The Experts below are selected from a list of 1266 Experts worldwide ranked by ideXlab platform
Richard H Stadler - One of the best experts on this subject based on the ideXlab platform.
-
D of chlormequat and Mepiquat in pear, tomato, and wheat flour using on-line solid-phase extraction (Prospekt) coupled with liquid chromatography-electrospray ionization tandem
2020Co-Authors: Sonja Riediker, Heinrich Obrist, Natalia Varga, Richard H StadlerAbstract:AbstractA sensitive and selective method is presented for the simultaneous analysis of the pesticides chlormequat and Mepiquat attrace levels in tomato, pear, and wheat flour. The method entails direct injection of the food extract onto an on-linesolid-phase extraction (SPE) instrument (Prospekt) using a strong cation-exchange resin. Analyte separation and detection isdone by liquid chromatography–electrospray ionization tandem mass spectrometry (LC–ESI-MS–MS). Surrogate standards(d 96 -chlormequat,d -Mepiquat) are employed to compensate for recovery losses and potential MS–MS signal suppression.The method achieves a limit of quantification for both cationic analytes at or below 5 mg/kg, and good intra- and inter-assayprecision with mean variability values ,7% over a concentration range up to 195 mg/kg. This study also addresses potentialanalyte carry-over in an SPE on-line system, as well as the robustness of the procedure and its applicability in routine qualitycontrol operations.2002 Elsevier Science B.V. All rights reserved.Keywords: Food analysis; Solid-phase extraction; Pesticides; Chlormequat; Mepiquat
-
heat induced formation of Mepiquat by decarboxylation of pipecolic acid and its betaine derivative part 2 natural formation in cooked vegetables and selected food products
Food Chemistry, 2017Co-Authors: Yuan Yuan, Adrienne Tarres, Thomas Bessaire, Wilhelm Rademacher, Richard H Stadler, Thierry DelatourAbstract:Abstract Mepiquat (N,N-dimethylpiperidinium) is a plant growth regulator registered for use as its chloride salt in many countries on cereals and other crops. Recent model system studies have shown that natural chemicals present in crop plants, such as pipecolic acid and pipecolic acid betaine, may furnish Mepiquat through different chemical pathways, when subjected to temperatures in the range of 200 °C. In this study, we cooked raw vegetables that did not contain Mepiquat to a palatable state using different traditional cooking methods, and detected Mepiquat in 9 out of 11 oven-cooked vegetables, reaching up to 189 μg/kg dry wt in oven-cooked broccoli. Commercial oven potato fries generated Mepiquat during cooking, typically in the range of 20–60 μg/kg. Only traces of Mepiquat (
-
heat induced formation of Mepiquat by decarboxylation of pipecolic acid and its betaine derivative part 1 model system studies
Food Chemistry, 2017Co-Authors: Yuan Yuan, Adrienne Tarres, Thomas Bessaire, Richard H Stadler, Thierry DelatourAbstract:Abstract This study describes, for the first time, the role of pipecolic acid betaine and pipecolic acid, naturally present in some foods, in the formation of the plant growth regulator N,N-dimethylpiperidinium (Mepiquat) under dry thermal conditions. The formation of Mepiquat and intermediate compounds was investigated in model systems using high performance liquid chromatography-quadrupole/time-of-flight mass spectrometry. Mepiquat is released with a yield of up to 0.66 mol% after thermal treatment (>150 °C) of pipecolic acid betaine. Similar conversion rates are attained with the congener piperidine-2-carboxylic acid ( dl -pipecolic acid), albeit in the presence of alkylating agents, such as choline, glycine betaine or trigonelline, that are fairly widespread in food crops. These new pathways to Mepiquat indicate that the occurrence of low levels of this thermally induced compound is probably more widespread in processed foods than initially suspected (see Part 2 of this study on the occurrence of Mepiquat in selected foodstuffs).
