Aqueous Model Systems Research Articles

The pathways for the removal of acrylamide in model systems using glycine based on the identification of reaction products

The reaction between acrylamide and glycine was studied in the aqueous model system heated at 150°C. The main reaction products were identified as C5H10N2O3, C8H15N3O4, C7H12N2O5 and C10H17N3O6 using HPLC-MS/MS, IT-TOF and NMR. Both of the critical intermediates were identified as glyoxylic acid and iminodiacetic acid. The pathways for the removal of acrylamide by glycine were proposed as the Michael addition between acrylamide and glycine with or without the initial oxidation of glycine. The changes in the contents of reactants and products provided quantitative evidence for the above pathways. The addition products between acrylamide and other 14 amino acids were identified by HPLC-MS/MS also.

Degradation of fluoranthene by a newly isolated strain of Herbaspirillum chlorophenolicum from activated sludge

A fluoranthene-degrading bacterial strain FA1 was isolated from activated sludge and identified as Herbaspirillum chlorophenolicum, a newfound bacterial species that can grow well on fluoranthene as sole carbon and energy source. The kinetic characteristic of strain FA1 was tested in the aqueous model system (AMS) and the effects of nonionic surfactants on fluoranthene biodegradation in the AMS were then investigated. Tween 80 exhibited the best solubilization capacity for fluoranthene among three surfactants and its bioavailability decreased with an increase in its concentration and its degradation kinetics fit well with the first-order of power index model. The biotransformation of fluoranthene was greatly improved by Tween 80, and 58.5% fluoranthene degradation was obtained as Tween 80 was 100 mg/l. However, the bioavailability of fluoranthene decreased gradually with the increase of Tween 80 concentration. Bioremediation tests for fluoranthene in soil-water system were designed further to examine the degrading ability of strain FA1 with the presence of indigenous flora or not. The measurements showed that in the presence of indigenous flora, the optimum 30-day fluoranthene degradation in soil-water system reached 77.4%. Evidently, strain FA1 seems both efficient and high-effective and deserves further exploration on the enhanced bioremediation technologies for the treatment of fluoranthene-polluted soil.

Effect of steviosides and system composition on stability and antimicrobial action of sorbates in acidified model aqueous systems

The effect of steviosides on sorbate stability and on its antimicrobial action was studied in aqueous systems (pH 3.0). The use of steviosides decreased sorbate destruction in all the systems. Its effect on nonenzymatic browning (NEB) depended on the system composition. From the point of view of microbial stability, the steviosides promoted a slight increase in the minimum inhibitory concentration (MIC) of sorbates against Zygosaccharomyces bailii and Zygosaccharomyces rouxii. However, the main effect of steviosides was the protected action on sorbate destruction. This action was essential to ensure that the preservative residual level was higher than the MIC of the preservative to prevent the growth Z. bailii or Z. rouxii during storage. The results reported highlight that the use of steviosides in aqueous model systems resembling low-calorie sweet products can be useful to protect potassium sorbate (KS) from destruction and depending on the system composition also to decrease browning development.

Effect of pressure on the Maillard reaction between ribose and cysteine in supercritical carbon dioxide

An aqueous ribose-cysteine model system, heated at 140°C under supercritical carbon dioxide (SC-CO<sub>2</sub>) and supercritical nitrogen (SC-N<sub>2</sub>), was investigated with emphasis on the formation of volatile compounds. In general, SC-CO<sub>2</sub> facilitated the overall intermediates accumulation while suppressing the advanced stage of browning. 3-Methyl-1, 2-dithian-4-one increased with increasing SC-CO<sub>2</sub> pressure, and was always more concentrated than in the case of SC-N<sub>2</sub>-treatment. The formation of thiols, disulfides, and formyl substituted thiophenes was also promoted in SC-CO<sub>2</sub>-treated reaction products, while the effect of high pressure on the individual components followed different patterns. The reversible pH decrease and reinforced acid-base catalysis of 2, 3-enolisation by SC-CO<sub>2</sub> could attribute to the decreased browning and higher amounts of most intense meaty aromatic compounds.  

