Volume 3, Issue 4 2007 Article 8
International Journal of Food
Engineering
Simplified Kinetics and Colour Formation in
Sucrose Solutions Based on A-Dicarbonyl
Compounds
Quido Smejkal, QUIDO-Engineering Berlin
Thorsten Fiedler, Pfeifer-Langen KG
Tomas Kurz, Technical University of Berlin
Lothar Kroh, Technical University of Berlin
Recommended Citation:
Smejkal, Quido; Fiedler, Thorsten; Kurz, Tomas; and Kroh, Lothar (2007) "Simplified Kinetics
and Colour Formation in Sucrose Solutions Based on A-Dicarbonyl Compounds," International
Journal of Food Engineering: Vol. 3: Iss. 4, Article 8.
DOI: 10.2202/1556-3758.1250
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Simplified Kinetics and Colour Formation in
Sucrose Solutions Based on A-Dicarbonyl
Compounds
Quido Smejkal, Thorsten Fiedler, Tomas Kurz, and Lothar Kroh
Abstract
Colour formation in technical and model sucrose solutions was investigated resulting in a
novel kinetic approach of MAILLARD reaction during thermal processing of sugar solutions.
Presented results describe new aspects of the non-enzymatic browning reaction (MAILLARD
reaction). Two temperature depending pathways of colour formation were found. Both reaction
mechanisms are based on the formation of a-dicarbonyl compounds, the key intermediates of
colour formation.
Discussing temperature dependence of colour formation, a change on MAILLARD reaction
mechanism takes place at 100.4 °C. Above this temperature the colour formation is strongly
accelerated. Activation energy of the non-enzymatic browning energy for temperatures from 65 °
to 100.4 °C amounts 77 kJ/mol. In this temperature range, D-glucosone is the most important a-
dicarbonyl compound for studied reaction systems. Above 100.4 °C, activation energy is equal to
112 kJ/mol and 3-deoxyosone is the dominant colour formation intermediate. Achieved results
bridge the gap between the termination step of a MAILLARD reaction –i.e. of colour formation
(represented by its activation energy) and intermediates formation (reaction kinetics). In particular,
a change of colour formation mechanism with reaction temperature was confirmed by specific
formation of two a-dicarbonyl compounds, responsible for MAILLARD reaction in technical
sugar solutions.
KEYWORDS: MAILLARD reaction, a-dicarbonyl compounds, colour formation, kinetics
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1. Introduction
The suppression of colour formation and thermal decomposition of sucrose
molecules in aqueous sucrose solutions has been major challenges in sugar
technology in the last decades. The colorants are formed in almost all periods of
sugar manufacture and influence not only technological performance of chemical
engineering units, but also the economics of any factory and consequently also
sugar prices. Thus, understanding, modelling and prediction of colour formation is
of peculiar importance.
The kinetics of colour formation during sugar processing, e.g. evaporation
and crystallisation, are influenced by many factors. The most relevant for sugar
production are temperature, time, invert sugar concentration and pH-value
(Vukov, 1981, Hollnagel, 1998, Van der Poel, 2000).
The mechanism of colour formation in technical sucrose solutions is based
on the reaction of reducing sugars D-fructose and D-glucose with an amino
compound e.g. γ-aminobutyric acid (GABA), the so-called MAILLARD reaction
(Ledl, 1990). In the early stage of the MAILLARD reaction α-dicarbonyl
compounds are formed (Westphal, 1985a, 1985 b). The latter are responsible for
colour formation in concentrated sucrose solutions (65 %). In sucrose solutions
and during several process steps of sugar processing, three major α-dicarbonyl
compounds could be determined. These are 3-deoxyosone, D-glucosone and
methylglyoxal (Fiedler, 2006).
Regarding a formation of these α-dicarbonyl compounds, a temperature
depending reaction pathway could be shown, see Figure 1. At temperatures above
110 °C 3-deoxyosone is the dominant dicarbonyl compound in technical sucrose
solutions with max. concentrations up to 640 mg/kg. At temperatures below
100°C D-glucosone is preferably formed. Methylglyoxal takes an intermediate
position of these dominant α-dicarbonyl compounds (in relation to the formation
of colour) and could not be assigned to any particular temperature range. The
concentration of methylglyoxal in studied sucrose solutions is very low and
therefore almost no influence on reaction kinetics at chosen process relevant
conditions could be found (Imming, 1994, Reinefeld, 1973).
