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Effect of sodium chloride on #-dicarbonyl compounds and 5hydroxymethyl-2-furfural formations from glucose under caramelization conditions – A multiresponse kinetic modelling approach Tolgahan Kocada#l#, and Vural Gökmen J. Agric. Food Chem., Just Accepted Manuscript • DOI: 10.1021/acs.jafc.6b01862 • Publication Date (Web): 30 Jul 2016 Downloaded from http://pubs.acs.org on August 6, 2016

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Journal of Agricultural and Food Chemistry

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Effect of sodium chloride on α-dicarbonyl compounds and 5-hydroxymethyl-2-

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furfural formations from glucose under caramelization conditions – A

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multiresponse kinetic modelling approach

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Tolgahan Kocadağlı, Vural Gökmen*

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Food Quality and Safety (FoQuS) Research Group, Department of Food Engineering,

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Hacettepe University, 06800 Beytepe Campus, Ankara, Turkey

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* Corresponding Author: Prof. Dr. Vural Gökmen

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e–mail: [email protected]

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phone: +90 312 2977108

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fax: +90 312 2992123

ACS Paragon Plus Environment

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Abstract

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This study aimed to investigate the kinetics of α-dicarbonyl compounds formation in

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glucose and glucose-sodium chloride mixture during heating under caramelization

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conditions. Changes in the concentrations of glucose, fructose, glucosone, 1–

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deoxyglucosone, 3–deoxyglucosone, 3,4–dideoxyglucosone, 5–hydroxymethyl–2–

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furfural, glyoxal, methylglyoxal and diacetyl were determined. A comprehensive

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reaction network was built and the multiresponse model was compared to the

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experimentally observed data. Interconversion between glucose and fructose

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became 2.5 times faster in the presence of NaCl at 180 and 200 °C. Effect of NaCl on

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the rate constants of α-dicarbonyl compound formation varied across the precursor

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and the compound’s itself and temperature. The decrease in rate constants of 3-

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deoxyglucosone and 1-deoxyglucosone formations by the presence of NaCl was

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observed. HMF formation was revealed to be mainly via isomerization to fructose

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and dehydration over cyclic intermediates and the rate constants increase 4 fold in

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the presence of NaCl.

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Keywords: Caramelization, 3-deoxyglucosone, α–dicarbonyl compounds, glucose

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degradation, 5-hydroxymethyl-2-furfural, multiresponse kinetic modeling, sodium

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chloride.


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Introduction

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Baked and roasted products are judged by the consumers in terms of their color,

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flavor and doneness, which are provided to a certain extent by the non-enzymatic

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browning reactions during thermal processing. On the contrary, in certain products,

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like milk, it is undesired in view of quality and nutritional aspects. Controlling

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caramelization and Maillard reaction during food processing has been a challenge

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due to the complex mechanisms of browning and flavor development, which

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comprise a wide range of reactive intermediates in parallel and consecutive

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reactions.1 Of these intermediates, α-dicarbonyl compounds originating from

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carbohydrate backbone are of particular importance from the viewpoint of flavor

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and browning reaction mechanisms on one hand and on the other they have been

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proposed to involve in carbonyl stress in vivo.2, 3 These reactive carbonyl compounds

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also causes nutritional loses by modifying proteins found in foods by formation of

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advanced glycation end products, which are often discussed to have negative health

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consequences.4 α-Dicarbonyl compounds also involve in the formation of other neo-

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formed food toxicants like acrylamide, furan and heterocyclic aromatic amines

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during food processing.5-7

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Reactive intermediates in sugar degradation show complex kinetics rather than the

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typical first order loss of sugars itself. Even though defining a reaction with a

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uniresponse kinetic models, i.e. zero, first and second order, can be easier for

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engineering purposes,8 it does not provide any control points in the cascade of

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reactions, which is observed in many foods as complex systems. Therefore, in a

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complex reaction, observing reactants, intermediates and products together and


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modeling the mechanisms behind all will be a better approach for optimizing food

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quality.9 Multiresponse kinetic modeling has been shown to be a powerful tool in

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this respect.10 It links reactants and products with intermediates in a quantitative

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way, which helps to gain insights of elementary reaction steps by estimating reaction

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rate constants and to build a mechanistic model. It is therefore possible to locate

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rate-determining steps, which may be control points. It should be noted that the

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concentrations of such reactive intermediates in a system do not imply its

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importance in a quantitative way on the outcomes of the reaction such as browning

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and flavor. Reaction rate constants thus become critical to find out the implications

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about reaction mechanism. Multiresponse modeling enables to test proposed

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reaction networks by law of mass action.11

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Dehydration of hexose sugars produce mainly 1-deoxyglucosone and 3-

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deoxyglucosone and 3,4-dideoxyglucosone while oxidation of hexoses produces

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glucosone, which all preserving the intact six carbon (Figure 1).12 Fragmentation of

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these α-dicarbonyl compounds yield to shorter chain α-dicarbonyl compounds

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glyoxal, methylglyoxal and diacetyl. α-Dicarbonyl compounds are also formed by the

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degradation of Amadori compounds in the Maillard reaction.13 Removal of three

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molecules of water from a hexose sugar ends with the formation of 5-

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hydroxymethyl-2-furfural (HMF). There are generally two pathways considered for

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the formation of HMF from glucose, (i) the ring opening and consecutive

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dehydration via open-chain intermediates (mainly 3-deoxyglucosone and 3,4-

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dideoxyglucosone) and (ii) the ring opening and isomerization to fructose and

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consecutive dehydration via fructofuranose ring intact.14-16 It has been shown by


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computational methods that the formation of HMF from glucose via isomerization to

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fructose (ii) has lower energy barriers under pyrolysis conditions.17

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Degradation of sugars is effected by many factors including water activity, pH,

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temperature, presence of catalyzers such as alkali metal ions and the physical state

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in low moisture conditions. NaCl is known to catalyze degradation of sugars and

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HMF, as a main dehydration product, increase.18 In addition to that, the interaction

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of NaCl with amino acids may produce sodium and chloride salts of amino acids and

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upon heating HCl can be formed, thereby increasing the acidity and the chlorinating

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potential of the Maillard reaction mixtures.19 Although catalyzer effect of NaCl on

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the degradation of glucose and on the formation of HMF is known, there is no

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information on the formation of α–dicarbonyl compounds from glucose in the

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presence of NaCl. Therefore, the questions arise here that whether dehydration of

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glucose produce more 3-deoxyglucosone and 3,4-dideoxyglucosone, or are these α–

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dicarbonyl compounds dehydrate faster and yield to lower concentrations

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themselves to form HMF, or does HMF formation become even more favorable via

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dehydration over fructofuranose? It is obvious that these questions cannot be truly

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answered without estimating the elementary reaction rate constants, which can be

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obtained by multiresponse kinetic modeling.

