Marie Francoise Devaux

Delineation of the structure of soft cheeses at the molecular level by fluorescence spectroscopy—relationship with texture

Tryptophan fluorescence spectra of eight different soft cheeses were recorded directly on cheese samples using front-face fluorescence spectroscopy. Discriminant ability of the data was investigated by discriminant analysis. A correct classification was observed for 95% and 92% of the calibration and validation samples, respectively. It was concluded that tryptophan fluorescence spectra enable the identity of individual cheeses to be finger-printed. Canonical correlation analysis was applied to soft-cheese sensory profile data and fluorescence spectral collection in order to measure the link between the two groups of variables measured on the same samples. The two groups of variables were found highly correlated since the squared canonical coefficients for canonical variates 1 and 2 were 0.93 and 0.80, respectively. A subset of four cheeses was investigated closely in order to establish a molecular basis of the discrimination. It was shown that molecular level information may be derived from the fluorescence spectra.

Monitoring the Secondary Structure of Proteins by Near-Infrared Spectroscopy

Despite the numerous applications of near-infrared spectroscopy in the agricultural and bio-industrial sectors, the relevance of this technique to the study of the secondary structure of proteins has received little attention. The present research investigated the near-infrared spectra of 12 model proteins in the solid state by taking the corresponding mid-infrared data into account. The second-derivative spectra of myoglobin, β-lactoglobulin, and β-casein in the near-infrared region revealed characteristic absorption bands. While myoglobin presented absorption bands at 2055, 2170, 2289, and 2350 nm, β-lactoglobulin exhibited specific peaks at 2203, 2267, and 2300 nm. The second-derivative spectrum of β-casein showed a particularly intense band at 2269 nm. The results derived from a generalized canonical correlation analysis confirmed the potential of near-infrared spectroscopy to characterize the secondary structure of proteins: 2172 and 2289 nm appeared to be representative of α-helix structure; 2205, 2264, and 2313 nm were observed for β-sheet; 2265 nm characterized the unordered structure.

Cartography of cell morphology in tomato pericarp at the fruit scale

In fleshy fruits, the variability of cell morphology at the fruit scale is largely unknown. It presents both a huge variability and a high level of organization. Better knowledge of cell morphology heterogeneity within the fruit is necessary to understand fruit development, to model fruit mechanical behaviour, or to investigate variations of physico‐chemical measurements. A generic approach is proposed to build cartographies of cell morphology at the fruit scale, which depict regions corresponding to different cell morphologies. The approach is based on: (1) sampling the whole fruit at known positions; (2) imaging and quantifying local cell morphology; (3) pooling measurements to take biological variability into account and (4) projecting results in a morphology model of the whole fruit. The result is a synthetic representation of cell morphology variations within the whole fruit. The method was applied to the characterization of cell morphology in tomato pericarp. Two different imaging scales that provided complementary descriptions were used: 3D confocal microscopy and macroscopy. The approach is generic and can be adapted to other fruits or other products.

Brachypodium Cell Wall Mutant with Enhanced Saccharification Potential Despite Increased Lignin Content

Plant lignocellulosic biomass, mostly composed of cell walls, is one of the largest, mostly untapped, reserves of renewable carbon feedstock on the planet. Energy-rich polysaccharide polymers of plant cell walls can be broken down to produce fermentable sugars used to produce bioethanol. However, the complex structure of plant cell walls, and in particular, the presence of lignin, makes them recalcitrant to enzymatic degradation. Reducing this recalcitrance represents a major technological challenge. Brachypodium distachyon is an excellent model to identify parameters underlying biomass quality of energy grasses. In this work, we identified a mutant line spa1 with a so far undescribed phenotype combining brittleness with increased elasticity of the internodes. Mutant cell walls contain less crystalline cellulose and changes in hemicellulose and lignin quality and quantity. Using a dedicated reactor to follow in real-time, the evolution of straw particle size and sugar release during enzymatic digestion, we show that, despite the increased lignin content, the spa1 mutant has a dramatic reduced recalcitrance to saccharification compared to the WT. These observations demonstrate that other parameters besides lignin content are relevant for the improvement of biomass recalcitrance in energy grasses.

