Factors affecting the retention of rennet in cheese curd

The coagulant retained in cheese curd is a major contributor to proteolysis during ripening. The objective of this study was to quantify the effects of several milk-related factors and parameters during cheese manufacture on the retention of coagulant in cheese curd. The amount of coagulant retained in curd was determined by its activity on a synthetic heptapeptide (Pro-Thr-Glu-Phe-[NO2-Phe]-Arg-Leu) using reversed-phase HPLC. The retention of chymosin in cheese curd increased significantly when the pH of milk was reduced at rennet addition below pH 6.1, the pH at whey drainage below pH 5.7, or the average casein micelle size in milk and when the ionic strength of milk was increased. The casein content of milk and the quantity of chymosin added to milk had no significant effect on the retention of chymosin in curd; the quantity of coagulant bound per gram of casein remained unchanged.     

Formation of Maillard reaction products during heat treatment of carrots

As indicators of the early stage of the Maillard reaction in carrots, N-(furoylmethyl) amino acids (FMAAs) formed during acid hydrolysis of the corresponding Amadori products were analyzed using RP-HPLC with UV detection. N(ε)-FM-Lys (furosine), FM-Gly, FM-Ala, FM-Val, FM-Ile, FM-Leu, and FM-GABA were identified using synthesized standard material by means of mass spectrometry. Furthermore, N(ε)-carboxymethyllysine (CML) and pyrraline were analyzed as indicators for advanced stages of glycation. For commercial samples with high water content, the formation of Amadori compounds predominates, whereas the advanced stage of Maillard reaction plays only a minor part. Carrot juices, baby food, and tinned carrots showed quite low rates of amino acid modification up to 5%. For dehydrated carrots, significantly higher values for Amadori products were measured, corresponding to a lysine derivatization of up to 58% and nearly 100% derivatization of GABA. Drying experiments revealed great differences in reactivity between the amino acids studied. Whereas furosine reached constant values quite quickly, some FMAAs showed a continuous increase with heating time, indicating that selected FMAAs can be used as a hallmark for the early Maillard reaction to control processing conditions.     

Milk excretion of ivermectin and moxidectin in dairy sheep: assessment of drug residues during cheese elaboration and ripening period

Ivermectin (IVM) and moxidectin (MXD) are broad-spectrum endectocide antiparasitic drugs extensively used in food-producing animals. The patterns of IVM and MXD excretion in milk were comparatively characterized following their subcutaneous administration (200 microg.kg(-1) of body weight) to lactating dairy sheep. The relationship between milk excretion and plasma disposition kinetics of both compounds was characterized. A pool of milk collected from all of the animals in each experimental group was used for cheese elaboration. IVM and MXD residual concentrations were assessed during the cheese-making process and ripening period. IVM and MXD concentrations were measured in plasma, milk, and milk product (whey, curd, and cheese) samples using an HPLC-based methodology with fluorescence detection. IVM and MXD were extensively distributed from the bloodstream to the mammary gland, and large quantities, particularly of MXD, were excreted in milk. Residual concentrations of both compounds were recovered in milk up to 30 (IVM) and 35 (MXD) days post-treatment. The total fraction of the administered dose excreted in milk for MXD was significantly higher than that of IVM. During cheese production, the highest residual concentrations of both molecules were measured in the curd. Thirty-four percent of the total drug residue measured in the pooled milk collected from treated sheep was lost during the cheese-making process. The lowest residual concentrations were measured in the whey. IVM and MXD concentrations in the elaborated cheese tended to increase during the ripening period, reaching the highest residual level at 40 days of cheese maturation. The long persistence of milk residual concentrations of MXD and IVM in lactating dairy sheep and the high concentrations found in cheese and other milk-related products should be seriously considered before recommendation of the extralabel use of these antiparasitic drugs in dairy animals.     

Enrichment of cheeses manufactured from cow's and sheep's milk blends with sheep-like species-related alkylphenols

Enhancement of concentrations of species-related sheep-like alkylphenols, p- and m-cresols and 3- and 4-ethylphenols, in experimental Manchego-type cheeses manufactured from cow's and sheep's milk blends (80:20) by using arylsulfatases was investigated. A food-grade arylsulfatase from Aspergillus oryzae (ATCC 20719) was produced using a stimulatory medium, and crude dried cells were used as the enzyme source. Exogenous arylsulfatases from Helix pomatia and A. oryzae were added to cheese curd, and the amounts of species-related alkylphenols were measured. Arylsulfatase from H. pomatia released limited amounts of alkylphenols in the cheese only when used at a high level. Arylsulfatase from A. oryzae released substantial amounts of alkylphenols during 2 months of ripening. The concentrations of alkylphenols in A. oryzae arylsulfatase-treated cheese were comparable to the previously reported levels present in aged Manchego-type cheeses manufactured from pure sheep's milk.     

