Abiotic degradations of legacy and novel flame retardants in environmental and food matrices - a review.

Flame retardants (FRs) are commonly added to commercial products to achieve flammability resistance. Since most of them are not chemically bonded to the materials, they could be leached to the environment during the production and disposal cycle. These FRs were categorised based on their chemical nature, including brominated, organophosphorus-, mineral- and nitrogen-based. This review summarised the abiotic degradation reactions of these four classes of FRs, with a focus on thermal and photodegradation reactions in environmental and food matrices. Only 24 papers have reported related information on abiotic degradation reactions that could be useful for predicting possible degradation pathways, and most focused on brominated FRs. Most studies also investigated the thermal degradation of FRs under high temperatures (>400 °C), which exceeds the normal cooking temperature at 100-300 °C. For photodegradation, studies have used up to five times the energy typically used in UV radiation during food processing. It is recommended that future studies investigate the fate of these FRs in foods under more realistic processing conditions, to provide a more comprehensive picture of the estimated consumption of FRs and their degradation products from foods, and facilitate a better risk assessment of the use of these novel FRs.

Chemical interaction between the sugar moieties in N, N-di-glycated alanine derivatives.

The chemistry of N,N-diglycated amino acids remains unexplored due to their transient nature in the Maillard reaction. Their increased reactivity is attributed to the presence of high concentrations of open ring forms in at least one of their sugar moieties. The N,N-diglycated alanine derivatives were generated in situ via dissociation from their stable precursors the bis[N,N-diglycated alanine]iron(II) complexes, in the alanine/glucose/FeCl2 model system heated at 110 °C for 2 h. The thermal degradations of these complexes were followed in the reaction mixture, using isotope-labelled reactants, such as [13C-3] alanine and [13C-U] glucose, and ESI/qTOF/MS analysis. The N,N-diglycated amino acids exhibited a unique and characteristic chemical interaction between the neighbouring sugar moieties generating hitherto unknown heterocyclic moieties. The origin of these products was tracked by identifying ions incorporating one C-3 atom from alanine and between seven to 12 carbon atoms from the sugar moieties in the same structure. Temperature-dependent FTIR spectra of di-glycated alanine generated through ball milling provided further evidence for their reactivity.

Mechanochemistry of Strecker degradation: Interaction of glyoxal with amino acids.

Mechanochemistry is rapidly evolving into a versatile and green method for chemical synthesis. Due to its unique reaction conditions, ball milling of sugars and amino acids mainly leads to the formation of Amadori products with minimum degradation. In this study, we milled glyoxal trimer dihydrate with twenty proteogenic amino acids to demonstrate the formation of Strecker degradation products. HS-GC/MS studies indicated that Strecker degradation proceeded to selectively generate Strecker aldehyde and unsubstituted pyrazine as the major volatiles. Moreover, ESI/qToF/MS studies demonstrated for the first time the formation of the proposed key Strecker degradation intermediates, such as the condensation products and their decarboxylated products, indicating the similarity of the mechanism of Strecker reaction under ball milling to that proposed under hydrothermal reaction conditions. These studies provided supporting evidence that ball milling at ambient temperatures could be used as a novel synthetic approach to prepare precursors of aroma-active volatiles through Strecker degradation.

Dual effects of dietary carnosine during in vitro digestion of a Western meal model with added ascorbic acid.

The beneficial role of carnosine during in vitro digestion of meat was previously demonstrated, and it was hypothesized that such benefits could also be obtained in a meal system. The current study, therefore, assessed carnosine effects on markers of lipid and protein oxidation and of advanced glycation end products (AGEs) during gastric and duodenal in vitro digestion of a burger meal model. The model included intrinsic (low) and enhanced (medium and high) carnosine levels in a mix of pork mince and bread, with or without ascorbic acid (AA) and/or fructose as anti- and prooxidants, respectively. In the presence of either AA or fructose, a carnosine prooxidative potential during digestion was observed at the medium carnosine level depending on markers and digestive phases. However, free carnosine found at the high carnosine level exerted a protective effect reducing the formation of 4-hydroxynonenal in the gastric phase and glyoxal in both the gastric and duodenal phases. Dual effects of carnosine are likely concentration related, whereby at the medium level, free radical production increases through carnosine's ferric-reducing capacity, but there is insufficient quantity to reduce the resulting oxidation, while at the higher carnosine level some decreases in oxidation are observed. In order to obtain carnosine benefits during meal digestion, these findings demonstrate that consideration must be given to the amount and nature of other anti- and prooxidants present and any potential interactions. PRACTICAL APPLICATION: Carnosine, a natural compound in meat, is a multifunctional and beneficial molecule for health. However, both pro- and antioxidative effects of carnosine were observed during digestion of a model burger meal when ascorbic acid was included at a supplemental level. Therefore, to obtain benefits of dietary carnosine during digestion of a meal, consideration needs to be given to the amount and nature of all anti- and prooxidants present and any potential interactions.