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Understanding the fate of the key intermediates α–dicarbonyl compounds during

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high temperature processing is critical for quality and safety viewpoints as discussed.

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In this study, the formation of fructose, glucosone, 1-deoxyglucosone, 3-

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deoxyglucosone, 3,4-dideoxyglucosone, glyoxal, methylglyoxal, diacetyl and 5-

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hydroxymethyl-2-furfural in glucose and glucose-NaCl mixture have been


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investigated under caramelization conditions at elevated temperatures. By using

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multiresponse kinetic modeling, elementary reaction steps were quantitatively

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criticized.

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Materials and Methods

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Chemicals and consumables

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3–Deoxyglucosone (75%), quinoxaline (99%), 2–methylquinoxaline (97%), 2,3–

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dimethylquinoxaline

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diethylenetriaminepentaacetic acid (DETAPAC) (98%), D–glucose (>99.5%), D–

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fructose (>99%), methanol, water and acetonitrile (all MS grade) were purchased

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from Sigma-Aldrich (Steinheim, Germany). 5–Hydroxymethyl–2–furfural (HMF) (98%)

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was purchased from Acros (Geel, Belgium). Formic acid (98%) was purchased from JT

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Baker (Deventer, Holland). Potassium hexacyanoferrate, zinc sulfate, disodium

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hydrogen phosphate anhydrous, sodium dihydrogen phosphate dihydrate and

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sodium chloride were purchased from Merck (Darmstadt, Germany). Syringe filters

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(nylon, 0.45 μm) and Oasis HLB solid phase extraction cartridges (30 mg, 1 ml) were

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supplied by Waters (Milford, MA, USA).

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Preparation, heat treatment and extraction of glucose and glucose-NaCl systems

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Glucose (0.1 M) and glucose-NaCl (0.1 M each) solutions were prepared in water and

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0.5 mL was transferred to glass tubes. By doing so, all tubes contained same amount

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of glucose by pipetting rather than weighting sugar crystals. Also glucose and NaCl

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became a homogenous mixture, otherwise when the solid mixture heated, glucose

(97%),

o–phenylenediamine


(98%),

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would melt but NaCl crystals would not disturbed. This would cause to an interaction

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limited to diffusion on the NaCl crystal surface. Hence, then the tubes were frozen at

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-80 °C and freeze-dried to observe caramelization conditions during heating. It

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should be noted that freeze-drying led glucose and glucose-NaCl systems to two

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different types of amorphous states, which was not characterized in this study, but

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amorphous state is the case for many food. The tubes were screwed with PTFE

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sealed caps and heated in an oil bath (Memmert, Germany) at 160, 180 and 200 °C

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for up to 30 min in duplicates. After cooling the tubes to room temperature, they

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were kept at -20 °C until extraction. The reaction mixtures were dissolved with 2.5

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mL of water by vortexing and shaking the tubes for 1 min.

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Analysis of α–dicarbonyl compounds

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Derivatization. Derivatization of α–dicarbonyl compounds was carried out with o–

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phenylenediamine according to a published procedure with minor modifications.20

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The derivatization of 0.5 mL extract was performed by adding 150 μL 0.1 M pH 7

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phosphate buffer and 150 μL 0.2% o–phenylenediamine in 10 mM DETAPAC. The

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mixture was immediately filtered into an autosampler vial through a syringe filter

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and kept in dark at room temperature for 2 h before analysis.

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HPLC–ESI–MS measurement. The quinoxaline derivatives of glucosone, 3–

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deoxyglucosone, 1–deoxyglucosone, 3,4–dideoxyglucosone, glyoxal, methylglyoxal

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and diacetyl were determined by LC–ESI–MS according to Kocadağlı and Gökmen

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(2014) by using an Agilent 1200 series HPLC system coupled with an Agilent 6130

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single quadrupole mass spectrometer.21 The chromatographic separation was


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performed on a Merck Purospher Star RP–18e column (150 mm × 4.6 mm id., 5 μm)

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using a gradient mixture of (A) 1% formic acid in water and (B) 1% formic acid in

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methanol as the mobile phase at a flow rate of 1 mL/min at 30 °C. The gradient

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mixture was started from 30% B and increased to 60% B in 10 min, then it was

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decreased to 30% B in 2 min and the 30% B remained for 3 min. The

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chromatographic run was completed in 15 min. The injection volume was 10 μL. The

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electrospray source had the following settings: drying gas (N2) flow of 13 L/min at

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300°C, nebulizer pressure of 40 psig and capillary voltage of 4000 V. Fragmentor

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voltage was set to 100 V. MS data were acquired in the positive mode and α–

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dicarbonyl compounds were identified by selected ion monitoring (SIM) mode. The

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SIM ions [M+H]+ were as follows for the quinoxaline derivatives of glucosone: 251;

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1– or 3–deoxyglucosone: 235; 3,4–dideoxyglucosone: 217; dimethylglyoxal: 159;

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methylglyoxal: 145; and glyoxal: 131. A dwell time was set at 97 ms for each.

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The SIM ions of the quinoxaline derivatives of α–dicarbonyl compounds were used

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for quantitation. Total and extracted ion chromatograms of the quinoxaline

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derivatives of α-dicarbonyl compounds identified in a heated glucose-NaCl mixture

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are given in the supporting information (Figure S1 and S2). The concentrations of

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quinoxaline, 2–methylquinoxaline and 2,3–dimethylquinoaxaline were calculated by

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means of external calibration curves in the range between 0.1 and 2 mg/L. Working

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solutions of 3–deoxyglucosone in the concentration range between 0.1 and 5 mg/L

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were derivatized and analyzed as described above to build its external calibration

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curve. Also, this calibration curve was used for semi-quantitation of glucosone, 1–


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deoxyglucosone and 3,4-dideoxyglucosone quinoxaline derivatives since both have

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same proton accepting groups. All working solutions were prepared in water.

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Analysis of glucose and fructose

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A part of the extract was filtered through a syringe filter into an autosampler vial

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prior to analysis. Analysis of sugars was performed on Agilent 1200 HPLC system

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consisting of a quaternary pump, an autosampler, a column oven and a refractive

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index detector. An isocratic elution of 5 mM H2SO4 in water at a flow rate of 1

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mL/min was used in Shodex Sugar SH–1011 column (300 mm × 8 mm i.d., 7 μm)

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(Tokyo, Japan) conditioned to 50 °C. The injection volume was 5 μL. Quantification of

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glucose and fructose was according to the external calibration curves built between

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the concentrations of 0.005–1 %.

