Asparagine-glucose Model System Research Articles

Antioxidant activity and reduction potential of dietary herbs on acrylamide formation in asparagine-glucose reaction model

ABSTRACT Natural ingredients are increasingly being used to prevent the formation of acrylamide during food processing. This study investigated the antioxidant activities of Ocimum basilicum (basil), Lippia adoensis var. adoensis (kesse), Lippia adoensis var. koseret (koseret), Rosmarinus officinalis (rosemary), and Thymus schimperi (tosign) extracts and their acrylamide reduction effect in the asparagine-glucose model system. Folin-Ciocalteu and aluminum chloride methods were used to calculate the total phenolic content (TPC) and total flavonoid content (TFC). Antioxidant activities were determined using 2,2-Diphenyl-1-Picryl-Hydrazyl (DPPH) scavenging and phosphomolybdenum assay methods. Acrylamide contents of the samples were determined by a reversed phase high-performance liquid chromatography (RP-HPLC-DAD) method. Kesse had the highest concentrations of TPC (30.20 ± 1.23 mg gallic acid equivalent per gram of herb extract), TFC (15.87 ± 0.55 mg catechin equivalents per gram), and the strongest DPPH scavenging activity (IC50 = 108 μg/mL). The amount of acrylamide formed during the frying process was decreased by a factor of 26.8% to 65.81% with the addition of dietary herb extracts to the asparagine-glucose reaction model. The amount of acrylamide formed from an asparagine-glucose reaction model containing herb extracts was negatively correlated with the total phenolic and total flavonoid content with, R2 values of 0.920 and 0.930. This study suggests a potential application of these dietary herb extracts as a natural antioxidant for lowering acrylamide formation during the Maillard reaction in fried food products.

Vitamin A and E Homologues Impacting the Fate of Acrylamide in Equimolar Asparagine-Glucose Model System.

This study aims to evaluate the influence of Vitamin A and E homologues toward acrylamide in equimolar asparagine-glucose model system. Vitamin A homologue as β-carotene (BC) and five Vitamin E homologues, i.e., α-tocopherol (AT), δ-tocopherol (DT), α-tocotrienol (ATT), γ-tocotrienol (GTT), and δ-tocotrienol (DTT), were tested at different concentrations (1 and 10 µmol) and subjected to heating at 160 °C for 20 min before acrylamide quantification. At lower concentrations (1 µmol; 431, 403, 411 ppm, respectively), AT, DT, and GTT significantly increase acrylamide. Except for DT, enhancing concentration to 10 µmol (5370, 4310, 4250, 3970, and 4110 ppm, respectively) caused significant acrylamide formation. From linear regression model, acrylamide concentration demonstrated significant depreciation over concentration increase in AT (Beta = −83.0, R2 = 0.652, p ≤ 0.05) and DT (Beta = −71.6, R2 = 0.930, p ≤ 0.05). This study indicates that different Vitamin A and E homologue concentrations could determine their functionality either as antioxidants or pro-oxidants.

Probing hemoglobin glyco-products by fluorescence spectroscopy.

Maillard reaction products (MRPs) participate in reactions of carbohydrate intermediates with proteins, resulting in the formation of advanced glycation end-products (AGEs). Dietary Maillard reaction products are recognized as potential chemical modifiers of human proteins. We have investigated the reaction of isolated MRPs from an asparagine–glucose model system with hemoglobin (Hb) to elucidate the binding effect of the MRPs in hemoglobin by fluorescence spectrophotometry. The tryptophan-specific fluorescence obtained for glycated hemoglobin exhibited a Stokes effect since the wavelength of the emission peak was shifted to a higher wavelength than that of native Hb. The formation of new fluorescence emission features indicates the formation of modified hemoglobin species. Fluorescence spectroscopic studies provide evidence that the conformational changes in the β-Trp 37 moiety induce motion of the distal His 64 (E7) in the heme binding pocket. This results in the formation of inactive hemichrome forms of hemoglobin which are related to blood disorders.