Time course and specificity of lipolysis in Swiss cheese

Controlling lipolysis in cheese is necessary to ensure the formation of desirable flavor. To get a better understanding of the mechanism of lipolysis in Swiss cheese, cheeses were manufactured with and without (control) the addition of Propionibacterium freudenreichii. Products of lipolysis were quantified throughout ripening. Half of the free fatty acids (FFA) released in milk (3.66 mg/g fat), in particular the short-chain FFA, were lost in the whey during curd drainage, whereas diglycerides and monoglycerides were retained within the curd. P. freudenreichii was responsible for the release of most FFA during ripening (10.84 and 0.39 mg/g fat in propionibacteria-containing and control cheeses, respectively). Indices of lipolysis displayed low specificity. All types of FFA were released, but butyric and palmitic acids more significantly, which could be due to a low sn-1,3 regioselectivity. All glycerides were hydrolyzed in the following order: monoglycerides>diglycerides>triglycerides. The results of this study show the quantitative and qualitative contributions of the different lipolytic agents to Swiss cheese lipolysis.     

Reversible and covalent binding of 5-(hydroxymethyl)-2-furaldehyde (HMF) with lysine and selected amino acids

The chemical reactivity of 5-(hydroxymethyl)-2-furaldehyde (HMF) with lysine, glycine, and proline was studied using isotope labeling technique. To confirm the formation of HMF adducts in glucose amino acid model systems, a useful strategy was developed in which products simultaneously possessing six glucose (HMF moiety) and any number of amino acid carbon atoms in addition to nitrogen were targeted using specifically labeled precursors such as [(15)N(α)]lysine·2HCl, [(15)N(ε)]lysine·2HCl, [U-(13)C(6)]lysine·2HCl, [(13)C(6)]lysine·2HCl, and [U-(13)C(6)]glucose in the case of lysine model system. In addition, model systems containing HMF and amino acids were also studied to confirm specific adduct formation. Complete labeling studies along with structural analysis using appropriate synthetic precursors such as HMF Schiff base adducts of piperidine and glycine have indicated that HMF generated in the glucose/amino acid model systems initially forms a Schiff base adduct that can undergo decarboxylation through an oxazolidin-5-one intermediate and form two isomeric decarboxylated Schiff bases. Unlike the Schiff bases resulting from primary amines or amino acids such as glycine or lysine, those resulting from secondary amino acids such as proline or secondary amines such as piperidine can further undergo vinylogous Amadori rearrangement, forming N-substituted 5-(aminomethyl)furan-2-carbaldehyde derivatives.     

Effect of processing and storage on the stability of flaxseed lignan added to dairy products

This study investigated the effects of processing and storage on the stability of purified, flaxseed-derived secoisolariciresinol diglucoside (SDG) added to milk prior to the manufacture of different dairy products. We analyzed the effect of high-temperature pasteurization, fermentation, and milk renneting as well as storage on the stability of SDG added to milk, yogurt, and cheese. Also, the stability of SDG in whey-based drinks was studied. Added SDG was found to withstand the studied processes well. In edam cheese manufacture, most of the added SDG was retained in the whey fraction and 6% was found in the cheese curd. SDG was also relatively stable in edam cheese during ripening of 6 weeks at 9 degrees C and in yogurt during storage of 21 days at 4 degrees C. Up to 25% of added SDG was lost in whey-based drinks during storage of 6 months at 8 degrees C. We conclude that SDG can be successfully supplemented in dairy-based products.     

Characterization of the geographical origin of Pecorino Sardo cheese by casein stable isotope ((13)c/(12)c and (15)n/(14)n) ratios and free amino acid ratios

The stable isotope ratios ((13)C/(12)C and (15)N/(14)N) of casein measured by isotope ratio mass spectrometry (IRMS) and some free amino acid ratios (His/Pro, Ile/Pro, Met/Pro, and Thr/Pro) determined by HPLC in samples of ewes' milk cheese from Sardinia, Sicily, and Apulia were found to be parameters independent of ripening time. Multivariate data treatments performed by applying both unsupervised (principal component analysis and cluster analysis) and supervised [linear discriminant analysis (LDA)] methods revealed good discrimination possibilities for the cheeses according to place of origin. In this respect, particularly significant were the variables Ile/Pro, Thr/Pro, (13)C/(12)C, and (15) N/(14)N ratios on which basis 100% discrimination and classification of the samples by LDA was obtained.     