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Analysis of 5–hydroxymethyl–2–furfural

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The extract was filtered through 0.45 μm syringe filter into an autosampler vial prior

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to analysis. The analysis was performed by Shimadzu UFLC system (Kyoto, Japan)

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consisting of a quaternary pump, an autosampler, a diode array detector and a

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temperature–controlled column oven. The chromatographic separation was

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performed on an Waters Atlantis dC18 column (250 mm x 4.6 mm i.d., 5 μm) using

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the isocratic mixture of 10 mM aqueous formic acid solution and acetonitrile (90:10)

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at a flow rate of 1.0 mL/min at 25 °C. Data acquisition was performed by recording

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chromatograms at 285 nm. Concentration of HMF was calculated by means of an

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external calibration curve built in the range between 0.1 and 10 mg/L.


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Multiresponse kinetic modeling

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A comprehensive reaction mechanism was built comprising major α–dicarbonyl

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compound formation pathways in caramelization (Figure 2). Each reaction step was

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characterized by its rate constant (k) as parameters. The reaction network was

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translated to a mathematical model by setting up differential equations for each

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elementary reaction step (Appendix A). This provided to observe how reactants and

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products are quantitatively linked. Athena Visual Studio software (v.14.2)

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(AthenaVisual Inc.) was used for numerical integration and the parameters were

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estimated by non–linear regression using the determinant criterion.22 The amount of

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reactants and products were expressed as μmol and individually measured

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concentrations of the repetitions were used during parameter estimation.

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Experimentally obtained data was compared with the mathematical model and the

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steps in the reaction network were criticized by model discrimination. The kinetic

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model was evaluated with the goodness of fit and also with the highest posterior

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density (HPD) intervals of the estimated parameters.

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Temperature dependence of the rate constants were evaluated by means of

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activation energies Ea (kJ/mol) defined by Arrhenius equation, which is

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reparameterized to the average base temperature studied (Tb = 180 °C) for statistical

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reasons.22 Reparameterized Arrhenius equation is:

= ×

1 −


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where, kb is reparameterized pre-exponential factor (equals to the rate constant at

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Tb), R is the universal gas constant (8.3145x10-3 kJ.mol-1.K-1) and T is the absolute

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temperature concerned. The rate constants (k) in the differential equations were

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replaced by the reparameterized Arrhenius equation and the data for 160, 180 and

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200 °C was simultaneously fitted during parameter estimation.

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Results and Discussion

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Degradation of glucose, formation of α–dicarbonyl compounds and effect of NaCl

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In Figure 3 and Figure 4, markers show experimentally observed data measured

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from individual repetitions for reactants and products formed in heated glucose and

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glucose-NaCl systems, respectively. In these figures, lines correspond to model fit,

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i.e. predicted values from the kinetic model, which are discussed in next sections.

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The initial amount of glucose was determined as 47.1±0.66 μmol in glucose

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caramelization model and it was 56.4±0.77 μmol in glucose-NaCl caramelization

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model. Degradation of glucose was apparently faster in the presence of NaCl.

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Fructose was formed with a very high initial rate and the apparent peak

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concentrations were observed in the first minute of heating performed. Afterwards,

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the concentration of fructose decreased and the rate of loss were higher in the

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presence of NaCl especially at 180 and 200 °C.

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Dehydration of sugars to 1-deoxyglucosone and 3-deoxyglucosone and oxidation to

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glucosone was started also in the early minutes of heating and degradation was

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observed afterwards, especially at 180 °C and 200 °C (Figures 3 and 4). The apparent

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peak concentrations of 3,4-dideoxyglucosone were followed to those of 3-


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deoxyglucosone. The amount of glucosone, 1-deoxyglucosone, 3-deoxyglucosone

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and 3,4-dideoxyglucosone per mole of glucose were lower in the presence of NaCl.

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In the glucose system, the average ratio of the amount of 3-deoxyglucosone to 1-

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deoxyglucosone was 4.6±0.5, 4.0±1.2 and 3.9±1.0 at 160, 180 and 200 °C,

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respectively. The ratio was slightly increased to 5.6±0.3, 5.2±1.5 and 5.3±1.2 in the

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glucose-NaCl system at 160, 180 and 200 °C, respectively. Shorter chain α–dicarbonyl

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compounds glyoxal, methylglyoxal and diacetyl were produced with lower initial

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rates than hexodiuloses detected. Their amounts formed were also lower in the

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presence of NaCl.

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High levels of HMF formation were observed and the rate of HMF formation was

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faster in the presence of NaCl as expected (Figures 3 and 4). The amount of HMF

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formed in the presence of NaCl was almost 10 fold higher for the same time-

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temperature treatment. The maximum mole conversions of glucose to HMF were

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0.4% at 160 °C (30 min), 1.6% at 180 °C (20 min) and 3.5% at 200 °C (15 min) during

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caramelization of glucose only. These maximum conversions in the presence of NaCl

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altered to 1.4% at 160 °C (20 min), 3.1% at 180 °C (10 and 15 min) and 3.7% at 200 °C

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(3 min).

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Building up a reaction network

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The comprehensive reaction mechanism given in Figure 1 was simplified for

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modeling purposes to the scheme given in Figure 2. To obtain this simplified version,

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model discrimination was performed as discussed for each compound in the

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following sections as if necessary. Model discrimination provided to reveal best


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kinetic model describing the experimentally observed data according to proposed

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reaction pathways. This was also necessary to keep unknown parameters

250

manageable.

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According to this reaction network (Figure 2), glucose is dehydrate to 3-

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deoxyglucosone and oxidized to glucosone. Dehydration of 3-deoxyglucosone

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produce 3,4-dideoxyglucosone and the later one further dehydrates to produce

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HMF. Glucose reversibly isomerizes to fructose and dehydration of fructose produce

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1-deoxyglucosone. Dehydration of fructose to form HMF via cyclic intermediates was

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reduced to two steps, comprising an undetermined intermediate (Int) for

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simplification. These undetermined intermediates could be the enol form of 2,5-

258

anhydro-D-mannose, which can be formed from dehydration of C2 hydroxyl of D-

259

fructofuranose, and subsequently this enol intermediate dehydrate from C3 to form

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a 2,3-dihydrofuran and further dehydration produce HMF as seen Figure 1.

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Formation of glyoxal from glucosone, methylglyoxal from 3-deoxyglucosone, and

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diacetyl from 1-deoxyglucosone were taken account in. Certain compounds shown in

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Figure 2 were considered with their degradation to undetermined end products

264

since these reactive intermediates are prone to complex degradation and

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polymerization reactions.

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This elementary reaction steps were transformed to differential equations and the

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mathematical model compared with the experimentally observed data. Primarily,

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the data for each temperature was fitted separately and reaction rate constants

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were determined as given in Table 1.

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dependence of the elementary reactions all data was fitted together as described

In order to determine temperature


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above by using Arrhenius equation. The parameters estimated for Arrhenius

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equation are given in Table 2, and model fits are given as supporting information

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(Figures S3 and S4).

