Non-enzymatic Browning Reactions Research Articles

Chemical structure of colored maillard reaction products

Visual color in processed foods is largely due to colored products of Maillard or nonenzymic browning reactions. In spite of the longstanding aesthetic and practical interest in Maillard‐derived food coloring materials, relatively little is known about the chemical structures responsible for visual color. In recent years numerous low molecular weight (<500 Da) colored products have been isolated from model Maillard reactions and their structures elucidated. Many colored products appear to be aldolization/dehydration products of sugars which may or may not be attached to proteins or other sources of amino nitrogen. The structures of high molecular weight Maillard pigments are still mostly undefined, but degradative studies have yielded identifiable fragments with chromogenic properties. This report summarizes the current knowledge of colored compounds formed in the Maillard reaction.

Non-enzymatic browning-induced water plasticization

An exotherm, observed in differential scanning calorimetry (DSC) scans of amorphous food materials above their glass transition temperature,T g, may occur due to sugar crystallization, nonenzymatic browning, or both. In the present study, this exothermal phenomenon in initially anhydrous skim milk and lactose-hydrolyzed skim milk was considered to occur due to browning during isothermal holding at various temperatures above the initialT g. The nonenzymatic, Maillard browning reaction produces water that in amorphous foods, may plasticize the material and reduceT g. The assumption was that quantification of formation of water from theT g depression, which should not be observed as a result of crystallization under anhydrous conditions, can be used to determine kinetics of the nonenzymatic browning reaction. The formation of water was found to be substantial, and the amount formed could be quantified from theT g measured after isothermal treatment at various temperatures using DSC. The rate of water formation followed zero-order kinetics, and its temperature dependence well aboveT g was Arrhenius-type. Although water plasticization of the material occurred during the reaction, and there was a dynamic change in the temperature differenceT−T g, the browning reaction was probably diffusioncontrolled in anhydrous skim milk in the vicinity of theT g of lactose. This could be observed from a significant increase in activation energy. The kinetics and temperature dependence of the Maillard reaction in skim milk and lactose-hydrolyzed skim milk were of similar type well above the initialT g. The difference in temperature dependence in theT g region of lactose, but above that of lactose-hydrolyzed skim milk, became significant, as the rate in skim milk, but not in lactose-hydrolyzed skim milk, became diffusion-controlled. The results showed that rates of diffusion-controlled reactions may follow the Williams-Landel-Ferry (WLF) equation, as kinetic restrictions become apparent within amorphous materials in reactions exhibiting high rates at the same temperature under non-diffusion-controlled conditions.

Degradation of Maillard reaction products by amylolytic enzymes. 2. Enzymatic degradation of heat-treated alpha-glucans with and without amino compounds

The enzymatic degradation of thermal treated alpha-glucans with amylolytic enzymes depends on the reaction environment (T, pH, moisture), the degree of polymerisation (DP) and the branch of the substrates as well as on the presence of amino compounds. The chemical changes of the alpha-glucans due to thermolysis at 180 degrees C are characterized by means of the amount of reducing substances and the amount of maltooligosaccharides (HPLC). In general the enzymatic degradability of the thermal treated alpha-glucans is decreased with increasing time of thermolysis, temperature and moisture content. The enzyme activity with the thermal treated alpha-glucans is diminished in the same way. The addition of amino compounds reduces the enzymatic degradability only at the beginning of the reaction. With increasing time of thermolysis the thermolysates without glycine addition are hardly degraded. As reason for these differences in the enzymatic degradation transglycosylation and non-enzymatic browning reactions (caramalisation/Maillard-reaction) are assumed.

Effect of certain additives on sorbate stability

The effect of several additives on sorbate stability was studied in aqueous model systems of 0.91 water activity at pH 5.0. The rate constants of sorbic acid destruction could be described by first order kinetics. Non-enzymatic browning reactions exhibited zero order kinetics and were greatly influenced by sorbic acid destruction and in all systems a correlation between the natural logarithm of sorbates retention and the increase in the absorbance at 420 nm was found. Polyphosphates and propylgallate protected sorbic acid from destruction. Ascorbic acid showed a dual behavior: in the absence of sodium nitrite, it exhibited a pro-oxidant effect. When nitrite was present, ascorbic acid behaved as a protector. In general, sucrose did not influence the rate of sorbic acid destruction and the effect of sodium nitrite was diverse. In all cases, inclusion of glycine enhanced sorbic acid destruction and browning development.