Thermally generated 3-aminopropionamide as a transient intermediate in the formation of acrylamide

On the basis of the recent findings that "biogenic amines" can also be formed during thermal food processing from their parent amino acids in a Strecker-type reaction, the formation of 3-aminopropionamide, the biogenic amine of asparagine, was investigated in model systems as well as in thermally processed Gouda cheese. The results of model studies revealed that, besides acrylamide, 3-aminopropionamide was also formed in amounts of 0.1-0.4 mol % when asparagine was reacted in the presence of either glucose or 2-oxopropionic acid. Results of a second series of model experiments in which [(13)C(4)(15)N(2)]-asparagine ([(13)C(4)(15)N(2)]-Asn) and unlabeled 3-aminopropionamide were reacted together in the presence of glucose revealed a >12-fold higher efficacy of 3-aminopropionamide in acrylamide generation as compared to asparagine. Both [(13)C(3)(15)N(2)]-3-aminopropionamide and [(13)C(3)(15)N(1)]-acrylamide were formed during [(13)C(4)(15)N(2)]-Asn degradation in a ratio of about 1:4, supporting the idea that 3-aminopropionamide is a transient intermediate in acrylamide formation. In this study, 3-aminopropionamide was identified and quantified for the first time in foods, namely, in Gouda cheese. Although the fresh cheese contained low amounts of 3-aminopropionamide, its concentrations were much increased to approximately 1300 mug/kg after thermal processing. In isotope labeling studies, performed by administering to the cheese [(13)C(4)(15)N(2)]-Asn in a ratio of 1:2 as compared to the "natural" concentrations of asparagine, similar ratios of unlabeled/labeled 3-aminopropionamide and unlabeled/labeled acrylamide were determined. Thus, 3-aminopropionamide could be verified as a transient intermediate of acrylamide formation during food processing.     

Spiro cross-links: representatives of a new class of glycoxidation products

Covalently cross-linked proteins are among the major modifications caused by the advanced Maillard reaction. So far, the chemical nature of these aggregates is largely unknown. Investigations are reported on the isolation of 6-[2-[[(4S)-4-amino-4-carboxybutyl]amino]-6,7-dihydroxy-6,7-dihydroimidazo[4,5-b]azepin-4(5H)-yl]-L-norleucine (10) and N-acetyl-6-[(6R,7R)-2-[[4-(acetylamino)-4-carboxybutyl]amino]-6,7,8a-trihydroxy-6,7,8,8a-tetrahydroimidazo[4,5-b]azepin-4(5H)-yl]-L-norleucine (12) formed by oxidation of the major Maillard cross-link glucosepane 1. Independent synthesis and unequivocal structural characterization are given for 10 and 12. Spiro cross-links, representing a new class of glycoxidation products, were obtained by dehydrogenation of the amino imidazolinimine compounds N6-[2-[[(4S)-4-ammonio-5-oxido-5-oxopentyl]amino]-5-[(2S,3R)-2,3,4-trihydroxybutyl]-3,5-dihydro-4H-imidazol-4-ylidene]-L-lysinate (DOGDIC 2) and N6-[2-[[(4S)-4-ammonio-5-oxido-5-oxopentyl]amino]-5-[(2S)-2,3-dihydroxypropyl]-3,5-dihydro-4H-imidazol-4-ylidene]-L-lysinate (DOPDIC 3). These new oxidation products were synthesized, and their unambiguous structural elucidation proved the formation of the spiro imidazolimine structures N6-[(7R,8S)-2-[[(4S)-4-ammonio-5-oxido-5-oxopentyl]amino]-8-hydroxy-7-(hydroxymethyl)-6-oxa-1,3-diazaspiro[4.4]non-1-en-4-ylidene]-L-lysinate (16), N6-(8R,9S)-2-[(4S)-4-ammonio-5-oxido-5-oxopentyl]amino]-8,9-dihydroxy-6-oxa-1,3-diazaspiro[4.5]dec-1-en-4-ylidene)-L-lysinate (19), and N6-[(8S)-2-[(4-amino-4-carboxybutyl)amino]-8-hydroxy-6-oxa-1,3-diazaspiro[4.4]non-1-en-4-ylidene]-L-lysinate (18), respectively. It was shown that reaction of the imidazolinone 15 led to the formation of spiro imidazolones, structurally analogous to 16 and 19.     

