Progress of the Maillard reaction and antioxidant action of Maillard reaction products in preheated model systems during storage

The progress of the Maillard reaction and the effect of Maillard reaction products (MRPs) on lipid oxidation in preheated model systems containing pregelatinized starch, glucose, lysine, and soybean oil have been studied during storage. The samples, either containing all components or excluding one or more of them, were heated at 100 degrees C for 90 min and then stored for up to 180 days at 25 degrees C. Browning indices and lipid oxidation were measured, and the results showed that, in samples containing oil, the Maillard reaction had a significant rate also at room temperature and confirmed the ability of MRPs to retard peroxide formation. Under the conditions adopted the rate of the Maillard reaction was increased by the presence of the oil and its oxidation products. The antioxidant action of the MRPs was also evaluated using a peroxide scavenging test based on crocin bleaching. The results demonstrated that antioxidant activity developed with increased browning of the samples.     

The fluorescence of advanced Maillard products is a good indicator of lysine damage during the Maillard reaction

The objective of this study was to determine whether in heat-treated milk-resembling models or milk there is a lag phase, before lactulosyllysine (LL) is converted into advanced Maillard products (AMP), and if there is a step during the heat treatment where LL is actively degraded into AMP. For that purpose, a low temperature (60-85 degrees C) and a long heat treatment (15-90 h) were chosen. We observe that the heat treatment first induces a parallel increase in furosine and AMP fluorescence, confirming that AMP are produced very early during the heat treatment. At this step, both indicators are correlated with each other and precisely reflect the lysine damage. After a time, however, furosine reaches a steady-state concentration, whereas AMP fluorescence still increases, remaining correlated with the lysine blockage. Nevertheless, heat treatment applied to milk does not reach this step so that AMP fluorescence appears as a rapid alternative to furosine quantification.     

Formation of early and advanced Maillard reaction products correlates to the ripening of cheese

The present study deals with the characterization of the ripening of cheese. A traditional German acid curd cheese was ripened under defined conditions at elevated temperature, and protein and amino acid modifications were investigated. Degree of proteolysis and analysis of early [Amadori compound furosine (6)] and advanced [N(ε)-carboxymethyllysine (4), N(ε)-carboxyethyllysine (5)] Maillard reaction products confirmed the maturation to proceed from the rind to the core of the cheese. Whereas 6 was decreased, 4 and 5 increased over time. Deeper insight into the Maillard reaction during the ripening of cheese was achieved by the determination of selected α-dicarbonyl compounds. Especially methylglyoxal (2) showed a characteristic behavior during storage of the acid curd cheese. Decrease of this reactive structure was directly correlated to the formation of 5. To extend the results of experimental ripening to commercial cheeses, different aged Gouda types were investigated. Maturation times of the samples ranged from 6 to 8 weeks (young) to more than 1 year (aged). Again, increase of 5 and decrease of 2 were able to describe the ripening of this rennet coagulated cheese. Therefore, both chemical parameters are potent markers to characterize the degree of maturation, independent of coagulation.     

Formation of a novel colored product during the Maillard reaction of D-glucose

Reactions between reducing sugars and proteins or amino acids (Maillard reaction) lead to the formation of yellow to brown products (melanoidins) that are important for food preparation and processing, such as baking, roasting, or malt production. Thus far, the structures of the melanoidins have not been elucidated, although some structural insights have been gained from model reactions. In this study, D-glucose was heated with an amine and two colored compounds were detected by HPLC/UV--vis. After purification, the main product was identified as [(4aS,6R,7S,8R,8aR)-4,4a,6,7,8,8a-hexahydro-7,8-dihydroxy-6-hydroxymethyl-1,4-dipropyl-1H-pyrano[2,3-b]pyrazine-2-yl]-1-hydroxy-3-buten-2-one (1a). For the minor compound (2a), some spectral data were obtained, but the structure was not fully characterized. 1a and 2a are the main colored compounds when the reaction is performed in alcoholic solution or on a cellulose surface. Thus, it was concluded that products with an analogous structure are important for the color formation of foodstuffs with low water activity.     

