Vural Gökmen | Hacettepe University (original) (raw)

Papers by Vural Gökmen

Research paper thumbnail of Enzymatically validated liquid chromatographic method for the determination of ascorbic and dehydroascorbic acids in fruit and vegetables

Journal of Chromatography A, 2000

A liquid chromatographic method has been described for the determination of total vitamin C, asco... more A liquid chromatographic method has been described for the determination of total vitamin C, ascorbic acid (AA) and dehydroascorbic acid (DHAA) in fruits and vegetables. The complete separation of AA and DHAA could be achieved on a C18 column using 0.2 M KH2PO4 (pH adjusted to 2.4 with H3PO4) as the mobile phase at a flow-rate of 0.5 ml/min. Since

Research paper thumbnail of Acrylamide formation is prevented by divalent cations during the Maillard reaction

Food Chemistry, 2007

... Several factors, such as the initial concentration of reactants and their ratio, temperature ... more ... Several factors, such as the initial concentration of reactants and their ratio, temperature and time of processing, pH and water activity, have been shown to influence the formation levels of acrylamide in heat-processed foods (Friedman, 2003). ...

Research paper thumbnail of Equilibrium and kinetic studies on the adsorption of dark colored compounds from apple juice using adsorbent resin

Journal of Food Engineering, 2002

Research paper thumbnail of Characterization of crude lipoxygenase extract from green pea using a modified spectrophotometric method

European Food Research and Technology, 2002

In the spectrophotometric assay of lipoxygenase (LOX), the buffered linoleic acid solution used a... more In the spectrophotometric assay of lipoxygenase (LOX), the buffered linoleic acid solution used as the reaction medium is not optically clear enough at neutral or lower pH values, due to its limited solubility, to provide a precise, accurate and reproducible estimation of activity as the increase in absorbance at 234 nm. Therefore, an optically clear solution was obtained by formation of the Na-salt of unreacted linoleic acid before absorbance measurement. The modified method was then used to characterize crude LOX from green peas in terms of pH and temperature optima, thermal stability, and kinetic parameters. The optimum pH and temperature for the activity of LOX from green peas were determined to be 6.0 and 30 °C, respectively. LOX was found to be very stable at 60 °C, but much less stable at 65 °C or higher temperatures. The Michaelis constant (K m) and maximum rate (V max) for linoleic acid were calculated to be 1666 units per mg protein per min and 2.33 mM, respectively.

Research paper thumbnail of A New Procedure To Measure the Antioxidant Activity of Insoluble Food Components

Journal of Agricultural and Food Chemistry, 2007

The measurement of antioxidant activity was limited to soluble components to date. Functional gro... more The measurement of antioxidant activity was limited to soluble components to date. Functional groups, which are bound to insoluble matters, may exert antioxidant activity by a surface reaction phenomenon. This hypothesis was tested on the insoluble matters of foods, food ingredients, and Maillard reaction products (MRPs). Insoluble matters were prepared by consecutive washes with water and methanol followed by a lyophilization of the insoluble residue. The measurement was performed by a new procedure using 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) and 2,2-diphenyl-1-picrylhydrazil (DPPH) colored radicals. These insoluble matters always showed antioxidant activity. Alkali hydrolysis reduced up to 90% the antioxidant activity of cereal-based insoluble matters, thus confirming that fiber-bound compounds have a major role in their antioxidant activity. The antioxidant activity of the insoluble MRPs was not significantly affected by processing conditions, but severe treatments increased the ratio between insoluble and soluble matters. The contribution of insoluble matter to total antioxidant activity was limited for fruits and vegetables, but it was relevant for cereal-based foods and increased over 50% for dietary-fiber-rich ingredients.