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Kinetics of glucose-fructose interconversion and effect of NaCl

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Glucose and fructose isomerize each other by 1,2–enediol intermediate and this

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rearrangement is known as Lobry de Bruyn-Alberda van Ekenstein transformation. In

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a parallel reaction, 1,2-enediol also involve in the epimerization of glucose to

278

mannose. However, it has been often observed to be of minor importance in

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proportion to aldose-ketose interconversion.23 During heating of glucose and

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glucose-NaCl systems no mannose formation was observed. In order to simplify the

281

model enediol intermediate was not included as the interconversion was obviously

282

fast. The importance of the enolization in the presence of amino compounds is

283

different.24

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According to estimated rate constants isomerization of fructose to glucose (k2) was

285

about 5 times higher than the isomerization of glucose to fructose (k1) both in

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glucose and glucose-NaCl systems (Table 1). The same difference and slightly lower

287

values for rate of isomerization was also reported in aqueous glucose-glycine

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Maillard reaction system.25 However it should be mentioned that the highest

289

posterior density intervals for the estimation of conversion of fructose to glucose (k2)

290

could not be determined at 180 °C and 200°C. This indicates a large uncertainty for

291

the estimate within a 95% confidence interval. This was the case also for activation

292

energies of glucose-fructose interconversion, which had a larger HPD than the most


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other estimates. Nonetheless, there were obvious differences between the optimal

294

estimates, which could lead us to make a proper comparison. The interconversion

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rate constants at 180 and 200 °C in the presence of NaCl become 2.5 times faster

296

while maintaining the 5 fold difference among forward and reverse direction rate

297

constants. The interaction of metal halides with glucose has been shown to catalyze

298

mutarotation and isomerization of glucose to fructose.26 It has been proposed that

299

sugar-metal coordination is responsible for the catalyzation and it was revealed that

300

the metal interacts with the hemiacetal portion of glucopyranose.26 The effect of

301

catalysis by Na+ on the conversion of glucose to fructose was also evident from

302

kinetic parameters obtained by computational methods considering energy states of

303

molecules and transition states.27 In that study, the rate constant of isomerization of

304

acyclic glucose to acyclic fructose was found to be 4.5 fold higher in the presence of

305

Na+ under pyrolysis conditions at 500 °C.

306

The activation energy of conversion of glucose to fructose was estimated to be 151.5

307

kj/mol (Table 2). This value was consistent with the theoretical calculation, which

308

was 146.7 kJ/mol under pyrolysis conditions.17 However, the reverse direction rate

309

of isomerization was reported to be lower and the activation energy was higher than

310

results of this study. It should be noted that the parameters of this step did not well

311

estimated according to the proposed kinetic model.

312

The temperature dependence of the interconversion was higher in the presence of

313

NaCl (Table 2). This seemed interesting because the rate constants were higher at

314

180 and 200 °C. But it was due to the limitation of Arrhenius equation, which does

315

not take the physical conditions of the system into consideration. Even though the


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obvious faster interconversion at 180 and 200 °C, the rate constants for

317

isomerization at 160 °C were not significantly different (Table 1). For any reaction to

318

occur mobility of the reactant molecule is a must, which could be obtained by

319

melting or glass transition in the case of dry heating of solids. You and Ludescher

320

(2008) investigated the effect of NaCl on the molecular mobility of amorphous

321

sucrose and revealed that NaCl decreased the matrix molecular mobility.28 They

322

proposed that the measures of spectral heterogeneity are consistent with a physical

323

model in which sodium and chloride ions interact with sucrose hydroxyls by ion–

324

dipole interactions, forming clusters of less mobile molecules within the matrix.28

325

This could explain the absence of any apparent catalytic activity of NaCl on glucose-

326

fructose interconversion at a lower temperature and obvious catalysis at higher

327

temperatures. Therefore, the activation energy estimated here should not be

328

considered as measure of an energy barrier for the reaction. The limitations of

329

Arrhenius equation in food systems and complex reactions were well discussed by

330

Peleg, Normand and Corradini (2012).29

331

Kinetics

332

dideoxyglucosone formation and effect of NaCl

333

Formation of glucosone was considered from only glucose oxidation, since its

334

amount was about five times higher than fructose. Formation of glucosone was

335

estimated with very high precision and a good fit (Figure 3). Rate constants indicated

336

that oxidation is of quantitatively minor importance than dehydration reactions

337

(Table 1). Degradation of glucosone proceeds to form glyoxal, which was also

338

estimated with high precisions and good fits. If degradation of glucosone to other

of

glucosone,

1-deoxyglucosone,

3-deoxyglucosone


and

3,4-

16

Page 17 of 38


339

undetermined products included to model, its rate constant was estimated to be

340

zero. In the presence of NaCl, the rate constant of glucosone formation (k9) was

341

slightly lower (≈15%) and the model fit was not as good as in the absence of NaCl

342

(Figures 3 and 4).

343

Similar to glucosone, formation of 3-deoxyglucosone was considered only from

344

glucose (k3). The rate constant of 3-deoxyglucosone formation from fructose was

345

estimated to be zero in every case, which indicated that it was of minor importance

346

due to high amounts formed from glucose. The model fits and uncertainty of the

347

estimated rate constants were acceptable. However, in the later stages of heating at

348

200 °C, the amount of 3-deoxyglucosone formed was less predicted by the model in

349

glucose system and it was also observed in glucose-NaCl model at 180 and 200 °C.

350

The rate constant of 3-deoxyglucosone formation (k3) was significantly lower in the

351

presence of NaCl at 160 °C and 180°C (Table 1). There was no significant difference

352

at 200 °C, due to the higher uncertainty for the parameter in glucose-NaCl system.

353

The decrease in rate constant of 3-deoxyglucosone formation (k3) is very interesting

354

since 3-deoxyglucosone is often considered together with HMF, as an intermediate.

355

However, higher HMF formation from glucose in the presence of NaCl did not

356

associate quantitatively with 3-deoxyglucosone formation (model discrimination for

357

HMF formation is given in the last section). The decrease in rate constant of 3-

358

deoxyglucosone formation from glucose was parallel with the theoretical

359

computational study of Mayes et al. (2015) who investigated the elementary

360

dehydration pathways of glucose in the presence of Na+ under pyrolysis conditions.27

361

They have reported that the rate constant of dehydration of acyclic glucose to acyclic


17


Page 18 of 38

362

enol form of 3-deoxyglucosone was 40% lower in the presence of sodium cation. As

363

3-deoxyglucosone is major α-dicarbonyl compound found in almost all sugar rich

364

processed foods, effect of metal cations should be investigated in detail as a possible

365

mitigation strategy.