Stereological estimation of cell wall density of DR12 tomato mutant using three-dimensional confocal imaging

BACKGROUND AND AIMS The cellular structure of fleshy fruits is of interest to study fruit shape, size, mechanical behaviour or sensory texture. The cellular structure is usually not observed in the whole fruit but, instead, in a sample of limited size and volume. It is therefore difficult to extend measurements to the whole fruit and/or to a specific genotype, or to describe the cellular structure heterogeneity within the fruit. METHODS An integrated method is presented to describe the cellular structure of the whole fruit from partial three-dimensional (3D) observations, involving the following steps: (1) fruit sampling, (2) 3D image acquisition and processing and (3) measurement and estimation of relevant 3D morphological parameters. This method was applied to characterize DR12 mutant and wild-type tomatoes (Solanum lycopersicum). KEY RESULTS The cellular structure was described using the total volume of the pericarp, the surface area of the cell walls and the ratio of cell-wall surface area to pericarp volume, referred to as the cell-wall surface density. The heterogeneity of cellular structure within the fruit was investigated by estimating variations in the cell-wall surface density with distance to the epidermis. CONCLUSIONS The DR12 mutant presents a greater pericarp volume and an increase of cell-wall surface density under the epidermis.

Investigating Lignin Key Features in Maize Lignocelluloses Using Infrared Spectroscopy

Lignins and their cross-linking to hemicelluloses detrimentally affect the cellulose-to-ethanol conversion of grass lignocelluloses. Screening appropriate grass cell walls and their compositional changes during the various steps of the process calls for a high-throughput analytical technique. Such a performance can be fulfilled by Fourier transform mid-infrared (FT-MIR) spectroscopy. In the present paper, a set of maize cell walls from mature stems were selected, including brown midrib samples. Lignin fractions were isolated by mild acidolysis to obtain a set of purified maize lignin standards. The lignin content and the percentage of lignin-derived p-hydroxyphenyl (H), guaiacyl (G), and syringyl (S) thioacidolysis monomers were determined. In addition, the composition of cell wall polysaccharides, as well as the amount of ester-linked p-coumaric (CA) and ferulic (FA) acids, was measured by wet chemistry. Partial least square (PLS) analyses were applied to infrared and chemical data of cell walls. The resulting models showed a good predictive ability with regard to the lignin content, to the frequency of S (or G) thioacidolysis monomers, and to the level of ester-linked CA of maize cell walls. The loading plots and regression coefficients revealed relevant infrared absorption bands.

Statistical mapping of maize bundle intensity at the stem scale using spatial normalisation of replicated images

The cellular structure of plant tissues is a key parameter for determining their properties. While the morphology of cells can easily be described, few studies focus on the spatial distribution of different types of tissues within an organ. As plants have various shapes and sizes, the integration of several individuals for statistical analysis of tissues distribution is a difficult problem. The aim of this study is to propose a method that quantifies the average spatial organisation of vascular bundles within maize stems, by integrating information from replicated images. In order to compare observations made on stems of different sizes and shapes, a spatial normalisation strategy was used. A model of average stem contour was computed from the digitisation of several stem slab images. Point patterns obtained from individual stem slices were projected onto the average stem to normalise them. Group-wise analysis of the spatial distribution of vascular bundles was applied on normalised data through the construction of average intensity maps. A quantitative description of average bundle organisation was obtained, via a 3D model of bundle distribution within a typical maize internode. The proposed method is generic and could easily be extended to other plant organs or organisms.

Phase transition of triglycerides in fat globules during semi-hard cheese ripening as studied by mid-infrared and front-face fluorescence spectroscopy

Texture is an important criteria used to evaluate the quality of cheeses. It is a reflection of their structure at the microscopic and molecular levels. Understanding the structure of cheeses, particularly protein and fat structures and the interactions betwen cheese components during and after manufacture, can provide information useful in determining what constitutes a quality product. It is well known that the cheese texture may change with the physical state of the fats depending on the storage temperature and time. Melting of the hundreds species of triacylglycerols of milk fat globule occurs over a large temperature range, ie, between -30 and +40 °C [1, 2]. Casal and Mantsch [3] have shown that the infrared bands appearing in the 3000–2800 cm-1 region are sensitive to the conformation and the packing of the phospholipid acyl chains. Frontface fluorescence spectroscopy allows investigation of the fluorescence of powdered, turbid and concentrated samples [4, 5, 6] and provides information on the presence of fluorescent molecules and their environment in samples such as food products.