Quantification of Color Change Resulting from Pheophytinization and Nonenzymatic Browning Reactions in Thermally Processed Green Peas

The visual green color degradation, as represented by the change of the −a value measured by a tristimulus colorimeter, was found to be caused by not only pheophytinization but also by nonenzymatic browning reactions in green peas at 100, 110, and 120 °C. Mathematical models were developed for predicting the change in the −a value as a function of time and temperature by knowing the kinetic parameters (rate constant and activation energy) of each mechanism. The rate of disappearance of greenness via pheophytinization followed a first-order kinetic model, while the rate of color loss due to nonenzymatic browning reactions followed a zeroth-order kinetic model after an initial lag period. The activation energies for pheophytinization and nonenzymatic browning were 20.4 and 22.3 kcal/mol, respectively. Keywords: Kinetics; visual green color; browning; colorimetry

Enzymes and Bread Flavor

Enzymes used in breadmaking and their influence on bread flavor are reviewed. Components of bread flavor originate from fermentative and thermal reactions. Enzymes provide precursors for both processes, and their influence should be controlled. Enzymes are now replacing other improving additives in breadmaking, indirectly affecting bread flavor. Amylases produce reducing sugars, which are (1) fermentable substrates for fermentative microflora leading to numerous aromatic compounds, those of lower volatility remaining in bread, and (2) precursors of many components (mainly carbonyls) after reacting with amino acids in nonenzymatic browning reactions. Proteases produce peptides and amino acids, which, like sugars, participate in metabolic and thermal reactions and can occasionally be a source of bitter peptides. Lipoxygenase from soy or faba flour, used in some breadmaking processes, gives unstable products decomposing to carbonyl compounds generating off flavors in bread. In addition, the ingredients, the breadmaking process, and the baking conditions modify enzymatic activity and bread flavor.

Degradation of 3-Chloro-p-toluidine Hydrochloride in Watermelon Bait. Identification and Chemical Characterization of Novel N-Glucoside and Oxopropanimine

Stability of the avicide 3-chloro-p-toluidine hydrochloride (CPTH) in watermelon bait was assessed. When exposed to light, the presence of CPTH accelerated nonenzymic browning (Maillard) reactions and degradation of the watermelon matrix. The addition of potassium metabisulfite appeared to hinder bait degradation. These experiments resulted in the identification and chemical characterization of two novel CPTH derivatives: N-β-d-glucopyranosyl-3-chloro-4-methylaniline and N-(3-chloro-4-methylphenyl)-2-oxopropanimine. Keywords: 3-Chloro-p-toluidine hydrochloride; CPTH; DRC-1339; N-β-d-glucopyranosyl-3-chloro-4-methylaniline; N-(3-chloro-4-methylphenyl)-2-oxopropanimine; nonenzymic browning; Maillard reaction

Food Browning and Its Prevention: An Overview

Enzymatic and nonenzymatic browning reactions of amino acids and proteins with carbohydrates, oxidized lipids, and oxidized phenols cause deterioration of food during storage and processing. The loss in nutritional quality and potentially in safety is attributed to destruction of essential amino acids, decrease in digestibility, inhibition of proteolytic and glycolytic enzymes, interaction with metal ions, and formation of antinutritional and toxic compounds. Studies in this area include influence of damage to essential amino acids on nutrition and food safety, nutritional damage as a function of processing conditions, and simultaneous formation of deleterious and beneficial compounds. These compounds include kidney-damaging Maillard reaction products, mutagens, carcinogens, antimutagens, antioxidants, antibiotics, and antiallergens. This overview covers the formation, nutrition, and safety of glycated proteins, characterized browning products, and heterocyclic amines. Possible approaches to inhibiting browning reactions and preventing adverse effects of browning during food processing and food consumption, including protection against adverse effects of heterocyclic amines by N-acetylcysteine, caffeine, chlorophyll, conjugated linoleic acid, lignin, and tea extracts, are also described. This research subject covers a complex relationship of the chemistry, biology, and pathology of browning products and the impact on human nutrition and health. Future study should differentiate antinutritional and toxicological relationships, define individual and combined potencies of browning products, and develop means to prevent the formation and to minimize the adverse manifestations of the most antinutritional and toxic compounds. Such studies should lead to better and safer foods and improved human health.