366

Formation of 3,4-dideoxyglucosone by dehydration of 3-deoxyglucosone was faster

367

in the presence of NaCl at 180 °C and 200 °C, but not significant for 180 °C. The rate

368

of formation of 3,4-dideoxyglucosone was lower at 160 °C in the presence of NaCl.

369

Since presence of NaCl decreases matrix mobility in sugars28, its effect as a catalyzer

370

could be reverse at 160 °C.

371

1-Deoxyglucosone is formed from fructose via 2,3-enolization, which does not occur

372

from glucose. The fit of kinetic model was good (Figures 2 and 3) and parameters

373

were estimated with high precision (Table 1). The presence of NaCl also lowered the

374

rate of formation of 1-deoxyglucosone from fructose.

375

Kinetics of glyoxal, methylglyoxal and diacetyl formation and effect of NaCl

376

Glyoxal can be formed from glucosone by cleavage of C2-C3 bond and also other

377

carbons in glucose have demonstrated to be as source.30 In this kinetic model only

378

glucosone was considered in the formation of glyoxal not to increase unknown

379

parameters. Since the model fits were good and the parameter estimation was

380

precise, there was no need to consider other pathways. The rate of glyoxal

381

formation was increased in the presence of NaCl depending on temperature (Table

382

1). There were apparently lower amount of glyoxal observed since degradation rates

383

were also increased, except at 200 °C which had an unacceptable uncertainty. The


18

Page 19 of 38


384

degradation rate of glyoxal showed a diminishing trend as temperature increase. The

385

reason for that was attempted to higher volatility of the compound, which diffuse to

386

the headspace of the tube during heating. This was also the case for methylglyoxal

387

and diacetyl. This observation was also reported during heating glucose-wheat flour

388

model system.24

389

Methylglyoxal forms from both 1-deoxyglucosone and 3-deoxyglucosone by retro-

390

aldol cleavage.30, 31 The model tended to estimate the rate constant of methylglyoxal

391

formation from 1-deoxyglucosone zero in most cases. Additionally, the precision of

392

the rate constants of methylglyoxal formation from 3-deoxyglucosone (k11) was

393

increased when the methylglyoxal formation from 1-deoxyglucosone omitted from

394

the model (Table 1). It should be noted that both pathways probably happens but

395

the one, which is predominant, become quantitatively important in parameter

396

estimation. The source of methylglyoxal would be different in a Maillard reaction

397

system, in which the product spectrum also depends on the degradation of Amadori

398

product. In a previous study, Kocadağlı and Gökmen (2016) proposed methylglyoxal

399

formation only from 1-deoxyglucosone, which was a predominantly formed α-

400

dicarbonyl compound in Maillard reaction from Amadori product degradation in

401

heated glucose-wheat flour system under low moisture conditions.24 This is in good

402

agreement with the present observation because in the previous study 1-

403

deoxyglucosone formation from fructose dehydration was estimated to be zero and

404

omitted from the model. Here in heated glucose system, the origin of 1-

405

deoxyglucosone was only fructose and was not predominant as in Maillard reaction.

406

Hence the main source of methylglyoxal may quantitatively depend on the amount


19


Page 20 of 38

407

of precursor α-dicarbonyl compound formed. This indicates the importance and

408

force of multiresponse kinetic modeling for investigating and understanding parallel

409

and consecutive reactions in foods.

410

No effect of NaCl on the formation rate constant of methylglyoxal was observed at

411

180 °C and 200 °C and the apparent lower amounts of methylglyoxal in the glucose-

412

NaCl system stemmed from the lower rate of 3-deoxyglucosone formation. At 160 °C

413

the rate was higher in the presence of NaCl. Formation rate constant of diacetyl from

414

1-deoxyglucosone slightly increased. However, the degradation of diacetyl was not

415

estimated with an appropriate uncertainty (Table 1). When all temperatures were

416

fitted together the degradation rate of diacetyl was estimated as zero (Table 2). In

417

general, due to the temperature independences observed in the degradation rates

418

of glyoxal, methylglyoxal and diacetyl, their formation rates were not much

419

conclusive in the presence of NaCl.

420

Kinetics of 5-hydroxymethyl-2-furfural formation and effect of NaCl

421

Consecutive removal of 3 molecules of water from a hexose sugar ends with the

422

formation of HMF. For the formation of 5 membered ring of HMF, a ring opening is

423

necessary from glucose. On the contrary, fructose dehydrate to HMF without ring

424

opening.14 A kinetic model constructed by omitting the formation of HMF from

425

fructose through an undetermined intermediate did not fit to the experimentally

426

observed data of either or both 3-deoxyglucosone, 3,4-dideoxyglucosone and HMF

427

by no means (Figure S5, see Supporting Information). In this test, other responses

428

not much affected (not shown). This indicates that HMF formation through only


20

Page 21 of 38


429

dehydration of 3-deoxyglucosone does not correspond to amounts of HMF observed

430

quantitatively. This observation was also evident in the multiresponse kinetic

431

modeling of Maillard reaction and caramelization during heating of glucose-wheat

432

flour system under low moisture conditions.24

433

The estimated rate constants clearly indicated that HMF is primarily formed from

434

fructose dehydration. In the presence of NaCl, the rate constants of HMF formation

435

from fructose (k6 and k7) increased about 4 fold. On the other hand, due to the

436

decrease in the rate of 3-deoxyglucosone formation from glucose, effect of NaCl

437

catalysis on the HMF formation stemmed only from fructose dehydration. Faster

438

dehydration of 3-deoxyglucosone to 3,4-dideoxyglucosone and further to HMF was

439

only significant at 200 °C in the presence of NaCl. Mayes et al (2014) indicated that

440

HMF formation from glucose through isomerization to fructose and dehydration

441

over cyclic intermediates has lower energy barriers than other pathways

442

investigated by computational methods.17 In a subsequent study, Mayes et al (2015)

443

showed that Na+ modifies rate constants by the interaction especially with the

444

transition states in a particular stereochemistry and the rate constants become

445

higher for dehydration over fructofuranose ring intact.27 Therefore, the results of the

446

present study are consistent with expected physical chemistry of dehydration

447

reactions.

448

Furthermore, the results of the present study confirms the findings of Gökmen &

449

Şenyuva (2007) who proposed the mitigation effect of metal cations on acrylamide

450

formation in glucose-asparagine system was due to the switch of the reaction of

451

glucose in Maillard reaction to dehydrate through fructofuranose to form HMF and


21


Page 22 of 38

452

furfural.18 It could be also speculated that the decrease in the rate of α-dicarbonyl

453

compounds formation could be also related to mitigation of acrylamide formation in

454

glucose-asparagine model system. Because conversion of asparagine to acrylamide

455

has been shown to enhance by neo-formed carbonyls from sugars.5,

456

studies are needed to reveal effects of sodium chloride on Maillard reaction

457

especially in real food systems.