Formation of aroma compounds from ribose and cysteine during the Maillard reaction

The headspace volatiles produced from a phosphate-buffered solution (pH 5) of cysteine and a 1 + 1 mixture of ribose and [(13)C(5)]ribose, heated at 95 degrees C for 4 h, were examined by headspace SPME in combination with GC-MS. MS data indicated that fragmentation of ribose did not play a significant role in the formation of the sulfur aroma compounds 2-methyl-3-furanthiol, 2-furfurylthiol, and 3-mercapto-2-pentanone in which the carbon skeleton of ribose remained intact. The methylfuran moiety of 2-methyl-3-(methylthio)furan originated from ribose, whereas the methylthio carbon atoms came partly from ribose and partly from cysteine. In 3-mercapto-2-butanone one carbon unit was split from the ribose chain. On the other hand, all carbon atoms in 3-thiophenethiol stemmed from cysteine. In another trial cysteine, 4-hydroxy-5-methyl-3(2H)-furanone and [(13)C(5)]ribose were reacted under the same conditions. The resulting 2-methyl-3-furanthiol was mainly (13)C(5)-labeled, suggesting that it stems from ribose and that 4-hydroxy-5-methyl-3(2H)-furanone is unimportant as an intermediate. Whereas 2-mercapto-3-pentanone was found unlabeled and hence originated from 4-hydroxy-5-methyl-3(2H)-furanone, its isomer 3-mercapto-2-pentanone was formed from both 4-hydroxy-5-methyl-3(2H)-furanone and ribose. A new reaction pathway from ribose via its 1,4-dideoxyosone is proposed, which explains both the formation of 2-methyl-3-furanthiol without 4-hydroxy-5-methyl-3(2H)-furanone as an intermediate and a new way to form 3-mercapto-2-pentanone.     

Allergenicity of Maillard reaction products from peanut proteins

It is known that peanut allergy is caused by peanut proteins. However, little is known about the impact of roasting on the allergenicity of peanuts. During roasting, proteins react with sugars to form Maillard reaction products, which could affect allergenicity. To determine if the Maillard reaction could convert a nonallergenic peanut protein into a potentially allergenic product, nonallergenic lectin was reacted with glucose or fructose at 50 degrees C for 28 days. Browning products from heat-treated peanuts were also examined. The products were analyzed in immunoblot and competitive assays, using a pooled serum (i.e., IgE antibodies) from patients with peanut anaphylaxis. Results showed that the products were recognized by IgE and had an inhibitory effect on IgE binding to a peanut allergen. Thus, the findings suggest that these Maillard reaction products are potentially allergenic and indicate the need to verify whether the Maillard reaction products formed in peanuts during roasting increase their allergenicity.     

Influence of Maillard reaction products on DNA damage in human lymphocytes

The effect of Maillard reaction products (MRPs) on induced DNA damage in human lymphocytes was investigated using single-cell gel electrophoresis (comet assay). Three MRPs, Xyl-Lys MRP, Glu-Lys MRP, and Fru-Lys MRP, were prepared by heating lysine with xylose, glucose, and fructose, respectively, at pH 9.0 and 100 degrees C for 3 h and called undialyzed MRPs. The prepared MRPs were further dialyzed, and three undialyzable MRPs were obtained. The undialyzed MRPs caused significant (p < 0.05) DNA damage in human lymphocytes at a concentration of 0.05-0.1 mg/mL by the comet assay. Compared with the control, the undialyzable Xyl-Lys MRP and Glu-Lys MRP caused significant DNA damage in human lymphocytes at a concentration >0.1 mg/mL, whereas Fru-Lys MRP did so at a concentration >0.2 mg/mL. Moreover, undialyzed MRPs caused less DNA damage than did undialyzable MRPs. The undialyzable MRPs did not affect the activity of glutathione peroxidase or lipid peroxidation in human lymphocytes at a concentration of 0.05-0.8 mg/mL. However, these three undialyzable MRPs decreased the glutathione (GSH) contents and the activities of GSH reductase and catalase in human lymphocytes. On the basis of the results of the formation of 8-hydroxy-2'-deoxyguanosine, radicals, and hydrogen peroxide, the radicals might play an important role in the DNA damage in human lymphocytes induced by these MRPs in this reaction system.     

