Influence of the acetification process on phenolic compounds

Little is known about the change of phenolic compounds and total phenolic content by the acetification process. The aim of this study was to assess the contents of selected phenolic compounds of cider and red and white wines in comparison to phenolic profiles in corresponding vinegars by using a new HPLC method for the simultaneous separation and quantification of polar phenolic acids and less polar flavonoids. Identifications were made by retention times and by means of mass spectra. Additionally, total phenolic contents of wines and vinegars were determined photometrically. The decrease in total phenol content by the acetification process was highest for cider vinegars (40%) and lower for red and white wine vinegars (13 and 8%, respectively). A decrease in the contents of individual phenolic compounds of vinegars from white white and ciders was not observed. In contrast, the contents of individual phenolic compounds in red wine vinegar decreased approximately 50%.     

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.     

Detection of alpha-dicarbonyl compounds in Maillard reaction systems and in vivo.

alpha-Dicarbonyl compounds are of major interest in food chemistry and biochemistry as important precursors of, for example, protein modifications and flavor. Due to their high reactivity most of the published structures were identified and quantitated as stable derivatives after reaction with trapping reagents. However, the present study showed for the first time that the trapping reagents are of dramatic impact on the final qualitative and quantitative alpha-dicarbonyl spectrum. As important representatives, aminoguanidine and o-phenylenediamine were used to compare trapping characteristics and to monitor the dicarbonyl structures arising from the degradation of an Amadori compound. Dicarbonyl structures with a reductone moiety could not be or were only insufficiently detected by slow-reacting reagents such as aminoguanidine. On the other hand, fast-reacting chemicals such as o-phenylenediamine imposed high oxidative stress on the investigated system and led to enhanced or false positive formation of dicarbonyl compounds generated by oxidative pathways.     

Effects of carnosine on volatile generation from Maillard reaction of ribose and cysteine

Carnosine occurs naturally in meat and meat products in significant quantity, and it possesses strong antioxidant activity that inhibits lipid oxidation and enhances shelf life. In this study, the effects of carnosine on thermal flavor generation were investigated using the model system of cysteine and ribose, which was heated to the roasting temperature of 180 degrees C for 2 h at pH 5 and pH 8.5. The results indicated that carnosine affected volatile formation in a complex manner. Volatiles identified from the liquid phase of the reaction systems of ribose and cysteine showed that the sulfur-containing compounds such as thiophenes, thiazoles, and polysulfides were the most abundant compounds. The addition of carnosine into the reaction mixtures in general caused a reduction in contents of thiophenes and some important meaty flavor compounds such as 2-methyl-3-furanthiol, 2-furfurylthiol, and their associated dimers. On the other hand, it facilitated the generation of several important nitrogen-containing volatiles such as pyrazine, methylpyrazine, 2,6-dimethylpyrazine, and other alkyl pyrazines and thiazoles, which are known to elicit roasty and nutty flavor notes. The results suggested that carnosine acts as a nitrogenous source to facilitate the formation of nitrogen-containing compounds, possibly by degradation to form ammonia.     

Effect of urea on volatile generation from Maillard reaction of cysteine and ribose

Urea occurs naturally in many food products, and its presence affects food quality. However, little is known about its impact on flavor generation in food production. In this study, the urea contents in beef, pork, and chicken were determined. The effects of urea and pH on thermal flavor generation were investigated using the model system of cysteine with ribose, which was heated to the roasting temperature of 180 degrees C for 2 h at pH 5 and pH 8.5. The results revealed relatively large amounts of urea in these meats and demonstrated that pH affects aroma generation. Volatiles identified from the reaction system of ribose and cysteine showed that sulfur-containing compounds such as thiophenes, thiazoles, and thiophenethiols were the most abundant compounds. The addition of urea into the reaction mixture caused the disappearance or reduction in content of some sulfur-containing compounds but resulted in the generation of several important nitrogen-containing volatiles, like pyrazine, methylpyrazine, 2,5- (and 2,6-)dimethylpyrazine and other alkylpyrazines, which are known to elicit roasty, nutty flavor notes. A plausible explanation for this phenomenon is that ammonia can be released from urea upon heating and the formed ammonia competes with hydrogen sulfide to react with Maillard reaction precursors to produce nitrogen-containing compounds such as alkylpyrazines.     

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.     