Molecular Basis for the Simultaneous Enhancement of the Aroma-Generating Capacity and Bioactivity of Maillard Reaction Precursors through Mechanochemistry.

Ball milling at ambient temperatures can accelerate the formation and accumulation of early-stage Maillard reaction intermediates considered important precursors of aromas and antioxidants. In this study, using chemical and biological assays, we explored the potential of sequential milling and heating to enhance the antioxidant and aroma-generating capacity of Maillard model systems. Milling (30 Hz/30 min) followed by dry heating (90 °C/30 min) of glycine or lysine with glucose significantly increased not only the intensity of their aroma-active compounds as analyzed by headspace-gas chromatography/mass spectrometry (HS-GC/MS) but also their free radical scavenging capacity as assessed by 2,2'-azino-bis-(3-ethylbenzothiazoneline-6-sulfonic acid) (ABTS) and oxygen radical absorbance capacity (ORAC) assays. This was attributed to the increased formation of redox-active endiol moieties and precursors of N,N-dialkyl-pyrazinium radical cation in the lysine system assessed by electrospray ionization-quadrupole time-of-flight/tandem mass spectrometry (ESI-QqTOF/MS/MS) analysis. The test samples also inhibited NO generation and cellular oxidative stress in RAW 264.7 murine macrophage cells, indicating size reduction induced by milling promoted paracellular absorption.

Mechanochemical generation of N,N-diglycated glycine and MS/MS characterization of its isomeric composition.

The formation of Schiff bases and Amadori rearrangement products (ARP) during the Maillard reaction in solutions is well documented, but their studies in solid-state are limited. Here we report mass-spectrometric characterization of N,N-diglycated Schiff bases and Amadori products obtained during ball milling of amino acids and glucose. Signal intensities of the diglycated adducts in mass-spectra depended on type of the amino acid and the MS ionization mode. Glycine provided for the highest yields of N,N-diglycation, followed by lysine, when the reaction was analyzed under negative ionization mode. Using diagnostic MS/MS fragmentation, we were able to distinguish between Schiff-Schiff, Schiff-Amadori, or Amadori-Amadori isomers. Milling glucose/glycine model for 30 min at ambient temperature produced diglycated glycine as a mixture of the three possible isomers in approximately equal molar proportions. Milling of synthetic Schiff base or ARP of glycine with [U-13C]-glucose generated the same but partially labelled isomers, with respective predominance of N,N-diglucosyl-glycine or N,N-difructosyl-glycine.

Insight into Isomeric Diversity of Glycated Amino Acids in Maillard Reaction Mixtures.

Maillard reactions generate a wide array of amino acid- and sugar-derived intermediates; the isomeric mixtures of glycated amino acids are of particular interest. Excluding stereoisomers, regioisomers, and various anomers, most amino acids can form two monoglycated and three N,N-diglycated isomers when reacted with sugars during the Maillard reaction. Using synthetic Schiff bases and Amadori compounds as standards, we have demonstrated that diagnostic ions obtained from MS/MS fragmentations in negative ionization mode can be used effectively for the discrimination between glucose-derived Schiff bases and their corresponding Amadori compounds in both mono- and diglycated forms. The utilization of these diagnostic ions and isotopic labeling in the glycine/glucose model system revealed that milling glucose/glycine mixtures for 30 min/30 Hz at ambient temperature produced monoglycated glycine in equal proportions of Amadori and Schiff base forms, whereas diglycated glycine was a mixture of the three isomers: Schiff-Schiff, Schiff-Amadori, or Amadori-Amadori in approximately equal molar proportions. The above results were further corroborated using a synthetic histidine Amadori product, N,N-difructosyl-ß-alanine, dipeptides, and ribose. Using mechanochemistry as a convenient synthetic tool in combination with MS/MS diagnostic ions, the isomeric diversity of the early stages of the Maillard reaction can be revealed.