Pioneer studies concerning kinetic modelling of the MAILLARD reaction
were based only on colour measurement (Vukov, 1981, Imming, 1994). Later on,
kinetic studies with α-dicarbonyl compounds were presented. However, the
elucidation of MAILLARD reaction (Martins, 2000, Martins, 2005, Mundt, 2003,
Wedzicha, 1995), was mostly related to model solutions and specific reaction
conditions far away from process praxis. In sugar production and other food
technologies with real sugar solutions, a degradation of sucrose occurs in a wide
mixture of reactive components. In above specified reaction step of MAILLARD
reaction, amino compounds could react with almost all α-dicarbonyls presented in
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the solution. Therefore, the results achieved with model solution systems should
be correlated to those of technical sucrose solution, i.e. to results achieved with
thick juice. If the results of both reaction systems are comparable, the reaction
pathways are the same and the selection of representatives for model solution was
correct. The aim of this contribution is to develop a simplified kinetic model for
the description of colour formation in technical sucrose solutions (thick juice) at
process relevant conditions and to derive its activation energies. The results will
be used for a discussion of overall reaction kinetics of MAILLARD reaction.
Fig. 1.: Schematic reaction pathway of the colour formation in sucrose solutions.
Achieved results gained by colour formation will be extended with simplified
kinetics based on α-dicarbonyl compounds in technical and model sucrose
solutions.
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2. Methods and Materials
2.1 Chemicals
D-glucose, D-fructose, sucrose, γ-aminobutyric acid (GABA), acetic anhydride,
pyridine, silica, glyoxal, quinoxaline and 1-butanol were obtained from Merck
(Darmstadt, Germany), methylquinoxaline and o-phenylenediamine from Fluka
(Buchs, Switzerland), toluene Pestanal® from Riedel-de Haën (Seelze, Germany),
methanol (HPLC grade), 2,3-diphenylquinoxaline and methylglyoxal supplied by
Sigma Aldrich (Steinheim, Germany) and dimethylquinoxaline by Lancaster
(Morecambe, England).
2.2 Technical sucrose solution
A diluted thick juice solution (65 %) from sugar production unit (last stage of
evaporation) was used as a technical sucrose solution for the corresponding
experimental measurements.
2.3 Carbohydrate model-solutions
The used aqueous sucrose MAILLARD reaction solutions contained 65% (w/w)
sucrose, 0.1% invert sugar (1:1) and 0.1% GABA, which corresponds to an
artificial thick juice. The acidity of the solutions were adjusted to pH = 8. During
the reaction, the pH value was not regulated.
2.4 Thermal treatment and derivatization
The solutions were heated in sealed ampoules for up to 300 min at defined
temperatures ± 1 °C by means of a thermoblock (Behr Labor Technik, behrotest
ET 2). The original samples were used for colour measurement. For quantification
of α-dicarbonyls, after a defined reaction time, the samples were stirred with 0.05
mol/L o-phenylenediamine to convert α-dicarbonyls into quinoxalines (post-
derivatization), which were analyzed after filtration by HPLC-DAD and by
GC/MS after acetylation.
2.5 High-performance liquid chromatography with diode array detection
(HPLC-DAD)
Degasser: Degasys DG-13000 (Knaur); pump: Shimadzu LC-10 AT; thermostat:
30 °C, Shimadzu CT0-6A; guard column: Nucleosil 120-5 C18 Macherey-Nagel;
column: Nucleosil 5 C18 (250 × 4.6 mm); detector: DAD Gynkotek UVD 340S;
flow: 1.0 m /min; injection volume: 40 mL; eluent: methanol/water gradient: 0
min – 5 min 30% methanol, 5 min – 12 min 30% – 50%, 12 min – 20 min 50% –
100%, 20 min – 30 min 100% methanol. Quinoxalines prepared from Hollnagel
(2000) were used as standards for quantification.
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2.6 Gas chromatography/mass spectrometry (GC/MS)
Before quantification, reaction mixture was extracted with 1-butanol. The solvent
was dried off and the residue was dissolved in toluene/pyridine (30:1) and acetic
anhydride was added (Nedvidek, 1992). Gas chromatograph: Finnigan GCQTM;
capillary column: BPX-5 (SGE, 30 m, 0.25 mm ID, 0.5 mm film thickness);
carrier gas: helium 4.6; detector: Finnigan Ion Trap Mass Analyzer GCQTM;
injection temperature: 270 °C; temperature program: initial temperature 95 °C,
hold 1 min, 95–200 °C 15 °C/min, 200 °C 1 min, 200–280 °C 3 °C/min, 280 °C 5
min, 280–300 °C 5 °C/min, 300 °C 5 min. Column effluents were analyzed by
selected ion monitoring (SIM). Quinoxalines prepared from Hollnagel (2005)
were used as standards for quantification.