Antioxidative Activity of Pyrrole, Imidazole, Dihydropyridine, and Pyridinium Salt Derivatives Produced in Oxidized Lipid/Amino Acid Browning Reactions

The antioxidative activity of several models of nonenzymatic browning reaction products was evaluated to determine if the lipid peroxidation process in the presence of amino acids is always accompanied by formation of products with antioxidative properties. 1-Methylpyrrole (1), 1,2,5-trimethylpyrrole (2), 2-(1-hydroxyethyl)-1-methylpyrrole (3), 2-acetyl-1-methylpyrrole (4), 1-methyl-4-pentyl-1,4-dihydropyridine-3,5-dicarbaldehyde (5), 1-(2-hydroxyethyl)-2-hexyl-3,5-dipentylpyridinium chloride (6), 1-(1-ethyl-2-formylethyl)-4-methylimidazole (7), and 1-(1-ethyl-3-hydroxypropyl)-4-methylimidazole (8) were added at two levels of concentration (100 and 200 ppm) to soybean oil which was oxidized under air in the dark at 60 °C. Oil peroxidation was evaluated by using the thiobarbituric acid-reactive substances assay. Compounds 2−8 significantly decreased TBARS formation on soybean oil (p < 0.05) and showed diverse activity as compared among them and with synthetic antioxidants. The order of effectiveness obtained at 200 ppm was 1 < 2 < 3 < 4 ≈ 6 < 7 ≈ 5 < 8 < butylated hydroxytoluene < propyl gallate. These results suggest that reactions between oxidized lipids and amino acids produce many compounds with antioxidative properties that may contribute to the stability of foods. Keywords: Amino acid modification; antioxidative activity; heterocyclic products; nonenzymatic browning; lipid peroxidation

Studies on Dental Stains Induced by Antibacterial Agents and Rational Approaches for Bleaching Dental Stains

Extrinsic stain resides in the dental pellicle and can be caused by introduction of chromogenic materials or therapeutic agents into the oral cavity. In contrast, intrinsic tooth stain is found within the tooth structure and can be caused by a variety of agents, including hematological and developmental abnormalities and drugs such as tetracycline. The mechanisms of extrinsic stain formation differ with respect to the causative agent. For example, stain induced by chlorhexidine (CH) can be explained by an increased rate in the non-enzymatic browning reactions occurring at the pellicle surface, while food stains are retained on the surface via ion exchange mechanisms. Although most extrinsic dental stain can be removed by abrasive and/or surface-active materials, removal of certain types of surface stain, e.g., staining due to cationic antimicrobial agents, requires specific agents such as aminoguanidine to reduce the stain.A broad-spectrum approach to reduce both intrinsic and extrinsic dental stains clinically requires oxygenating agents. To evaluate this approach and understand the mechanisms of stain removal, we developed a spectroscopic method for measuring stain in vivo. A series of clinical studies was performed to evaluate stain removal by the agents. The results showed that carbamide peroxide in combination with surfactants and anti-redeposition agents, e.g., sodium pyrophosphate, was more effective in bleaching dental stain compared with carbamide peroxide alone. A detailed examination of the tooth structure by microhardness measurements, x-ray photoelectron spectroscopy, and scanning electron microscopy showed that stain decolorization with this system did not have any adverse effects.

Antioxidative Activity of (E)-2-Octenal/Amino Acids Reaction Products

The effects of several compounds, previously identified in nonenzymatic browning reactions between oxidized lipids and amino acids, on protecting bulk vegetable oils against oxidation were evaluated to investigate if these naturally formed products may contribute to the overall antioxidative activity of foods. Two amino acid residue analogs, N-(carbobenzyloxy)-L-histidine (Z-His) and N2-(carbobenzyloxy)-L-lysine (Z-Lys), and their products of reaction with (E)-2-octenal, the Michael adduct 1 and two pyridinium salts, 2 and 3, were added at three levels of concentration (50, 100, and 200 ppm) to soybean oil which was oxidized under air in the dark at 60 degrees C. Oil peroxidation was evaluated by using the thiobarbituric acid-reactive substances (TBARS) assay. Compounds 1-3 significantly decreased TBARS formation on soybean oil (p < 0.05) and showed diverse activity as compared with synthetic antioxidants. The order of effectiveness obtained was 1 << 2 approximately butylated hydroxytoluene approximately 3 < propyl gallate. These results suggest that some reactions between oxidized lipids and amino acids may contribute to the antioxidant activity of foods in addition to the development of color and fluorescence.