Simultaneous inhibition of acrylamide and hydroxymethylfurfural formation by sodium glutamate microcapsules in an asparagine–glucose model system

Inhibiting the formation of acrylamide (AA) and hydroxymethylfurfural (HMF) during food heating processes has attracted considerable investigative efforts due to potential health concerns associated with these compounds. The main purpose of this work is to demonstrate a strategy to simultaneously inhibit the formation of AA and HMF with sodium glutamate microcapsules selected to confirm the efficacy of this strategy. An asparagine-glucose aqueous model system was prepared containing free sodium glutamate and sodium glutamate microcapsules. Compared to adding free sodium glutamate, the maximum inhibition efficiency for AA and HMF was found to increase by addition of sodium glutamate microcapsules to 19.07 and 84.32%, respectively. Moreover, the kinetics of AA and HMF formation were studied in this model system. The AA inhibition efficiency significantly increased from 6.75 to 60.35% and the HMF inhibition efficiency significantly increased from 5.98 to 79.72% with increasing the reaction time from 25 to 40min, indicating that the sodium glutamate microcapsules strategy proves to be far superior at prolonged heating times. These findings suggested that this inhibition strategy may provide promising characteristics for a variety of applications in food processing.

Protective effect of chitosan on acrylamide formation in model and batter systems

In recent years high contents of acrylamide, a potentially carcinogenic substance, have been found in a wide range of fried and baked foods. For this reason, the health authorities together with the food industry have carried out research to find ways to minimize the presence of acrylamide during food processing. The addition of chitosan may be an excellent alternative for achieving this goal because due to their richness in amino groups, they would interfere with the Maillard reaction that unleashes the formation of acrylamide. The main aims of this study were to analyze the addition of different concentrations of chitosan in model systems as a new way of mitigating generation of acrylamide during frying processes, while evaluating the influence of pH, reducing sugars (glucose and fructose) present in the system and frying temperature, and to determine the functionality of adding chitosan in fried batter systems. The results showed that chitosan is capable of inhibiting the formation of acrylamide in model systems and in fried batters. In model systems, a reduction in acrylamide ranging from 49 to 85% was achieved for 1% of chitosan, the maximum inhibition taking place in asparagine–fructose model systems and the lowest in asparagine–glucose model systems. In fried batter, acrylamide was mitigated by 59 ± 6% with a chitosan concentration of 0.27% in batter formulations. Double concentrations of chitosan (0.54%) did not considerably improve the inhibition capacity.

Effects of metal ions on formation of acrylamide and 5‐hydroxymethylfurfural in asparagine–glucose model system

SummaryUndesirable substances of thermal food processing such as acrylamide (AA) and 5‐hydroxymethylfurfural (HMF) have been intensively studied in recent decades. The aim of this work was to investigate the evolution mechanism of AA and HMF contents in the presence of various valence metal cations at various concentrations in asparagine–glucose model system. Three interesting phenomena were found. Firstly, the AA contents first decreased and then increased, whereas the HMF contents first increased and then decreased, with increasing metal cations concentration; secondly, the concentration of cations for maximal HMF contents was lower than the concentration of cations for minimal AA contents; thirdly, the maximum AA‐inhibiting or HMF‐promoting efficiency was achieved more readily with trivalent, then divalent and lastly monovalent cations. These phenomena can be explained by that increasing the metal cations concentration can increase the protonated product contents, thus increasing the AA‐inhibiting efficiency and HMF‐promoting efficiency. With higher metal cations concentration in the model system, HMF as a reactant can react with the asparagine to form AA or directly decompose into furfural. These interesting results can provide a theoretical foundation to simultaneously control the formation of AA and HMF during food processing.

Model studies on the role of 5-hydroxymethyl-2-furfural in acrylamide formation from asparagine

This study aimed to investigate the mechanism of acrylamide formation during heating asparagine (ASN) at elevated temperatures with glucose (GLC), and 5-hydroxymethyl-2-furfural (HMF). The results revealed that HMF rapidly reacted with ASN, leading to acrylamide formation. The ASN–HMF model system generated acrylamide more efficiently than the ASN–GLC model system during heating at 180°C. A significantly higher amount of 3-aminopropionamide (3-APA) was formed in the ASN–HMF model system than in the ASN–GLC model system within 5min at 180°C. The amount of 3-APA decreased after 5min of heating in both model systems while the amount of acrylamide continued to increase in the ASN–HMF model system. In-depth high resolution mass spectrometry analyses of reaction products formed in the model systems together with the kinetic data suggested that HMF is a potent carbonyl accelerating acrylamide formation during heating. 3-APA was found as one of the key intermediates leading to acrylamide formation.