Maillard reaction products inhibit oxidation of human low-density lipoproteins in vitro

Dietary intake of antioxidants has been associated with a reduced risk of cardiovascular diseases, which is very likely caused by their capability of prevent oxidation of low-density lipoproteins (LDL). During food processing and storage, substances with antioxidative properties are formed by Maillard reactions. In this study, the activity of Maillard products to inhibit copper-induced oxidation of human LDL in vitro was investigated. d-Glucose was heated with an equimolar amount of glycine, l-lysine, or l-arginine, for 1 h under reflux. The increase of the antioxidative activity (AOA) of the Maillard mixtures was highly significant compared to the control mixtures. Additionally, two defined Maillard products with amino reductone structure were tested. 3-Hydroxy-4-(morpholino)-3-buten-2-one (1) and amino hexose reductone (2) showed a significant and dose dependent AOA. Compound 1 was about half as active as ascorbic acid, which served as positive control. Thus, it can be concluded that Maillard products, particularly those with amino reductone structure, have the strong potential to inhibit LDL oxidation.     

Site-specific formation of Maillard, oxidation, and condensation products from whey proteins during reaction with lactose

Heat treatment of dairy products leads to structural changes of proteins, which can severely decrease the nutritional value [Mauron, J. J. Nutr. Sci. Vitaminol. (Tokyo) 1990, 36 (Suppl. 1), S57-69]. In this study, model solutions of the two main whey proteins, alpha-lactalbumin and beta-lactoglobulin, respectively, were incubated with lactose, and modifications were monitored by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS). Lactulosyl residues were the most abundant modifications of alpha-lactalbumin and beta-lactoglobulin. Up to four of these adducts were identified on the proteins. Enzymatical digest with endoproteinase AspN prior to mass spectrometric analysis allowed the detection of further modifications and their localization in the amino acid sequence. Most prominent modifications were lactulosyllysine, Nepsilon-carboxymethyllysine, oxidation of lysine to aminoadipic semialdehyde, oxidation of methionine to methionine sulfoxide, cyclization of N-terminal glutamic acid to a pyrrolidone, and oxidation of cysteine or tryptophan. The presence of methionine oxidation was deduced from a control protein that had been oxidized by hydrogen peroxide. These studies establish MALDI-TOF-MS as a reliable tool to monitor chemical modifications of nutritional proteins during food processing.     

Formation of carcinogenic 4(5)-methylimidazole in Maillard reaction systems

4(5)-Methylimidazole has received the attention of federal and state regulatory agencies because of its carcinogenicity and common presence in foods and beverages. In the present study, the formation of 4(5)-methylimidazole in Maillard reaction model systems consisting of D-glucose/NH(3), L-rhamnose/NH(3), methylglyoxal/NH(3), and methylglyoxal/formaldehyde/NH(3) was investigated. 4(5)-Methylimidazole was formed at levels ranging from 0.49 to 0.71 mg/mL in the d-glucose/NH(3) model system. The formation of 4(5)-methylimidazole was slightly higher in the L-rhamnose/NH(3) system (0.91 mg/mL) than in the d-glucose/NH(3) system (0.71 mg/mL) under the conditions used in the present study. A methylglyoxal/NH(3) system produced significantly higher levels of 4(5)-methylimidazole (5.70 mg/mL), suggesting that methylglyoxal is an important precursor of 4(5)-methylimidazole. Ammonolysis of methylglyoxal, which is one of the glucose degradation products, was proposed to form formamide, which subsequently reacted with 2-aminopropanal (α-aminocarbonyl intermediate) formed from methylglyoxal to give 4- or 5-methylimidazole. The levels of 4(5)-methylimidazole found in commercial cola soft drinks range from 0.30 μg/mL (brand 3) to 0.36 μg/mL (brands 1 and 5).     

木糖-草鱼肽美拉德反应产物的抗氧化性

为了探讨美拉德反应对草鱼肽抗氧化性的影响,该文以分子量小于5 KDa的草鱼肽为原料,加入木糖进行美拉德反应,并与单独加热的样品进行比较。分别检测分析了不同反应时间的热降解产物和美拉德反应产物的还原力、氧自由基吸收能力(ORAC,oyxgen radical absorbance capacity)值及挥发性成分组成,并对反应产物中挥发性物质与其抗氧化活性之间的关系进行了探讨。试验结果表明:草鱼肽添加木糖反应比其单独加热的褐变程度更高,抗氧化性更强。且随着反应时间的延长,美拉德反应产物的抗氧化性能逐步增强,并产生了大量的呋喃、吡嗪等杂环化合物,通过相关性分析,发现美拉德反应产物的抗氧化性与上述挥发性组分含量显著相关(P0.95)。草鱼肽与木糖质量比为1∶1混合并在100℃下反应3 h具有较强抗氧化性。因此,美拉德反应修饰可使草鱼肽表现出更强的抗氧化性,是一种优秀的食品抗氧化原料。     