2.7 Colour measurement
Mentioned colour of all solutions were measured with a ICUMSA (International
Commission for Uniform Methods for Sugar Analysis) method (Reinefelder,
1978) at an absorption wavelength of 420 nm. Abbe-Refractometer: Carl-Zeiss,
Jena; Photometer: Novaspec II Pharmacia LKB.
2.8 Modelling of colour formation
The experiments give for any reaction temperature a time-dependence of the
colour index which is a linear function for short time periods (Vukov, 1981,
Westphal, 1985). That means, the colour formation could be described in a good
approximation as a zero-order reaction for the initial conditions of the non-
enzymatic browning (Smejkal, 2005). The reaction rate is derived from the slopes
of colour increase dF/dt (1):
k
dt
dF = [IU/min] (1)
The formal kinetic constants k [IU/min] were determined for all experimental
conditions. The reaction rates of different temperatures allow to calculate the
activation energy Ea according to the theory of the reaction kinetics (Westphal,
1985, Imming, 1994), see Equation (2):
2
ln
RT
E
ka
=
∂
∂
ϑ
(2)
This equation results after integration in the Arrhenius dependence of kinetic
constants k on temperature:
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⎟⎠
⎞
⎜⎝
⎛−
=∞RT
E
kk a
exp. ∞
+
⎟⎠
⎞
⎜⎝
⎛−
=kE
RT
kaln
1
ln [min
-1] (3)
where k
∞
is the frequency factor. If the natural logarithm of kinetic constant will
be plotted against -1000/RT, the slope of this dependence represents the activation
energy (in [kJ/mol]) of the overall chemical reaction for a given temperature
interval.
2.9 Kinetic Modelling of reaction intermediates
Extended kinetic experiments were performed with the aim to elucidate the
formation of reaction intermediates by sucrose degradation. The concentration of
main intermediates was followed by developed analytical methods. The
concentrations as a function of reaction time could be used for the determination
of reaction rates. For initial reaction periods the increase of concentration with
time can be described by a linear function, if a first-order approach will be used
(Vukov, 1981, Smejkal, 2006). From the slopes of concentration differences in
reaction time at given temperature, the reaction rate is withdrawn as:
kc
dt
dc
A
A= [mg/kg/min] (4)
and after integration
.
ln constk
t
cA+= [mg/kg/min] (5)
Resulted kinetic constants enable to calculate the activation energy of the reaction,
see above Equations 2 and 3.
3. Results and Discussion
A prediction of colour formation in technical sucrose solutions is very important
for operative use in almost every sugar factory. Thus, in a first part of the paper,
the results of colour formation in technical and model sucrose solutions will be
given. Based on activation energies derived from colour formation experiments in
both sugar solutions used, first comparison of reaction mechanism of colour
formation in technical and model solution will be withdrawn. However, the colour
formation is only the last step of complex MAILLARD reaction in technical
sucrose solutions. The thick juice contains a spectrum of minor components,
which take part in the studied browning reaction as well.
Thus, later on detailed analytical measurements of chosen intermediates,
i.e. of α-dicarbonyl compounds, will be performed. Related to achieved results,
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the representatives of α-dicarbonyl (which are believed to be responsible for the
colour formation) will be selected for further kinetic experiments. These
components will be used for simplified kinetic model of MAILLARD reaction
with the aim to confirm the results achieved by experiments with technical
sucrose solution.
3.1 Balance of colour formation
3.1.1 Activation energy of colour formation in technical sucrose solution based
on colour measurement
The terminating step of non-enzymatic browning experiments were analysed
according to Equations 2 and 3 with the aim to calculate the activation energy of
the reaction based on colour measurement. Experimental results are listed in an
Arrhenius plot in Figure 2.
Activation energy of the non-enzymatic browning reaction amounts for
temperatures up to ϑ = 100 °C Ea = 76.8±3 kJ/mol and for temperatures above
100°C Ea = 112.1±2.7 kJ/mol. Activation energy changes at 100.4 °C. The
residuals of all measured experimental points used in Figure 2 equal to 0.068
below ϑ = 100 °C and 0.083 above ϑ = 100 °C. The standard experimental
deviation remains 0.0768.
The activation energies presented in Figure 2 support the already given
assumption of overall reaction mechanism of non-enzymatic browning reaction.
