The Experts below are selected from a list of 327 Experts worldwide ranked by ideXlab platform
D. Chassagne - One of the best experts on this subject based on the ideXlab platform.
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Influence of the drying processes of yeasts on their volatile phenol sorption capacity in model wine.
International Journal of Food Microbiology, 2009Co-Authors: R. Pradelles, Susanna Vichi, H. Alexandre, D. ChassagneAbstract:Volatile phenols, such as 4-Ethylphenol, are responsible for a "horsey" smell in wine. Thus, the study of volatile phenol sorption in yeasts, and their subsequent elimination from wine, helps to optimize eco-friendly wine curative processes. Here, we compared the influences of spray drying, lyophilization and evaporative drying at low water activity on yeast, for improving the 4-Ethylphenol sorption capacity in a synthetic model wine. The changes that occur in the physico-chemical characteristics of the yeast surface (surface hydrophobicity, electron-donor character and zeta potential) during these drying processes were determined to assess if any correlation exists between these factors and the 4-Ethylphenol sorption capacities of the cells. Evaporative drying at low water activity, spray drying and lyophilization induced, respectively, 61.5%, 169% and 192% greater 4-Ethylphenol sorption than biomass without drying treatment. Surface hydrophobicity of yeasts was also significantly greater, but the zeta potential of yeast cells was significantly lower after the drying processes. This is the first report investigating changes to the physico-chemical variables affected during yeast drying. These cell surface modifications were correlated with the 4-ethyphenol sorption value measured.
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Influence of the drying processes of yeasts on their volatile phenol sorption capacity in model wine
International Journal of Food Microbiology, 2009Co-Authors: R. Pradelles, Susanna Vichi, H. Alexandre, D. ChassagneAbstract:Volatile phenols, such as 4-Ethylphenol, are responsible for a "horsey" smell in wine. Thus, the study of volatile phenol sorption in yeasts, and their subsequent elimination from wine, helps to optimize eco-friendly wine curative processes. Here, we compared the influences of spray drying, lyophilization and evaporative drying at low water activity on yeast, for improving the 4-Ethylphenol sorption capacity in a synthetic model wine. The changes that occur in the physico-chemical characteristics of the yeast surface (surface hydrophobicity, electron-donor character and zeta potential) during these drying processes were determined to assess if any correlation exists between these factors and the 4-Ethylphenol sorption capacities of the cells. Evaporative drying at low water activity, spray drying and lyophilization induced, respectively, 61.5%, 169% and 192% greater 4-Ethylphenol sorption than biomass without drying treatment. Surface hydrophobicity of yeasts was also significantly greater, but the zeta potential of yeast cells was significantly lower after the drying processes. This is the first report investigating changes to the physico-chemical variables affected during yeast drying. These cell surface modifications were correlated with the 4-ethyphenol sorption value measured. © 2009 Elsevier B.V. All rights reserved.
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Effects of yeast cell-wall characteristics on 4-Ethylphenol sorption capacity in model wine.
Journal of Agricultural and Food Chemistry, 2008Co-Authors: R. Pradelles, Hervé Alexandre, Anne Ortiz-julien, D. ChassagneAbstract:Saccharomyces cerevisiae is an efficient biosorbant, used in winemaking to reduce the concentration of undesirable molecules such as fatty acids. Volatile phenols such as 4-Ethylphenol, which causes a horsy smell in wine, are particular targets of this type of curative process. This study demonstrates that the sorption capacity of 4-Ethylphenol by yeasts is greatly influenced by strain nature, methods, and medium used for biomass production and drying after harvesting. S. cerevisiae mutant strains with deletion of genes encoding specific proteins involved in cell-wall structure and composition were studied, and a major role for mannoproteins in 4-Ethylphenol sorption was identified. It was confirmed that 4-Ethylphenol sorption occurs at the surface of the yeast wall and that not all mannoproteins are determinants of sorption: the sorption capacity of cells with deletion of the Gas1p-encoding gene was 75% lower than that of wild type. Physicochemical properties of yeast cell surface have been also studied.
Eduardo Dellacassa - One of the best experts on this subject based on the ideXlab platform.
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determination of volatile phenols in red wines by dispersive liquid liquid microextraction and gas chromatography mass spectrometry detection
Journal of Chromatography A, 2007Co-Authors: Laura Farina, Eduardo Boido, Francisco Carrau, Eduardo DellacassaAbstract:Abstract A new method was developed for analysing 4-ethylguaiacol and 4-Ethylphenol in the aroma of red wines using dispersive liquid–liquid microextraction (DLLME) coupled with gas chromatography–mass spectrometry detection (GC–MS). Parameters such as extraction solvent, sample volume and disperser solvent were studied and optimised to obtain the best extraction results with the minimum interference from other substances, thus giving clean chromatograms. The response linearity was studied in the usual concentration ranges of analytes in wines (50–1500 μg/L). Repeatability and reproducibility of this method were lower than 5% for both volatile phenols. Limits of detection and limits of quantification were also determined, and the values found were 28 and 95 μg/L for 4-ethylguaiacol and 44 and 147 μg/L for 4-Ethylphenol, respectively. This new method has been used for the determination of the volatile phenols concentration in different samples of Tannat wine affected by Brettanomyces contamination.