Effect of physical changes on the rates of nonenzymic browning and related reactions

Nonenzymic browning (NEB) due to reaction of d-xylose and l-lysine was studied in a dehydrated matrix based on poly(vinylpyrrolidone) (PVP) of different average molecular weights. Physical changes (collapse) and NEB were studied temperatures ( T) and moisture contents resulting in different values of ( T − T g), where T g is the glass transition temperature. Nonenzymic browning rates at low and intermediate moisture contents in a polymeric matrix above its glass transition were shown to be closely related to ( T − T g). The initially porous matrices underwent a time-dependent shrinkage (collapse) above T g and this shrinkage increased the rate of browning, presumably by minimizing diffusion paths for reactants. When the reactants (xylose and lysine in PVP) were separated by a reactant-free layer of PVP, the reaction rate decreased as the thickness of the empty layer increased. A lag time was observed, which was directly related to the thickness of this layer.

Non-enzymatic browning reactions in irradiated glucose-glycine aqueous model systems

Non-enzymatic browning reactions in irradiated glucose-glycine aqueous model systems

Influence of oxidized lipids on the non-enzymic browning reaction: interaction between linolenic acid and an Amadori compound

The formation of 4-( d- arabino-tetritol-1-yl)-1-butyl-3-pyrrolecarbaldehyde ( 1) and 3-( d- arabino-tetritol-1-yl)-1-butyl-4-pyridone ( 2) in the non-enzymic browning reaction at pH 6 of 1-butylamino-1-deoxy- d-fructose (BAF) in the presence of linolenic acid (LNA) was studied. 1 and 2 are products of the reaction of the amino sugar with the malondialdehyde (MDA) that results from the oxidative degradation of the LNA. Identification and quantification of both heterocycles was carried out using high resolution gas chromatography (HRGC) and GC-MS of their O-trimethylsilyl derivatives. Oxidative conditions were necessary for browning development in the interaction BAF-LNA and the results were different according to oxidative conditions. Thus, using the 13-OOH of LNA (13-LNOOH), the initial level of thiobarbituric acid reactive substances (TBARS) and the browning were lower than when chemically oxidized LNA was used. In addition, the quantification of the heterocycle 2 (>99% extractable with ethyl acetate from aqueous reaction solutions) was used to determine the amount of MDA produced and reacted with BAF. 13-LNOOH was found to produce a lower amount of MDA (0.06%) than chemically oxidized LNA (0.54%). In the latter case, the amount of MDA had a threefold increase (1.48%) when the reaction mixture was preincubated for 24 h at room temperature.

Tristimulus colour reflectance measurement of milk and dairy products

A tristimulus reflectance technique was applied to the objective assessment of the colour of milk and dairy products. A variety of milk and dairy products (Iiquid milk, cultured products, cheese, butter, milk powder) was characterized based on the L a', b' (CIE-LAS) colour parameters. The b' value was not suitable for estimating the B-carotene content of butter, whereas storage defects (non-enzymatic browning reactions) of whey powder could be monitored using this parameter.

Flavour of heated milks. A review

Abstract The flavour of fresh milk is due to the combined effect of a great number of compounds from diverse origins. This flavour may change when milk is submitted to thermal treatments. The kind and intensity of the heated milk flavour depends on the intensity of the thermal treatment. The heating of milk causes the formation of volatile compounds from milk proteins, carbohydrates and lipids, as well as from some other compounds. From milk proteins some compounds are originated via the release of sulphidryl compounds during the heat denaturation of the whey proteins and proteins in the milk fat globule membrane; other compounds are formed via the non-enzymatic browning reaction. The heating of milk produces the formation of some methyl ketones, lactones and aldehydes from milk fat. The formation of the volatile compounds, responsible for flavour of heated milk, during the heat treatment of milk has been reviewed in this work.