Dietary plant materials reduce acrylamide formation in cookie and starch-based model systems

Dietary plant materials have attracted much attention because of their health benefits to humans. Acrylamide is found in various heated carbohydrate-rich foods. Our previous results showed that crude aqueous extracts from diverse dietary plants and some phenolic compounds could mitigate acrylamide formation in an asparagine-glucose model system. Based on our previous study, several plant materials were selected to further investigate their inhibitory effects on acrylamide formation in cookies and starch-based model systems. Addition of raw powders from selected dietary plants and their crude aqueous extracts could considerably reduce acrylamide formation in both cookie and potato starch-based models. Aqueous extracts of clove at 4% caused the largest reduction (50.9%) of acrylamide in cookies, whereas addition of 2% proanthocyanidins from grape seeds gave the greatest acrylamide reduction (62.2%) in a starch-based model system. It may be feasible to use some of the tested dietary plant materials to reduce acrylamide formation in cookies and other starchy foods.

A pulsed electric field procedure for promoting Maillard reaction in an asparagine–glucose model system

SummaryEffects of pulsed electric field (PEF) on pH, intermediate products, asparagine and glucose content, browning value, reducing power as well as antioxidant activity of an asparagine–glucose solution were explored in this paper. Results showed that the solution’s UV–Vis absorbance at 294 nm and 420 nm was significantly increased from 0 to approximately 1.14 and 0.74, respectively, at PEF intensity of 40 kV cm−1 for 7.35 ms treatment. The temperature of PEF treated samples were overall lower than 40 °C. It was also detected that the antioxidant activity of treated sample was correspondingly increased by 20.33%. Meanwhile, 14% reduction of asparagine content and 66% reduction of glucose content were observed. It was demonstrated from high performance liquid chromatography analysis that Maillard reaction in the model system had been enhanced by PEF treatment as no 5‐hydroxymethyl‐2‐furaldehyde was generated. This study indicates that pulsed electric field treatment, especially with higher intensities, is a means to significantly promote the Maillard reaction in an asparagine–glucose solution.

Investigations on the Effect of Amino Acids on Acrylamide, Pyrazines, and Michael Addition Products in Model Systems

Acrylamide and pyrazine formation, as influenced by the incorporation of different amino acids, was investigated in sealed low-moisture asparagine-glucose model systems. Added amino acids, with the exception of glycine and cysteine and at an equimolar concentration to asparagine, increased the rate of acrylamide formation. The strong correlation between the unsubstituted pyrazine and acrylamide suggests the promotion of the formation of Maillard reaction intermediates, and in particular glyoxal, as the determining mode of action. At increased amino acid concentrations, diverse effects were observed. The initial rates of acrylamide formation remained high for valine, alanine, phenylalanine, tryptophan, glutamine, and leucine, while a significant mitigating effect, as evident from the acrylamide yields after 60 min of heating at 160 degrees C, was observed for proline, tryptophan, glycine, and cysteine. The secondary amine containing amino acids, proline and tryptophan, had the most profound mitigating effect on acrylamide after 60 min of heating. The relative importance of the competing effect of added amino acids for alpha-dicarbonyls and acrylamide-amino acid alkylation reactions is discussed and accompanied by data on the relative formation rates of selected amino acid-AA adducts.

Kinetics of Acrylamide Formation/Elimination Reactions as Affected by Water Activity

The influence of water activity on the kinetics of acrylamide formation and elimination reaction was investigated using low-moisture equimolar asparagine-glucose model systems, which were heated at temperatures between 120 and 200 degrees C for variable heating times. To determine the water content corresponding to the water activities tested, a sorption moisture isotherm was constructed experimentally. The acrylamide concentrations measured at different water activities could be modeled on the basis of a reaction scheme including not only acrylamide formation and elimination reactions but also an alternative Maillard reaction between both reactants. The corresponding rate constants and activation energies were estimated using nonlinear regression analysis. Whereas the rate constant for acrylamide formation varied only slightly with the initial water activity of the model system, the elimination rate constant showed a clear minimum around a water activity of 0.82. The opposite trend, namely, a maximum at a water activity of 0.82, was found for the Maillard reaction rate constant as a function of water activity, which confirms data from literature. The activation energies for the different reactions changed in a comparable way as the corresponding rate constant with water activity.