R. Pradelles - One of the best experts on this subject based on the ideXlab platform.
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Influence of the drying processes of yeasts on their volatile phenol sorption capacity in model wine.
International Journal of Food Microbiology, 2009Co-Authors: R. Pradelles, Susanna Vichi, H. Alexandre, D. ChassagneAbstract:Volatile phenols, such as 4-Ethylphenol, are responsible for a "horsey" smell in wine. Thus, the study of volatile phenol sorption in yeasts, and their subsequent elimination from wine, helps to optimize eco-friendly wine curative processes. Here, we compared the influences of spray drying, lyophilization and evaporative drying at low water activity on yeast, for improving the 4-Ethylphenol sorption capacity in a synthetic model wine. The changes that occur in the physico-chemical characteristics of the yeast surface (surface hydrophobicity, electron-donor character and zeta potential) during these drying processes were determined to assess if any correlation exists between these factors and the 4-Ethylphenol sorption capacities of the cells. Evaporative drying at low water activity, spray drying and lyophilization induced, respectively, 61.5%, 169% and 192% greater 4-Ethylphenol sorption than biomass without drying treatment. Surface hydrophobicity of yeasts was also significantly greater, but the zeta potential of yeast cells was significantly lower after the drying processes. This is the first report investigating changes to the physico-chemical variables affected during yeast drying. These cell surface modifications were correlated with the 4-ethyphenol sorption value measured.
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Influence of the drying processes of yeasts on their volatile phenol sorption capacity in model wine
International Journal of Food Microbiology, 2009Co-Authors: R. Pradelles, Susanna Vichi, H. Alexandre, D. ChassagneAbstract:Volatile phenols, such as 4-Ethylphenol, are responsible for a "horsey" smell in wine. Thus, the study of volatile phenol sorption in yeasts, and their subsequent elimination from wine, helps to optimize eco-friendly wine curative processes. Here, we compared the influences of spray drying, lyophilization and evaporative drying at low water activity on yeast, for improving the 4-Ethylphenol sorption capacity in a synthetic model wine. The changes that occur in the physico-chemical characteristics of the yeast surface (surface hydrophobicity, electron-donor character and zeta potential) during these drying processes were determined to assess if any correlation exists between these factors and the 4-Ethylphenol sorption capacities of the cells. Evaporative drying at low water activity, spray drying and lyophilization induced, respectively, 61.5%, 169% and 192% greater 4-Ethylphenol sorption than biomass without drying treatment. Surface hydrophobicity of yeasts was also significantly greater, but the zeta potential of yeast cells was significantly lower after the drying processes. This is the first report investigating changes to the physico-chemical variables affected during yeast drying. These cell surface modifications were correlated with the 4-ethyphenol sorption value measured. © 2009 Elsevier B.V. All rights reserved.
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Effects of yeast cell-wall characteristics on 4-Ethylphenol sorption capacity in model wine.
Journal of Agricultural and Food Chemistry, 2008Co-Authors: R. Pradelles, Hervé Alexandre, Anne Ortiz-julien, D. ChassagneAbstract:Saccharomyces cerevisiae is an efficient biosorbant, used in winemaking to reduce the concentration of undesirable molecules such as fatty acids. Volatile phenols such as 4-Ethylphenol, which causes a horsy smell in wine, are particular targets of this type of curative process. This study demonstrates that the sorption capacity of 4-Ethylphenol by yeasts is greatly influenced by strain nature, methods, and medium used for biomass production and drying after harvesting. S. cerevisiae mutant strains with deletion of genes encoding specific proteins involved in cell-wall structure and composition were studied, and a major role for mannoproteins in 4-Ethylphenol sorption was identified. It was confirmed that 4-Ethylphenol sorption occurs at the surface of the yeast wall and that not all mannoproteins are determinants of sorption: the sorption capacity of cells with deletion of the Gas1p-encoding gene was 75% lower than that of wild type. Physicochemical properties of yeast cell surface have been also studied.
Bruce C. Gates - One of the best experts on this subject based on the ideXlab platform.
