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.     

Autoxidation of packed almonds as affected by maillard reaction volatile compounds derived from roasting

Shelled almonds of two Italian varieties, Romana and Pizzuta, peeled and unpeeled, were roasted and packed under different conditions: air (control), vacuum, and Maillard reaction volatile compounds (MRVc) derived from the roasting process. Samples were stored for approximately 8 months at room temperature, without light, and, at regular intervals, were collected and analyzed to evaluate the progress of lipid oxidation. Peroxide values, triglyceride oligopolymers, and oxidized triglycerides were evaluated during the storage time. Results showed that, although the MRVc atmosphere did not protect the lipid fraction of almonds as well as the vacuum condition; nevertheless, it was more protective than the control atmosphere, showing an antioxidant effect. The effect of the natural coating was a strong protection against lipid oxidation; in fact, only the unpeeled samples showed peroxide values lower than the threshold of acceptability (25 milliequiv of O(2)/kg of oil). Moreover, at the end of the storage period, Pizzuta almonds showed a greater deterioration than those of the Romana variety.     

Sugar fragmentation in the maillard reaction cascade: formation of short-chain carboxylic acids by a new oxidative alpha-dicarbonyl cleavage pathway

The formation of short-chain carboxylic acids was studied in Maillard model systems (90 degrees C, pH 6-10) with emphasis on the role of oxygen and water. The total amount of acetic acid formed did not depend on the reaction atmosphere. In the presence of labeled dioxygen or water (18O2, H2 17O), labeled oxygen was partially incorporated into acetic acid. Thermal treatment of 1-deoxy-d-erythro-2,3-hexodiulose (1) and 3-deoxy-d-erythro-hexos-2-ulose in the presence of 17O-enriched water under alkaline conditions led to acetic and formic acid, respectively, as indicated by 17O NMR spectroscopy. The suggested mechanism involves an oxidative alpha-dicarbonyl cleavage leading to an intermediary mixed acid anhydride that releases the acids, e.g., acetic and erythronic acid, from 1. Similarly, glyceric and lactic acids were formed from 1-deoxy-3,4-hexodiuloses, corroborated by complementary analytical techniques. This paper provides for the first time evidence for the direct formation of acids from C6-alpha-dicarbonyls by an oxidative mechanism and incorporation of a 17OH group into the carboxylic moiety. The experimental data obtained support the coexistence of at least two newly described reaction mechanisms leading to carboxylic acids, i.e., (i) a hydrolytic beta-dicarbonyl cleavage as a major pathway and (ii) an alternative minor pathway via oxidative alpha-dicarbonyl cleavage induced by oxidizing species.     

Effect of maillard reaction on allergenicity of scallop tropomyosin

Scallop tropomyosin (TM), the major allergen of shellfish, was prepared from adductor muscles and reacted with four reducing sugars to investigate the effect of the Maillard reaction on the allergenicity of TM. The IgE-binding ability of TM increased significantly with the progress of the reaction with glucose, ribose, and maltose, but not with maltotriose. The allergenicity was enhanced at the early stage of the Maillard reaction, and the trend of the effect depended on the type of reducing sugar used. 2,4,6-Trinitrobenzenesulfonic acid treatment of the lysine residues in TM showed that the protein surface charge resulting from the Maillard reaction had no effect on the enhancement of the allergenicity. Thus, the change in the allergenicity would be closely related to the structural change caused by the Maillard reaction.     

Sugar fragmentation in the maillard reaction cascade: isotope labeling studies on the formation of acetic acid by a hydrolytic beta-dicarbonyl cleavage mechanism