The reaction mechanism shifts at 100.4 °C. Above ϑ = 100.4°C the reaction is
speeded up and the degradation of sucrose molecules becomes more important.
Thus, from technological point of view it is generally desired to reduce the
temperature in sugar production, e.g. in evaporation units.
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Fig. 2.: Determination of activation energy based on colour measurement; ln (k) as
a function of -1000/RT, technical sucrose solution.
Derived from Fig. 2, a decrease of temperature from 130 °C to 120 °C in
evaporation reduces the colour formation with factor of 2.5. Such a temperature
reduction improves seriously sugar quality (Smejkal, 2005, Smejkal, 2006) and
should be implemented e.g. to the layout of evaporation units.
3.1.2 Activation energy of colour formation in model sucrose solution based on
colour measurement
To support the presented shift on derived reaction mechanism, a balance of colour
formation was repeated with a model sucrose solution. The composition of the
model sucrose solution used in this study is given above in Experimental. From
the spectrum of chemical individuals in technical sugar solution only those
components were selected, which are believed to be responsible for sucrose
degradation. Colour formation in these solutions (and, later on also simplified
reaction kinetics of intermediates formation) should later on confirm the selection
of these characteristic components.
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The aim of activation energy recalculation was focused in simplified
reaction mechanism, introduced already in this chapter. If the assumption of
reaction pathway is correct, the reaction system will be determined by chosen
intermediate in dependence on temperature for both the model as well as for the
technical sucrose solution. In a first approach, the intersection on activation
energy profile should be found in model solution again. Thus, the results of
experiments with model sucrose solution should roughly confirm the shift on
reaction mechanism already shown in technical sucrose solution.
Colour formation experiments were repeated with model sucrose solutions.
Acquired formal kinetic constants based on colour measurement were plotted in
Arrhenius dependence and the results are given in Figure 3.
From Figures 2 and 3 it could be generally concluded that the activation
energy of colour formation remains almost the same for both sucrose solutions
used. We can state a good agreement between experiments with technical sucrose
solution (thick juice) and a model sucrose solution. The intersection on the
reaction mechanism in model solution from Figure 3 remains 100.1°C. This value
corresponds to 100.4°C found in technical sucrose solution. Moreover, at reaction
temperatures below 100 °C, activation energy equals to 77 and 73 kJ/mol, resp..
For ϑ > 100 °C, activation energy amounts 112 and 118 kJ/mol. Pre-exponential
factors are comparable in both solutions, too.
Fig. 3.: Determination of activation energy based on colour measurement; ln (k) as a function of -
1000/RT, model sucrose solution.
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Presented results show that proposed reaction mechanism seems to be reliable.
Also the change in the reaction mechanism at roughly 100 °C was found in both
studied sucrose solutions.
3.1.3 Key intermediates of MAILLARD reaction in technical sucrose solutions
The discussion above illustrated a reaction mechanism, responsible without any
doubt for the last step of non-enzymatic browning reaction, i.e. for colour
formation. However, the colour formation consists of a complex of parallel and
consecutive reactions and to withdraw the conclusions of reaction pathway from
activation energy only is almost impossible. Thus, the kinetics of colour formation
was enhanced by the simplified elucidation of intermediates formation according
to overall reaction scheme from Figure 1 (Fiedler & Kroh, 2006). The assumption
that 3-deoxyosone and D-glucoson are responsible for the colour formation should
be confirmed in following discussion.
In Figure 4 the formation of 3-deoxyosone at temperatures between 100 °C
and 130 °C is shown. The concentration increases with rising temperature and
maximal concentrations of 3-deoxyosone of approx. 640 mg/kg was reached at
130 °C.
30 60 90 120 180 240 300
100°C
110°C
120°C
130°C
0
100
200
300
400
500
600
700
concentration [mg/kg]
reaction time [min]
100°C 110°C 120°C 130°C
Fig. 4.: Formation of 3-deoxyosone in a technical sucrose solution between 100
and 130 °C.
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At temperatures below 100 °C the dominant α-dicarbonyl compound
changes from 3-deoxyosone to D-glucosone, see Figure 5. In Figure 5
methylglyoxal is shown, which is formed independently on temperature.
However, its concentration remains almost two order lower value compared to D-
glucosone (Reinefeld, 1973) in the regarded temperature interval between 80 and
110 °C. The influence of methylglyoxal on the reaction system at these reaction
conditions cannot be documented and thus will be neglected (Fiedler & Kroh,
2006).
