PCA: The Basic Building Block of Chemometrics

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3D Fluorescence Spectroscopy and its Applications

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3D-front-face fluorescence spectroscopy and independent components analysis: a new way to monitor bread dough development

Following bread dough development can be a hard task as no reliable method exists to give the optimal mixing time. Dough development is linked to the evolution of gluten proteins, carbohydrates and lipids which can result in modifications in the spectral properties of the various fluorophores naturally present in the system. In this paper, we propose to use 3-D-front-face-fluorescence (3D-FFF) spectroscopy in the 250-550 nm domain to follow the dough development as influenced by formulation (addition or not of glucose, glucose oxidase and ferulic acid in the dough recipe) and mixing time (2, 4, 6 and 8 min). In all the 32 dough samples as well as in flour, three regions of maximum fluorescence intensities have been observed at 320 nm after excitation at 295 nm (Region 1), at 420 nm after excitation at 360 nm (Region 2) and 450 nm after excitation at 390 nm (Region 3). The principal components analysis (PCA) of the evolution of these maxima shows that the formulations with and without ferulic acid are clearly separated since the presence of ferulic acid induces a decrease of fluorescence in Region I and an increase in Regions 2 and 3. In addition, a kinetic effect of the mixing time can be observed (decrease of fluorescence in the Regions 1 and 2) mainly in the absence of ferulic acid. The analysis of variance (ANOVA) on these maximum values statistically confirms these observations. Independent components analysis (ICA) is also applied to the complete 3-D-FFF spectra in order to extract interpretable signals from spectral data which reflect the complex contribution of several fluorophores as influenced by their environment. In all cases, 3 signals can be clearly separated matching the 3 regions of maximal fluorescence. The signals corresponding to regions 1 and 2 can be ascribed to proteins and ferulic acid respectively, whereas the fluorophores associated with the 3rd signal (corresponding to region 3) remain unidentified. Good correlations are obtained between the IC score values of the 3 signals and the fluorescence intensities in Region 1, Region 2 and Region 3. Ferulic acid addition increases fluorescence in Region 2 and decreases fluorescence in Region 1, probably via a reabsorption of the protein fluorescence by ferulic acid. These phenomena are less pronounced when glucose oxidase is present. The enzymatic oxidation of ferulic acid by the glucose oxidase-peroxidase association could explain some of these effects

The Guyana and the West-African shield paleoproterozoic groupin : new paleomagnetic data from French Guyana and the Ivory-Coast.

International audienceThe aim of this study is to document the Palaeoproterozoic palaeomagnetic database for the Guiana and West African Shields in order to better understand the paleogeographic evolution of these two cratons. A total of 59 sites were sampled (33 in French Guiana and 26 in the Ivory Coast) in granites and metavolcanic rocks. Magnetic, petrographic and palaeomagnetic investigations were carried out on these rocks. Magnetic experiments and petrographic observations show that undeformed magnetite is the main magnetic remanent carrier in granites of French Guiana and both magnetite and haematite in rocks from the Ivory Coast. Both thermal and magnetic alternating-field demagnetizations were applied to the rocks. Four high-temperature magnetic remanent directions were isolated in French Guiana and the Ivory Coast. These directions are distinct from the present Earth's field and to the local Early Jurassic palaeomagnetic components. Reversal and contact tests were obtained for the collection from French Guiana. Based on these arguments and mineralogical investigations, we propose that the magnetic remanence represent a Palaeoproterozoic magnetization. Four virtual palaeomagnetic poles were calculated: GUI1, GUI2 for French Guiana; IC1 and IC2 for the Ivory Coast with their corresponding coordinates: GUI1: GUI1=-62°N, GUI1= 61°E, k= 18, A95= 10°, N= 15 ; GUI2: GUI2=-5°N, GUI2= 50°E, k= 26, A95= 18°, N= 5 ; IC1: IC1=-82°N, IC1= 292°N, k= 28, A95= 13°, N= 6 ; IC2: IC2=-25°N, IC2= 83°E, k= 11, A95= 16°, N= 9 . The magnetization age ranged from 2.04 to 1.97 Ga for the French Guiana poles (40Ar/39Ar) and between 2.10 to 2.00 Ga for the Ivory Coast poles (startigraphic ages). Combining these new palaeomagnetic poles and previously published data, two apparent polar wander paths were proposed for these two shields. The comparison of these two Palaeoproterozoic paths seems to indicate that the two cratons belonged to the same block at about 2.00 Ga but separated prior to 2.02 Ga. Although this hypothesis is supported by geological and tectonic observations in both shields, further palaeomagnetic, geochronological and petrographic constraints are needs between 2.04 and 2.10 Ga