The formation of acetic acid was elucidated based on volatile reaction products and related nonvolatile key intermediates. The origin and yield of acetic acid were determined under well-controlled conditions (90-120 degrees C, pH 6-8). Experiments with various 13C-labeled glucose isotopomers in the presence of glycine revealed all six carbon atoms being incorporated into acetic acid: C-1/C-2 ( approximately 70%), C-3/C-4 ( approximately 10%), and C-5/C-6 (approximately 20%). Acetic acid is a good marker of the 2,3-enolization pathway since it is almost exclusively formed from 1-deoxy-2,3-diulose intermediates. Depending on the pH, the acetic acid conversion yield reached 85 mol % when using 1-deoxy-2,3-hexodiulose (1) as a precursor. Hydrolytic beta-dicarbonyl cleavage of 1-deoxy-2,4-hexodiuloses was shown to be the major pathway leading to acetic acid from glucose without the intermediacy of any oxidizing agents. The presence of key intermediates was corroborated for the first time, i.e., tetroses and 2-hydroxy-3-oxobutanal, a tautomer of 1-hydroxy-2,3-butanedione, also referred to as 1-deoxy-2,3-tetrodiulose. The hydrolytic beta-dicarbonyl cleavage represents a general pathway to organic acids, which corresponds to an acyloin cleavage or a retro-Claisen type reaction. Although alternative mechanisms must exist, the frequently reported hydrolytic alpha-dicarbonyl cleavage of 1 can be ruled out as a pathway forming carboxylic acids.     

Alpha-mercaptoketone formation during the maillard reaction of cysteine and [1-(13)C]ribose

The volatiles formed from [1-(13)C]-ribose and cysteine during 4 h at 95 degrees C in aqueous phosphate buffer (pH 5) were analyzed by headspace SPME in combination with GC-MS. The extent and position of the labeling were determined using MS data. The identified volatiles comprised sulfur compounds such as 2-[(13)C]methyl-3-furanthiol, 2-[(13)CH(2)]furfurylthiol, [1-(13)C]-3-mercaptopentan-2-one, [1-(13)C]-3-mercaptobutan-2-one, [4-(13)C]-3-mercaptobutan-2-one, and 3-mercaptobutan-2-one. The results confirm furan-2-carbaldehyde as an intermediate of 2-furfurylthiol, as well as 1,4-dideoxypento-2,3-diulose as an intermediate of 2-methyl-3-furanthiol and 3-mercaptopentan-2-one. Loss of the C-1 and C-5 carbon moieties during the formation of 3-mercaptobutan-2-one suggests two different mechanisms leading to the key intermediate butane-2,3-dione.     

利用电子自旋共振技术研究美拉德反应自由基变化

为寻求简便而准确地对食品加工和贮藏过程中的美拉德反应进行鉴定的方法,该文研究加热食品中葡萄糖和乳球蛋白建立的美拉德反应体系的自由基变化,主要考察影响美拉德反应的温度和pH值变化导致的自由基改变,从而确定美拉德反应与其自由基变化之间的相互关系。在3种不同温度、有无氧气和3种不同pH值条件下,利用电子自旋共振(electron spin resonance,ESR)光谱检测美拉德反应自由基变化趋势,结果随温度升高,自由基数量增加,反应速度加快;随pH值由酸性向碱性移动,自由基数量增加;自由基数量在无氧条件时多于有氧条件。当自由基积累到一定浓度,由于聚合反应生成高分子聚合物使信号强度下降,最后消失。比较美拉德产物与2种底物产生的自由基发现,无论类型、数量还是生成速率都存在明显差异。研究结果表明,采用自旋捕集剂对不稳定的自由基进行捕集来分析信号能够有效表征加热食品中美拉德反应初中期阶段的自由基变化,从而有效表征和分析美拉德反应过程。与传统研究美拉德反应的分析方法比较,ESR光谱是一种简便灵敏的分析方法,可以作为研究加热食品美拉德反应的重要方法之一。     

Relationship between virgin olive oil phenolic compounds and acrylamide formation in fried crisps

In this paper the relationship between virgin olive oil (VOO) phenol compounds and the formation of acrylamide in potato crisps was investigated. The phenol compositions of 20 VOO samples were screened by LC-MS, and 4 oils, characterized by different phenol compound patterns, were selected for frying experiments. Slices of potatoes were fried at 180 degrees C for 5, 10, and 15 min, and acrylamide content was determined by LC-MS. Results demonstrated that VOO phenolic compounds are not degraded during frying, and crisp color was not significantly different among the four VOOs. Acrylamide concentration in crisps increased during frying time, but the formation was faster in the oil having the lowest concentration of phenolic compounds. Moreover, the VOO having the highest concentration of ortho-diphenolic compounds is able to efficiently inhibit acrylamide formation in crisps from mild to moderate frying conditions. It was concluded that the use of ortho-diphenolic-rich VOOs can be proposed as a reliable mitigation strategy to reduce acrylamide formation in domestic deep-frying.     