The concentrations of chosen dominant α-carbonyls changes between 100
°C and 110 °C. At lower temperatures an oxidation mechanism with main product
D-glucosone occurs and at temperatures above 110 °C an ionic mechanism with
the dominant α-dicarbonyl 3-deoxyosone could be reported (Fiedler & Moritz,
2006, Fiedler & Kroh, 2006). Surprisingly, initial concentration of D-glucosone in
technical sucrose solution is almost 60 times higher than initial concentration of 3-
Deoxyosone (3-DO) This phenomena supports changing reaction mechanisms
after thermal loading of thick juice, first at temperatures above 100°C.
In Figure 5, the shift of the reaction mechanism is presented by dotted (D-
glucoson) and full (3-DO) arrows. The formation of 3-DO (full line) is speeded up
above 100 °C.
Fig. 5.: Temperature depending change of α-dicarbonyl concentration of thermally
treated technical sucrose solutions at 180 min.
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The decrease of D-Glucosone in Figure 5 indicates already at temperature of 100 °C, where the
change of reaction mechanism occurs. Between 100°C and 115 °C an intermediate interval can be
stated, where both components play an important role. Presented change in reaction mechanism in
MAILLARD reaction is supported by the Arrhenius plot from Figure 2 and 3, where the
intersection was found at roughly 100 °C. Above shown pathway of dicarbonyl compounds in
technical sucrose solutions can be transferred to model sucrose solutions (Fiedler, 2006) and could
be correlated to several process units in the sugar production. This phenomena was approved in
e.g. in the evaporation station, where a very high concentration of 3-deoxyosone at temperatures
above 100 °C was found.
3.2 Simplified reaction kinetics of overall MAILLARD reaction
3.2.1 Formal kinetics of key compounds in technical sucrose solutions
The performed kinetic experiments presented in chapter 3.1 were analysed and from ln(cA)/t
dependencies the kinetic constants at both, given temperature and composition were achieved (see
Equations 2 and 3). Experimental temperature interval was divided according to above mentioned
activation energy into temperatures above 100 °C (ϑ ∈ (100-130) °C) and below 100 °C, i.e.
ϑ ∈ (80-100) °C.
In following figures, a time-depending formation of reaction intermediates in technical
sucrose solutions is given and corresponding kinetic constants are withdrawn. For kinetic
evaluation data from Chapter 3.1.3 was used. In Figure 6, a formation of 3-deoxyosone in reaction
time at different temperatures is shown.
Fig. 6.: Formation of 3-deoxyosone in reaction time; ln (c) in (mg/kg) as a function of time (min),
technical sucrose solution for ϑ ∈ (100-130) °C; c0,3-DO = 0.4 mg/kg
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The concentration-dependences were evaluated in ln (c) versus time
coordinates and repeated for D-glucosone. Unfortunately, the concentration of D-
glucosone at temperatures below 100 °C as well as at extended technology-
relevant times up to 300 minutes is very low. For every reaction temperature, the
corresponding slope of linear dependence was analysed. The value of achieved
slope is proportional to kinetic constant at given conditions. Evaluated kinetic
constants are listed in Table I (see Appendix).
Presented kinetic constants for both 3-deoxyosone and D-glucosone are not
directly comparable. The reason therefore are different initial concentrations of 3-
deoxyosone (c0,3-DO = 0,04 mg/kg) and D-glucosone (c0,D-glucoson = 2.3 mg/kg) in
technical sucrose solutions. This is due to the chemical composition of common
German thick juices, which were used for experiments. Thus, the results presented
in Table I should be taken as a base for an activation energy calculation. Limited
temperature interval applied for measurement (process relevant temperatures and
retention times) results in increased relative errors of 10 – 15 % with respect to
evaluated kinetic constants and consequently to activation energies.
However, considering enormous demand on analysis at very low
concentrations of key components and limited pool of reliable experimental
conditions, the results are acceptably accurate for target discussion, i.e. for basic
elucidation of colorants reaction mechanism in technical sucrose solutions.
The kinetic constants were plotted in an Arrhenius diagram and the
activation energies remain:
for 3-deoxyosone EA = 92 kJ/mol, and
for D-glucosone EA = 78-80 kJ/mol
These values will later on be compared with those from experiments with
α-dicarbonyl model-solutions.
3.2.2 Formal kinetics of key compounds in model sucrose solutions
Presented kinetic experiments were repeated with model sucrose solutions. These
were performed similarly to those mentioned above in Chapter 3.2.1.