-
Mepiquat a process induced byproduct in roasted cereal based foodstuffs
Journal of Agricultural and Food Chemistry, 2016Co-Authors: Thomas Bessaire, Adrienne Tarres, Richard H Stadler, Silke Wermann, Viviane Theurillat, Jocelyne Hofmann, Raphael Combremont, Thierry DelatourAbstract:Mepiquat, a growth regulator widely used in agriculture, is also known as a process-induced byproduct formed in coffee from natural constituents during heat treatments such as roasting. This study examines Mepiquat formation in cereal-based foodstuffs treated at sufficiently high temperature to trigger methyl transfer reactions that involve glycine betaine and choline naturally present in cereals. Color measurements of roasted barley grains revealed a correlation between thermal treatment and Mepiquat content. Trials at industrial scale on instant beverages composed of roasted cereals demonstrated significant increases in Mepiquat during the thermal process (in the range of 140–205 μg/kg in final products). A targeted survey of commercial products showed Mepiquat in the range 69–381 μg/kg in powdered cereal instant drinks and 42–168 μg/kg in mugicha tea, a roasted barley infusion. These findings will not significantly affect the exposure of consumers to Mepiquat due to the low amounts detected.
-
role of choline and glycine betaine in the formation of n n dimethylpiperidinium Mepiquat under maillard reaction conditions
Food Additives and Contaminants Part A-chemistry Analysis Control Exposure & Risk Assessment, 2014Co-Authors: Thomas Bessaire, Adrienne Tarres, Richard H Stadler, Thierry DelatourAbstract:This study is the first to examine the role of choline and glycine betaine, naturally present in some foods, in particular in cereal grains, to generate N,N-dimethylpiperidinium (Mepiquat) under Maillard conditions via transmethylation reactions involving the nucleophile piperidine. The formation of Mepiquat and its intermediates piperidine – formed by cyclisation of free lysine in the presence of reducing sugars – and N-methylpiperidine were monitored over time (240°C, up to 180 min) using high-resolution mass spectrometry in a model system comprised of a ternary mixture of lysine/fructose/alkylating agent (choline or betaine). The reaction yield was compared with data recently determined for trigonelline, a known methylation agent present naturally in coffee beans. The role of choline and glycine betaine in nucleophilic displacement reactions was further supported by experiments carried out with stable isotope-labelled precursors (13C- and deuterium-labelled). The results unequivocally demonstrated that...
Sonja Riediker - One of the best experts on this subject based on the ideXlab platform.
-
D of chlormequat and Mepiquat in pear, tomato, and wheat flour using on-line solid-phase extraction (Prospekt) coupled with liquid chromatography-electrospray ionization tandem
2020Co-Authors: Sonja Riediker, Heinrich Obrist, Natalia Varga, Richard H StadlerAbstract:AbstractA sensitive and selective method is presented for the simultaneous analysis of the pesticides chlormequat and Mepiquat attrace levels in tomato, pear, and wheat flour. The method entails direct injection of the food extract onto an on-linesolid-phase extraction (SPE) instrument (Prospekt) using a strong cation-exchange resin. Analyte separation and detection isdone by liquid chromatography–electrospray ionization tandem mass spectrometry (LC–ESI-MS–MS). Surrogate standards(d 96 -chlormequat,d -Mepiquat) are employed to compensate for recovery losses and potential MS–MS signal suppression.The method achieves a limit of quantification for both cationic analytes at or below 5 mg/kg, and good intra- and inter-assayprecision with mean variability values ,7% over a concentration range up to 195 mg/kg. This study also addresses potentialanalyte carry-over in an SPE on-line system, as well as the robustness of the procedure and its applicability in routine qualitycontrol operations.2002 Elsevier Science B.V. All rights reserved.Keywords: Food analysis; Solid-phase extraction; Pesticides; Chlormequat; Mepiquat
-
Determination of chlormequat and Mepiquat in pear, tomato, and wheat flour using on-line solid-phase extraction (Prospekt) coupled with liquid chromatography-electrospray ionization tandem mass spectrometry.