An overview of recent developments in volatile compounds analysis from edible oils: Technique-oriented perspectives

International audienceThe analysis of the volatile compounds from edible oils is a tool used for the evaluation of aroma compounds, the quantitative determination of contaminants or the study of oil degradation and represents a major analytical challenge. This review deals with the recent evolution of methods for vapor phase sampling of the headspace of edible oils combined with gas chromatography. Non-selective sampling methods, such as static headspace (SHS), sampling techniques with adsorbents, including direct thermal desorption (DTD) and dynamic headspace (DHS), and high concentration capacity headspace techniques (HCC-HS), as headspace solid phase microextraction (HS-SPME) and headspace sorptive extraction (HSSE), are presented. Advantages, drawbacks, and applications to edible oils are critically discussed. HS-SPME is shown to be the most popular technique for the volatile fraction sampling of edible oils. Finally, other promising in-tube sorptive extraction techniques that are not yet applied to edible oils are also described.Practical applications: The analysis of the volatile compounds from edible oils is a major analytical challenge and is applied in many fields. An overview of different sampling techniques with a critical point of view can be useful to determine the best technique to apply in a specific context.The composition of the headspace of edible oils can provide different information related to the evaluation of aroma compounds, the quantitative determination of contaminants, or the study of oil degradation. Several techniques can be considered to respond to this challenge with different advantages and drawbacks, such as static headspace, solid phase microextraction, dynamic headspace, or headspace sorptive extraction

Comprehensive two-dimensional gas chromatography for analysis of the volatile compounds and fishy odor off-flavors from heated rapeseed oil

International audienceLipid oxidation leads to the formation of volatile compounds involved in the aroma of edible oils. Specifically, the use of rapeseed oil for frying causes an emission of off-flavors, characterized by a fishy odor. The aim of the present study was to identify the compounds present in the headspace of degraded rapeseed oil, and in particular, to determine the presence of six compounds commonly considered as responsible for the fishy odor: 1-penten-3-one, 1-octen-3-one, (Z)-4-heptenal, (E,Z)-2,6-nonadienal, (E,Z)-2,4-heptadienal, and (E,Z,Z)-2,4,7-decatrienal. Because of the complexity of the headspace of degraded oils, comprehensive two-dimensional gas chromatography (GC × GC) coupled to mass spectrometry (MS) was the technique of choice, providing a suitable separation power and sensitivity. The extraction of volatile compounds was performed by headspace solid-phase microextraction (HS-SPME). First, three different column sets were evaluated (apolar–polar, polar–apolar, apolar–medium polar) by means of a mixture of 33 standards representative of those involved in the aroma of edible oils. The apolar–polar column set was considered as providing a satisfactory separation with an excellent occupation of the separation space. The developed method was then applied to a real sample of heated rapeseed oil and 110 compounds were identified, which included the six compounds of interest. The contribution of GC × GC in terms sensitivity was evaluated by means of a comparison with analyses in 1D-GC. Finally, the concentrations of the compounds involved in the fishy odor in heated oil were determined

Effect of ammonia exposure and acclimation on the performance and the microbiome of anaerobic digestion

International audienceThis is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain

Investigation of the effect of magnesium on the microstructure and mechanical properties of NiTi shape memory alloy prepared by self-propagating high-temperature synthesis

This work aims to describe the effect of magnesium on the microstructure, phase composition, amount of undesirable Ti2Ni phase, martensitic transformation, mechanical properties, and corrosion resistance of NiTi alloy. To minimize the quantity of Ti2Ni phase, we use the magnesium as an element with high affinity to oxygen, because this phase is stabilized by oxygen. Various quantities of magnesium (1, 3, and 5 wt pct) were tested. Self-propagating high-temperature synthesis (SHS) was used as a production method of the alloys. The samples prepared by SHS were pulverized by a vibrating mill, and the obtained powders were used for consolidation by means of spark plasma sintering. Results showed a significant reduction of the content of undesirable Ti2Ni phase by the addition of magnesium. Further, magnesium increased corrosion resistance and yield strength