Two novel beta-carboline compounds from the Maillard reaction between xylose and tryptophan

Two nonvolatile beta-carboline alkaloids were isolated from the Maillard reaction between xylose and tryptophan by solvent extraction and flash silica gel column chromatography. Their structures were elucidated by spectral methods (UV, MS, and NMR) as 1-(1,4-dihydroxybutyl)-beta-carboline and 1-(1,3, 4-trihydroxybutyl)-beta-carboline.     

Efficiency of natural phenolic compounds regenerating alpha-tocopherol from alpha-tocopheroxyl radical

Benzoic acid-derived phenolics (p-hydroxybenzoic acid, 3,4-dihydroxybenzoic acid, vanillic acid, syringic acid, and gallic acid) and the polyphenols epicatechin and epigallocatechin gallate (EGCG) were evaluated for their efficiency in regenerating alpha-tocopherol from alpha-tocopheroxyl radical in comparison with ascorbyl palmitate, which is known to regenerate alpha-tocopherol. Ethanolic solutions of phenolic compounds were added to a homogeneous hexane medium containing alpha-tocopheroxyl radical generated by reaction of alpha-tocopherol in molar excess with 1,1-diphenyl-2-picrylhydrazyl radical, and the alpha-tocopheroxyl radical was monitored by electron spin resonance spectroscopy. p-Hydroxybenzoic acid, vanillic acid, and syringic acid (400 microM) did not exhibit a significant effect on alpha-tocopheroxyl radical concentration (0.6-0.7 microM). In contrast, 3,4-dihydroxybenzoic acid and gallic acid were able to reduce the concentration of alpha-tocopheroxyl radical by 16 and 64%, respectively. Epicatechin showed a reduction of alpha-tocopheroxyl radical similar to gallic acid, and EGCG and ascorbyl palmitate were the most effective, reducing alpha-tocopheroxyl radical completely at a much lower phenolic concentration (66.7 microM). The moles of alpha-tocopheroxyl radical reduced per mole of ascorbyl palmitate (0.93), EGCG (0.066), gallic acid (4.3 x 10(-4)), and epicatechin (4.5 x 10(-4)) were determined, and the logarithm of these stoichoimetric ratios showed a negative linear relationship with the bond dissociation enthalpies of the O-H bond of the phenolics. The relative capacity to reduce alpha-tocopheroxyl radical was found to be ascorbyl palmitate (2142) > EGCG (151) > gallic acid (1) approximately epicatechin (1).     

Antioxidative activity of heterocyclic compounds found in coffee volatiles produced by Maillard reaction

Typical heterocyclic compounds substituted with various functional groups found in Maillard reaction products were examined for antioxidant activity. Pyrroles exhibited the greatest antioxidant activity among all heterocyclic compounds tested. All pyrroles inhibited hexanal oxidation by almost 100% at a concentration of 50 microg/mL over 40 days. Addition of formyl and acetyl groups to a pyrrole ring enhanced antioxidative activity remarkably. Pyrrole-2-carboxaldehyde, 2-acetylpyrrole, 1-methyl-2-pyrrolecarboxaldehyde, and 2-acetyl-1-methylpyrrole inhibited hexanal oxidation by >80% at 10 microg/mL. Unsubstituted furan exhibited the greatest antioxidant activity among furans tested. Addition of all functional groups used in this study to furan decreased antioxidative activity. The antioxidant activity of thiophene increased with the addition of methyl and ethyl groups, but the addition of formyl or acetyl groups to thiophene decreased antioxidant activity. Thiazoles and pyrazines were ineffective antioxidants at all concentrations tested. Reaction of all heterocyclic compounds with hydrogen peroxide resulted in the formation of various oxidized products.     

Influence of jam processing on the radical scavenging activity and phenolic content in berries

Six selected phenolic aglycons (caffeic and ellagic acids, kaempferol, quercetin, myricetin, and morin) in nine types of berries, and their changes as influenced by jam processing, have been evaluated using optimized HPLC with diode-array detection. The berry samples, fresh and after jam processing, were analyzed, and the total amounts of selected phenolics as aglycons were identified and determined by acid hydrolysis. Their contents in fresh and jam samples did not indicate appreciable changes; therefore, the influence of jam processing on these selected phenolics in berries was suggested to be small, and was mostly present in berries as several conjugated forms that were glycosylated, esterified, etc., in the samples. The total phenolic content of each sample was also determined by the Folin-Ciocalteu method. The three samples of each berry, namely fresh, jam, and acid hydrolysate of the berry, had similar total phenolic contents. On the other hand, the scavenging effect on the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical was measured, and acid hydrolysates showed stronger activity than that of the fresh and jam-processed samples for all of the berry types.     