Journal of chromatography. A, 2002Co-Authors: Sonja Riediker, Heinrich Obrist, Natalia Varga, Richard H StadlerAbstract:A sensitive and selective method is presented for the simultaneous analysis of the pesticides chlormequat and Mepiquat at trace levels in tomato, pear, and wheat flour. The method entails direct injection of the food extract onto an on-line solid-phase extraction (SPE) instrument (Prospekt) using a strong cation-exchange resin. Analyte separation and detection is done by liquid chromatography-electrospray ionization tandem mass spectrometry (LC-ESI-MS-MS). Surrogate standards (d9-chlormequat, d6-Mepiquat) are employed to compensate for recovery losses and potential MS-MS signal suppression. The method achieves a limit of quantification for both cationic analytes at or below 5 microg/kg, and good intra- and inter-assay precision with mean variability values
-
determination of chlormequat and Mepiquat in pear tomato and wheat flour using on line solid phase extraction prospekt coupled with liquid chromatography electrospray ionization tandem mass spectrometry
Journal of Chromatography A, 2002Co-Authors: Sonja Riediker, Heinrich Obrist, Natalia Varga, Richard H StadlerAbstract:A sensitive and selective method is presented for the simultaneous analysis of the pesticides chlormequat and Mepiquat at trace levels in tomato, pear, and wheat flour. The method entails direct injection of the food extract onto an on-line solid-phase extraction (SPE) instrument (Prospekt) using a strong cation-exchange resin. Analyte separation and detection is done by liquid chromatography–electrospray ionization tandem mass spectrometry (LC–ESI-MS–MS). Surrogate standards (d9-chlormequat, d6-Mepiquat) are employed to compensate for recovery losses and potential MS–MS signal suppression. The method achieves a limit of quantification for both cationic analytes at or below 5 μg/kg, and good intra- and inter-assay precision with mean variability values <7% over a concentration range up to 195 μg/kg. This study also addresses potential analyte carry-over in an SPE on-line system, as well as the robustness of the procedure and its applicability in routine quality control operations.
Thierry Delatour - One of the best experts on this subject based on the ideXlab platform.
-
heat induced formation of Mepiquat by decarboxylation of pipecolic acid and its betaine derivative part 2 natural formation in cooked vegetables and selected food products
Food Chemistry, 2017Co-Authors: Yuan Yuan, Adrienne Tarres, Thomas Bessaire, Wilhelm Rademacher, Richard H Stadler, Thierry DelatourAbstract:Abstract Mepiquat (N,N-dimethylpiperidinium) is a plant growth regulator registered for use as its chloride salt in many countries on cereals and other crops. Recent model system studies have shown that natural chemicals present in crop plants, such as pipecolic acid and pipecolic acid betaine, may furnish Mepiquat through different chemical pathways, when subjected to temperatures in the range of 200 °C. In this study, we cooked raw vegetables that did not contain Mepiquat to a palatable state using different traditional cooking methods, and detected Mepiquat in 9 out of 11 oven-cooked vegetables, reaching up to 189 μg/kg dry wt in oven-cooked broccoli. Commercial oven potato fries generated Mepiquat during cooking, typically in the range of 20–60 μg/kg. Only traces of Mepiquat (
-
heat induced formation of Mepiquat by decarboxylation of pipecolic acid and its betaine derivative part 1 model system studies
Food Chemistry, 2017Co-Authors: Yuan Yuan, Adrienne Tarres, Thomas Bessaire, Richard H Stadler, Thierry DelatourAbstract:Abstract This study describes, for the first time, the role of pipecolic acid betaine and pipecolic acid, naturally present in some foods, in the formation of the plant growth regulator N,N-dimethylpiperidinium (Mepiquat) under dry thermal conditions. The formation of Mepiquat and intermediate compounds was investigated in model systems using high performance liquid chromatography-quadrupole/time-of-flight mass spectrometry. Mepiquat is released with a yield of up to 0.66 mol% after thermal treatment (>150 °C) of pipecolic acid betaine. Similar conversion rates are attained with the congener piperidine-2-carboxylic acid ( dl -pipecolic acid), albeit in the presence of alkylating agents, such as choline, glycine betaine or trigonelline, that are fairly widespread in food crops. These new pathways to Mepiquat indicate that the occurrence of low levels of this thermally induced compound is probably more widespread in processed foods than initially suspected (see Part 2 of this study on the occurrence of Mepiquat in selected foodstuffs).