458

The results indicated that sodium chloride decrease the amount of α-dicarbonyl

459

compounds and increase the amount of HMF formed from glucose. Effect of salt on

460

the rate constants of α-dicarbonyl compound formation varied across the precursor

461

and the compound’s itself and also on the temperature. Formation of 3-

462

deoxyglucosone, which is the major source of α-dicarbonyl compound exposure, was

463

found to be decreasing from glucose in the presence of sodium chloride. It can be

464

hypothesized that degradation of glucose switch to cyclic intermediates in the

465

presence of sodium chloride, as evident from decrease in the rate of α-dicarbonyl

466

compounds formation and elevation of fructose degradation to HMF through cyclic

467

intermediates.

468

The proposed kinetic model revealed how α-dicarbonyl compounds are

469

quantitatively link to their precursors and how they reactively degrade to end

470

products. The model showed its robustness for the formation of α-dicarbonyl

471

compounds and HMF since it responded well enough to the catalyzer effect of

472

sodium chloride. Nonetheless, since presence of salt altered the rate of the

473

formation of reactive intermediates and so the end products, more research needed

474

to figure out the undetermined compounds, especially cyclic ones, to better


33

Further

22

Page 23 of 38


475

understand how cations effect the kinetics of browning and flavor development. The

476

effect of salt on browning and flavor development should be also considered in

477

order to archive efforts of salt reduction especially in cereal products in view of

478

consumer acceptance. Lastly, the impact of several minerals, largely varying in the

479

raw food materials, should be evaluated on the formation of α-dicarbonyl

480

compounds for understanding food quality and safety.

481


23


Page 24 of 38

482

Abbreviations

483

Glc: glucose; Fru: fructose; 1–DG: 1–deoxyglucosone; 3–DG: 3–deoxyglucosone; 3,4–

484

DG: 3,4–dideoxyglucosone; G: glucosone; GO: glyoxal; MG: methylglyoxal; DA:

485

diacetyl; HMF: 5–hydroxymethyl–2–furfural; Int: intermediate; P: products; HPD:

486

highest posterior density.

487

Supporting Information.

488

Total and extracted ion chromatograms of the quinoxaline derivatives of α-

489

dicarbonyl compounds (Figure S1 and S2). Kinetic model fits according to the

490

Arrhenius equation for heated glucose (Figure S3) and glucose-NaCl system (Figure

491

S4). Kinetic model fits when HMF formation from fructose omitted (Figure S5).

492


24

Page 25 of 38


493

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494

1.

495

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496

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497

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acrylamide formation in coffee during roasting: role of sucrose decomposition and

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lipid oxidation. Food Funct. 2012, 3, 970-975.

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Yaylayan, V. A., Classification of the Maillard reaction: A conceptual

Rabbani, N.; Thornalley, P. J., Dicarbonyl stress in cell and tissue dysfunction

Yaylayan, V. A., Recent advances in the chemistry of Strecker degradation

Sebekova, K.; Somoza, V., Dietary advanced glycation endproducts (AGEs)

Kocadağlı, T.; Göncüoğlu, N.; Hamzalıoğlu, A., Gökmen V., In depth study of

Perez Locas, C.; Yaylayan, V. A., Origin and mechanistic pathways of

Furihata, C.; Matsushima, T., Mutagens and carcinogens in foods. Annu. Rev.


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Labuza, T. P., Application of chemical kinetics to deterioration of foods. J.

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Compr. Rev. Food Sci. Food Saf. 2008, 7, 144-158.

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multiresponse approach as applied to chlorophyll degradation in foods. Food Res.

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Raton, Fla., 2009.

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rearrangement products: analysis, synthesis, kinetics, reactions, and spectroscopic

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properties. Crit. Rev. Food Sci. Nutr. 1994, 34, 321-69.

526

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(hydroxymethyl)-2-furaldehyde from D-fructose and sucrose. Carbohydr. Res. 1990,

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529

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compounds. Part I. 5-Hydroxymethylfurfuraldehyde and some derivatives. J. Chem.

531

Soc. (Resumed). 1944, 667.

van Boekel, M. A. J. S., Kinetic modeling of food quality: a critical review.

van Boekel, M. A. J. S., Testing of kinetic models: usefulness of the

van Boekel, M. A. J. S., Kinetic modeling of reactions in foods. CRC Press: Boca

Kroh, L. W., Caramelisation in food and beverages. Food Chem. 1994, 51, 373-

Yaylayan,

V.

A.;

Huyghues-Despointes,

A.,

Chemistry

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Antal, M. J., Jr.; Mok, W. S.; Richards, G. N., Mechanism of formation of 5-

Haworth, W. N.; Jones, W. G. M., 183. The conversion of sucrose into furan


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Locas, C. P.; Yaylayan, V. A., Isotope labeling studies on the formation of 5-

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(hydroxymethyl)-2-furaldehyde (HMF) from sucrose by pyrolysis-GC/MS. J. Agric.

534

Food Chem. 2008, 56, 6717-6723.

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17.

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Alpha–Bet(a) of Glucose Pyrolysis: Computational and Experimental Investigations of

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5-Hydroxymethylfurfural and Levoglucosan Formation Reveal Implications for

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Cellulose Pyrolysis. ACS Sustain. Chem. Eng. 2014, 2, 1461-1473.

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18.

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acrylamide and furfurals in glucose-asparagine model system. Eur. Food Res.

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Technol. 2007, 225, 815-820.

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chloride in the presence of amino acids. Food Chem. 2015, 166, 301-308.

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Consumed Foods. J. Agric. Food Chem. 2012, 60, 7071-7079.

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Baby Foods by High-Performance Liquid Chromatography Coupled with Electrospray

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Ionization Mass Spectrometry. J. Agric. Food Chem. 2014.

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problems. J. Food Sci. 1996, 61, 477-486.

Mayes, H. B.; Nolte, M. W.; Beckham, G. T.; Shanks, B. H.; Broadbelt, L. J., The

Gökmen, V.; Şenyuva, H. Z., Effects of some cations on the formation of

Rahn, A. K. K.; Yaylayan, V. A., Mechanism of chemical activation of sodium

Degen, J.; Hellwig, M.; Henle, T., 1,2-Dicarbonyl Compounds in Commonly

Kocadağlı, T.; Gökmen, V., Investigation of alpha-Dicarbonyl Compounds in

van Boekel, M. A. J. S., Statistical aspects of kinetic modeling for food science


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Angyal, S. J., The Lobry de Bruyn-Alberda van Ekenstein Transformation and

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Related Reactions. In Glycoscience: Epimerisation, Isomerisation and Rearrangement

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Reactions of Carbohydrates, Stütz, A. E., Ed. Springer: Germany, 2001; pp 1-14.

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24.

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reaction and caramelisation in a heated glucose/wheat flour system. Food Chem.