The effect of thermal history on the maillard reaction in a glassy matrix

To test whether the extent of physical aging affected the reaction rate, Maillard reaction kinetics were studied in glassy model preservation systems subjected to two different thermal histories. The glass transition temperature and physical aging of the matrix were determined using differential scanning calorimetry, and the normalized heat capacities were modeled using the Tool-Narayanaswamy-Moynihan approach. Samples prepared using the different thermal histories initially had different degrees of aging, but these were practically indistinguishable after 10 h under the reaction conditions (65 degrees C); the samples underwent rapid structural relaxation at that temperature. The reaction of glucose and lysine in an amorphous trehalose/sucrose matrix was followed using spectrophotometric and chromatographic analysis. A difference in reaction rate could only be distinguished in the rate of consumption of glucose, which was approximately 20% faster in the minimally aged matrix; no significant differences were seen in any other indicator of reaction.     

Covalent protein adduct formation and protein cross-linking resulting from the maillard reaction between cyclotene and a model food protein.

Covalent Maillard products of the reactions of carbonyl compounds with proteins are often described in the literature, but, until recently, evidence for their existence has been indirect. Cyclotene (2-hydroxy-3-methylcyclopent-2-enone), a common flavor compound, was incubated with a model food protein, ribonuclease, and found to cross-link the protein. Size exclusion high-performance liquid chromatrography and electrospray mass spectrometry of the early stages of the reaction provide strong evidence for covalent adducts that we believe to be intermediates in the cross-linking reaction.     

A comparison of color formation and maillard reaction products of a lactose-lysine and lactose-N(alpha)-acetyllysine model system

The formation of color and Maillard reaction products in two model systems consisting of lactose and lysine or N(alpha)-acetyllysine has been investigated. During heating, the blockage of the N(alpha) group of lysine determined a faster color and antioxidative ability development compared to the system with free lysine. This is combined to a greater amount of melanoidin formation in the acetylated lysine system, while in the free lysine system a higher amount of pyrraline and hydroxymethyl furfural were detected. The pattern of low molecular weight products suggests that 3-deoxyglucosone and 1-deoxyglucosone degradation pathways are favored for free lysine and N(alpha)-acetyllysine, respectively. Whole data allow us to hypothesize that in a lactose-N(alpha)-acetyllysine model system the formation of colored high molecular weight polymer proceeds faster because less material is dispersed in reaction pathways, mainly the Strecker degradation, which leads to small and intermediate molecular weight products.     

Simultaneous quantitative analysis of maillard reaction precursors and products by high-performance anion exchange chromatography

A new analytical setup allowing the simultaneous analysis of precursors and products of the Maillard reaction is described. It is based on high-performance anion exchange chromatography with electrochemical (ECD) and diode array detectors (DAD) coupled in series. Chromatography and detection were optimized to permit simultaneous monitoring of compounds relevant to the Maillard reaction, such as the sugar, the amino acid, and the corresponding Amadori compound as well as the cyclic intermediates 5-(hydroxymethyl)-2-furaldehyde, maltol, and 2,3-dihydro-3,5-dihydroxy-6-methyl-4(H)-pyran-4-one. Separation was achieved on a CarboPac PA-1 column using a gradient of sodium acetate in aqueous sodium hydroxide. The Amadori compound, glucose, and glycine were monitored by an ECD operating in the integrated amperometry mode. The number of analyzed compounds was further increased by coupling the ECD with a DAD for the analysis of ultraviolet-active constituents. This method was successfully applied to model Maillard reaction mixtures based on glucose and glycine.     

Kinetics of formation of three indicators of the maillard reaction in model cookies: influence of baking temperature and type of sugar

The Maillard reaction (MR), despite its impact on flavor, color, and texture of cereal products, must be controlled for possible deleterious effects on protein nutritional quality. The present study aims to simultaneously monitor three indicators of the MR reaction (acid-released lysine, furosine, and carboxymethyllysine (CML)) by GC/MS in model cookies and evaluate the effect of formulation and baking temperature. Whereas furosine followed a bell-shape kinetic, indicative of an intermediary compound, CML linearly accumulated, proving to be a good indicator of the advanced MR. Acid-released lysine continuously decreased during baking. A reference baking level was defined to compare differently processed cookies using fluorescence synchronous spectra, highly sensitive to the dough physicochemical properties. Furosine was maximal in glucose-containing cookies, but only accounted for 5-50% lysine blockage, depending on the sugar and baking temperature. High oven temperatures and the use of fructose as the sugar source were associated with lowest the lysine damage and CML formation.     