-
Mepiquat a process induced byproduct in roasted cereal based foodstuffs
Journal of Agricultural and Food Chemistry, 2016Co-Authors: Thomas Bessaire, Adrienne Tarres, Richard H Stadler, Silke Wermann, Viviane Theurillat, Jocelyne Hofmann, Raphael Combremont, Thierry DelatourAbstract:Mepiquat, a growth regulator widely used in agriculture, is also known as a process-induced byproduct formed in coffee from natural constituents during heat treatments such as roasting. This study examines Mepiquat formation in cereal-based foodstuffs treated at sufficiently high temperature to trigger methyl transfer reactions that involve glycine betaine and choline naturally present in cereals. Color measurements of roasted barley grains revealed a correlation between thermal treatment and Mepiquat content. Trials at industrial scale on instant beverages composed of roasted cereals demonstrated significant increases in Mepiquat during the thermal process (in the range of 140–205 μg/kg in final products). A targeted survey of commercial products showed Mepiquat in the range 69–381 μg/kg in powdered cereal instant drinks and 42–168 μg/kg in mugicha tea, a roasted barley infusion. These findings will not significantly affect the exposure of consumers to Mepiquat due to the low amounts detected.
-
role of choline and glycine betaine in the formation of n n dimethylpiperidinium Mepiquat under maillard reaction conditions
Food Additives and Contaminants Part A-chemistry Analysis Control Exposure & Risk Assessment, 2014Co-Authors: Thomas Bessaire, Adrienne Tarres, Richard H Stadler, Thierry DelatourAbstract:This study is the first to examine the role of choline and glycine betaine, naturally present in some foods, in particular in cereal grains, to generate N,N-dimethylpiperidinium (Mepiquat) under Maillard conditions via transmethylation reactions involving the nucleophile piperidine. The formation of Mepiquat and its intermediates piperidine – formed by cyclisation of free lysine in the presence of reducing sugars – and N-methylpiperidine were monitored over time (240°C, up to 180 min) using high-resolution mass spectrometry in a model system comprised of a ternary mixture of lysine/fructose/alkylating agent (choline or betaine). The reaction yield was compared with data recently determined for trigonelline, a known methylation agent present naturally in coffee beans. The role of choline and glycine betaine in nucleophilic displacement reactions was further supported by experiments carried out with stable isotope-labelled precursors (13C- and deuterium-labelled). The results unequivocally demonstrated that...
-
n n dimethylpiperidinium Mepiquat part 2 formation in roasted coffee and barley during thermal processing
Food Additives and Contaminants Part A-chemistry Analysis Control Exposure & Risk Assessment, 2014Co-Authors: Silke Wermann, Thierry Delatour, Viviane Theurillat, Ludovica Verzegnassi, Jocelyne Hofmann, Ralf Kuchenbecker, Anne Constable, Richard H StadlerAbstract:Previous work in model systems has demonstrated that Mepiquat can be formed under typical roasting conditions from the amino acid lysine via the Maillard reaction and trigonelline, the latter alkaloid serving as a methyl donor. This study shows for the first time that Mepiquat is formed in low mg kg–1 amounts during the coffee roasting process and consequently can be detected in roast and ground as well as soluble coffee up to levels of 1.4 mg kg–1. Darker roast coffees contain relatively higher amounts of Mepiquat versus light roasted beans, with an excellent correlation of Mepiquat formation to roast colour (r2 = 0.99) in robusta beans. A survey of 20 of the major green coffee origins (robusta and arabica coffees) showed the absence of Mepiquat (<0.005 mg kg–1). Preliminary studies indicate that Mepiquat is not formed during processing (thermal treatment) in most of the cereal-based foods such as pizza and ready-to-eat cereals, but was detected in barley after roasting (0.64 mg kg–1). Mepiquat can there...
