Marie-Françoise Devaux

Characterization of edible oils, butters and margarines by Fourier transform infrared spectroscopy with attenuated total reflectance

The combination of attenuated total reflectance (ATR) and mid-infrared spectroscopy (MIRS) with statistical multidimensional techniques made it possible to extract relevant information from MIR spectra of lipid-rich food products. Wavenumber assignments for typical functional groups in fatty acids were made for standard fatty acids: Absorption bands around 1745 cm−1, 2853 cm−1, 2954 cm−1, 3005 cm−1, 966 cm−1, 3450 cm−1 and 1640 cm−1 are due to absorption of the carbonyl group, C−H stretch, =CH double bonds of lipids and O−H of lipids, respectively. In lipid-rich food products, some bands are modified. Water strongly absorbs in the region of 3600–3000 cm−1 and at 1650 cm−1 in butters and margarines, allowing one to rapidly differentiate the foods as function of their water content. Principal component analysis was used to emphasize the differences between spectra and to rapidly classify 27 commercial samples of oils, butters and margarines. As the MIR spectra contain information about carbonyl groups and double bonds, the foods were classified with ATR-MIR, in agreement with their degree of esterification and their degree of unsaturation as determined from gas-liquid chromatography analysis. However, it was difficult to differentiate the studied food products in terms of their average chainlength.

Chemometric methods for the coupling of spectroscopic techniques and for the extraction of the relevant information contained in the spectral data tables

The coupling of infrared (IR) and fluorescence spectroscopies was used for studying the modifications affecting proteins during cheese ripening. The data treatment was performed using appropriate chemometric methods: Common Components and Specific Weights Analysis and Canonical Correlation Analysis. These methods demonstrated their ability to describe the overall spectral information collected and to extract the relevant information addressing the modifications of proteins. The results obtained showed that the overall methodology, i.e. coupling of spectroscopies with appropriate chemometric methods, was efficient to monitor modifications of proteins intervening during ripening.

Number of particles for the determination of size distribution from microscopic images

Abstract The aim of this study was to determine the minimal number of particles required for assessing a reliable particle size distribution from images acquired using microscopy. The proposed methodology used the one-sample Kolmogorov–Smirnov statistic to choose an a priori number of particles and the two-sample Kolmogorov–Smirnov test to validate the sub-sampling procedure inherent to microscopic preparation. The methodology was applied to number-based particle size distributions of starch granules.

Application of Multidimensional Analyses to the Extraction of Discriminant Spectral Patterns from NIR Spectra

A method for extracting NIR discriminant spectral patterns without any reference to chemical values is suggested. First, groups of samples have to be defined a priori. Second, this method involves two procedures: the application of Principal Component Analysis (PCA) on spectral data and Factorial Discriminant Analysis (FDA) on the PC scores. Discriminant spectral patterns are assessed as linear combinations of PCA eigenvectors with weights determined by FDA. This method was applied on an illustrative collection of wheat semolina conditioned at 3 levels of water concentration. Three groups were made on the basis of the 3 water levels. Two discriminant spectral patterns representative of water concentration were extracted. They showed the commonly known bands of water at 1940 and 1450 nm. The band at 1450 nm was resolved into two bands at 1410 and 1460 nm, which could be assigned to free and bound OH, respectively. The discriminant spectral patterns therefore modeled the relative proportion of free and bound water. Suitability of the method for other applications is discussed.

Down-regulation of an Auxin Response Factor in the tomato induces modification of fine pectin structure and tissue architecture

It has previously been shown that down-regulation of an auxin response factor gene (DR12) results in pleiotropic phenotypes including enhanced fruit firmness in antisense transgenic tomato (AS-DR12). To uncover the nature of the ripening-associated modifications affecting fruit texture, comparative analyses were performed of pectin composition and structure in cell wall pericarp tissue of wild-type and AS-DR12 fruit at mature green (MG) and red-ripe (RR) stages. Throughout ripening, pectin showed a decrease in methyl esterification and in the content of galactan side chains in both genotypes. At mature green stage, pectin content in methyl ester groups was slightly higher in AS-DR12 fruit than in wild type, but this ratio was reversed at the red-ripe stage. The amount of water- and oxalate-soluble pectins increased at the red-ripe stage in the wild type, but decreased in AS-DR12. The distribution of methyl ester groups on the homogalaturonan backbone differed between the two genotypes. There was no evidence of more calcium cross-linked homogalacturan involved in cell-to-cell adhesion in AS-DR12 compared with wild-type fruit. Furthermore, the outer pericarp contains higher proportion of small cells in AS-DR12 fruit than in wild type and higher occurrence of (1-->5) alpha-L-arabinan epitope at the RR stage. It is concluded that the increased firmness of transgenic fruit does not result from a major impairment of ripening-related pectin metabolism, but rather involves differences in pectin fine structure associated with changes in tissue architecture.