Removal of cholesterol from Cheddar cheese by beta-cyclodextrin

This study was carried out to determine the cholesterol removal rate and resulting changes in flavor, fatty acid and bitter amino acid production in reduced-cholesterol Cheddar cheese, made by cream separation followed by 10% beta-cyclodextrin (beta-CD) treatment. The cholesterol removal from the cheese was 92.1%. The production of short-chain free fatty acids (FFAs) increased the ripening time in control and cream-treated cheeses. The quantity of short-chain FFAs released between treatments during ripening was different, while not much difference was found in the production of neutral volatile compounds in the samples. Reduced-cholesterol cheese produced much higher levels of bitter amino acids than the control. In sensory analysis, the texture score of control Cheddar cheese increased significantly with ripening time; however, that of the cream treatment group decreased dramatically with ripening time. On the basis of our results, we conclude that the cheese made from beta-CD-treated cream had a higher rate of cholesterol removal and ripened rapidly.     

Analysis of glycated and ascorbylated proteins by gas chromatography-mass spectrometry

Proteins or poly-L-lysine which were incubated in the presence of ascorbic acid, dehydroascorbic acid (ascorbylation), or various sugars (glycation) were analyzed by gas chromatography-mass spectrometry (GC-MS). To also detect more labile reaction products, the Maillard modified proteins or poly-L-lysine were enzymatically hydrolyzed and reacted with N-methyl-N-(tert-butyldimethylsilyl)trifluoroacetamide to form the N(O)-tert-butyldimethylsilyl (tBDMS) derivatives prior to GC analysis. Under these conditions, the known Maillard products N (epsilon)-(carboxymethyl)lysine (1), oxalic acid mono-N (epsilon)-lysinylamide (2), and N (epsilon)-(carboxyethyl)lysine (3) could be simultaneously detected and quantified in glycated and ascorbylated proteins. Additionally, N (epsilon)-(1-carboxy-3-hydroxypropyl)-L-lysine (4) was identified for the first time as a Maillard product of proteins. Under the conditions applied here, 4 was found only in ascorbylated proteins or poly-L-lysine, but not in glycated proteins. Maillard-modified poly-L-lysine was further subjected to high-performance liquid chromatography (HPLC) analysis after enzymatic hydrolysis and formation of the phenyl isothiocyanate derivatized amino acids. Using this method, N (epsilon)-formyl-L-lysine (5), which cannot be distinguished from 2 by GC-MS analysis, was identified for the first time as a glycation product. Compound 5 is mainly formed from ribose, lactose, and fructose. The indicated Maillard products were quantified in beta-lactoglobulin (GC-MS) or poly-L-lysine (HPLC) which were glycated or ascorbylated using different precursors.     

Antioxidant properties of malt model systems

The aim of this study was to investigate the effect of kilning and roasting temperatures on antioxidant activity of malt model systems prepared from combinations of glucose, proline, and ferulic acid. Model systems (initial a(w) = 0.09, 6% moisture) were heated at 60 degrees C for up to 24 h, at 90 degrees C for up to 120 min, and at 220 degrees C for up to 15 min. The antioxidant activity of the glucose-proline-ferulic acid model system increased significantly on heating at 60 degrees C for 24 h or at 90 degrees C for 120 min. In contrast, the glucose-proline, ferulic acid-glucose, and ferulic acid-proline systems presented either nonsignificantly increased or unchanged antioxidant activity. The antioxidant activity of both the glucose-proline-ferulic acid and glucose-proline model systems increased significantly after heating at 220 degrees C for 10 min, followed by a significant decrease at 15 min. The data suggest that (1) at 60 degrees C, ferulic acid reacts with Maillard reaction products, resulting in a significant increase in antioxidant activity; (2) at 90 degrees C, the antioxidant activity of the glucose-proline-ferulic system comes from both ferulic acid and Maillard reaction products; and (3) at 220 degrees C, the major contributors to antioxidant activity in glucose-proline-ferulic acid and glucose-proline systems are glucose-proline reaction products.     

