been achieved from both equilibrium and kinetic experiments. The heat capacity change from the denatured state to the transition state (3.2 kJ mol-1 K-1) is half of the heat capacity difference between the native and denatured states (6.3 kJ mol-1 K-1), while the solvent accessibility of the transition state (0.36) indicates that its compactness is closer to that of the native than that of the denatured state. The high value for the change in heat capacity upon unfolding results in the observation of cold denaturation at moderate denaturant concentrations. Refolding from high denaturant concentrations is, however, slow. The rate constant of folding in water, kfH2O (14.9 s-1), is small compared to that reported for other proteins of similar size under similar conditions. This indicates that very fast refolding is not a universal character of small globular proteins which fold in the absence of detectable intermediates.