The kinetics of acrylamide formation/elimination in asparagine–glucose systems at different initial reactant concentrations and ratios

The effect of initial reactant concentration and ratio on the kinetics of acrylamide formation and elimination was studied using diluted asparagine–glucose model systems, heated at temperatures between 120 and 200 °C. By means of single response modelling, acrylamide concentrations measured could be modelled using a simplified kinetic model, in which acrylamide formation and elimination reactions were included. Changing the reactant concentration in equimolar systems did not affect significantly the kinetic parameters ( k Fref and E aF) for acrylamide formation, whereas the rate constant for acrylamide elimination increased with increasing reactant concentration, in the range from 0.01 M to 0.125 M. Modifying the reactant ratio, while keeping one of the reactants at a fixed concentration (0.125 M), did not affect the estimated parameters as compared to the equimolar system. In addition, multiresponse modelling was applied on three model systems with a different initial reactant ratio. Besides acrylamide, the concentration of the reactants and fructose and the level of browning were quantified. By means of deduction, a mechanistic model was proposed which was able to model all responses simultaneously in an adequate way. It appeared that caramelisation has a predominant role in browning, however, only in the system with an excess of sugar. The corresponding kinetic parameters estimated were in some cases significantly different, but in the same order of magnitude.

Reduction of Acrylamide and Its Kinetics by Addition of Antioxidant of Bamboo Leaves (AOB) and Extract of Green Tea (EGT) in Asparagine–Glucose Microwave Heating System

This study investigated the effect of antioxidant of bamboo leaves (AOB) and extract of green tea (EGT) on the formation and kinetics of acrylamide in an equimolar asparagine-glucose model system. The substrates spiked with AOB and EGT were microwave-heated at 180 degrees C and the acrylamide content in final reaction products was quantified by ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). The results showed that both AOB and EGT could effectively reduce the formation of acrylamide in an asparagine-glucose microwave heating model system and achieved a maximum reduction rate when the addition levels of AOB and EGT were both 10(-6) mg/mL reaction solution. To describe the kinetic behavior of acrylamide, a simplified kinetic model was optimized and relative kinetic rate constants were evaluated under isothermal conditions. The results indicated that the reduction effect of AOB and EGT on the acrylamide formation may partly be ascribed to the decrease of the formation rate constant (k(F)) in both AOB and EGT-spiked systems (43.4% and 32.3% of decrease, respectively, P < 0.05). The kinetic parameter k(E), which represents the elimination rate of acrylamide in both AOB and EGT-spiked systems, was not significantly different (6.9% of increase and 10.9% of decrease, respectively, P > 0.05). The results of the kinetic study indicated that addition of AOB and EGT could significantly reduce the formation rate constant (k(F)) of acrylamide, but could not significantly affect the elimination rate constant (k(E)) of acrylamide.

Effect of natural antioxidants on kinetic behavior of acrylamide formation and elimination in low-moisture asparagine–glucose model system

The present study investigated the effect of two natural antioxidants, i.e. antioxidant of bamboo leaves (AOB) and extract of green tea (EGT), on the mitigation and the kinetic behavior of acrylamide in an equimolar asparagine–glucose model system (pH 6.80). The substrates with addition of AOB or EGT were oven-heated at 180 °C under low-moisture conditions and the acrylamide content in final reaction products was quantified by ultra-performance liquid chromatography tandem mass spectrometry (UPLC–MS/MS). Results of mitigation effect on the generation of acrylamide showed that both AOB and EGT could effectively reduce the formation of acrylamide and achieve a maximum reduction rate (74.4% for the use of AOB and 74.3% for the use of EGT) when the addition levels of AOB and EGT were both 10 −4 mg. Such mitigation effect in the model system was further confirmed by addition of homoorientin and epigallocatechin gallate (EGCG), the representative components in AOB and EGT. To describe the kinetic behavior of acrylamide, a logistic-exponential model was selected among three kinetic model candidates while relative kinetic rate constants were calculated by the Marquardt non-linear regression method. Results indicated that there were significant differences on kinetic parameters ( k g and t cg) between AOB/EGT-spiked and non-spiked model system studies, which suggested that addition of AOB or EGT could reduce the formation of acrylamide during the formation-predominant kinetic stage and prolong the formation progress of acrylamide in the low-moisture reaction system. However, such addition method was not able to reduce the acrylamide content during the elimination-predominant kinetic stage of acrylamide.