Furosine as indicator of maillard reaction in jams and fruit-based infant foods

To investigate the presence of furosine in commercial samples of jams and fruit-based infant foods a simple method by ion-pair reversed-phase liquid chromatography is described. The yield of furosine during the hydrolysis with hydrochloric acid was optimized. The reproducibility in the repeatability and recovery of the method, expressed in relative standard deviation percentages, proved to be in the ranges of 4.1-8.3% and 1.0-4.4%, respectively. The recovery percentages of furosine varied between 86.7 and 95.3%. The obtained results support the suitability of the method. Furosine was detected in all studied samples. Although a high variability in the content of furosine was noticed, in general terms, the lowest levels of furosine were observed in samples of fruit-based infant foods and the highest were observed in jams of more than 60% sugar. These results could be due to different heat treatment, storage conditions, and/or differences in the values of water activity (a(w)) and amounts of sugar. The results obtained in the present paper point out the usefulness of furosine as an indicator of Maillard reaction for jams and fruit-based infant foods.     

Identification of new heterocyclic nitrogen compounds from glucose-lysine and xylose-lysine maillard model systems

Aqueous sugar (glucose or xylose)-lysine model systems were heated at 80 degrees C for 6 h with the pH maintained at a predetermined value (3, 4, or 5). Selected compounds were isolated by combinations of solvent extraction and semipreparative HPLC, prior to identification by NMR and mass spectrometry. Two compounds were identified from the pH 5 glucose system and were identified as epsilon-[2-formyl-5-(hydroxymethyl)pyrrole-1-yl]-L-norleucine (pyrraline) and the new compound, 1-(5-carboxy-5-aminopentyl)-2-formyl-3-(1,2,3-trihydroxypropyl)pyrrole. A third compound was partially characterized. 2-Acetyl-5-hydroxymethyl-5,6-dihydro-4H-pyridinone was identified in the pH 3 xylose system, and the new compound, 8-furan-2-yl-methyl-5-hydroxymethyl-5,6-dihydro-indolizine-1,7-dione, was identified in the pH 4 xylose system. 2-Furfurylidene-4-hydroxy-5-methyl-3(2H)-furanone was identified in both xylose systems. Mechanisms of formation are proposed for the novel compounds.     

Metal complexation by the peptide-bound maillard reaction products N(epsilon)-fructoselysine and N(epsilon)-carboxymethyllysine

Although the Maillard reaction between proteins and carbohydrates is of central importance for food processing and in vivo processes, only little is known about changes of the metal-binding properties induced by protein glycation. The purpose of this study was to examine the complex formation of the quantitatively important peptide-bound Maillard reaction products (MRPs) N(epsilon)-fructoselysine and N(epsilon)-carboxymethyllysine with the biologically relevant metal ions copper(II) and zinc(II). The MRPs were synthesized as the N(alpha)-hippuryllysine derivatives in order to block the coordination function of the alpha-amino group. Stability constant measurements were performed in aqueous solution using pH potentiometry. N(alpha)-Hippuryl-N(epsilon)-fructoselysine forms moderate Cu(II) complexes (Log(10) K(1) = 5.8; Log(10) K(2) = 4.0) but fails to form any complexes with Zn(II). N(alpha)-Hippuryl-N(epsilon)-carboxymethyllysine gives slightly stronger complexes with Cu(II) (Log(10) K(1) = 7.3; Log(10) K(2) = 6.3), but again no complexation with Zn(II) was observed. These results show that post-translational modification of proteins by carbohydrates leads to the formation of new coordination centers for metal ions within a protein chain. Further studies are necessary to clarify the consequences of this phenomenon in terms of protein quality and physiological processes.     