Distribution of pectic epitopes in cell walls of the sugar beet root

Immunolabelling techniques with antibodies specific to partially methyl-esterified homogalacturonan (JIM5: unesterified residues flanked by methylesterified residues. JIM7: methyl-esterified residues flanked by unesterified residues), a blockwise de-esterified homogalacturonan (2F4), 1,4-galactan (LM5) and 1,5-arabinan (LM6) were used to map the distribution of pectin motifs in cell walls of sugar beet root (Beta vulgaris). PME and alkali treatments of sections were used in conjunction with JIM5-7 and 2F4. The JIM7 epitope was abundant and equally distributed in all cells. In storage parenchyma, the JIM5 epitope was restricted to some cell junctions and the lining of intercellular spaces while in vascular tissues it occurred at cell junctions in some phloem walls and in xylem derivatives. After secondary wall formation, the JIM5 epitope was restricted to inner cell wall regions between secondary thickenings. The 2F4 epitope was not detected without de-esterification treatment. PME treatments prior to the use of 2F4 indicated that HG at cell corners was not acetylated. The LM5 epitope was mainly present in the cambial zone and when present in storage parenchyma, it was restricted to the wall region closest to the plasma membrane. The LM6 epitope was widely distributed throughout primary walls but was more abundant in bundles than in medullar ray tissue and storage parenchyma. These data show that the occurrence of oligosaccharide motifs of pectic polysaccharides are spatially regulated in sugar beet root cell walls and that the spatial patterns vary between cell types suggesting that structural variants of pectic polymers are involved in the modulation of cell wall properties.

French Bread Loaf Volume Variations and Digital Image Analysis of Crumb Grain Changes Induced by the Minor Components of Wheat Flour

ABSTRACT A standard quality flour for French breadmaking was fractionated by extraction of water-soluble components (6% db) and by defatting (<1%db) to study the impact of soluble components and lipids on bread quality in terms of loaf specific volume (vs) and crumb structure. Addition of puroindolines (<0.2%) was also tested. Crumb cell structure was assessed by digital image analysis (DIA) according to erosion-dilation and closing treatments. The fraction of cells area with size <1 mm (%d<1) was defined as an index of fineness of crumb structure. Both DIA procedures allowed differentiation of crumb structures obtained by various formulations and, in the range of composition modifications tested, variations by a factor of 2 of both criteria (vs and %d1) were obtained. Soluble fraction increased vs and decreased fineness. Defatting and adding puroindolines increased fineness with no effect on vs. The possible role of molecular components of each flour fraction was discussed in terms of rheological and foa...

Principal component regression, ridge regression and ridge principal component regression in spectroscopy calibration

Ridge regression (RR) and principal component regression (PCR) are two popular methods intended to overcome the problem of multicollinearity which arises with spectral data. The present study compares the performances of RR and PCR in addition to ordinary least squares (OLS) and partial least squares (PLS) on the basis of two data sets. An alternative procedure that combines both PCR and RR is also introduced and is shown to perform well. Furthermore, the performance of the combination of RR and PCR is stable in so far as sufficient information is taken into account. This result suggests discarding those components that are unquestionably identified as noise, when the ridge constant tackles the degeneracy caused by components with small variances.

Relations between Mid-Infrared and Near-Infrared Spectra Detected by Analysis of Variance of an Intervariable Data Matrix

A mathematical procedure based on the analysis of variance of an intervariable data matrix (AVID) was used to relate wavenumbers and wavelengths between the mid-infrared and near-infrared domains. Initially the method calculates for each sample the product of intensities at all combinations of the frequencies in the two domains. This data matrix is submitted to analysis of variance (ANOVA) based on a classification criterion. This procedure gives a matrix of Fisher F values for all possible combinations of wavenumbers and wavelengths. To remove the masking effect due to a few extremely significant frequencies and to highlight the relations between the frequencies, this matrix of F values was corrected by subtraction of a matrix of independence. The examination of the corrected data matrix allowed the assignment of the most important peaks for the discriminating criterion. This procedure also allows the study of vector profiles, where one spectral domain is examined in relation to a particular frequency in the other domain. The study of vector profiles is a very useful tool to see the relations between the wavenumbers and wavelengths of the two domains under study.

Firming of fruit tissues by vacuum-infusion of pectin methylesterase: Visualisation of enzyme action.

Apple pieces were vacuum-impregnated with either a pectin methylesterase (PME) and calcium solution or with water prior to pasteurization. Pasteurized apple pieces impregnated with PME and calcium showed a significantly higher firmness. Moreover, solid state (13)C NMR spectroscopy of apple cell wall residues revealed an increase of their molecular rigidity. Exogenous PME addition involved a decrease from 82% to 45% of apple pectin degree of methyl-esterification. Microscopic observations of apple slices immunolabelled with antibodies specific for pectins showed that (i) demethyl-esterification was more intense in the cell wall region lining intercellular spaces (demonstrating a key role for these intercellular channels in the enzyme penetration in the tissue during vacuum-infusion) and that (ii) the number of calcium-dimerized deesterified homogalacturonan chains increased. The results corroborate the hypothesis that vacuum-impregnated PME action liberates free carboxyl groups along pectin chains that could interact with calcium, increasing the rigidity of pectins and finally the mechanical rigidity of apple tissue.