Research paper thumbnail of A simplified approach for the kinetic characterization of acrylamide formation in fructose-asparagine model system

Food Additives and Contaminants Part A-chemistry Analysis Control Exposure & Risk Assessment, 2006

The potential of acrylamide formation and degradation was studied in fructose-asparagine reaction... more The potential of acrylamide formation and degradation was studied in fructose-asparagine reaction system at different temperatures (120-200 degrees C). Kinetic data for concurrent formation and degradation of acrylamide was analysed based on a simplified form of chemical reaction in series in which acrylamide occurred as an intermediate. Experimental results revealed that the reaction proceeds zero order and first order with respect to asparagine and fructose, respectively. The thermal degradation of acrylamide was determined to be first order in fructose-glycine reaction system. The concurrent formation and degradation of acrylamide followed a typical kinetic pattern at the temperatures studied. Thermal degradation was observed within 60 min at T>150 degrees C, while only the accumulation was noted at T<150 degrees C. The mathematical model fitted to experimental data very well within temperature range of 120-200 degrees C. The temperature dependence of both acrylamide formation and degradation were found to obey Arrhenius law, and the activation energies were 52.1 kJ/mol and 72.9 kJ/mol, respectively.

Research paper thumbnail of Relation between the acrylamide formation and time–temperature history of surface and core regions of French fries

Journal of Food Engineering, 2006

Research paper thumbnail of Direct measurement of the total antioxidant capacity of cereal products

Journal of Cereal Science, 2008

Research paper thumbnail of Survey of acrylamide in Turkish foods by an in-house validated LCMS method

Food Additives and Contaminants Part A-chemistry Analysis Control Exposure & Risk Assessment, 2005

A survey of retail Turkish foods was conducted for acrylamide using an in-house validated LC-MS m... more A survey of retail Turkish foods was conducted for acrylamide using an in-house validated LC-MS method. The recoveries obtained for a variety of food matrices ranged between 81.2 and 96.8% for a spiking level of 500 ng g–1. The limit of quantification was determined as 15–20 ng g–1 depending on the food matrix in the basis of a signal-to-noise ratio of 5. A total of 120 food samples were analysed for acrylamide. The mean acrylamide levels in different food groups were in the order: crackers > potato chips > biscuits > cakes > baby foods > corn chips > cookies > breakfast cereals > breads > grilled vegetables > wafers > chocolates. The crumb of bread was free of acrylamide, whilst significant concentrations were found in the crust.

Research paper thumbnail of Study of colour and acrylamide formation in coffee, wheat flour and potato chips during heating

Food Chemistry, 2006

... patterns of CIE colour parameters of L* a* b* and acrylamide was investigated in detail. ... ... more ... patterns of CIE colour parameters of L* a* b* and acrylamide was investigated in detail. ... Şenyuva and Gökmen, 2005 HZ Şenyuva and V. Gökmen, Study of acrylamide in coffee ... on acrylamide content in yeast-leavened wheat bread, Journal of Agricultural and Food Chemistry 52 ...

Research paper thumbnail of Interference-free determination of acrylamide in potato and cereal-based foods by a laboratory validated liquid chromatography–mass spectrometry method

Food Chemistry, 2006

A simple and rapid method was developed and validated for the determination of acrylamide in pota... more A simple and rapid method was developed and validated for the determination of acrylamide in potato and cereal-based foods by using a single quadrupole liquid chromatography–mass spectrometry (LC–MS) interfaced with positive atmospheric pressure chemical ionization (APCI+). Acrylamide was simply extracted with 0.01mM acetic acid in a vortex mixer prior to LC–MS analysis. The applicability of validated method was shown for

Research paper thumbnail of Analysis of furan in foods. Is headspace sampling a fit-for-purpose technique

Food Additives and Contaminants Part A-chemistry Analysis Control Exposure & Risk Assessment, 2005

Headspace GC-MS has been opitimized for the determination of furan in foods. The conditions of sa... more Headspace GC-MS has been opitimized for the determination of furan in foods. The conditions of sample preparation, headspace sampling and GC separation were optimized to enhance sensitivity during GC-MS analysis. Green coffee was used to prepare a matrix matched calibration curve for furan. However, it was unexpectedly found that a green coffee sample was not blank. GC-MS analysis performed after equilibration for 30 min at 40°C showed the presence of 4.2 ng/g furan in green coffee. In order to understand whether furan was naturally present or formed during headspace sampling, green coffee was investigated in time-dependent manner at headspace equilibration temperatures of 40 and 70°C. It was observed that furan response continued to increase in a way similar to first order formation kinetics. The same behavior was found for freshly squeezed tomato and orange juices leading to the suspicion of furan formation during headspace equilibration. It is concluded that a matrix matched calibration for each particular food matrix is necessary to compensate for furan formation during headspace sampling, and thus, to quantify furan more accurately.