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Conversion of 4-Methylanisole Catalyzed by Pt/γ-Al_2O_3 and by Pt/SiO_2-Al_2O_3: Reaction Networks and Evidence of Oxygen Removal
Catalysis Letters, 2012Co-Authors: Ron C. Runnebaum, Tarit Nimmanwudipong, Ryan R. Limbo, David E. Block, Bruce C. GatesAbstract:The conversion of 4-methylanisole, a prototypical bio-oil compound, was catalyzed by Pt/Al_2O_3, Pt/SiO_2-Al_2O_3, or HY zeolite at 573 K and atmospheric pressure. More than a dozen products were formed with each catalyst, the most abundant being 4-methylphenol, 2,4-dimethylphenol, and 2,4,6-trimethylphenol; toluene was also a major product when the catalyst was supported platinum with H_2 as a co-reactant. 4-Methylphenol was the only methylphenol isomer formed in significant yields, which indicates that migration of the methyl group on the aromatic ring is not significant under the selected reaction conditions. The data determine approximate reaction networks including reactions forming 4-methylphenol, 2,4-dimethylphenol, and toluene as primary products. The kinetically significant reaction classes were transalkylation, observed with all three catalysts, and hydrogenolysis (including hydrodeoxygenation) and hydrogenation, observed only with the platinum-containing catalysts operating in the presence of H_2. Data such as those reported here provide a starting point for predicting the conversion of whole bio-oils for removal of oxygen and upgrading of fuel properties. Graphical Abstract
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Conversion of 4-Methylanisole Catalyzed by Pt/γ-Al2O3 and by Pt/SiO2-Al2O3: Reaction Networks and Evidence of Oxygen Removal
Catalysis Letters, 2011Co-Authors: Ron C. Runnebaum, Tarit Nimmanwudipong, Ryan R. Limbo, David E. Block, Bruce C. GatesAbstract:The conversion of 4-methylanisole, a prototyp- ical bio-oil compound, was catalyzed by Pt/Al2O3, Pt/SiO2- Al2O3, or HY zeolite at 573 K and atmospheric pressure. More than a dozen products were formed with each catalyst, the most abundant being 4-methylphenol, 2,4-dimethyl- phenol, and 2,4,6-trimethylphenol; toluene was also a major product when the catalyst was supported platinum with H2 as a co-reactant. 4-Methylphenol was the only methylphenol isomer formed in significant yields, which indicates that migration of the methyl group on the aromatic ring is not significant under the selected reaction conditions. The data determine approximate reaction networks including reac- tions forming 4-methylphenol, 2,4-dimethylphenol, and toluene as primary products. The kinetically significant reaction classes were transalkylation, observed with all three catalysts, and hydrogenolysis (including hydrodeoxygen- ation) and hydrogenation, observed only with the platinum- containing catalysts operating in the presence of H2. Data such as those reported here provide a starting point for pre- dicting the conversion of whole bio-oils for removal of oxygen and upgrading of fuel properties.
Willem J. H. Van Berkel - One of the best experts on this subject based on the ideXlab platform.
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Multigram Scale Enzymatic Synthesis of (R)‐1‐(4′‐Hydroxyphenyl)ethanol Using Vanillyl Alcohol Oxidase
Advanced Synthesis & Catalysis, 2018Co-Authors: Tom A. Ewing, Jasmin Kühn, Silvia Segarra, Marta Tortajada, Ralf Zuhse, Willem J. H. Van BerkelAbstract:The enantioselective oxyfunctionalisation of C−H bonds is a highly interesting reaction, as it provides access to chiral alcohols that are important pharmaceutical building blocks. However, it is hard to achieve using traditional methods. One way in which it can be achieved is through the action of oxidative enzymes. Although many reports of the oxyfunctionalisation capabilities of enzymes at an analytical scale have been published, reports on the use of enzymes to achieve oxyfunctionalisation on a synthetically relevant scale are fewer. Here, we describe the scale-up of the conversion of 4-Ethylphenol to (R)-1-(4′-hydroxyphenyl)ethanol using the flavin-dependent enzyme vanillyl alcohol oxidase. The process was optimised by testing different reaction media and substrate and enzyme concentrations and by performing it under an oxygen atmosphere. Under optimised reaction conditions, 4.10 g (R)-1-(4′-hydroxyphenyl)ethanol at 97% ee was obtained from 10 g 4-Ethylphenol (isolated yield 36%). These results highlight some of the challenges that can be encountered during scale-up of an enzymatic oxyfunctionalisation process to a synthetically relevant scale and will be of use for the development of enzymatic processes for the synthesis of industrially relevant compounds. (Figure presented.).