Electrochemical study of the Maillard reaction

Electrochemical properties of beta-alanine/carbohydrate Maillard reaction products were measured using a combination platinum/Ag-AgCl (Cl(-)) redox electrode. Changes toward more negative voltages were observed, which were consistent with reductone formation during the course of the Maillard reaction. Using voltage change as a guide, the propensity for reductone formation among various sugars was ribose > xylose approximately arabinose > glucose approximately rhamnose approximately mannose approximately lactose > fructose. Similar electrochemical behavior indicative of reductone formation was observed in the decomposition products of a model Amadori compound, N-(1-deoxyfructos-1-yl)piperidine (1).     

LC/MS analysis and antioxidative efficiency of Maillard reaction products from a lactose-lysine model system

Aqueous solutions of lactose and lysine were refluxed for up to 4 h without pH control. Samples were collected every hour, and the reaction was monitored by measuring the pH, the optical density at 420 nm, and the relative antioxidative efficiency (RAE). The greatest change in optical density and antioxidative efficiency occurred for the mixture heated for 4 h. The 4 h solution was separated into three fractions according to the molecular weights of the components and tested for RAE. The high molecular weight fraction was more colored, and it had the highest antioxidative activity. The low molecular weight fraction was separated by high-performance liquid chromatography (HPLC). RAE values were measured for each purified compound. HPLC coupled with diode array and electrospray mass spectrometry allowed a rapid screening of the solutions and a tentative identification of several peaks. Nuclear magnetic resonance analysis allowed the identification of galactosylisomaltol and pyrraline. The resonance assignments for these compounds were revised.     

Reduction of tetrazolium salt XTT by aminoreductone formed during the Maillard reaction of lactose

Lactose, a reducing disaccharide abundant in milk, reacts extensively with the amino groups of protein through the Maillard reaction. The Maillard reaction products showed 3'-[1-[(phenylamino)carbonyl]-3,4-tetrazolium]bis(4-methoxy-6-nitro)benzensulfonic acid hydrate (XTT) reducibility. The objective of this study was to clarify the Maillard reaction products responsible for the XTT reducibility. When lactose and butylamine were heated at 100 degrees C, the characteristic UV maximum at 320 nm was recognized and the relationship between the XTT reducibility and the compound with absorption maximum at 320 nm was investigated. The time course and the dependence on the heating temperature of the formation of the compound with absorption maximum at 320 nm were similar to those of the XTT reducibility. Their relationship showed a significant correlation (r = 0.967, n = 19). Furthermore, the spectrum change of the heated model solution by the addition of XTT suggested that the compound with absorption maximum at 320 nm would be involved in the reduction of XTT. Because the compound with absorption maximum at 320 nm was identified as an aminoreductone, 1-(butylamino)-1,2-dehydro-1,4-dideoxy-3-hexulose, by NMR analysis, it can be concluded that this was the main XTT-reducing substance.     

Chemical and antioxidant properties of casein peptide and its glucose Maillard reaction products in fish oil-in-water emulsions

Maillard reaction products (MRPs) were prepared by reacting casein peptides with different concentrations of glucose at 80 °C for up to 12 h. The chemical properties of MRPs and their effects on lipid oxidation in fish oil-in-water emulsions were investigated. Increasing browning development and absorbance in 294 nm in the MRPs caused an increase in DPPH radical scavenging, but a decrease in iron chelation, which could be related to the loss of free amino groups in the peptides. The MRPs produced with longer reaction time or higher glucose concentrations were less effective in inhibiting lipid oxidation in emulsions at pH 7.0 compared to casein peptides alone. However, the antioxidant activity of MRPs in emulsions at pH 3.0 was not decreased by prolonged heating. The bitterness of MRPs was less than that of the original casein peptides, and bitterness decreased with increasing heating time and glucose concentrations. Therefore, the Maillard reaction was a potential method to reduce the bitterness of casein peptides while not strongly decreasing their antioxidant activity.     