Bis(alaninato)iron(II) complexes as molecular scaffolds for the generation of N,N-di-glycated alanine derivatives in the presence of glucose.

Metal ions are known to influence the course of the Maillard reaction through formation of various complexes such as bis(amino acids), these complexes are known to undergo more facile reaction with sugars. Due to this enhanced reactivity, the possible formation of di-glycated amino acids in glucose/alanine model systems with and without FeCl2 was investigated using isotope labelling technique in conjunction with ESI/qTOF/MS/MS. Forty-eight derivatives of bis[N,N'-di-glycated alanine] iron(II) complexes were tentatively identified. These complexes incorporated one iron atom, two [13C-3] atoms from alanine and up-to twenty-four carbon atoms from glucose [13C-U], were incorporated as triose (C3), tetrose (C4), pentose (C5) or hexose (C6) moieties. Furthermore, the dissociation of the above complexes released variously substituted N,N-di-glycated alanine derivatives incorporating one alanine [13C-3] atom and up to twelve carbon atoms from glucose [13C-U]. The MS/MS analysis of diglycated alanines indicated that they follow similar fragmentation pathways as Amadori product of alanine.

Interaction pattern of histidine, carnosine and histamine with methylglyoxal and other carbonyl compounds.

The ability of histidine to scavenge sugar-derived 1,2-dicarbonyl compounds was investigated using aqueous methanolic model systems containing histidine or histamine in the presence of glucose, methylglyoxal, or glyoxal. The samples were prepared either at room temperature (RT) or at 150 °C and analyzed using ESI-qTOF-MS/MS and isotope labeling technique. Replacing glucose with [U-13C6]glucose allowed the identification of glucose carbon atoms incorporated in the products. Various sugar-generated carbonyl compounds ranging in size from C1 to C6 were captured by histidine or histamine. The majority of the fragments incorporated were either C3 or C2 units originating from glyoxal (C2) or methylglyoxal (C3). The ESI-qTOF-MS/MS analysis indicated that histamine could react with either of the two carbonyl carbons of methylglyoxal utilizing the α-amino group and/or the imidazolium moiety. Furthermore, when histidine was added to 2-amino-1-methyl-6-phenylimidazo(4,5-b)pyridine (PhIP) generating model system, it completely suppressed the formation of PhIP due to scavenging of phenylacetaldehyde.

Identification of the Maillard reaction intermediates as divalent iron complexes in alanine/glucose/FeCl2 model system using ESI/qTOF/MS/MS and isotope labelling technique.

Due to their high reactivities and short half-lives, the detection of Maillard reaction intermediates is relatively difficult to achieve in a single analytical run. In this study, the formation of Maillard reaction intermediates from heated alanine/glucose mixtures (110 â€‹°C for 2 â€‹h) was investigated through their complexation with divalent iron using electrospray ionization/quadrupole time-of-flight mass spectrometry and isotope labeling techniques. Analysis of the mixtures indicated that this approach allows the simultaneous detection of many important labile and reactive Maillard reaction intermediates along with unreacted alanine and glucose in addition to various other Maillard reaction products, such as glyceraldehyde, erythrose, ribose, acetol, glycolaldehyde, fructosamine, glucosone, osones, deoxyosones, and Amadori products. Some osones and deoxyosones also formed their corresponding Schiff bases with alanine. The above mentioned Maillard reactions intermediates were detected either as binary metal complexes with alanine or with other enediol generating species including self-complexation adducts and they formed positively charged ions such as [M + H]+, [M + Na]+, [M + K]+, [M â€‹+ â€‹Fe35Cl]+, and [M â€‹+ â€‹Fe37Cl]+, that can be detected using the positive ionization mode.

Protective effects of dietary carnosine during in-vitro digestion of pork differing in fat content and cooking conditions.