Lipolysis during ripening of Emmental cheese considering organization of fat and preferential localization of bacteria

This study followed the progression of lipolysis in Emmental cheese by quantifying the concentrations of individual free fatty acids (FFA) released during ripening in each of the different rooms: 12 days at 12 degrees C, 28 days at 21 degrees C, and 8 days at 4 degrees C. Lipolysis, which corresponded to 1.56% of fat, mainly occurred in the 21 and 4 degrees C rooms, with 68 and 16.5% of total FFA, respectively. The nonselectivity of lipolytic enzymes was evidenced: all fatty acids were released with level of > or =1%. Differential scanning calorimetry experiments showed that the thermal properties of cheese were affected by (i) lipolysis of fat, that is, the monoacylglycerols, diacylglycerols, and FFA that may be localized at the fat/whey interface, and/or by (ii) hydrolysis of high-melting-point triacylglycerols constituted mainly by long-chain saturated fatty acids (e.g., palmitic acid). Analysis of the cheese microstructure was performed using confocal laser scanning microscopy. Fat globules were mainly disrupted after pressing of curd grains, leading to the release of the milk fat globule membrane (MFGM); fat inclusions were surrounded by pockets of whey, delimited by casein strands. Moreover, colonies of bacteria were preferentially localized in situ at the fat/protein interface. This study showed that both the localization of bacteria and the supramolecular organization of fat which was not protected by the MFGM can help the accessibility of milk fat to lipolytic enzymes and then contribute to the quality of cheese.     

N(delta)-(5-hydroxy-4,6-dimethylpyrimidine-2-yl)-l-ornithine, a novel methylglyoxal-arginine modification in beer

N(delta)-(5-Hydroxy-4,6-dimethylpyrimidine-2-yl)-L-ornithine, or Argpyrimidine, was identified and quantified in beer by high-performance liquid chromatography (HPLC) and coupled gas chromatography-mass spectrometry (HRGC-MS). This novel fluorescent arginine Maillard modification represents the first amino acid modification reported in beer retaining the full backbone of the original amino acid. Two mechanisms of formation could be verified: the major pathway via methylglyoxal and the minor pathway via 5-deoxypentoses. Argpyrimidine concentrations, determined in 35 lager-type beer varieties, reached up to 27 nmol/L and could be positively correlated to beer color and wort content. Within this context, 5-deoxy-D-ribose was identified as a novel intermediate of the Maillard reaction of maltose by HRGC-MS and independent synthesis.     

Reaction of folic acid with reducing sugars and sugar degradation products

The reaction of folic acid with reducing sugars (nonenzymatic glycation) under conditions that can occur during food processing and preparation was studied by high-performance liquid chromatography with diode array detection. N-(p-Aminobenzoyl)-L-glutamic acid, a well-established oxidation product, was detected in the reaction mixtures. Furthermore, a new product was isolated and identified as N2-[1-(carboxyethyl)]folic acid (CEF). CEF was the main product that was formed by the nonenzymatic glycation of folic acid. For preparation, N2-[1-(carboxyethyl)]folic acid was obtained in high yields when folic acid and dihydroxyacetone (DHA), a sugar degradation product, were heated at 100 degrees C in phosphate buffer. Mixtures of folic acid and different sugars or DHA were heated under variation of reaction time and temperature, and CEF was quantified. Up to 50% of the vitamin was converted to CEF, with highest yields formed from maltose (49%) and lactose (43%).     

Chemical and microbiological characteristics of ewes' milk cheese manufactured with extracts from flowers of Cynara cardunculus and Cynara humilis as coagulants

The chemical and microbial characteristics as well as the flavor and aroma of Los Pedroches cheese made using aqueous extracts of Cynara cardunculus L. flowers were compared with those of cheeses manufactured with extracts of Cynara humilis L. throughout ripening. The two thistle species assayed were found to have no appreciable effect on the moisture, fat, protein, and NaCl contents of the cheese or on its water activity, flavor, and aroma; however, the use of C. humilis resulted in reduced lactic acid content (p < 0.001) and higher pH values (p < 0.05) relative to those of cheese specimens produced with C. cardunculus. The protein breakdown of the cheeses was assessed in terms of soluble nitrogen (SN), nonprotein nitrogen (NPN), and amino acid nitrogen (AAN). Proteolysis was more marked and rapid in cheese containing C. cardunculus as coagulant, the SN and NPN contents of which were significantly higher (p < 0. 01) than those of the cheese obtained with the species C. humilis; AAN contents were similar in both species of Cynara throughout ripening. Although total viable, coliform, and lactobacilli counts were similar in cheeses produced with both types of plant coagulant throughout ripening, enterobacteria and yeasts counts (p < 0.01) and molds counts (p < 0.05) were higher in cheese produced with C. humilis than in cheese obtained with C. cardunculus.     