Potential impact of medium characteristics on the isomerisation of hop α-acids in wort and buffer model systems

Many brewing variables, e.g., pH, boiling time, temperature, and the presence of metal catalysts, are essential in view of the isomerisation of hop α-acids into iso-α-acids. In this work, a comparative study on the impact of several selected factors on α-acids isomerisation was performed in both buffer model solutions and wort, in order to find out enhanced boiling conditions for higher isomerisation yields. Increase of the pH of the reaction mixture has a positive effect on the isomerisation yield, in particular in wort, whereas wort gravity only becomes a limiting factor for α-acids conversion at high extract levels. Of the metal catalysts tested, in particular Mg 2+, Al 3+, and especially Fe 3+ showed to have a pronounced positive impact on iso-α-acids formation in wort. However, due to precipitation phenomena, this effect was not observed for Al 3+ and Fe 3+ in the aqueous buffer model system. Neither the presence of glucose or polyphenols, nor ionic strength seem to exert any influence on α-acids conversion.

Reduction of acrylamide by taurine in aqueous and potato chip model systems

Abstract Acrylamide in foods is mainly produced by Maillard reaction. Taurine can participate in the reaction, which has led us to investigate the possibility of reducing acrylamide formation by use of taurine. In an aqueous system, the lower the pH of the solution the greater the inhibition of acrylamide formation within a pH range of 5.0–8.0 was found, and the inhibition of acrylamide formation by taurine was dose-dependent. In a fried potato chip model, prior to frying at 170 °C for 3 min, the potato slices soaked in 0.l% to 2% taurine solution for 30 min showed significant reductions of acrylamide formation; however, these reductions were not dose-dependent. Also, the soaking treatments for 15–60 min significantly reduced acrylamide formation, but the inhibitory effects were not time-dependent. Thus, taurine, when used in a narrow range of reasonably low levels, is a candidate to inhibit acrylamide formation during frying process.

Comparison of volatile Maillard reaction products from tagatose and other reducing sugars with amino acids

In this study, in order to investigate the effects of tagatose on the Maillard reaction, volatile Maillard reaction products (V-MRPs) produced from aqueous model systems containing various reducing sugars (glucose, galactose, fructose, and tagatose) and amino acids (glycine, valine, leucine, asparagine, and cysteine) were analyzed and then compared. Furans, furan derivatives, pyrazines, and some sulfur-containing heterocyclic compounds, such as thiazoles, thiophenes, and thiols, were mainly identified. The amounts of furans and furan derivatives were higher in the model systems of ketoses (fructose or tagatose) with amino acids than those of aldoses (glucose or galactose) with amino acids. In particular, 2-acetylfuran was detected 2-20 times more in the V-MRPs of tagatose as compared to those produced from the other reducing sugars. Also, 2-acetylpyrrole, one of nitrogen-containing heterocyclic compounds, was more abundant from the thermal reactions of tagatose-glycine and tagatose-valine compared to those of other reducing sugars-amino acids. More 2-acetylthiazole and thiophenes were found in tagatose-cysteine model system than in those of glucose with cysteine.

Lycopene Epoxides and Apo‐Lycopenals Formed by Chemical Reactions and Autoxidation in Model Systems and Processed Foods

To gain a better understanding of the reactions and the underlying mechanisms of the oxidative degradation of lycopene, the products formed by epoxidation with m-chloroperbenzoic acid (MCPBA), oxidative cleavage with KMnO(4), and autoxidation in low-moisture and aqueous model systems, under light exposure, at ambient temperature were identified. The presence of oxidation products was also verified in processed products (tomato juice, tomato paste, tomato puree, guava juice, "goiabada"). A total of 8 lycopene epoxides and a cyclolycopene diol were formed by the reaction of lycopene with MCPBA and 6 apo-lycopenals were produced with KMnO(4). Some of these oxidation products were not detected in the model systems and in the foods analyzed, but the acid-catalyzed rearrangement product 2,6-cyclolycopene-1,5-diol and apo-12'-lycopenal were found in all model and food systems and lycopene-1,2-epoxide and 2,6-cyclolycopene-1,5-epoxide were found in the model systems and in all but 1 ("goiabada") of the 5 foods analyzed. Other epoxides and apo-lycopenals were found in some systems. The inability to detect an intermediate product could be due to a fast turn over. Increased Z-isomerization was also observed and Z-isomers of the oxidation products were detected.

