Loïc Foucat

Lytic polysaccharide monooxygenases disrupt the cellulose fibers structure

Lytic polysaccharide monooxygenases (LPMOs) are a class of powerful oxidative enzymes that breakdown recalcitrant polysaccharides such as cellulose. Here we investigate the action of LPMOs on cellulose fibers. After enzymatic treatment and dispersion, LPMO-treated fibers show intense fibrillation. Cellulose structure modifications visualized at different scales indicate that LPMO creates nicking points that trigger the disintegration of the cellulose fibrillar structure with rupture of chains and release of elementary nanofibrils. Investigation of LPMO action using solid-state NMR provides direct evidence of modification of accessible and inaccessible surfaces surrounding the crystalline core of the fibrils. The chains breakage likely induces modifications of the cellulose network and weakens fibers cohesion promoting their disruption. Besides the formation of new initiation sites for conventional cellulases, this work provides the first evidence of the direct oxidative action of LPMOs with the mechanical weakening of the cellulose ultrastructure. LPMOs can be viewed as promising biocatalysts for enzymatic modification or degradation of cellulose fibers.

23Na magnetic resonance imaging: distribution of brine in muscle.

Magnetic resonance imaging (MRI) has been used to characterize tissues in morphological studies. Here, 23Na NMR imaging was used to study the distribution in muscle of brine (5 M NaCl), injected before onset of rigor mortis. First, the distribution of brine was monitored in excised muscle from rabbits for 6 hr following arterial brine injection. Immediately after injection, distribution was clearly heterogeneous. After 6 hr, a steady state was achieved but the observed brine distribution was not fully homogeneous. Second, the same was done for ham processed in various ways (tumbling, cooking). Tumbling increased the homogeneity of distribution in our experimental conditions but only cooking afforded full homogenization of brine in ham. Concentrations of NMR-visible sodium in the muscles were appreciably lower than the expected values calculated from the volume of injected brine. The invisible sodium presumably has T2 values which are too short compared with the echo time in our conventional spectrometer.

Effect of brine injection on water dynamics in postmortem muscle: Study of T2 and diffusion coefficients by MR microscopy

The dynamics of water in postmortem muscle were studied by magnetic resonance microscopy (MRM). Rabbit muscles were arterially injected with 3 and 5 M NaCl brine. T2 and diffusion mapping were performed during the onset of rigor mortis. A wide spread of T2 values and widely differing postmortem evolutions were observed for injected muscles, whereas T2 was spatially homogeneous for intact muscle. Also, highly variable spatial distribution of diffusion coefficients along (Dz) and across (Dx) the muscle fibers was observed and diffusion anisotropy Dz/Dx) was less marked in injected muscles. The results indicate heterogeneity of brine distribution far from the injection site soon after injection. The postmortem evolution of the parameters is discussed in terms of structural changes induced by brine injection. MRM provides insight into how water dynamics respond to different NaCl concentrations inside muscle.

Nuclear magnetic resonance micro-imaging and X-radiography as possible techniques to study seed germination

Abstract Nuclear magnetic resonance (NMR) micro-imaging and X-radiography were compared to assess their potential as non-destructive techniques for studying the germination of pepper (Capsicum annuum L.) seeds. The radiography technique provided information about internal seed quality in dry seeds but yielded foggy images during their imbibition phase. In contrast, NMR micro-imaging clearly displayed the radicle, cotyledons and vascular system of the imbibed seeds. Dry seeds were selected from X-ray pictures and NMR images were recorded during their imbibition at a 1H frequency of 400 MHz with an in-plane resolution of 33 μm × 33 μm. The chemical shift difference between water and lipid proton resonances was exploited to monitor changes in the distribution of the two bulk fractions. The experiments showed the effectiveness of NMR micro-imaging in the study of the morphology of germinating seeds.