Muscle carnosine represents an important health advantage of meat. Ground pork samples with intrinsic or added carnosine; fat content; and cooked under low or high intensity as a 2 × 2 × 2 factorial were digested in-vitro. Changes in free carnosine and in markers of lipid (hexanal, 4-hydroxynonenal (4-HNE), malondialdehyde (MDA) and protein (protein-carbonyls, thiols) oxidation, and of advanced glycation end-products (AGEs) Nε -(carboxymethyl)lysine (CML) were determined in the saliva, gastric, and duodenal digests. During digestion, the different markers overall indicated increased oxidation and decreased free carnosine. Increasing pork carnosine level significantly reduced protein carbonyls, loss of thiols, and 4-HNE during in-vitro gastric digestion, irrespective of fat and cooking level of the meat. Increased carnosine also significantly reduced hexanal, MDA and CML up to the duodenum phase in moderately cooked lean pork. Besides substantiating the formation of AGEs during digestion, these results show a potentially important role of dietary carnosine occurring in the gastrointestinal tract. PRACTICAL APPLICATIONS: The ailments epidemiologically associated with red meat consumption could be counteracted by ingesting carnosine into meat. The health advantages of dietary carnosine, however, have never been demonstrated during digestion, a unique and complex oxidative environment compounded by the composition and cooking of the meat. The results obtained substantiated that AGEs formation occurred in-vitro in the GIT. They also showed that increased carnosine had an immediate health beneficial role during pork digestion in reducing the formation of different harmful molecules, including AGEs, modulated by the composition and cooking of the meat. However, in exerting this protective role in the GIT, the remaining free level of carnosine, gradually decreased during digestion. Carnosine, as an important meat compositional factor may, depending on the fat content and cooking conditions, change the image of meat from representing a health risk to a health benefit. Carnosine level may also explain discrepancies observed in the literature.

Profiling of glucose degradation products through complexation with divalent metal ions coupled with ESI/qTOF/MS/MS analysis.

Sugar degradation products generated through thermal treatment of foods are considered the key precursors for various flavor compounds, toxicants and browning, but their high reactivity makes their detection difficult. In this study, a convenient analytical procedure for profiling of various reactive sugar intermediates having enediol or α -dicarbonyl moieties through complexation with divalent metal ions combined with electrospray ionization/quadrupole time-of-flight mass spectrometry was developed. Excess divalent iron chloride (FeCl2) was added to glucose or 13U6-[glucose] solutions in methanol either before or after heating at 110 °C for 2 h, and the samples were analyzed by tandem mass spectrometry. The results indicated the formation of ethylene glycol, glycolaldehyde, glyceraldehyde, glycerol, methylglyoxal, glyoxylic acid, erythrose, erythrosone, 3-deoxy-erythrosone, erythritol, ribose, ribosone, 3-deoxy-ribose, ribitol, 3-deoxy-glucosone, and rhamnose. These sugars and sugar degradation products acting as bidentate ligands were detected as positively charged mono- and bis-sugar iron complexes in the form of [M + H]+, [M + Na]+, [M + K]+, [M + Fe35Cl]+, and [M + Fe37Cl]+, as well as by charge localization on iron [M]+. The divalent metal complexation technique was applied for the profiling of sugar degradation products in aged manuka honey.

Monitoring of methylglyoxal/indole interaction by ATR-FTIR spectroscopy and qTOF/MS/MS analysis.

Sugar derived reactive 1,2-dicarbonyl intermediates are considered important precursors for the formation of Maillard reaction products. Efficient strategies are needed to modulate their formation in food. Indole a major thermal degradation product of tryptophan, has been shown to scavenge such 1,2-dicarbonyls at high temperatures. In this study, the trapping of methylglyoxal by indole was monitored at various temperatures either by (a) ATR-FTIR spectroscopy or (b) in-solution using qTOF/MS/MS analysis. Information obtained through these studies have indicated that even at room temperature indole can quickly react with methylglyoxal forming an adduct as confirmed by the emergence of a new peak at 1729 cm-1 and by qTOF/MS/MS analysis. On the open surface of the ATR crystal this adduct underwent a fast oxidization into carboxylic acid as evidenced by the disappearance of the band at 1729 cm-1 and the formation of a new band at 1712 cm-1 and its subsequent conversion into a carboxylate band under basic conditions.

