Biomedical subjects

Jean-Pierre Dufour

Publications and source records attributed to Jean-Pierre Dufour.

9 recordsLinked to original sources

PubMed2006

Analysis of volatile compounds as spoilage indicators in fresh king salmon (Oncorhynchus tshawytscha) during storage using SPME-GC-MS.

A method was developed for the analysis of salmon volatiles using solid-phase microextraction and gas chromatography-mass spectrometry. This method was used to monitor the volatiles of fresh king salmon (Oncorhynchus tshawytscha) stored in ambient air or in a 40:60 (v/v) mixture of CO2:N2 over time. The levels of several of the volatile compounds were found to change during storage, with some showing a clear difference between storage in air and storage in CO2:N2. Of these, several alcohols (cyclopentanol, Z-2-penten-1-ol, 1-penten-3-ol, and 1-octen-3-ol) and aldehydes (hexanal, octanal, E-2-pentenal, and E-2-hexenal) were identified as potential markers for salmon freshness. Several other volatiles (acetoin, ethyl benzene, propyl benzene, styrene, 3-methyl butanoic acid, and acetic acid) were identified as potential markers for salmon spoilage. A comparison of salmon harvested with and without the "rested harvesting" technique showed that E- and Z-isoeugenol levels were increased by the use of the isoeugenol based anesthetic. The use of the anesthetic did not affect the levels of any of the other compounds identified.

Air↗

PubMed2006

The combination of gas chromatography-olfactometry and multidimensional gas chromatography for the characterisation of essential oils.

A research area of great interest to the flavour industry is the analysis of odour active compounds in essential oils. In this paper, a methodology is presented for the identification of character-impact odorants in essential oil samples using (a) gas chromatography-olfactometry (GC-O); (b) comprehensive two-dimensional gas chromatography (GC x GC) combined to time-of-flight mass spectrometry (TOFMS) and (c) heart-cut multidimensional gas chromatography-olfactometry (MDGC-O). The specific advantages and limitations of each technique are discussed. The advantage of combining these techniques in a strategy to identify character-impact odorants is demonstrated using examples from coriander leaf (Coriandrum sativum) and hop (Humulus lupulus) essential oils. In particular, resolution of co-eluting regions of compounds and evaluation of their individual odour activity is discussed. In coriander leaf, only E-2-dodecenal was found to contribute to a co-eluting odour region, E-2-dodecen-1-ol and 1-dodecanol being present below detection threshold. Using MDGC on a hop essential oil sample, eight significant peaks were resolved from an 18 s heart-cut where a potent odorant was perceived during GC-O.

Chromatography, Gas↗

PubMed2006

Gas chromatography-olfactometry.

GC-olfactometry (GC-O) refers to the use of human assessors as a sensitive and selective detector for odour-active compounds. The aim of this technique is to determine the odour activity of volatile compounds in a sample extract, and assign a relative importance to each compound. Methods can be classified into three types: detection frequency, dilution to threshold and direct intensity. Dilution to threshold methods measure the potency of odour-active compounds by using a series of extract dilutions, whereas detection frequency and direct-intensity methods measure odour-active compound intensity, or relative importance, in a single concentrated extract. Factors that should be considered to improve the value of GC-O analysis are the extraction method, GC instrument conditions, including the design and operation of the odour port, methods of recording GC-O data and controlling the potential for human assessor bias using experimental design and a trained panel. Considerable emphasis is placed on the requirement for multidimensional GC analysis, and on best practice when using human assessors.

Chromatography, Gas↗

PubMed2005

Identification of character-impact odorants in coriander and wild coriander leaves using gas chromatography-olfactometry (GCO) and comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry (GC x GC-TOFMS).

The essential oil of coriander leaves (Coriandrum sativum) and wild coriander leaves (Eryngium foetidum) grown in Fiji was obtained by steam distillation. The aroma profiles were characterised using gas chromatography-olfactometry (GCO) and CharmAnalysis. The character-impact odorants were identified using comprehensive two-dimensional gas chromatography (GC x GC) combined with time-of-flight mass spectrometry (TOFMS). During GCO analysis, the co-elution of E-2-alkenals and E-2-alken-1-ols resulted in the perception of 'odour-clusters'. The most important odorants in C. sativum were found to be Z-2-decenal, a co-eluting odour-cluster (E-2-dodecenal, E-2-dodecen-1-ol, and 1-dodecanol), beta-ionone, eugenol, and E-2-decenal. E-2-decen-1-ol was the most abundant compound in C. sativum (26.0% TIC) but only contributed 0.39% of the total odour activity. The most abundant compound in E. foetidum was E-2-dodecenal (63.5% TIC), which also contributed the most odour activity (52.9%). Other important odorants were either eugenol or a trimethylbenzaldehyde isomer, beta-ionone, Z-4-dodecenal, dodecanal, and E-2-tetradecenal. GC x GC-TOFMS allowed the identification of 42 and 20 compounds not previously reported in the literature for C. sativum and E. foetidum, respectively. In particular, beta-ionone was determined to be an important odorant in both samples but could not be identified with GC-qMS.

Chromatography, Gas↗

PubMed2004

Application of comprehensive multidimensional gas chromatography combined with time-of-flight mass spectrometry (GC x GC-TOFMS) for high resolution analysis of hop essential oil.