Influence of epicatechin reactions on the mechanisms of Maillard product formation in low moisture model systems

The influence of the polyphenolic compound epicatechin on Maillard chemistry was investigated under simulated roast conditions (10% moisture at 220 degrees C for 10 min). Quantitative gas chromatography (GC) analysis indicated that the addition of epicatechin to glucose or fructose/glycine model systems significantly reduced the generation of hydroxyacetone, 2-methylpyrazine, 2,3,5-trimethylpyrazine, furfural, 2-acetylfuran, 5-methylfurfural, 2(5H)-furanone, 2-acetylpyrrole, and furfuryl alcohol. These analytes were reported to be primarily generated from intact C2, C3, C4, C5, and C6 sugar fragments based on gas chromatography/mass spectrometry quantitative isotopomeric analysis of a 1:1 13C6:12C6 hexose sugar/glycine model system. Liquid chromatography/mass spectrometry qualitative isotopomeric analysis of a 1:1 13C6:12C6 hexose sugar/glycine/epicatechin model systems confirmed epicatechin reacted with Maillard reactants in the model systems; two main reaction products were reported, epicatechin-C5 and -C6 sugar fragment adducts. In addition, LC/MS analysis of a model system consisting of only 3-deoxy-2-hexosulose and epicatechin identified 3-deoxy-2-hexosulose as a precursor of the epicatechin-C5 and -C6 sugar fragment adducts reaction products. These results imply that epicatechin quenched 3-deoxy-2-hexosulose (a key source C6 to C1 sugar fragments) and consequently inhibited Maillard product formation.     

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).     

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 effect of high pressure-high temperature processing conditions on acrylamide formation and other Maillard reaction compounds

The effect of high pressure-high temperature (HPHT) processing on the formation of acrylamide and other Maillard-type reaction compounds was investigated in order to elucidate the impact of HPHT conditions on the different stages of the Maillard reaction. This study was performed in equimolar asparagine-glucose model systems that were treated at various HP/HT conditions (100-115 °C, 400-700 MPa, 0-60 min), and, for comparison, the model system was also heat-treated at ambient pressure. On the treated samples, the concentration of acrylamide, reactants, hydroxymethylfurfural, organic acids, and melanoidins was determined and the pH prior to and after treatment was measured. Based on the measured responses, the retarding effect of high pressure on the overall Maillard reaction was demonstrated; no or little differences were observed between 400 and 700 MPa. The study was conducted in two types of buffer, i.e. phosphate and MES buffer. In case of acrylamide, aspartic acid and browning, a higher concentration was generated in the MES buffer system, but these differences with the phosphate buffer system could be ascribed to pH changes resulting from the application of combined high pressure and high temperature. Based on the results, acrylamide formation is not expected to pose a major hazard to HPHT-treated products.     

High-pressure effects on Maillard reaction between glucose and lysine

Glucose-lysine model systems prepared over a range of pH values (5-10) in unbuffered and buffered media were incubated at 60 degrees C either under atmospheric pressure or at 400 MPa. The results obtained showed that high pressure affected in different ways the different stages of the Maillard reaction and that such effects were strongly influenced by pressure-induced changes in the pH of the systems. In unbuffered media, at an initial pH < or =8.0, the formation of Amadori rearrangement products (ARP) was not considerably affected by pressure, whereas the intermediate and advanced stages of the Maillard reaction were suppressed, suggesting a retardation of the degradation of the ARP. In buffered media, at pH values < or =8.0, pressure slowed the Maillard reaction from the initial stages. These effects are attributed to the pH drop caused by the pressure-induced dissociation of the acid groups. In unbuffered and buffered media at initial pH = 10.2, high pressure accelerated the formation and subsequent degradation of ARP, leading to increased levels of intermediate and advanced reaction products.     