Mechanochemical generation of Schiff bases and Amadori products and utilization of diagnostic MS/MS fragmentation patterns in negative ionization mode for their analysis.

The use of tandem mass spectrometry under positive ionization mode was previously developed as a tool for distinguishing isomeric Schiff bases and Amadori products. In this paper, similar diagnostic MS/MS fragmentation patterns were identified under negative ionization mode and was utilized to study the composition of mechanochemically generated Maillard reaction mixtures. The major diagnostic ion of the Schiff base was found to be a diose attached to the amino acid residue, while that of the Amadori compound was a triose. The structures of the diagnostic ions were confirmed through isotope labeling technique and elemental composition. Furthermore, application of this technique showed that ball milling of glucose with different amino acids almost exclusively results in the formation of a mixture of Schiff bases and Amadori compounds, and that amino acids with basic side chains generated more Schiff bases and those with acidic side chains generated more Amadori products.

Exploring the scope of indole interaction with 1,2-dicarbonyl compounds.

The 1,2-dicarbonyl compounds have received extensive attention due to their high reactivity and toxicity in vitro and in vivo. Availability of scavenging compounds may facilitate development of efficient strategies for their control. The concept of in situ generation of carbonyl trapping agents is an intriguing proposition and has been demonstrated with amino acid tryptophan. Ability of indole to undergo electrophilic aromatic substitution reaction was studied in the past with methylglyoxal. To confirm the generality of this reaction, model systems containing indole and several 1,2-dicarbonyl compounds were prepared and reacted at room temperature (RT) and at 150 °C and analyzed by ESI-qTOF-MS/MS and isotopic labeling technique. Indole showed ability to capture all the tested 1,2-dicarbonyls. Longer chain 1,2-dicarbonyls showed higher temperature dependency than shorter chain in their reactivity towards indole. Furthermore, the ability of indole to scavenge Strecker aldehydes was also demonstrated in alanine/glucose and in a bread model systems using [13C-2]indole.

Diagnostic MS/MS fragmentation patterns for the discrimination between Schiff bases and their Amadori or Heyns rearrangement products.

Schiff bases, the Amadori and Heyns rearrangement products are the most important isomeric intermediates involved in the early Maillard reaction; distinguishing between them by analytical mass spectroscopic techniques remains a challenge. Here we demonstrate that MS/MS fragmentation patterns can be used for the discrimination between glucose derived Schiff bases, Amadori, and Heyns compounds with glycine. An ESI-qTOF-MS system operated in the positive mode under both acidic and neutral conditions was employed to generate unique MS/MS fragmentation patterns of the molecules. Analysis of the MS data has indicated that acidic medium is suitable for generating characteristic and diagnostic ions. At high collision energy (20 eV), the spectrum of Schiff base was largely uninformative, whereas both Amadori and Heyns compounds undergo characteristic fragmentations with high diagnostic value. At low collision energy values (10eV), we observed formation of prominent diagnostic ions from the Schiff base precursor, as well as extensive dehydration reactions of all three molecules. Under acidic conditions, the diagnostic fragmentation pattern of the Amadori compound featured consecutive dehydration reactions. At higher values (20 eV) it underwent the α-fission at the carbonyl group and produced a prominent diagnostic ion [AA + H + CH2]+ at m/z 88. The Schiff base was found to preferentially undergo the retro-aldol degradation and produce diagnostic ions at m/z 118 [AA + H + diose]+ and m/z 140 [AA + Na + diose]+, together with their sugar complements at m/z 85 [tetrose + H-2H2O]+ and m/z 143 [tetrose + Na]+. In the case of Heyns compound, several diagnostic ions were also detected, including the ions at m/z 154 [M + H-2H2O-C2H4O2]+, m/z 170 [AA + Na + triose]+ and m/z 142 [AA + H + Furan]+.

Indole: A Promising Scavenging Agent for Methylglyoxal and Related Carbonyls in Tryptophan Containing Maillard Model Systems.