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2016, 211, 892–902.

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25.

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glucose/glycine Maillard reaction pathways. Food Chem. 2005, 90, 257-269.

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solvents convert sugars to 5-hydroxymethylfurfural. Science. 2007, 316, 1597-600.

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alpha–bet(a) of salty glucose pyrolysis: computational investigations reveal

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carbohydrate pyrolysis catalytic action by sodium ions. ACS Catal. 2015, 5, 192-202.

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28.

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in amorphous sucrose detected by phosphorescence from the triplet probe

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erythrosin B. Carbohydr. Res. 2008, 343, 350-63.

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revisited. Crit. Rev. Food Sci. Nutr. 2012, 52, 830-51.

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alpha-Dicarbonyl compounds. J. Agric. Food Chem. 2009, 57, 8591-8597.

Kocadağlı, T., Gökmen, V., Multiresponse kinetic modelling of Maillard

Martins, S. I. F. S.; van Boekel, M. A. J. S., A kinetic model for the

Zhao, H.; Holladay, J. E.; Brown, H.; Zhang Z. C., Metal chlorides in ionic liquid

Mayes, H. B.; Nolte, M. W.; Beckham, G. T.; Shanks, B. H.; Broadbelt, L. J., The

You, Y.; Ludescher, R. D., The effect of sodium chloride on molecular mobility

Peleg, M.; Normand, M. D.; Corradini, M. G., The Arrhenius equation

Gobert, J.; Glomb, M. A., Degradation of glucose: reinvestigation of reactive


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Yaylayan, V. A.; Keyhani, A., Origin of carbohydrate degradation products in

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L-alanine/D-[(13)C]glucose model systems. J. Agric. Food Chem. 2000, 48, 2415-2419.

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32.

574

mono- and disaccharides under caramelization and Maillard reaction conditions. Z.

575

Lebensm.-Unters. -Forsch. A. 1998, 207, 50-54.

576

33.

577

role of 5-hydroxymethyl-2-furfural in acrylamide formation from asparagine. Food

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Chem. 2012, 132, 168-174.

Hollnagel, A.; Kroh, L. W., Formation of alpha-dicarbonyl fragments from

Gökmen, V.; Kocadağlı, T.; Göncüoğlu, N., Mogol, B. A., Model studies on the

579


29


Page 30 of 38

580

Figure Captions

581

Figure 1. Mechanism of α-dicarbonyl compounds and HMF formation from glucose

582

and fructose degradation.

583

Figure 2. Reaction network used for multiresponse kinetic modeling. Glc: glucose;

584

Fru: fructose; 1–DG: 1–deoxyglucosone; 3–DG: 3–deoxyglucosone; 3,4–DG: 3,4–

585

dideoxyglucosone; G: glucosone; GO: glyoxal; MG: methylglyoxal; DA: diacetyl; HMF:

586

5–hydroxymethyl–2–furfural; Int: intermediate; P: products.

587

Figure 3. Kinetic model fit (lines) to the individually obtained experimental data

588

(markers) of reactants and products in heated glucose system. Blue color for markers

589

and lines designates 160 °C, green 180 °C and red 200 °C. Open gem (◊) marker

590

designates glucose; open triangle (Δ) fructose; others (o) as indicated in their y-axis

591

labels.

592

Figure 4. Kinetic model fit (lines) to the individually obtained experimental data

593

(markers) of reactants and products in heated glucose-NaCl system. Blue color for

594

markers and lines designates 160 °C, green 180 °C and red 200 °C. Open gem (◊)

595

marker designates glucose; open triangle (Δ) fructose; others (o) as indicated in their

596

y-axis labels.


30

Page 31 of 38


Table 1. Reaction rate constants with 95% highest posterior density (HPD) intervals at different temperatures according to the proposed kinetic model (Figure 2) for caramelization of glucose and glucose-NaCl mixture. Glc: glucose; Fru: fructose; 1–DG: 1–deoxyglucosone; 3–DG: 3– deoxyglucosone; 3,4–DG: 3,4–dideoxyglucosone; G: glucosone; GO: glyoxal; MG: methylglyoxal; DA: diacetyl; HMF: 5–hydroxymethyl–2–furfural; Int: intermediate; P: products. Glucose 160 °C Elementary reaction steps

Glucose-NaCl

180 °C

200 °C

160 °C

180 °C

200 °C

k (min-1×103)

HPD

k (min-1×103)

HPD

k (min-1×103)

HPD

k (min-1×103)

HPD

k (min-1×103)

HPD

k (min-1×103)

HPD

1

Glc→Fru

237

123

1804

81

3845

305

212

79

4712

599

9489

1388

2

Fru→Glc

1284

737

10409

ind*

17657

ind*

1000

543

24962

ind*

52998

ind*

3

Glc→3-DG

0.91

0.19

4.14

1.71

3.60

1.26

0.39

0.07

0.99

0.31

4.06

2.34

4

3-DG→3,4-DG

23.1

4.03

30.5

4.71

49.3

10.1

10.6

2.26

43.3

9.58

101

28.0

5

3,4-DG→HMF

160

35.0

110

28.2

137

46.1

46.0

29.5

163

57.0

418

120

6

Fru→Int

100

8.6

344

26.0

1058

96.6

391

60.5

1335

184

4297

622

7

Int→HMF

0.31

0.07

1.87

0.15

9.31

1.74

1.15

0.15

10.0

2.62

41.1

13.1

8

Fru→1-DG

0.61

0.15

2.47

0.73

5.89

1.93

0.50

0.13

1.34

0.19

1.96

0.52

9

Glc→G

0.023

0.002

0.054

0.006

0.294

0.017

0.020

0.002

0.054

0.009

0.27

0.03

10

G→GO

361

34.9

594

80.8

2129

149

770

159

787

171

3129

611

11

3-DG→MGO

96.0

20.8

338

29.4

863

98.1

167

24.0

257

65.3

890

217

12

1-DG→DA

2.71

0.58

14.3

1.79

68.8

4.99

10.7

1.45

11.6

0.81

88.4

17.4

13

3-DG→P1

555

153

2241

1117

841

678

202

105

169

222

827

1157

14

1-DG→P2

347

94.5

925

293

2035

719

398

126

516

76.0

445

99.6

15

GO→P3

66.1

11.1

6.49

16.9

33.1

10.1

83.2

20.7

35.1

30.0

5.69

27.4

16

MGO→P4

23.7

19.9

85.0

13.4

65.6

13.2

91.6

24.4

84.2

49.3

35.6

44.7

17

DA→P5

5.53

18.1

28.8

14.4

0

2.15

14.7

0

18

HMF→P6

20.6

11.9

36.7

7.76

203

0.0

0.0

263

56.4

0 86.0

955

313

*ind: indeterminate, which means a large uncertainty in the estimated parameter within 95% confidence interval.