Effect of pH on the stability of plant phenolic compounds

It is not uncommon to treat plant-derived foods and feeds with alkali. Such exposure to high pH is being used to recover proteins from cereals and legumes, to induce the formation of fiber-forming meat analogue vegetable protein, for preparing peeled fruits and vegetables, and for destroying microorganisms. In addition to their profound effects on functional and nutritional properties in such foods, such treatments may also cause other side reactions, including the destruction of natural polyphenolic compounds. Because plants contain a large number of structurally different antioxidant, anticarcinogenic, and antimicrobial polyphenolic compounds, it is of interest to know whether such compounds are stable to heat and to high pH. In this model study, the stability of the following natural polyphenols to pH in the range 3-11 was studied with the aid of ultraviolet spectroscopy: caffeic acid, (-)-catechin, chlorogenic acid, ferulic acid, gallic acid, (-)-epigallocatechin, rutin, and the nonphenolic compound trans-cinnamic acid. This study demonstrates that caffeic, chlorogenic, and gallic acids are not stable to high pH and that the pH- and time-dependent spectral transformations are not reversible. By contrast, chlorogenic acid is stable to acid pH, to heat, and to storage when added to apple juice. (-)-Catechin, (-)-epigallocatechin, ferulic acid, rutin, and trans-cinnamic acid resisted major pH-induced degradation. The results are rationalized in terms of relative resonance stabilization of phenoxide ions and quinone oxidation intermediates. The possible significance of these findings to food chemistry and microbiology is discussed.     

Characterization of phenolic compounds in rooibos tea

Polyphenols present in rooibos, a popular herbal tea from Aspalathus linearis, were isolated in two steps. First, phenolic ingredients were separated by multilayer countercurrent chromatography (MLCCC). Preparative high-performance liquid chromatography (HPLC) was then applied to obtain pure flavonoids. The purity and identity of isolated compounds was confirmed by different NMR experiments, HPLC-diode array detector (DAD), or gas chromatography-mass spectrometry (GC-MS) analysis. This strategy proved to be valid to isolate material in up to gram quantities and to verify known and previously not published polyphenol structures. In addition the chemistry of dihydrochalcones and related intermediates was studied. The dihydrochalcone aspalathin was oxidized to the corresponding flavanone- C-glycosides (( R)/( S)-eriodictyol-6- C-beta- D-glucopyranoside and ( R)/( S)-eriodictyol-8- C-beta- D-glucopyranoside). Flavanone-6- C-beta- D-glucopyranosides were further degraded to flavones isoorientin and orientin.     

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.     

Correlations of the phenolic compounds and the phenolic content in some Spanish and French olive oils

The total content of phenolic compounds (TAP) in 29 different monocultivar olive oil samples from France (Aglandau and Tanche) and Spain (Cornicabra, Picual, and Verdial) was assessed by the colorimetric Folin-Ciocalteu method. Also, individual phenolic compounds were determined and quantified by liquid chromatography coupled to mass spectrometry (LC-MS). The French olive oil samples had a lower TAP compared to Spanish samples. The quantity of individual phenolics was similar except for pinoresinol, which was lower in the French olive oil samples. TAP moderately correlated to the sum of quantified compounds (r = 0.64 and p < 0.01) Partial least-squares (PLS) regression analysis emphasized the importance of hydroxytyrosol and the total amount of quantified phenolic compounds by LC-MS in the prediction of the total amount of phenolic compounds as determined by the Folin-Ciocalteu method. The amount of alpha-tocopherol was generally different among the cultivars (Tanche > Picual > Verdial > Aglandau > Cornicabra). Of all quantified phenolic compounds in French olive oil samples, only luteolin correlated well to the altitude of the olive orchards (r = 0.76, p < 0.01).     

Functional improvements in dried egg white through the Maillard reaction.

The effects of the Maillard reaction on the functional properties of dried egg white (DEW) were investigated. Maillard-reacted DEW (M-DEW) was prepared by storing sugar-preserved DEW (SP-DEW) at 55 degrees C and 35% relative humidity for 0-12 days. The M-DEW developed an excellent gelling property, and hydrogen sulfide production from heat-induced M-DEW gels decreased. Surface sulfhydryl (SH) group content of M-DEW increased while total SH group and alpha-helix contents decreased with increasing heating time in the dry state. Breaking strength, breaking strain, water-holding capacity, and hydrogen sulfide of heat-induced M-DEW gels significantly correlated with surface and total SH group contents in M-DEW. SDS-PAGE revealed that M-DEW proteins were polymerized in which covalent bonds were involved. The present study demonstrated that the Maillard reaction partially unfolds and polymerizes proteins of SP-DEW and, consequently, improved gelling property of SP-DEW under certain controlled conditions.