Research paper thumbnail of Incidence of patulin in apple juice concentrates produced in Turkey

Journal of Chromatography A, 1998

Research paper thumbnail of Effects of dough formula and baking conditions on acrylamide and hydroxymethylfurfural formation in cookies

Food Chemistry, 2007

The effects of dough formula and baking conditions on the formations of acrylamide and hydroxymet... more The effects of dough formula and baking conditions on the formations of acrylamide and hydroxymethylfurfural (HMF) were studied in a cookie model system. Increasing the sugar concentration in the dough formula increased acrylamide formation during baking at 205° ...

Research paper thumbnail of Study of acrylamide in coffee using an improved liquid chromatography mass spectrometry method: Investigation of colour changes and acrylamide formation in coffee during roasting

Food Additives and Contaminants Part A-chemistry Analysis Control Exposure & Risk Assessment, 2005

An improved analytical method for the determination of acrylamide in coffee is described using li... more An improved analytical method for the determination of acrylamide in coffee is described using liquid chromatography coupled to mass spectrometric detection (LC-MS). A variety of instant, ground and laboratory roasted coffee samples were analysed using this method. The sample preparation entails extraction of acrylamide with methanol, purification with Carrez I and II solutions, evaporation and solvent change to water, and clean-up with an Oasis HLB solid-phase extraction (SPE) cartridge. The chromatographic conditions allowed separation of acrylamide and the remaining matrix co-extractives with accurate and precise quantification of acrylamide during MS detection in SIM mode. Recoveries for the spiking levels of 50, 100, 250 and 500?microg/kg ranged between 99 and 100% with relative standard deviations of less than 2%. The effects of roasting on the formation of acrylamide and colour development were also investigated at 150, 200 and 225 degrees C. Change in the CIE (Commission Internationale de l'Eclairage) a* colour value was found to show a good correlation with the change in acrylamide. CIE a* and acrylamide data was fitted to a non-linear logarithmic function for the estimation of acrylamide level in coffee. Measured acrylamide levels in commercial roasted coffees compared well with the predicted acrylamide levels from the CIE a* values.

Research paper thumbnail of Liquid chromatographic method for the determination of patulin in apple juice using solid-phase extraction

Analytica Chimica Acta, 2005

Research paper thumbnail of Determination of acrylamide in potato chips and crisps by high-performance liquid chromatography

Journal of Chromatography A, 2005

A simple and rapid method using liquid chromatography coupled to diode array detection (LC-DAD) w... more A simple and rapid method using liquid chromatography coupled to diode array detection (LC-DAD) was developed for the determination of acrylamide in potato-based foods at low levels. The method entails extraction of acrylamide with methanol, purification with Carrez I and II solutions, evaporation and solvent change to water, and cleanup with a Oasis HLB solid-phase extraction (SPE) cartridge. The final extract was analyzed by LC-DAD for quantification and by liquid chromatography coupled to mass spectrometry (LC-MS) for confirmation. The chromatographic separations were performed on a hydrophilic and a hydrophobic interaction columns having good retention of acrylamide under 100% aqueous flow conditions (k' 3.67 and 2.54, respectively). The limit of quantitation was estimated to be 4.0 microg/kg based on the signal-to-noise ratio of 3 recorded at 226 nm. Recoveries of acrylamide from potato chips samples spiked at levels of 250, 500 and 1000 (n = 4 for each level) microg/kg ranged between 92.8 and 96.2% with relative standard deviations of less than 5%. The results of this study revealed that a conventional LC instrument coupled to DAD can also be used accurately and precisely, as an alternative to tandem LC-MS methods for the determination of acrylamide in potato-based foods.