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Inversion of stereospecificity of vanillyl-alcohol oxidase
Proceedings of the National Academy of Sciences of the United States of America, 2000Co-Authors: Robert H. H. Van Den Heuvel, Marco W. Fraaije, Miriam Ferrer, Andrea Mattevi, Willem J. H. Van BerkelAbstract:Vanillyl-alcohol oxidase (VAO) is the prototype of a newly recognized family of structurally related oxidoreductases sharing a conserved FAD-binding domain. The active site of VAO is formed by a cavity where the enzyme is able to catalyze many reactions with phenolic substrates. Among these reactions is the stereospecific hydroxylation of 4-Ethylphenol-forming (R)-1-(4′-hydroxyphenyl)ethanol. During this conversion, Asp-170 is probably critical for the hydration of the initially formed p-quinone methide intermediate. By site-directed mutagenesis, the putative active site base has been relocated to the opposite face of the active site cavity. In this way, a change in stereospecificity has been achieved. Like native VAO, the single mutants T457E, D170A, and D170S preferentially converted 4-Ethylphenol to the (R)-enantiomer of 1-(4′-hydroxyphenyl)ethanol. The double mutants D170A/T457E and D170S/T457E exhibited an inverted stereospecificity with 4-Ethylphenol. Particularly, D170S/T457E was strongly (S)-selective, with an enantiomeric excess of 80%. The crystal structure of D170S/T457E, in complex with trifluoromethylphenol, showed a highly conserved mode of ligand binding and revealed that the distinctive catalytic properties of this mutant are not caused by major structural changes.
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Enantioselective hydroxylation of 4‐alkylphenols by vanillyl alcohol oxidase
Biotechnology and Bioengineering, 1998Co-Authors: Falko P. Drijfhout, Marco W. Fraaije, Willem J. H. Van Berkel, Hugo Jongejan, Maurice C. R. FranssenAbstract:Vanillyl alcohol oxidase (VAO) from Penicillium simplicissimum catalyzes the enantioselective hydroxylation of 4-Ethylphenol, 4-propylphenol, and 2-methoxy-4-propylphenol into 1-(4'-hydroxyphenyl)ethanol, 1-(4'-hydroxyphenyl)propanol, and 1-(4'-hydroxy-3'-methoxyphenyl)propanol, respectively, with an ee of 94% for the R enantiomer. The stereochemical outcome of the reactions was established by comparing the chiral GC retention times of the products to those of chiral alcohols obtained by the action of the lipases from Candida antarctica and Pseudomonas cepacia. Isotope labeling experiments revealed that the oxygen atom incorporated into the alcoholic products is derived from water. During the VAO-mediated conversion of 4-Ethylphenol/4-propylphenol, 4-vinylphenol/4-propenylphenol are formed as side products. With 2-methoxy-4-propylphenol as a substrate, this competing side reaction is nearly abolished, resulting in less than 1% of the vinylic product, isoeugenol. The VAO-mediated conversion of 4-alkylphenols also results in small amounts of phenolic ketones indicative for a consecutive oxidation step.
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Kinetic mechanism of vanillyl‐alcohol oxidase with short‐chain 4‐alkylphenols
FEBS Journal, 1998Co-Authors: Marco W. Fraaije, Robert H. H. Van Den Heuvel, Jules C.a.a. Roelofs, Willem J. H. Van BerkelAbstract:The kinetic mechanism of vanillyl-alcohol oxidase with 4-methylphenol, 4-Ethylphenol, 4-propylphenol and their Cα-deuterated analogs has been studied at pH 7.5 and 25°C. Conversion of 4-methylphenol is extremely slow (0.005 s-1) while the enzyme is largely in the reduced form during turnover. 4-Ethylphenol and 4-propylphenol are readily converted while the enzyme is mainly in the oxidized form during turnover. The deuterium kinetic isotope effect for overall catalysis ranges between 7-10 whereas the intrinsic deuterium kinetic isotope effect for flavin reduction ranges over 9-10. With all three 4-alkylphenols, flavin reduction appeared to be a reversible process with the rate of reduction being in the same range as the rate for the reverse reaction. During the reductive half-reaction of vanillyl-alcohol oxidase with 4-Ethylphenol and 4-propylphenol, a transient intermediate is formed with an absorbance maximum at 330 nm. This intermediate has been tentatively identified as the p-quinone methide of the aromatic substrate in complex with reduced enzyme. It is concluded that vanillyl-alcohol oxidase catalysis with 4-Ethylphenol and 4-propylphenol favors an ordered sequential binding mechanism in which the rate of flavin reduction determines the turnover rate while the reduced enzyme-p-quinone methide binary complex rapidly reacts with dioxygen. During the reaction of vanillyl-alcohol oxidase with 4-methylphenol, a fluorescent enzyme species is stabilized. Based on its spectal characteristics and crystallographic data, it is proposed that this species represents a covalent 5-(4'-hydroxybenzyl)-FAD adduct. With 4-Ethylphenol and 4-propylphenol, similar N5 flavin adducts may be formed but their rate of formation is too slow to be of catalytic relevance.