In vitro digestion of emulsions: diffusion and particle size distribution using diffusing wave spectroscopy and diffusion using nuclear magnetic resonance

Diffusing wave spectroscopy (DWS) is one of the few techniques enabling the investigation of structures and dynamics in turbid systems that is in the multiple light scattering domain. This makes it an important technique to study colloidal dispersions such as foam, gel or emulsion. In this article, DWS in both back- and forward-multiple scattering was used to monitor the in vitro digestion of turbid undiluted emulsions. Eight formulations were tested using two triglycerides, two emulsifiers and two emulsifier concentrations. The main goal of the study was to interpret the DWS data and compare the results to those from other techniques. We first extended the cumulants/moments fit method used for single scattering to obtain a particle size distribution (PSD) by DWS for multiple scattering. In the case of unimodal distributions, this compares well to PSD obtained from single scattering by dynamic light scattering (DLS). A second interpretation based on the multiple forward-scattering allowed the time-resolved diffusion coefficient to be measured. This was compared to the diffusion monitored by nuclear magnetic resonance (NMR) of turbid undiluted emulsions. Both techniques report similar diffusion coefficients, although NMR measures a true molecular diffusion in different environments whereas DWS measures the diffusion of supramolecular objects in the aqueous phase. These techniques are thus complementary, NMR resolving the kinetics of lipolysis, and DWS resolving the structural transitions, found to be first from a droplet to a vesicle and then from a vesicle to a micelle. In this study, the main formulation parameter influencing the digestion was found to be the type of triglyceride.

The effect of salt content on the structure of iota-carrageenan systems: (23)Na DQF NMR and rheological studies.

23Na NMR spectroscopy has been used to study the effects of Na+ ion concentrations on the structure of 1% (w/w) iota‐carrageenan systems, a natural gelling polysaccharide used as a thickener in the food industry. Rheological and 23Na T1 relaxation time measurements revealed that gel formation correlates with decreases in ion mobility over the range of 0–3% (w/w) sodium content. 23Na single‐quantum (SQ) and double‐quantum‐filtered (DQF) NMR experiments performed on these systems provided evidence for a ‘bound’ sodium ion fraction in a specifically ordered environment. These results have allowed us to propose a model for the carrageenan gelation mechanism in the presence of Na+ ions. Copyright

Distribution and mobility of phosphates and sodium ions in cheese by solid-state 31P and double-quantum filtered 23Na NMR spectroscopy

The feasibility of solid‐state magic angle spinning (MAS) 31P nuclear magnetic resonance (NMR) spectroscopy and 23Na NMR spectroscopy to investigate both phosphates and Na+ ions distribution in semi‐hard cheeses in a non‐destructive way was studied. Two semi‐hard cheeses of known composition were made with two different salt contents. 31P Single‐pulse excitation and cross‐polarization MAS experiments allowed, for the first time, the identification and quantification of soluble and insoluble phosphates in the cheeses. The presence of a relatively ‘mobile’ fraction of colloidal phosphates was evidenced. The detection by 23Na single‐quantum NMR experiments of all the sodium ions in the cheeses was validated. The presence of a fraction of ‘bound’ sodium ions was evidenced by 23Na double‐quantum filtered NMR experiments. We demonstrated that NMR is a suitable tool to investigate both phosphates and Na+ ions distributions in cheeses. The impact of the sodium content on the various phosphorus forms distribution was discussed and results demonstrated that NMR would be an important tool for the cheese industry for the processes controls. Copyright

1H NMR studies: dynamics of water in gelatin

Abstract Proton magnetic resonance was used to characterize the dynamics of water in gelatin. Both sol and gel states were investigated. Transverse relaxation rates (R2) were dependent on the proton frequency measurement. (R2) measured with the Carr-Purcell-Meiboom-Gill pulse sequence was dependent on pulse spacing. These observations were interpreted in terms of chemical exchanges between water protons and those of the macromolecules in the sol state, whereas in the gel state the contribution of diffusion through microheterogeneities in the sample seems to provide an additional transverse relaxation mechanism.

A subzero 1H NMR relaxation investigation of water dynamics in tomato pericarp

(1)H NMR relaxation times (T1 and T2) were measured at low field (0.47 T) in pericarp tissues of three tomato genotypes (Ferum, LA0147 and Levovil) at subzero temperature (-20 °C) and two ripening stages (mature green and red). The unfrozen water dynamics was characterised by two T1 and three T2 components. The relaxation time values and their associated relative populations allowed differentiating the ripening stage of only LA0147 and Levovil lines. But the three genotypes were unequivocally discriminated at the red ripe stage. The unfrozen water distribution was discussed in terms of specific interactions, especially with sugars, in relation with their osmoprotectant effects.

Cavitation and water fluxes driven by ice water potential in Juglans regia during freeze–thaw cycles

Highlight The dynamics of water fluxes and cavitation events induced by ice formation were analyzed by visualization (X-ray microtomography and MRI), and detected with a microdendrometer and ultrasonic acoustic emissions.