Development, simulation, and validation of NMR relaxation-based exchange measurements

Two-dimensional (2D) nuclear magnetic resonance correlation experiments have recently been proposed as a means for studying exchange in porous media. Most notable of these is the T(2)-T(2) relaxation exchange spectroscopy (REXSY) experiment. Unfortunately, quantifying exchange with this method requires a relatively long, three-dimensional acquisition. To reduce acquisition times, novel 2D methods for quantifying exchange were developed. For each method, model equations were derived (for an arbitrary N-pool system), tested via simulation studies, and validated via experimental studies in an aqueous urea model system. Results indicate that the novel methods outperform REXSY-in terms of uncertainty per unit time for the fitted exchange rate-for certain model systems. The relative merits of each method are discussed in the text.

Effect of carboxymethyl cellulose concentration on rheological behavior of milk and aqueous systems. A creep and recovery study

AbstractCarboxymethyl cellulose (CMC) is an anionic polysaccharide used mainly as stabilizer and thickener agent. The purpose of this study was to investigate the effect of CMC concentration on viscoelasticity of dairy and aqueous model systems through the analysis of creep and recovery tests. The viscoelastic properties of different concentrations of CMC (0.75, 1.00, 1.25, and 1.50% w/w) in two milk systems (skimmed milk and whole milk) were compared with those of the same concentration of biopolymer in aqueous solution. Creep curves were fitted to a six parameter mechanical model (Burger + Kelvin‐Voigt), whereas an empirical equation was used for recovery. The creep and recovery properties of samples were clearly affected by both the type of dispersing media and the CMC concentration. The whole‐milk system was more elastic than both the biopolymer (CMC) aqueous solution and the skimmed‐milk sample, indicating that in whole‐milk samples some new interactions could take place between macromolecules. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Simple models for two-dimensional tunable colloidal crystals in rotating ac electric fields

We compare the behavior of a new two-dimensional aqueous colloidal model system with a simple numerical treatment. To the first order the attractive interaction between the colloids induced by an in-plane rotating ac electric field is dipolar, while the charge stabilization leads to a shorter ranged, Yukawa-like repulsion. In the crystal-like "rafts" formed at sufficient field strengths, we find quantitative agreement between experiment and Monte Carlo simulation, except in the case of strongly interacting systems, where the well depth of the effective potential exceeds 250 times the thermal energy. The "lattice constant" of the crystal-like raft is located approximately at the minimum of the effective potential, resulting from the sum of the Yukawa and dipolar interactions. The experimental system has display applications, owing to the possibility of tuning the lattice spacing with the external electric field. Limitations in the applied field strength and relative range of the electrostatic interactions of the particles result in a reduction in tunable lattice spacing for small and large particles, respectively. The optimal particle size for maximizing the lattice spacing tunability was found to be around 1000 nm.

Study of Maillard reaction products derived from aqueous model systems with different peptide chain lengths

Abstract Maillard reaction products (MRPs) were prepared from aqueous model mixtures containing 0.2 M glucose and 0.2 M each of glycine, diglycine, and triglycine, heated at 100 °C, for different times (10, 60, 120, 180 and 240 min), with an initial pH control set to 7.8. The browning and intermediate products of MRPs derived from the Glu-Di model system were the most prominent. The pH of all MRP samples decreased considerably as the heating time increased ( P

Generation of 4-Hydroxy-2,5-Dimethyl-3(2H)-Furanone from Rhamnose as Affected by Reaction Parameters: Experimental Design Approach

The formation of 4-hydroxy-2,5-dimethyl-3(2H)-furanone (HDMF) was studied in aqueous model systems containing L-rhamnose and L-lysine. The approach consisted in systematically varying four reaction parameters (rhamnose concentration, rhamnose to lysine ratio, pH, and phosphate concentration) at 3 levels. A fractional factorial design was used to reduce the number of trials. The degradation of rhamnose was followed by high performance anion exchange chromatography and the formation of HDMF by solid phase extraction in combination with GC/MS. The study permitted the identification of critical reaction parameters that affect the formation of HDMF from rhamnose in aqueous systems. Although all studied parameters have some impact on the HDMF formation and rhamnose degradation kinetics, the effect of phosphate is by far the most important, followed by concentration of precursors and pH. The experimental design approach permitted us, with a limited number of experiments, to accurately model the effects of the four investigated reaction parameters on the kinetics of rhamnose degradation and HDMF formation (R(2)>0.93). Overall, the results indicate that rhamnose can be an excellent precursor of HDMF (yield >40 mol%), if the reaction conditions are well mastered.