Natalia Varga - One of the best experts on this subject based on the ideXlab platform.
-
D of chlormequat and Mepiquat in pear, tomato, and wheat flour using on-line solid-phase extraction (Prospekt) coupled with liquid chromatography-electrospray ionization tandem
2020Co-Authors: Sonja Riediker, Heinrich Obrist, Natalia Varga, Richard H StadlerAbstract:AbstractA sensitive and selective method is presented for the simultaneous analysis of the pesticides chlormequat and Mepiquat attrace levels in tomato, pear, and wheat flour. The method entails direct injection of the food extract onto an on-linesolid-phase extraction (SPE) instrument (Prospekt) using a strong cation-exchange resin. Analyte separation and detection isdone by liquid chromatography–electrospray ionization tandem mass spectrometry (LC–ESI-MS–MS). Surrogate standards(d 96 -chlormequat,d -Mepiquat) are employed to compensate for recovery losses and potential MS–MS signal suppression.The method achieves a limit of quantification for both cationic analytes at or below 5 mg/kg, and good intra- and inter-assayprecision with mean variability values ,7% over a concentration range up to 195 mg/kg. This study also addresses potentialanalyte carry-over in an SPE on-line system, as well as the robustness of the procedure and its applicability in routine qualitycontrol operations.2002 Elsevier Science B.V. All rights reserved.Keywords: Food analysis; Solid-phase extraction; Pesticides; Chlormequat; Mepiquat
-
Determination of chlormequat and Mepiquat in pear, tomato, and wheat flour using on-line solid-phase extraction (Prospekt) coupled with liquid chromatography-electrospray ionization tandem mass spectrometry.
Journal of chromatography. A, 2002Co-Authors: Sonja Riediker, Heinrich Obrist, Natalia Varga, Richard H StadlerAbstract:A sensitive and selective method is presented for the simultaneous analysis of the pesticides chlormequat and Mepiquat at trace levels in tomato, pear, and wheat flour. The method entails direct injection of the food extract onto an on-line solid-phase extraction (SPE) instrument (Prospekt) using a strong cation-exchange resin. Analyte separation and detection is done by liquid chromatography-electrospray ionization tandem mass spectrometry (LC-ESI-MS-MS). Surrogate standards (d9-chlormequat, d6-Mepiquat) are employed to compensate for recovery losses and potential MS-MS signal suppression. The method achieves a limit of quantification for both cationic analytes at or below 5 microg/kg, and good intra- and inter-assay precision with mean variability values
-
determination of chlormequat and Mepiquat in pear tomato and wheat flour using on line solid phase extraction prospekt coupled with liquid chromatography electrospray ionization tandem mass spectrometry
Journal of Chromatography A, 2002Co-Authors: Sonja Riediker, Heinrich Obrist, Natalia Varga, Richard H StadlerAbstract:A sensitive and selective method is presented for the simultaneous analysis of the pesticides chlormequat and Mepiquat at trace levels in tomato, pear, and wheat flour. The method entails direct injection of the food extract onto an on-line solid-phase extraction (SPE) instrument (Prospekt) using a strong cation-exchange resin. Analyte separation and detection is done by liquid chromatography–electrospray ionization tandem mass spectrometry (LC–ESI-MS–MS). Surrogate standards (d9-chlormequat, d6-Mepiquat) are employed to compensate for recovery losses and potential MS–MS signal suppression. The method achieves a limit of quantification for both cationic analytes at or below 5 μg/kg, and good intra- and inter-assay precision with mean variability values <7% over a concentration range up to 195 μg/kg. This study also addresses potential analyte carry-over in an SPE on-line system, as well as the robustness of the procedure and its applicability in routine quality control operations.