Glycylglycine-derived 1,3-disubstituted imidazole in nonenzymic browning reactions

Glycylglycine-derived 1,3-disubstituted imidazole in nonenzymic browning reactions

Formation of pentosidine during nonenzymatic browning of proteins by glucose. Identification of glucose and other carbohydrates as possible precursors of pentosidine in vivo

A fluorescent compound has been detected in proteins browned during Maillard reactions with glucose in vitro and shown to be identical to pentosidine, a pentose-derived fluorescent cross-link formed between arginine and lysine residues in collagen (Sell, D. R., and Monnier, V. M. (1989) J. Biol. Chem. 264, 21597-21602). Pentosidine was the major fluorophore formed during nonenzymatic browning of ribonuclease and lysozyme by glucose, but accounted for less than 1% of non-disulfide cross-links in protein dimers formed during the reaction. Pentosidine was formed in greatest yields in reactions of pentoses with lysine and arginine in model systems but was also formed from glucose, fructose, ascorbate, Amadori compounds, 3-deoxyglucosone, and other sugars. Pentosidine was not formed from peroxidized polyunsaturated fatty acids or malondialdehyde. Its formation from carbohydrates was inhibited under nitrogen or anaerobic conditions and by aminoguanidine, an inhibitor of advanced glycation and browning reactions. Pentosidine was detected in human lens proteins, where its concentration increased gradually with age, but it did not exceed trace concentrations (less than or equal to 5 mumol/mol lysine), even in the 80-year-old lens. Although its precise carbohydrate source in vivo is uncertain and it is present in only trace concentrations in tissue proteins, pentosidine appears to be a useful biomarker for assessing cumulative damage to proteins by nonenzymatic browning reactions with carbohydrates.

Role of sorbic acid in nonenzymic browning reactions in liquid and solid model food systems

SummaryRole of sorbic acid (SA) in browning development in model systems has been studied. In liquid model systems containing water‐glycerol‐glucose (WGG), water‐glycerol‐sucrose (WGS), 45% sucrose and 30% sucrose plus 15% glucose, SA degraded when stored at 37°C forming brown pigments. Addition of amino acids (glycine or lysine monohydrochloride) increased the rate of browning development while Cu2+ reduced SA degradation and browning development. In the absence of amino acids and SA, WGG and WGS systems did not brown appreciably.In solid systems with SA adsorbed on microcrystalline cellulose, the maximum rate of browning occurred at 0.73aw, but maximum rate of SA loss was at 1.0aw. In all systems inclusion of amino acids reduced SA degradation but increased browning development. The rate of SA‐induced browning was considerably higher than that caused by sugar‐amino acid interactions.

L-Ascorbic acid ? A carbonyl component of non-enzymatic browning reactions

Model systems (phosphate citrate buffer,\(c_{0_{AA} }\), 364 K,t=5–8 h) were used for studies into non-enzymatic browning behaviour ofl-ascorbic acid (l-AA), depending on pH (5.0, 7.0, 8.0), with involvement of absorption measurements (λ=430 nm) and determination ofl-AA concentrations (absorbance at 265 nm, enzyme electrode). Kinetic evaluations gave linear reactions (of pseudo-zero order) for both pigment formation andl-AA degradation. While the reaction rate constant for non-enzymatic browning (kB) ofl-AA was found to increase with increasing pH, the percentage loss of total ascorbic acid content (AA and AA(−) remained constant when measured after 5 h. ‚Static‘ or ‚dynamic‘ equilibrium, depending on hydrogen ion concentration, was found to exist between the non-dissociated AA molecule (AA) and its monovalent anion (AA(−). At pH 5.0, the existing dynamic AA-AA(−) equilibrium tended to be strongly shifted toward the AA molecule which was preferentially capable of reaction via the direct route of degradation to furfural. Direct degradation was also predominant under neutral conditions of reaction (pH 7.0), although a static equilibrium seemed to prevail between AA and AA(−). In basic medium (pH 8.0), the dynamic equilibrium between AA and AA(−) was found to be on the side of the monovalent anion which was subsequently involved in processes of non-enzymatic browning via the oxidatively induced route of degradation and with concomitant formation of 2,3-diketo-l-gulonic acid.