Research paper thumbnail of Study of lipoxygenase and peroxidase as indicator enzymes in green beans: change of enzyme activity, ascorbic acid and chlorophylls during frozen storage

Journal of Food Engineering, 2005

Research paper thumbnail of Effects of various clarification treatments on patulin, phenolic compound and organic acid compositions of apple juice

European Food Research and Technology, 2001

The purpose of this study was to investigate the comparative clarification techniques in apple ju... more The purpose of this study was to investigate the comparative clarification techniques in apple juice processing and their effects on the patulin content and some other quality parameters including phenolic compounds and organic acids. The clarification techniques varied significantly in their effects for the removal of patulin from apple juice. Conventional clarification using gelatin, bentonite, and activated charcoal was found to be more effective than others. However, this technique also caused a significant decrease in apple juice phenolics adversely affecting the juice authenticity. Adsorbent resin treatment just after ultrafiltration also resulted in a remarkable decrease in patulin and brought an improvement in juice color and clarity. PVPP itself had no observable effect on patulin, but specifically adsorbed apple juice phenolics. Organic acid compositions of the samples were not significantly affected from the clarification techniques applied in this study.

Research paper thumbnail of Rapid reversed-phase liquid chromatographic determination of patulin in apple juice

Journal of Chromatography A, 1996

A rapid, simple and economical method using a limited amount of organic solvent is described for ... more A rapid, simple and economical method using a limited amount of organic solvent is described for the determination of patulin in apple juice. The sample was extracted with ethyl acetate and the extract was cleaned up by extraction with sodium carbonate solution. Patulin was then determined by reversed-phase liquid chromatography using a MicroPack C18 column and a variable-wavelength UV-Vis detector set at 276 nm. Patulin and 5-hydroxymethylfurfural were completely resolved by using water-acetonitrile (99:1, v/v) as the mobile phase at a flow-rate of 1.0 ml/min. The detection limit was < 5 micrograms/l and the recovery was 98%.

Research paper thumbnail of Enzymatically validated liquid chromatographic method for the determination of ascorbic and dehydroascorbic acids in fruit and vegetables

Journal of Chromatography A, 2000

A liquid chromatographic method has been described for the determination of total vitamin C, asco... more A liquid chromatographic method has been described for the determination of total vitamin C, ascorbic acid (AA) and dehydroascorbic acid (DHAA) in fruits and vegetables. The complete separation of AA and DHAA could be achieved on a C18 column using 0.2 M KH2PO4 (pH adjusted to 2.4 with H3PO4) as the mobile phase at a flow-rate of 0.5 ml/min. Since

Research paper thumbnail of Acrylamide formation is prevented by divalent cations during the Maillard reaction

Food Chemistry, 2007

... Several factors, such as the initial concentration of reactants and their ratio, temperature ... more ... Several factors, such as the initial concentration of reactants and their ratio, temperature and time of processing, pH and water activity, have been shown to influence the formation levels of acrylamide in heat-processed foods (Friedman, 2003). ...

Research paper thumbnail of Equilibrium and kinetic studies on the adsorption of dark colored compounds from apple juice using adsorbent resin

Journal of Food Engineering, 2002

Research paper thumbnail of Characterization of crude lipoxygenase extract from green pea using a modified spectrophotometric method

European Food Research and Technology, 2002

In the spectrophotometric assay of lipoxygenase (LOX), the buffered linoleic acid solution used a... more In the spectrophotometric assay of lipoxygenase (LOX), the buffered linoleic acid solution used as the reaction medium is not optically clear enough at neutral or lower pH values, due to its limited solubility, to provide a precise, accurate and reproducible estimation of activity as the increase in absorbance at 234 nm. Therefore, an optically clear solution was obtained by formation of the Na-salt of unreacted linoleic acid before absorbance measurement. The modified method was then used to characterize crude LOX from green peas in terms of pH and temperature optima, thermal stability, and kinetic parameters. The optimum pH and temperature for the activity of LOX from green peas were determined to be 6.0 and 30 °C, respectively. LOX was found to be very stable at 60 °C, but much less stable at 65 °C or higher temperatures. The Michaelis constant (K m) and maximum rate (V max) for linoleic acid were calculated to be 1666 units per mg protein per min and 2.33 mM, respectively.