Changes in allergenicity and digestibility of squid tropomyosin during the Maillard reaction with ribose

The effect of the Maillard reaction on the allergenicity of squid tropomyosin (TM) was investigated. When TM was reacted with ribose (TM-ribose), its human-specific IgE-binding ability decreased markedly and alpha-chymotryptic digestibility of TM was also altered at the early stage of the Maillard reaction. On the other hand, the modification of the lysine residues in TM using 2,4,6-trinitrobenzenesulfonic acid had no effect on the allergenicity and alpha-chymotryptic digestibility of TM. Therefore, the structural change in TM induced by the Maillard reaction would cause the reduction of the allergenicity, rather than the block of lysine residues. Although peptic digestion diminished the specific IgE-binding ability of TM, the reduction of the allergenicity by the Maillard reaction remained after peptic digestion. These results suggest that hypersensitive reaction of TM-ribose in the human body might be lower than that of native TM.     

胡萝卜渗透脱水传质试验研究

通过研究胡萝卜在不同浓度、温度的蔗糖溶液中的传质现象，探讨了渗透溶液浓度和温度对胡萝卜传质的影响显著性及规律。蔗糖溶液浓度和温度的取值分别为40%、50%、60%和30℃、40℃、57℃；渗透时间为0～240 min。结果表明：蔗糖溶液温度比浓度对胡萝卜传质影响更显著；随着渗透溶液温度或浓度的增加，胡萝卜在渗透脱水时传质越明显。在渗透前30 min传质速率最快。对传质指标运用多指标综合评分法，得出了胡萝卜渗透脱水的最佳方案为渗透时间240 min，渗透溶液温度57℃，浓度60%。     

添加美拉德反应底物对黑木耳菌糠腐解期间腐殖质组成的影响

针对黑木耳菌糠木质素含量高、独立腐解难的问题,通过添加美拉德（Maillard）反应底物来提高此类菌糠的腐解效果,为其科学堆肥提供技术参考。采用室内培养法,以黑木耳菌糠为基础材料,通过邻苯二酚、葡萄糖和甘氨酸3种Maillard反应底物的添加,以不添加任何反应底物为对照,结合黑木耳菌糠培养过程中腐解物料腐殖质组成的变化,探索各底物在黑木耳菌糠腐殖化作用中的贡献。结果表明：（1）随培养进行,各处理条件下黑木耳菌糠总有机碳（TOC）均表现为逐渐降低的趋势,其中添加葡萄糖更有利于TOC的损失,Maillard反应底物的添加使45 d培养内的矿化作用更为明显。各处理均有利于黑木耳菌糠水溶性物质碳含量（CWSS）的增加,其中邻苯二酚对CWSS的提升幅度最大,其次为葡萄糖;（2）各处理均有利于黑木耳菌糠可提取腐殖酸的积累,在促进黑木耳菌糠胡敏酸分子结构复杂程度方面更有优势;（3）添加Maillard反应底物可促进黑木耳菌糠富里酸向胡敏酸的转化,其中甘氨酸的作用最为明显,此外,甘氨酸还能有效促进惰性腐殖质组分胡敏素的分解。综上所述,添加甘氨酸更有利于黑木耳菌糠的高效腐解,矿化惰性腐殖质组分的同时有利...     

Formation of cholesterol oxidation products in marinated foods during heating

The objectives of this study were to develop a gas chromatography-mass spectrometry (GC-MS) method to analyze the contents of cholesterol oxidation products (COPs) in marinated eggs, pork, and juice and to compare the effect of heating time and soy sauce or sugar on the formation of COPs. By using a silica cartridge for purification and GC-MS with selected ion monitoring for detection, seven COPs, including 7alpha-hydroxycholesterol, 7beta-hydroxycholesterol, 5,6alpha-epoxycholesterol, 5,6beta-epoxycholesterol, 5alpha-cholestane-3beta, 5,6beta-triol, 5-cholesten-3beta-25-diol, and 7-ketocholesterol, as well as internal standard 5alpha-cholestane, were resolved within 16 min by using a HP-5MS capillary column. During marinating, the levels of most COPs followed an increasing trend with increasing heating time. However, a higher amount of COPs was generated for ground pork as compared to eggs. The incorporation of soy sauce or sugar (1 and 10%) was effective in inhibiting COPs formation, with the latter being more pronounced than the former in both marinated eggs and pork.