The selection and quality of hops is a major determinant in beer flavour. Brewers acknowledge that distinctive characteristics of different hop varieties can be traced to the composition of their essential oils. The difficulty in characterising complex mixtures such as hop oil using 1-D chromatography is that many compounds co-elute. With the introduction of comprehensive multidimensional capillary gas chromatography (GC x GC), there is a tremendous improvement in the separation power or peak capacity. Recent work using GC x GC with flame ionisation detection has suggested that there may be over 1,000 compounds in hop oil. This work describes the use of GC x GC combined with TOFMS detection (Leco Pegasus 4D instrument) to analyse Target hop oil. The TOFMS spectral acquisition rate of 60 Hz provided sufficient spectra per peak (2-D peak base width of 0.1-0.2 s) for identification (119 components were identified with 45 previously unreported compounds). When analysing results, an advantage of GC x GC coupled to TOFMS is that 2-D chromatograms can be viewed for individual masses that are characteristic of particular functional groups. This allows the analyst to view the various homologous series of compounds although in certain cases coelution may still be present as shown by the esters with mass 75.

Journal Article↗

PubMed2004

The Saccharomyces cerevisiae alcohol acetyl transferase Atf1p is localized in lipid particles.

The yeast alcohol acetyl transferase I, Atf1p, is responsible for the major part of volatile acetate ester production in fermenting Saccharomyces cerevisiae cells. Some of these esters, such as ethyl acetate and isoamyl acetate, are important for the fruity flavours of wine, beer and other fermented beverages. In order to reveal the subcellular localization of Atf1p and further unravel the possible physiological role of this protein, ATF1::GFP fusion constructs were overexpressed in brewer's yeast. The transformant strain showed a significant increase in acetate ester formation, similar to that of an ATF1 overexpression strain, indicating that the Atf1p-GFP fusion protein was active. UV fluorescence microscopy revealed that the fusion protein was localized in small, sphere-like organelles. These organelles could be selectively stained by the fluorescent dye Nile red, indicating that they contained high amounts of neutral lipids and/or sterols, a specific characteristic of yeast lipid particles. Purification of lipid particles from wild type and ATF1 deletion cells confirmed that the Atf1p-GFP fusion protein was located in these organelles. Furthermore, a clear alcohol acetyl transferase activity could be measured in the purified lipid particles of both wild type and transformed cells. The localization of Atf1p in lipid particles may indicate that Atf1p has a specific role in the lipid and/or sterol metabolism that takes place in these particles.

Acetyltransferases↗

PubMed2003

Retention time reproducibility in comprehensive two-dimensional gas chromatography using cryogenic modulation. II. An interlaboratory study.

An interlaboratory survey was conducted to determine the reproducibility of retention times in both the first (1D) and second dimension (2D) axes of the two-dimensional separation space, using the longitudinal cryogenic modulation comprehensive two-dimensional gas chromatographic approach. Intralaboratory reproducibility has been demonstrated in part 1 of this investigation [J. Chromatogr. A 968 (2002) 161]. Confidence in absolute retention times (hence component positions) in the two-dimensional separation space is critical to component identification. Comparing data from four independent laboratories, five independent gas chromatographs, five independent LMCS units, and numerous operators has determined that the LMCS cryogenic modulation approach provides reliable comprehensive two-dimensional GC results.

Chromatography, Gas↗

PubMed2003

Expression levels of the yeast alcohol acetyltransferase genes ATF1, Lg-ATF1, and ATF2 control the formation of a broad range of volatile esters.

Volatile aroma-active esters are responsible for the fruity character of fermented alcoholic beverages such as beer and wine. Esters are produced by fermenting yeast cells in an enzyme-catalyzed intracellular reaction. In order to investigate and compare the roles of the known Saccharomyces cerevisiae alcohol acetyltransferases, Atf1p, Atf2p and Lg-Atf1p, in volatile ester production, the respective genes were either deleted or overexpressed in a laboratory strain and a commercial brewing strain. Subsequently, the ester formation of the transformants was monitored by headspace gas chromatography and gas chromatography combined with mass spectroscopy (GC-MS). Analysis of the fermentation products confirmed that the expression levels of ATF1 and ATF2 greatly affect the production of ethyl acetate and isoamyl acetate. GC-MS analysis revealed that Atf1p and Atf2p are also responsible for the formation of a broad range of less volatile esters, such as propyl acetate, isobutyl acetate, pentyl acetate, hexyl acetate, heptyl acetate, octyl acetate, and phenyl ethyl acetate. With respect to the esters analyzed in this study, Atf2p seemed to play only a minor role compared to Atf1p. The atf1Delta atf2Delta double deletion strain did not form any isoamyl acetate, showing that together, Atf1p and Atf2p are responsible for the total cellular isoamyl alcohol acetyltransferase activity. However, the double deletion strain still produced considerable amounts of certain other esters, such as ethyl acetate (50% of the wild-type strain), propyl acetate (50%), and isobutyl acetate (40%), which provides evidence for the existence of additional, as-yet-unknown ester synthases in the yeast proteome. Interestingly, overexpression of different alleles of ATF1 and ATF2 led to different ester production rates, indicating that differences in the aroma profiles of yeast strains may be partially due to mutations in their ATF genes.

Acetyltransferases↗

PubMed2003

Flavor-active esters: adding fruitiness to beer.

As they are responsible for the fruity character of fermented beverages, volatile esters constitute an important group of aromatic compounds in beer. In modern high-gravity fermentations, which are performed in tall cylindroconical vessels, the beer ester balance is often sub-optimal, resulting in a clear decrease in beer quality. Despite the intensive research aimed at unravelling the precise mechanism and regulation of ester synthesis, our current knowledge remains far from complete. However, a number of factors that influence flavor-active ester production have already been described, including wort composition, wort aeration and fermentor design. A thoughtful adaptation of these parameters allows brewers to steer ester concentrations and thus to control the fruity character of their beers. This paper reviews the current knowledge of the biochemistry behind yeast ester synthesis and discusses the different factors that allow ester formation to be controlled during brewery fermentation.

Journal Article↗