Degradation of Lycopene and β‐carotene in Model Systems and in Lyophilized Guava during Ambient Storage: Kinetics, Structure, and Matrix Effects

Being highly unsaturated, carotenoids are susceptible to isomerization and oxidation during the processing and storage of food. In the present study, the degradation of acyclic lycopene and dicyclic beta-carotene in low-moisture and aqueous model systems, as well as in lyophilized guava, during storage at ambient temperature, in the absence or presence of light, was investigated. Both carotenoids followed first order kinetics under the various conditions investigated. Lycopene degraded much faster than beta-carotene in all the model systems. In a comparison of lycopene isolated from guava, tomato, and watermelon, greater losses were observed with lycopene from tomato. Since the model system was identical in the 3 cases, these results indicated that other compounds from the food sources, co-extracted with lycopene, might have influenced the oxidation. Light consistently and strongly promoted degradation under all conditions studied. The susceptibility of lycopene to degradation was much less in lyophilized guava than in the model systems, showing the marked protective influence of the food matrix. Loss of beta-carotene, found at a concentration of about 18 times lower than lycopene, was only slightly lower than that of lycopene in lyophilized guava, indicating that the effect of matrix and/or the initial concentration overshadowed the structural influence.

Ions at Aqueous Interfaces: From Water Surface to Hydrated Proteins

The surfaces of aqueous solutions are traditionally viewed as devoid of inorganic ions. Molecular simulations and surface-selective spectroscopic techniques show, however, that large polarizable anions and hydronium cations can be found (and even enhanced) at the surface and are involved in chemistry at the air/water interface. Here, we review recent studies of ions at the air/water interface and compare from this perspective water with other polar solvents. For water, we focus in particular on the surface behavior of its ionic product (i.e., hydronium and hydroxide ions). We also investigate the feasibility of dielectric models for the description of the protein/water interface, in analogy to the air/water interface. Little correlation is found between these two interfaces in terms of ion segregation. Therefore, we suggest a local model of pairing of ions from the solution with charged and polar groups at the protein surface. We also describe corresponding results of experimental studies on aqueous model systems.

Extracts of plant cell cultures of Lavandula vera and Rosa damascena as sources of phenolic antioxidants for use in foods

Ethanolic extracts of plant cell cultures of lavender (Lavandula vera) and rose (Rosa damascena) have been examined as potential food antioxidants. The L. vera cell extract quenched the radicals Fremy’s salt, DPPH (2,2-diphenyl-1-picrylhydrazyl radical), and ABTS·+ (2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic) radical) more efficiently than the R. damascena extract. Also the L. vera extract inhibited lipid oxidation in a methyl linoleate emulsion more efficiently than the R. damascena extract. However, the L. vera extract had a prooxidative effect on the iron-based Fenton reaction in an aqueous model system. A similar effect was observed for pure rosmarinic acid, but not for the R. damascena extract. The addition of L. vera extract to minced chicken meat reduced lipid oxidation (measured as thiobarbituric acid reactive species) and the loss of α-tocopherol during cold storage after the meat was cooked. This suggests the antioxidative properties of L. vera extracts dominate in a real food system.