Mozzarella干酪加工过程中主要理化指标变化及其产率计算

该文目的在于为干酪功能特性、含水率和产率的控制提供理论依据，使用标准化原料乳经低温巴氏杀菌，采用无盐渍新工艺生产Mozzarella干酪，从添加发酵剂开始，到制成新鲜干酪，测定各阶段干酪凝块的温度、水分含量、pH值和滴定酸度及各阶段乳清和凝块的蛋白和脂肪含量，计算Mozzarella干酪的效能和产率。试验结果表明：在排乳清和粉碎加盐阶段，干酪凝块中的水分含量变化幅度最大，排出乳清中的蛋白和脂肪数量明显增加；干酪的脂肪回收率达到92.22%，实际测得的乳清中脂肪的损失率为7.62%；乳蛋白的回收率达到83.60%，仅有16.72%的蛋白质损失于乳清中；在堆酿阶段pH值有一个从6.3(干酪凝块5.5)至5.25的快速下降过程。Mozzarella干酪的实际产率达到12.38%，达到了同类型干酪的产率要求。Mozzarella干酪的理化指标达到了美国全脂Mozzarella干酪的标准。     

Peptides identified during Emmental cheese ripening: origin and proteolytic systems involved

To determine the proteolytic changes occurring during Emmental cheese ripening, peptides released in cheese aqueous phase were analyzed by reversed-phase HPLC and identified by tandem mass spectrometry sequencing, for which different strategies were illustrated by some examples. Among the 91 peptides identified, most of them arose from alpha(s1)- (51) and beta-caseins (28), and a few arose from alpha(s2)- (9) and kappa-caseins (1). An attempt was made to correlate the released peptides with the proteolytic systems potentially involved during Emmental cheese manufacture. Besides the well-known action of plasmin on beta- and alpha(s2)-caseins, and in the absence of residual fungal coagulant from Endothia parasitica, two other proteinases seem to be involved in the hydrolysis of alpha(s1)-casein in Emmental cheese: cathepsin D originated from milk and cell-envelope proteinase from thermophilic starters. Moreover, peptidases from starters were also active throughout ripening, presumably like those from nonstarter lactic acid bacteria, in contrast to those from propionic acid bacteria.     

Relative quantification of N(epsilon)-(Carboxymethyl)lysine,imidazolone A,and the Amadori product in glycated lysozyme by MALDI-TOF mass spectrometry

The nonenzymatic glycation of proteins by reducing sugars, also known as the Maillard reaction, has received increasing recognition from nutritional science and medical research. In this study, we applied matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) to perform relative and simultaneous quantification of the Amadori product, which is an early glycation product, and of N(epsilon)-(carboxymethyl)lysine and imidazolone A, two important advanced glycation end products. Therefore, native lysozyme was incubated with d-glucose for increasing periods of time (1, 4, 8, and 16 weeks) in phosphate-buffered saline pH 7.8 at 50 degrees C. After enzymatic digestion with endoproteinase Glu-C, the N-terminal peptide fragment (m/z 838; amino acid sequence KVFGRCE) and the C-terminal peptide fragment (m/z 1202; amino acid sequence VQAWIRGCRL) were used for relative quantification of the three Maillard products. Amadori product, N(epsilon)-(carboxymethyl)lysine, and imidazolone A were the main glycation products formed under these conditions. Their formation was dependent on glucose concentration and reaction time. The kinetics were similar to those obtained by competitive ELISA, an established method for quantification of N(epsilon)-(carboxymethyl)lysine and imidazolone A. Inhibition experiments showed that coincubation with N(alpha)-acetylargine suppressed formation of imidazolone A but not of the Amadori product or N(epsilon)-(carboxymethyl)lysine. The presence of N(alpha)-acetyllysine resulted in the inhibition of lysine modifications but in higher concentrations of imidazolone A. o-Phenylenediamine decreased the yield of the Amadori product and completely inhibited the formation of N(epsilon)-(carboxymethyl)lysine and imidazolone A. MALDI-TOF-MS proved to be a new analytical tool for the simultaneous, relative quantification of specific products of the Maillard reaction. For the first time, kinetic data of defined products on specific sites of glycated protein could be measured. This characterizes MALDI-TOF-MS as a valuable method for monitoring the Maillard reaction in the course of food processing.