Research paper thumbnail of A New Procedure To Measure the Antioxidant Activity of Insoluble Food Components

Journal of Agricultural and Food Chemistry, 2007

The measurement of antioxidant activity was limited to soluble components to date. Functional gro... more The measurement of antioxidant activity was limited to soluble components to date. Functional groups, which are bound to insoluble matters, may exert antioxidant activity by a surface reaction phenomenon. This hypothesis was tested on the insoluble matters of foods, food ingredients, and Maillard reaction products (MRPs). Insoluble matters were prepared by consecutive washes with water and methanol followed by a lyophilization of the insoluble residue. The measurement was performed by a new procedure using 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) and 2,2-diphenyl-1-picrylhydrazil (DPPH) colored radicals. These insoluble matters always showed antioxidant activity. Alkali hydrolysis reduced up to 90% the antioxidant activity of cereal-based insoluble matters, thus confirming that fiber-bound compounds have a major role in their antioxidant activity. The antioxidant activity of the insoluble MRPs was not significantly affected by processing conditions, but severe treatments increased the ratio between insoluble and soluble matters. The contribution of insoluble matter to total antioxidant activity was limited for fruits and vegetables, but it was relevant for cereal-based foods and increased over 50% for dietary-fiber-rich ingredients.

Research paper thumbnail of A simplified approach for the kinetic characterization of acrylamide formation in fructose-asparagine model system

Food Additives and Contaminants Part A-chemistry Analysis Control Exposure & Risk Assessment, 2006

The potential of acrylamide formation and degradation was studied in fructose-asparagine reaction... more The potential of acrylamide formation and degradation was studied in fructose-asparagine reaction system at different temperatures (120-200 degrees C). Kinetic data for concurrent formation and degradation of acrylamide was analysed based on a simplified form of chemical reaction in series in which acrylamide occurred as an intermediate. Experimental results revealed that the reaction proceeds zero order and first order with respect to asparagine and fructose, respectively. The thermal degradation of acrylamide was determined to be first order in fructose-glycine reaction system. The concurrent formation and degradation of acrylamide followed a typical kinetic pattern at the temperatures studied. Thermal degradation was observed within 60 min at T>150 degrees C, while only the accumulation was noted at T<150 degrees C. The mathematical model fitted to experimental data very well within temperature range of 120-200 degrees C. The temperature dependence of both acrylamide formation and degradation were found to obey Arrhenius law, and the activation energies were 52.1 kJ/mol and 72.9 kJ/mol, respectively.

Research paper thumbnail of Relation between the acrylamide formation and time–temperature history of surface and core regions of French fries

Journal of Food Engineering, 2006

Research paper thumbnail of Direct measurement of the total antioxidant capacity of cereal products

Journal of Cereal Science, 2008

Research paper thumbnail of Survey of acrylamide in Turkish foods by an in-house validated LCMS method

Food Additives and Contaminants Part A-chemistry Analysis Control Exposure & Risk Assessment, 2005

A survey of retail Turkish foods was conducted for acrylamide using an in-house validated LC-MS m... more A survey of retail Turkish foods was conducted for acrylamide using an in-house validated LC-MS method. The recoveries obtained for a variety of food matrices ranged between 81.2 and 96.8% for a spiking level of 500 ng g–1. The limit of quantification was determined as 15–20 ng g–1 depending on the food matrix in the basis of a signal-to-noise ratio of 5. A total of 120 food samples were analysed for acrylamide. The mean acrylamide levels in different food groups were in the order: crackers > potato chips > biscuits > cakes > baby foods > corn chips > cookies > breakfast cereals > breads > grilled vegetables > wafers > chocolates. The crumb of bread was free of acrylamide, whilst significant concentrations were found in the crust.