A model system study of the inhibition of heterocyclic aromatic amine formation by organosulfur compounds

Organosulfur compounds and sodium bisulfite significantly inhibited (P < 0.05) heterocyclic aromatic amine (HAA) formation in model systems containing phenylalanine, creatinine, and glucose. There was, however, no inhibition by the same compounds in a model system containing only phenylalanine and creatinine. Diallyl disulfide (DAD) and dipropyl disulfide (DPD) concentrations in the model systems were significantly decreased (P < 0.05) after heating for 10 min at 180 degrees C. Only very low concentrations of sulfhydryl groups (4.19 and 4.00 micromol) were produced on heating DAD and DPD for 30 min. Reaction of glucose and DAD produced several sulfur-containing compounds. After 10 min of heating at 180 degrees C, HAA formation in the control model systems was increased significantly, and DAD was an effective inhibitor during this heating period. Tetrahydrothiophene-3-one (THT) and tetrahydrothiophene (THP); two products resulting from the interaction of glucose and DAD, had no direct influence on HAA formation in the model systems.     

Influence of storage practices on acrylamide formation during potato frying

A number of parameters linked to storage of potatoes were evaluated with regard to their potential to influence the acrylamide formation in French fries. Acrylamide, which is a potential human carcinogen, is reported to be formed during the frying of potatoes as a result of the reactions between asparagine and reducing sugars. This study was conducted using three potato varieties (Bintje, Ramos, and Saturna) typically used in Belgium, The Netherlands, and the northern part of France for French fry and crisp production. Saturna, mainly used in crisp production, appeared to be the least susceptible for acrylamide formation during frying. Especially storage at low temperatures (4 degrees C) compared to storage at 8 degrees C seemed to enhance acrylamide formation due to a strong increase in reducing sugars caused by low-temperature storage. Because of the reversible nature of this physiological reaction, it was possible to achieve a significant reduction of the reducing sugars after a reconditioning of the cold-stored potatoes for 3 weeks at 15 degrees C. All changes in acrylamide concentrations could mainly be explained by the reducing sugar content of the potato (R2 = 0.84, n = 160). This means that, by ensuring a low reducing sugar content of the potato tuber, the risk for acrylamide formation will largely be reduced. Finally the use of a sprout inhibitor did not influence the composition of the potato, and thus acrylamide formation was not susceptible to this treatment.     

Effects of plant sulfur nutrition on acrylamide and aroma compounds in cooked wheat

Wheat flour from plants deficient in sulfur has been shown to contain substantially higher levels of free amino acids, particularly asparagine and glutamine, than flour from wheat grown where sulfur nutrition was sufficient. Elevated levels of asparagine resulted in acrylamide levels up to 6 times higher in sulfur-deprived wheat flour, compared with sulfur-sufficient wheat flour, for three varieties of winter wheat. The volatile compounds from flour, heated at 180 degrees C for 20 min, have been compared for these three varieties of wheat grown with and without sulfur fertilizer. Approximately 50 compounds were quantified in the headspace extracts of the heated flour; over 30 compounds were affected by sulfur fertilization, and 15 compounds were affected by variety. Unsaturated aldehydes formed from aldol condensations, Strecker aldehydes, alkylpyrazines, and low molecular weight alkylfurans were found at higher concentrations in the sulfur-deficient flour, whereas low molecular weight pyrroles and thiophenes and sugar breakdown products were found at higher concentrations in the sulfur-sufficient flour. The reasons for these differences and the relationship between acrylamide formation and aroma volatile formation are discussed.     

Effects of water content on volatile generation and peptide degradation in the maillard reaction of glycine, diglycine, and triglycine

Peptides abundant in food and protein hydrolysates are known to be important to process flavors. The present study reports the volatile profile of the Maillard reactions of glycine, diglycine, and triglycine. The reaction with glucose was conducted at 0-100% water content in glycerol medium at 160 degrees C for 1 h. Volatile compounds were quantified by stir bar sorptive extraction-gas chromatography-mass spectrometry, and nonvolatile compounds were quantified by high-performance liquid chromatography-tandem mass spectrometry. The major volatiles produced from each of the reaction systems were trimethylpyrazine and 2,5-dimethylpyrazine. Volatile generation increased as water decreased, and the overall reactivity of the glycine and glycine peptides in volatile formation was glycine approximately triglycine > diglycine. Triglycine was very unstable and mainly degraded into cyclic Gly-Gly and glycine, whereas diglycine had a higher stability than triglycine toward hydrolytic cleavage of the peptide bond. The amounts of glycine, diglycine, cyclic (Gly-Gly), and triglycine in the peptide-glucose reaction mixtures at different water content were reported.