Heinrich Obrist - One of the best experts on this subject based on the ideXlab platform.
-
D of chlormequat and Mepiquat in pear, tomato, and wheat flour using on-line solid-phase extraction (Prospekt) coupled with liquid chromatography-electrospray ionization tandem
2020Co-Authors: Sonja Riediker, Heinrich Obrist, Natalia Varga, Richard H StadlerAbstract:AbstractA sensitive and selective method is presented for the simultaneous analysis of the pesticides chlormequat and Mepiquat attrace levels in tomato, pear, and wheat flour. The method entails direct injection of the food extract onto an on-linesolid-phase extraction (SPE) instrument (Prospekt) using a strong cation-exchange resin. Analyte separation and detection isdone by liquid chromatography–electrospray ionization tandem mass spectrometry (LC–ESI-MS–MS). Surrogate standards(d 96 -chlormequat,d -Mepiquat) are employed to compensate for recovery losses and potential MS–MS signal suppression.The method achieves a limit of quantification for both cationic analytes at or below 5 mg/kg, and good intra- and inter-assayprecision with mean variability values ,7% over a concentration range up to 195 mg/kg. This study also addresses potentialanalyte carry-over in an SPE on-line system, as well as the robustness of the procedure and its applicability in routine qualitycontrol operations.2002 Elsevier Science B.V. All rights reserved.Keywords: Food analysis; Solid-phase extraction; Pesticides; Chlormequat; Mepiquat
-
Determination of chlormequat and Mepiquat in pear, tomato, and wheat flour using on-line solid-phase extraction (Prospekt) coupled with liquid chromatography-electrospray ionization tandem mass spectrometry.
Journal of chromatography. A, 2002Co-Authors: Sonja Riediker, Heinrich Obrist, Natalia Varga, Richard H StadlerAbstract:A sensitive and selective method is presented for the simultaneous analysis of the pesticides chlormequat and Mepiquat at trace levels in tomato, pear, and wheat flour. The method entails direct injection of the food extract onto an on-line solid-phase extraction (SPE) instrument (Prospekt) using a strong cation-exchange resin. Analyte separation and detection is done by liquid chromatography-electrospray ionization tandem mass spectrometry (LC-ESI-MS-MS). Surrogate standards (d9-chlormequat, d6-Mepiquat) are employed to compensate for recovery losses and potential MS-MS signal suppression. The method achieves a limit of quantification for both cationic analytes at or below 5 microg/kg, and good intra- and inter-assay precision with mean variability values
-
determination of chlormequat and Mepiquat in pear tomato and wheat flour using on line solid phase extraction prospekt coupled with liquid chromatography electrospray ionization tandem mass spectrometry
Journal of Chromatography A, 2002Co-Authors: Sonja Riediker, Heinrich Obrist, Natalia Varga, Richard H StadlerAbstract:A sensitive and selective method is presented for the simultaneous analysis of the pesticides chlormequat and Mepiquat at trace levels in tomato, pear, and wheat flour. The method entails direct injection of the food extract onto an on-line solid-phase extraction (SPE) instrument (Prospekt) using a strong cation-exchange resin. Analyte separation and detection is done by liquid chromatography–electrospray ionization tandem mass spectrometry (LC–ESI-MS–MS). Surrogate standards (d9-chlormequat, d6-Mepiquat) are employed to compensate for recovery losses and potential MS–MS signal suppression. The method achieves a limit of quantification for both cationic analytes at or below 5 μg/kg, and good intra- and inter-assay precision with mean variability values <7% over a concentration range up to 195 μg/kg. This study also addresses potential analyte carry-over in an SPE on-line system, as well as the robustness of the procedure and its applicability in routine quality control operations.