Effects of organic acids, amino acids and ethanol on the radio-degradation of patulin in an aqueous model system

The effects of organic acids, amino acids, and ethanol on the radio-degradation of patulin by gamma irradiation in an aqueous model system were investigated. The patulin, dissolved in distilled water at a concentration of 50 ppm, was practically degraded by the gamma irradiation at the dose of 1.0 kGy, while 33% of the patulin remained in apple juice. In the aqueous model system, the radio-degradation of patulin was partially inhibited by the addition of organic acids, amino acids, and ethanol. The proportions of remaining patulin after irradiation with the dose of 1.0 kGy in the 1% solution of malic acid, citric acid, lactic acid, acetic acid, ascorbic acid, and ethanol were 31.4%, 2.3%, 31.2%, 6.1%, 50.8%, and 12.5%, respectively. During 30 days of storage, the remaining patulin was reduced gradually in the solution of ascorbic acid and malic acid compared to being stable in other samples. The amino acids, serine, threonine, and histidine, inhibited the radio-degradation of patulin. In conclusion, it was suggested that 1 kGy of gamma irradiation (recommended radiation doses for radicidation and/or quarantine in fruits) is effective for the reduction of patulin, but the nutritional elements should be considered because the radio-degradation effects are environment dependent.

Influence of Different Extraction Parameters on a Solid-Phase Dynamic Extraction for the Gas Chromatographic Determination of d-Limonene Degradation Products by Using a Fractional Factorial Design

Through the application of a solid-phase dynamic extraction (SPDE) method for the determination of volatile substances, different parameters may influence the extraction and desorption process and are, therefore, vital for the determination of the extracted substances via gas chromatography (GC). In this study, the influence of extraction und desorption parameters of an SPDE-GC method for the determination of the d-limonene degradation products, namely, alpha-terpineol, (-)-carveol, and (S)-carvone, in an aqueous model system was evaluated using a factorial fractional design. The aim was to reduce the number of factors that should be considered for the optimization of an SPDE procedure for different applications. It could be shown that the extraction efficiency of alpha-terpineol, (-)-carveol, and (S)-carvone is significantly influenced by the extraction parameters incubation temperature, number of extraction strokes, and amount of added NaCl. All 3 parameters have a positive effect on the extraction and determination of the examined d-limonene degradation products. Due to the identification of significant factors on the basis of an experimental design, the results of this study can be very useful for further development of SPDE methods for different applications.

Effects of temperature and pH on the kinetics of caramelisation, protein cross-linking and Maillard reactions in aqueous model systems

Solutions of either glucose, bovine serum albumin (BSA), casein, glucose–BSA or glucose–casein were heated at 60 to 100 °C at pH 8.0 and pH 9.7, and the kinetics of the reaction markers (disappearance of the glucose and amino groups, development of UV absorbance and browning, and protein reticulation) were monitored. All the markers were enhanced at increasing temperatures, and, except for the disappearance of the free amino group and protein polymerisation, at alkaline pH levels. The loss of the amino group occurred in parallel with increase in polymerisation. The two proteins reacted in line with their amino content and solubility. The activation energy ( E a) of the amino group loss in the protein–glucose mixture was around 100 kJ per mol and that in the protein heated alone was higher. The E a associated with the disappearance of glucose was around 90 kJ per mol. The E a of UV absorbance and browning processes, which showed parallel time courses, were found to range from 90 to 150 kJ per mol.

Acrylamide in bread. Effect of prooxidants and antioxidants

Addition of 1% aqueous rosemary extract with approximately 40 mg of gallic acid equivalents or comparable addition of rosemary oil or of dried rosemary leaves to wheat dough reduced the content of acrylamide in wheat buns by 62, 67 and 57%, respectively, compared to wheat buns without rosemary. Increasing the addition of aqueous rosemary extract to 10% did not decrease the acrylamide content further compared to the addition of a 1% extract. The spice dittany showed less effect in wheat buns compared to rosemary and even increased acrylamide formation slightly. The effect of antioxidants on acrylamide formation was confirmed by addition of 1.0 mM (but not 0.1 mM) of the green tea flavonoids epicatechin or epigallocatechin gallate to an aqueous food model. Free radicals were detected by ESR using the spin trap α-(4-Pyridyl 1-oxide)-N-tert-butylnitrone (POBN) in an aqueous model system of 0.060 M glucose and 0.060 M asparagine heated under conditions generating acrylamide, further confirming the impact of free radical intermediates in formation of acrylamide. A modest effect of the peroxides in oxidized oil on acrylamide elimination was observed pointing towards an oxidative induced polymerization of acrylamide. The impact of oxidative processes on acrylamide elimination should not be neglected, since oxidized vegetable oil seems to promote degradation of acrylamide.