Research paper thumbnail of Study of colour and acrylamide formation in coffee, wheat flour and potato chips during heating

Food Chemistry, 2006

... patterns of CIE colour parameters of L* a* b* and acrylamide was investigated in detail. ... ... more ... patterns of CIE colour parameters of L* a* b* and acrylamide was investigated in detail. ... Şenyuva and Gökmen, 2005 HZ Şenyuva and V. Gökmen, Study of acrylamide in coffee ... on acrylamide content in yeast-leavened wheat bread, Journal of Agricultural and Food Chemistry 52 ...

Research paper thumbnail of Interference-free determination of acrylamide in potato and cereal-based foods by a laboratory validated liquid chromatography–mass spectrometry method

Food Chemistry, 2006

A simple and rapid method was developed and validated for the determination of acrylamide in pota... more A simple and rapid method was developed and validated for the determination of acrylamide in potato and cereal-based foods by using a single quadrupole liquid chromatography–mass spectrometry (LC–MS) interfaced with positive atmospheric pressure chemical ionization (APCI+). Acrylamide was simply extracted with 0.01mM acetic acid in a vortex mixer prior to LC–MS analysis. The applicability of validated method was shown for

Research paper thumbnail of Analysis of furan in foods. Is headspace sampling a fit-for-purpose technique

Food Additives and Contaminants Part A-chemistry Analysis Control Exposure & Risk Assessment, 2005

Headspace GC-MS has been opitimized for the determination of furan in foods. The conditions of sa... more Headspace GC-MS has been opitimized for the determination of furan in foods. The conditions of sample preparation, headspace sampling and GC separation were optimized to enhance sensitivity during GC-MS analysis. Green coffee was used to prepare a matrix matched calibration curve for furan. However, it was unexpectedly found that a green coffee sample was not blank. GC-MS analysis performed after equilibration for 30 min at 40°C showed the presence of 4.2 ng/g furan in green coffee. In order to understand whether furan was naturally present or formed during headspace sampling, green coffee was investigated in time-dependent manner at headspace equilibration temperatures of 40 and 70°C. It was observed that furan response continued to increase in a way similar to first order formation kinetics. The same behavior was found for freshly squeezed tomato and orange juices leading to the suspicion of furan formation during headspace equilibration. It is concluded that a matrix matched calibration for each particular food matrix is necessary to compensate for furan formation during headspace sampling, and thus, to quantify furan more accurately.

Research paper thumbnail of Incidence of patulin in apple juice concentrates produced in Turkey

Journal of Chromatography A, 1998

Research paper thumbnail of Effects of dough formula and baking conditions on acrylamide and hydroxymethylfurfural formation in cookies

Food Chemistry, 2007

The effects of dough formula and baking conditions on the formations of acrylamide and hydroxymet... more The effects of dough formula and baking conditions on the formations of acrylamide and hydroxymethylfurfural (HMF) were studied in a cookie model system. Increasing the sugar concentration in the dough formula increased acrylamide formation during baking at 205° ...

Research paper thumbnail of Study of acrylamide in coffee using an improved liquid chromatography mass spectrometry method: Investigation of colour changes and acrylamide formation in coffee during roasting

Food Additives and Contaminants Part A-chemistry Analysis Control Exposure & Risk Assessment, 2005

An improved analytical method for the determination of acrylamide in coffee is described using li... more An improved analytical method for the determination of acrylamide in coffee is described using liquid chromatography coupled to mass spectrometric detection (LC-MS). A variety of instant, ground and laboratory roasted coffee samples were analysed using this method. The sample preparation entails extraction of acrylamide with methanol, purification with Carrez I and II solutions, evaporation and solvent change to water, and clean-up with an Oasis HLB solid-phase extraction (SPE) cartridge. The chromatographic conditions allowed separation of acrylamide and the remaining matrix co-extractives with accurate and precise quantification of acrylamide during MS detection in SIM mode. Recoveries for the spiking levels of 50, 100, 250 and 500?microg/kg ranged between 99 and 100% with relative standard deviations of less than 2%. The effects of roasting on the formation of acrylamide and colour development were also investigated at 150, 200 and 225 degrees C. Change in the CIE (Commission Internationale de l'Eclairage) a* colour value was found to show a good correlation with the change in acrylamide. CIE a* and acrylamide data was fitted to a non-linear logarithmic function for the estimation of acrylamide level in coffee. Measured acrylamide levels in commercial roasted coffees compared well with the predicted acrylamide levels from the CIE a* values.