In the beginning, a time-depending formation of 3-deoxyosone was
studied and the results are given in Figure 7. Later on, the chemical conversion of
model sucrose solution to D-glucosone was monitored and summarised at Figure 8
for a chosen temperature interval.
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Fig. 7.: Formation of 3-deoxyosone in reaction time; ln (c) in (mg/kg) as a function of
time (min), model sucrose solution for ϑ ∈ (100-130) °C, c0,3-DO = 0.12 mg/kg
Fig. 8.: Formation of D-glucosone in reaction time; ln (c) in (mg/kg) as a function of time
(min), model sucrose solution for ϑ ∈ (80-100) °C; c0,D-glucoson = 99 mg/kg
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The results from Figures 7 and 8 show the difference in reaction rate of
both reaction systems. Below 100 °C, the rates of formation are roughly one order
lower compared with the formation of 3-deoxyosone above 100 °C, where the
colour formation is speeded up. Kinetic constants of the reaction pathway
acquired with model solution are summarised in Table II (see Appendix).
From kinetic constants an activation energy of 3-deoxyosone and D-
glucosone formation could be calculated, according to the derivation from
Chapter 2. The results are charged with an error of roughly ±10 kJ/mol. An
absolute value of activation energy is very difficult to obtain. On contrary - the
major aim of this contribution is to show the trends of colour formation at
different temperature levels and the measurements were done at comparable
conditions. Therefore, the experimental error will be reduced.
Figure 9 supposes an enhanced reaction pathway with activation energies.
These were achieved from kinetic experiments listed above and extended with
activation energies derived from model sucrose solutions. The activation energy
of sucrose degradation to invert sugar (initial step of colour formation) was
studied separately (Smejkal, 2005). Presented values are in a good agreement with
previous results of various authors (Bohn, 1970, Westphal,1985).
Fig. 9.: Reaction pathway of colour formation, derived from i) technical sucrose
solution (thick juice) and ii) model solution.
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From Figure 9 can be concluded that achieved activation energies of
colour formation pathway for technical and model solutions are in very good
agreement. The formation of both chosen predominant intermediates could be
described in technical as well as in a model solution with almost identical
activation energies. Despite the problem of a not pronounced formation of 3-DO,
the presented simplified kinetic model describes sucrose degradation in technical
sugar solutions with acceptable accuracy.
In last years, a lot of complex and not always transparent kinetic models
were shown. However, neither an approximation of overall sucrose degradation,
nor a kinetic model for technical sucrose solution (thick juice) was presented.
Our kinetic study is constrained by two representatives. Therefore, in
Figure 9 an imaginative reaction pathway is shown, which is extended by not-yet
detected intermediates. A complex study of reaction mechanism in technical
sucrose solution could be another aim for further scientific work. Another
challenging task is to complete presented reaction pathway from 3-Deoxyoson
and D-Glucoson to colour compounds. The preparation of all intermediates has
been already described in literature (Fiedler, 2006), nevertheless the acquisition of
starting material is still the crucial complication by planning of future
experiments.
4. Conclusions
Achieved results comprise practical aspects of colour prediction in sugar
production with kinetics study at a simplified reaction system. Our motivation was
focused to the balance of colour formation, resulting in reliable elucidation of the
last step of MAILLARD reaction. On the other hand, a simplified kinetic model
was developed using key intermediates of sugar molecule degradation.
The most important conclusion is the change (shift) of reaction pathway in
colour formation at about 100 °C. Above 100°C, the colour formation is speeded
up rapidly and the characteristic intermediate changes from D-glucosone to 3-
deoxyozone. This phenomena was confirmed independently by balance of colour
formation and by formation of chosen dominant α-Dicarbonyl compounds.
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5. Appendix
Table I: Kinetic constants of proposed reaction system
Temperature Kinetic constant (min-1)
( °C) k1,A 3-deoxyosone k1,B D-glucosone*
80 n.d. 0.0088
90 n.d. 0.0235
100 0.0048 0.0481
110 0.0161 -
120 0.0303 -
130 0.0442 -
* at temperatures above 100 °C, the decomposition of D-glucosone occurs
Table II: Kinetic constants of proposed reaction system, model sucrose solution
Temperature Kinetic constant (min-1)
( °C) k1,A 3-deoxyosone k1,B D-glucosone*
80 n.d. 0.001
90 n.d. 0.0029
100 0.0087 0.0041
110 0.0174 -
120 0.0384 -
130 0.0695 -
* at temperatures above 100 °C, the decomposition of D-glucosone occurs
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