Impact of pH on the Kinetics of Acrylamide Formation/Elimination Reactions in Model Systems

The effect of pH on acrylamide formation and elimination kinetics was studied in an equimolar (0.1 M) asparagine-glucose model system in phosphate or citrate buffer, heated at temperatures between 120 and 200 degrees C. To describe the experimental data, a simplified kinetic model was proposed and kinetic parameters were estimated by combined nonlinear regression and numerical integration on the data obtained under nonisothermal conditions. The model was subsequently validated in a more realistic potato-based matrix with varying pH. By increasing acidity, the reaction rate constants at T(ref) (160 degrees C) for both acrylamide formation and elimination can significantly be reduced, whereas the temperature dependence of both reaction rate constants increases. The introduction of a lyophilized potato matrix (20%) did not affect the acrylamide formation reaction rate constant at reference temperature (160 degrees C) as compared to the asparagine-glucose model system; the elimination rate constant at T(ref), on the contrary, was almost doubled.

Linear and Non-Linear Kinetics in the Synthesis and Degradation of Acrylamide in Foods and Model Systems

Isothermal acrylamide formation in foods and asparagine-glucose model systems has ubiquitous features. On a time scale of about 60 min, at temperatures in the approximate range of 120−160°C, the acrylamide concentration-time curve has a characteristic sigmoid shape whose asymptotic level and steepness increases with temperature while the time that corresponds to the inflection point decreases. In the approximate range of 160−200°C, the curve has a clear peak, whose onset, height, width and degree of asymmetry depend on the system's composition and temperature. The synthesis-degradation of acrylamide in model systems has been recently described by traditional kinetic models. They account for the intermediate stages of the process and the fate of reactants involved at different levels of scrutiny. The resulting models have 2–6 rate constants, accounting for both the generation and elimination of the acrylamide. Their temperature dependence has been assumed to obey the Arrhenius equation, i.e., each step in the reaction was considered as having a fixed energy of activation. A proposed alternative is constructing the concentration curve by superimposing a Fermian decay term on a logistic growth function. The resulting model, which is not unique, has five parameters: a hypothetical uninterrupted generation-level, two steepness parameters; of the concentration climbs and fall and two time characteristics; of the acrylamide synthesis and elimination. According to this model, peak concentration is observed only when the two time constants are comparable. The peak's shape and height are determined by the gap between the two time constants and the relative magnitudes of the two “rate” parameters. The concept can be extended to create models of non-isothermal acrylamide formation. The basic assumption, which is yet to be verified experimentally, is that the momentary rate of the acrylamide synthesis or degradation is the isothermal rate at the momentary temperature, at a time that corresponds to its momentary concentration. The theoretical capabilities of a model of this kind are demonstrated with computer simulations. If the described model is correct, then by controlling temperature history, it is possible to reduce the acrylamide while still accomplishing much of the desirable effects of a heat process.

Effect of Amino Acids on Acrylamide Formation and Elimination Kinetics

The effect of amino acids other than asparagine on acrylamide (AA) formation/elimination kinetics was studied in an asparagine-glucose model system (0.01 M, pH 6) heated at temperatures between 140 and 200 degrees C. Addition of cysteine or lysine to the model significantly lowered the AA yield, whereas addition of glutamine had a strong promoting effect and of alanine a rather neutral effect on the AA formation. This was also reflected by AA formation/elimination kinetics, which for all model systems studied could be modeled by two consecutive first-order reactions. The ratio of the elimination to the formation rate constant increased from the systems to which glutamine or alanine was added, over the control model system, to the model systems that contained lysine or cysteine.