31 ACS Paragon Plus Environment


Page 32 of 38

Table 2. Optimal estimates with 95% highest posterior density (HPD) intervals for reparameterized Arrhenius equation according to the proposed kinetic model (Figure 2) for caramelization of glucose and glucose-NaCl mixture. Glc: glucose; Fru: fructose; 1–DG: 1–deoxyglucosone; 3–DG: 3– deoxyglucosone; 3,4–DG: 3,4–dideoxyglucosone; G: glucosone; GO: glyoxal; MG: methylglyoxal; DA: diacetyl; HMF: 5–hydroxymethyl–2–furfural; Int: intermediate; P: products.

Elementary reaction steps

Glucose kb (min-1×103)

HPD

Glucose-NaCl Ea (kJ/mol)

HPD

kb (min-1×103)

HPD

Ea (kJ/mol)

HPD

1

Glc→Fru

2039

±83

151.5

±99.8

5279

±484

263.6

±23.1

2

Fru→Glc

10942

ind*

146.4

±104.2

27705

ind*

280.8

±29.8

3

Glc→3-DG

4.19

±2.44

107.2

±52.7

1.11

±0.20

85.2

±11.2

4

3-DG→3,4-DG

30.5

±3.39

36.9

±6.3

36.6

±4.18

117.7

±11.1

δ

103

±26.2

169.8

±22.0

5

3,4-DG→HMF

119

±19.8

0

6

Fru→Int

330

±22.8

100.4

±6.6

1402

±122

94.9

±8.1

7

Int→HMF

1.84

±0.70

151.4

±34.3

8.79

±1.67

149.8

±19.0

8

Fru→1-DG

2.11

±0.40

99.3

±21.8

1.36

±0.23

93.9

±18.8

9

Glc→G

0.069

±0.005

125.9

±4.9

0.059

±0.007

131.8

±9.2

10

G→GO

737

±58.9

93.8

±6.4

1033

±170

95.2

±15.1

11

3-DG→MGO

304

±33.5

84.8

±6.9

309

±52.8

95.3

±13.9

12

1-DG→DA

12.2

±1.12

150.8

±8.8

16.1

±3.00

139.9

±18.3

δ

13

3-DG→P1

2239

±1504

90.9

±59.5

231

±131

0

14

1-DG→P2

873

±178

77.9

±23.9

574

±107

55.3

15

GO→P3

32.6

±8.83

0δ

28.5

±21.0

0δ

16

MGO→P4

55.4

±13.2

0δ

73.4

±30.1

0δ

17

DA→P5

0

18

HMF→P6

36.9

±63.0

137.8

±21.1

0 ±64.2

152.8

±154.4

227

±24.6

*ind: indeterminate, which means a large uncertainty in the estimated parameter within 95% confidence interval. δZero activation energy (Ea) indicates that the reaction rate constant (k) of the elementary step does not follow Arrhenius equation and the Ea was fixed to zero during parameter estimation.


32

Page 33 of 38


Figure 1 1-deoxyglucosone

methylglyoxal

diacetyl

[o]

glyoxal

fructofuranose fructose

glucose

glucosone

enol

2,3-dihydrofuran

methylglyoxal

5-hydroxymethyl-2-furfural 3,4-dideoxyglucosone

3-deoxyglucosone


33


Page 34 of 38

Figure 2 P2

14

1-DG

H2O

Int

12

DA

17

P5

8

Fru 6

9

2

Glc

10

G

GO

1 15 3

7 H2O

P3

H2O 11

HMF

3-DG

3,4-DG 5

18

P6

MGO

4 13

P1


16

P4

34

Page 35 of 38


Figure 3

0.07

40 30 20 10

0.05 0.04 0.03 0.02 0.01

5

10 15 20 time, min

25

1-deoxyglucosone, µmol

1.8 1.5 1.2 0.9 0.6 0.3 0

5

10 15 20 time, min

25

5

10 15 20 time, min

25

0.006 0.004 0.002

30

0.02

0.005

0.016

0.004

0.012 0.008 0.004

30

5

10 15 20 time, min

25

30

0.008 diacethyl, µmol

0.2

methylglyoxal, µmol

0.04

0

0.15 0.1 0.05

5

10

15 20 time, min

25

30

30

0

5

10 15 20 time, min

25

30

0

5

10 15 20 time, min

25

30

0.006 0.004 0.002

0 0

25

0 0

0.01

0.01

10 15 20 time, min

0.002

0.25

0.02

5

0.003

0.05

0.03

0

0.001

0 0

0.008

0 0

30

glucosone, µmol

0

HMF, µmol

0.06

0

0

glyoxal, µmol

0.01 3,4-dideoxyglucosone, µmol


glucose/fructose, µmol

50

0 0

5

10 15 20 time, min

25

30


35


Page 36 of 38

Figure 4

0.07

50 40 30 20 10

0

5

10 time, min

15

0.05 0.04 0.03 0.02 0.01 0

20

5

10 time, min

15

1.5 1 0.5 0

0.012

0.008

0.004

0 0

5

10 time, min

15

20

5

10 time, min

15

0.01 0.005 0 5

10 time, min

15

20

0

5

0

5

0

5

10 time, min

15

20

10 time, min

15

20

10 time, min

15

20

0.002

0.001

0.004

0.12

0.08

0.04

0.003 0.002 0.001

0 0

0

0.005

diacetyl, µmol

methylglyoxal, µmol

0.015

0.002

20

0.16

0.02

0.004

0 0

0.025

0.006

0.003

glucosone, µmol

2

0.008

20

0.016 1-deoxyglucosone, µmol

2.5

HMF, µmol

0.06

0

0

glyoxal, µmol

0.01 3,4-dideoxyglucosone, µmol


glucose/fructose, µmol

60

0 0

5

10 time, min

15

20


36

Page 37 of 38


Appendix A. Differential equations, which are built from the kinetic model given in Figure 2. [] = [] − + +! "[] [] = [] − # +$ + "[] [3-'] = [] − ( + + "[3-'] [3,4-'] = ( [3-'] − + [3,4-'] [,-] = + [3,4-'] + . [/0] − $ [HMF] [1-'] = $ [] − + ( "[1-'] [] = ! [] − 5 [] [6] = 5 [] − + [6] [-6] = [3-'] − # [-6] ['7] = [1-'] − . ['7] [/0] = # [] − . [/0] [8 ] = [3-'] [8 ] = ( [1-'] [8 ] = + [6] [8( ] = # [-6] [8+ ] = . ['7] [8# ] = $ [,-]


37


Page 38 of 38

TOC graphic

NaCl

5-hydroxymethyl-2-furfural increased

fructose

glucose


α-dicarbonyls decreased

38

Effect of Sodium Chloride on Î±-Dicarbonyl ... - ACS Publications

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