Research paper thumbnail of Liquid chromatographic method for the determination of patulin in apple juice using solid-phase extraction

Analytica Chimica Acta, 2005

Research paper thumbnail of Determination of acrylamide in potato chips and crisps by high-performance liquid chromatography

Journal of Chromatography A, 2005

A simple and rapid method using liquid chromatography coupled to diode array detection (LC-DAD) w... more A simple and rapid method using liquid chromatography coupled to diode array detection (LC-DAD) was developed for the determination of acrylamide in potato-based foods at low levels. The method entails extraction of acrylamide with methanol, purification with Carrez I and II solutions, evaporation and solvent change to water, and cleanup with a Oasis HLB solid-phase extraction (SPE) cartridge. The final extract was analyzed by LC-DAD for quantification and by liquid chromatography coupled to mass spectrometry (LC-MS) for confirmation. The chromatographic separations were performed on a hydrophilic and a hydrophobic interaction columns having good retention of acrylamide under 100% aqueous flow conditions (k' 3.67 and 2.54, respectively). The limit of quantitation was estimated to be 4.0 microg/kg based on the signal-to-noise ratio of 3 recorded at 226 nm. Recoveries of acrylamide from potato chips samples spiked at levels of 250, 500 and 1000 (n = 4 for each level) microg/kg ranged between 92.8 and 96.2% with relative standard deviations of less than 5%. The results of this study revealed that a conventional LC instrument coupled to DAD can also be used accurately and precisely, as an alternative to tandem LC-MS methods for the determination of acrylamide in potato-based foods.

Research paper thumbnail of Study of lipoxygenase and peroxidase as indicator enzymes in green beans: change of enzyme activity, ascorbic acid and chlorophylls during frozen storage

Journal of Food Engineering, 2005

Research paper thumbnail of Effects of various clarification treatments on patulin, phenolic compound and organic acid compositions of apple juice

European Food Research and Technology, 2001

The purpose of this study was to investigate the comparative clarification techniques in apple ju... more The purpose of this study was to investigate the comparative clarification techniques in apple juice processing and their effects on the patulin content and some other quality parameters including phenolic compounds and organic acids. The clarification techniques varied significantly in their effects for the removal of patulin from apple juice. Conventional clarification using gelatin, bentonite, and activated charcoal was found to be more effective than others. However, this technique also caused a significant decrease in apple juice phenolics adversely affecting the juice authenticity. Adsorbent resin treatment just after ultrafiltration also resulted in a remarkable decrease in patulin and brought an improvement in juice color and clarity. PVPP itself had no observable effect on patulin, but specifically adsorbed apple juice phenolics. Organic acid compositions of the samples were not significantly affected from the clarification techniques applied in this study.

Research paper thumbnail of Rapid reversed-phase liquid chromatographic determination of patulin in apple juice

Journal of Chromatography A, 1996

A rapid, simple and economical method using a limited amount of organic solvent is described for ... more A rapid, simple and economical method using a limited amount of organic solvent is described for the determination of patulin in apple juice. The sample was extracted with ethyl acetate and the extract was cleaned up by extraction with sodium carbonate solution. Patulin was then determined by reversed-phase liquid chromatography using a MicroPack C18 column and a variable-wavelength UV-Vis detector set at 276 nm. Patulin and 5-hydroxymethylfurfural were completely resolved by using water-acetonitrile (99:1, v/v) as the mobile phase at a flow-rate of 1.0 ml/min. The detection limit was < 5 micrograms/l and the recovery was 98%.