1,721,008 research outputs found
Correlation of microbial response in model food systems with physico-chemical and mobility (NMR molecular and structural) descriptors of the media
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1H and2H NMR mobility in cellulose
No full textMobility of water in cellulose was studied by solid-state 1H and high-resolution 2H NMR as a function of moisture content within the unfreezable moisture range (0–19% dry basis). Measurements of relative mobilities were based on relative intensities, transverse and longitudinal relaxation times and lineshape analysis. At 2–16% moisture content (dry basis), water molecules reoriented anisotropically, suggesting an interaction with cellulose fibers. At moisture content below the monolayer value (2.8%, dry basis), 90% of the protons were immobile and no liquid deuterium signal was detected. A sharp increase in liquid or mobile 1H intensity (accompanied by a decreased LW) and increases in 2H NMR T1 and T2 relaxation times were observed as moisture increased above 9% (dry basis). At this moisture content the molecular mobility approached the fast exchange regime. The data confirmed earlier reports that unfreezable water could be highly mobile and not in a rigid state.
No glass transition was observed by DSC. However, NMR showed a significant mobility transition as the material transformed from a slow exchange (retarded mobility) to a fast exchange regime
Mobility of water in NaCl and brain heart infusion (BHI) solutions as studied by 17 O NMR
No full textThe molecular dynamic behaviour of water molecules in aqueous solution has been determined by oxygen-17 NMR according to the anisotropic reorientation, two-correlation-time model for bound water. Solutions of brain heart infusion (BHI), NaCl and their 1:1 mixture have been analysed. The anisotropic water population was distinguished into a slow (τs bw) and a fast (τf bw) relaxing component. The slow relaxing component was affected by the nature of the solute, while the fast relaxing component was not. NaCl was found to bind water molecules more strongly (higher τs bw) than BHI. Water was more bound in the 1:1 mixture than in the solution containing only BHI. The population of bound water (P bw) was concentration dependent and increased with increasing solids content. BHI, at the suspension point, bound ∼50% of the total water, while NaCl at saturation bound only ∼10%. The 1:1 mixture bound water in a synergistic manner that resulted in a slightly higher Pbw, than in BHI at each solid concentration. The Pbw correlated well with the amount of unfreezable water (as measured by DSC) present in the BHI samples
Effect of physico-chemical and molecular mobility parameters on Staphylococcus aureus growth
No full textThe role played by water activity, ‘mobility’ and physico‐chemical properties of the media in modulating microbial response has been the object of large debate in the scientific community. In this study, Staphylococcus aureus growth parameters (lag phase and cell density at 24 h) in brain heart infusion (BHI) and BHI:NaCl (1:1) were analysed in their correlation with physico‐chemical/mobility parameters descriptive of the media [solid content, aw, kinematic viscosity, 17O NMR (R2, Pbw and inline image)]. In these high moisture content, liquid and ‘homogeneous’ media S.aureus growth related to all the physico‐chemical and molecular mobility parameters analysed in a similar manner and it was found to be influenced more significantly by added NaCl than by the physico‐chemical and molecular mobility of the media. Staphylococcus aureus growth parameters correlated better with aw (relatively independent of NaCl concentration) than with any other parameter considered in this study
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