In situ generation of efficient carbonyl trapping agents from amino acids during food processing can be considered a useful approach to control the accumulation of harmful Maillard reaction products in food. Tryptophan is one such amino acid that can be used to generate carbonyl trapping agents. Indole, the main thermal degradation product of tryptophan, is known to react with simple aldehydes through electrophilic aromatic substitution type reactions mainly at carbon positions 2 and 3 in addition to the ring nitrogen. The ability of indole to scavenge three moles of reactive aldehydes per mole of indole such as formaldehyde, methylglyoxal, and phenylacetaldehyde was investigated using model systems containing tryptophan or indole. The model systems were either (a) heated in an aqueous solution in stainless steel reactors at specified time and temperatures and analyzed by qTOF-MS/MS or (b) directly pyrolyzed and analyzed by GC/MS using isotope labeling technique. Unlike the other aldehydes, the initial alcohol formed with phenylacetaldehyde was able to dehydrate and form an stable conjugated system with the indole. In general, indole was able to capture three moles of paraformaldehyde, three moles of methylglyoxal and three moles of phenylacetaldehyde and suppress the formation of 2-amino-1-methyl-6-phenylimidazo(4,5-b)pyridine (PhIP) generated in a model system.

Mechanochemically Induced Controlled Glycation of Lysozyme and Its Effect on Enzymatic Activity and Conformational Changes.

Protein glycation through heating of a mixture of protein and reducing sugars is one of the most commonly used methods of protein modification; however, in most cases, this approach can lead to uncontrolled glycation. The hypothesis that mechanical energy supplied through ball milling can induce glycation of proteins was tested using a well-characterized enzyme lysozyme. The Q-TOF/MS analysis of the milled samples has indicated that the milling of sugar-protein mixtures in stainless steel jars for 30 min and at a frequency of 30 Hz generated mainly monoglycated proteins even with the highly reactive ribose. Increasing the sugar concentration or the milling time did not influence the overall yield or generate more glycoforms. Enzymatic activity measurements, FTIR, and fluorescence spectroscopic studies have indicated that milling of lysozyme alone leads to a significant loss in enzymatic activity and structural integrity in contrast to milling in the presence of sugars.

Mechanochemical depolymerization of inulin.

Although chemical reactions driven by mechanical force is emerging as a promising tool in the field of physical sciences, its applications in the area of food sciences are not reported. In this paper, we propose ball milling as an efficient tool for the controlled generation of fructooligosaccharide (FOS) mixtures from inulin with a degree of polymerization (dp) ranging between 4 and 7. The addition of catalytic amounts of AlCl3 together with ball milling (30 min, at 30 Hz) generated mixtures rich in dehydrated disaccharides such as di-D-fructose dianhydrides. Based on anion exchange chromatography in conjunction with ESI/qTOF/MS/MS analysis, catalysis increased the overall content of mono-, di-, and tri-saccharides by around 30 fold compared to un-catalyzed milling. In addition, dialysis results of the untreated and treated samples have indicated that under catalysis the percent of depolymerization (dp < 12) reached 73.4% from the starting value of 27.6% in the untreated sample. Both processes resulted in mixtures of prebiotic value. The use of mechanical energy may be suitable for a fast, cost-efficient and green conversion of inulin to value-added food ingredients.

Interaction of free arginine and guanidine with glucose under thermal processing conditions and formation of Amadori-derived imidazolones.

To investigate the reactivity of free guanidine and arginine in the formation of imidazolinone derivatives, model systems of guanidine or arginine/glucose or 13[C-6]-glucose were heated in aqueous solutions at110°C for 3h and the residues were analyzed by ESI/qTOF/MS using MS/MS and isotope labeling techniques. The analysis of the data indicated that guanidine and arginine formed both covalent and non-covalent interaction products. Covalent interactions included Amadori rearrangement at the α-nitrogen with glucose and imidazolinone formation with 3-deoxy-glucosone at the guanidine side-chain. Non-covalent interactions, such as self-interaction and interaction with free guanidine or arginine and glucose, were also observed. Guanidine underwent three sequential Amadori rearrangements and the free and mono-glycated guanidine also formed imidazolinone derivatives and their corresponding dehydration products and at the same time exhibiting various non-covalent interactions. On the other hand, arginine formed free Amadori product, free imidazolinone and Amadori-derived imidazolinone derivative in addition to methylglyoxal-derived hydroimidazolones.