Antioxidant capacity of 1-deoxy-D-erythro-hexo-2,3-diulose and D-arabino-hexo-2-ulose

Rapid Characterization of Maillard Reaction Products in Heat-Treated Honey by Nanoelectrospray Ionization Mass Spectrometry

Amadori rearrangement products (ARPs) and α-dicarbonyl compounds (α-DCs) are critical intermediates in the Maillard chemistry. The screening of artificially heated honey (AH) is currently based on chromatography-mass spectrometry, which is commonly accompanied with the longer pretreatment and detection time. Here, low-abundance ARPs were detected directly in high-sugar environment by nanoelectrospray ionization mass spectrometry (nanoESI-MS) coupled with borosilicate glass capillaries (O-tips). When O-tips were replaced by borosilicate theta capillaries (θ-tips), the microdroplets allowed the derivatization of α-DCs to be accomplished on the millisecond timescale, rather than hours in conventional protocols. The results indicated that two ARPs and α-DCs of m/z 235 were significantly up-regulated in AH. Meanwhile, the straightforward differentiation between naturally matured honey (NH) and AH was achieved by nanoESI-MS fingerprints combined with multivariate analysis. The method may provide a rapid characterization of Maillard reaction products (MRPs), which exhibits the great application potential in other complex food matrix.

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.

Effect of hydroxyl on antioxidant properties of 2,3-dihydro-3,5-dihydroxy-6-methyl-4H-pyran-4-one to scavenge free radicals

It is well known that 2,3-dihydro-3,5-dihydroxy-6-methyl-4H-pyran-4-one (DDMP) is usually formed in the Maillard reaction and it contributes to the antioxidant properties of Maillard reaction intermediates. A series of hydroxyl group protected DDMP derivatives were synthesized to further understand the source of antioxidant activity. Antioxidant abilities of the DDMP derivatives were evaluated by scavenging the 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonate) cationic radical (ABTS˙+), 2,2'-diphenyl-1-picrylhydrazyl radical (DPPH), and galvinoxyl radical, respectively. It was found that the introduction of protecting groups to the free hydroxyl groups of DDMP decreases their reducing abilities. In particular, the hydroxyl group at the olefin position exhibited a remarkable impact on the antioxidant activity of DDMP, indicating that the unstable enol structure in the DDMP moiety is the key factor for its antioxidant activity.

The effect of amino acids on non-enzymatic browning of glucosamine: Generation of butterscotch aromatic and bioactive health compounds without detectable levels of neo-formed alkylimidazoles

A mixture of glucosamine (GlcN, 15% w/v) and different amino acids in 1:1 M ratio was incubated at 70 °C for 12 h. The resulting GlcN-amino acid caramels were analysed for α-dicarbonyl compounds, polyhydroxyalkyl pyrazines, heterocyclic compound and alkylimidazoles. All the analyses were performed by using HPLC-MS/MS followed by pooling the variables with principal component analysis (PCA). GlcN-Gly caramels generated the greatest amount of butterscotch aromatic compound diacetyl and polyhydroxyalkyl pyrazines (fructosazine and deoxyfructosazine). The potentially toxic heterocyclic compound, 5-hydroxymethylfurfural (HMF) was generated in greater amounts with the GlcN-Arg caramels. However, the toxic alkylimidazoles (4-MEI and THI) were not present in any of the GlcN-amino acid caramels. The results suggest that caramel with butterscotch aroma and bioactivity can be produced with GlcN-amino acid at 70 °C. The PCA performed discriminated the majority of the GlcN-amino acid combinations; GlcN-Gly and GlcN-Ser were best discriminated.

Cold non-enzymatic browning of glucosamine in the presence of metmyoglobin induces glucosone and deoxymyoglobin formation

Glucosamine (GlcN) and GlcN-myoglobin reaction systems were incubated at 4 °C to verify that GlcN can go through non-enzymatic browning at this low temperature, and to test the hypothesis that certain reductones from GlcN non-enzymatic browning can promote the formation of deoxy- and oxymyoglobin from metmyoglobin reduction. Remarkably, alpha-dicarbonyls and self-condensation products, fructosazine and deoxyfructosazine, were produced at this relatively low temperature. The presence of myoglobin shifted GlcN non-enzymatic browning toward the formation of glucosone and fructosazine. When glucosone (250-2000 mg/L) was incubated with myoglobin it contributed to the formation of deoxymyoglobin, indicating its capacity to reduce metmyoglobin. This study opens the possibility of using GlcN in meat products to increase oxy- and deoxymyoglobin and enhance the color of meat.

Maillard reaction products derived from food protein-derived peptides: insights into flavor and bioactivity

Food protein-derived peptides serve as food ingredients that can influence flavor and bioactivity of foods. The Maillard reaction plays a crucial role in food processing and storage, and generates a wide range of Maillard reaction products (MRPs) that contribute to flavor and bioactivity of foods. Even though the reactions between proteins and carbohydrates have been extensively investigated, the modifications of food protein-derived peptides and the subsequent impacts on flavor and bioactivity of foods have not been fully elucidated. In this review, the flavor and bioactive properties of food-derived peptides are reviewed. The formation mechanisms with respect to MRPs generated from food protein-derived peptides have been discussed. The state-of-the-art studies on impacts of the Maillard reaction on flavor and bioactivity of food protein-derived peptides are also discussed. In addition, some potential negative effects of MRPs are described.

Obesity leads to distinct metabolomic signatures in follicular fluid of women undergoing in vitro fertilization

Although obesity negatively influences the metabolic homeostasis of cells within a broad range of tissues, its impact on oocyte metabolism is not fully understood. Prior evidence suggests that obesity increases expression of oocyte genes associated with inflammation, oxidative stress, and lipid metabolism; however, the metabolic impact of these genetic differences is not known. To address this gap, we conducted an exploratory assessment of the follicular fluid (FF) metabolome in eight overweight/obese (OW) and nine normal-weight (NW) women undergoing in vitro fertilization. FF and serum were collected and analyzed by untargeted metabolomics using gas chromatography-quadrupole time-of-flight mass spectrometry and charged-surface hybrid column-electrospray ionization quadrupole time-of-flight tandem mass spectrometry. Untargeted metabolomics identified obesity-associated changes in FF metabolites related to oxidative stress/antioxidant capacity, xenometabolism/amino acid biosynthesis, and lipid metabolism. Discriminant FF metabolites included elevated uric acid, isothreonic acid, one unknown primary metabolite, and six unknown complex lipids in OW compared with NW women. Conversely, 2-ketoglucose dimethylacetal, aminomalonate, two unknown primary metabolites, and two unknown complex lipids were decreased in FF of OW relative to NW women. Indole-3-propionic acid (IPA), a bacteria-derived metabolite, was also decreased in both FF and serum of OW women ( P < 0.05). The significant correlation between antioxidant IPA in serum and FF ( R = 0.95, P < 0.0001) suggests a potential serum biomarker of FF antioxidant status or reflection of the gut metabolism interaction with the follicle. These results suggest that obesity has important consequences for the follicular environment during the preconception period, a window of time that may be important for lifestyle interventions to ameliorate obesity-associated risk factors.

2-Deoxyglucosone: A New C6-α-Dicarbonyl Compound in the Maillard Reaction of d-Fructose with γ-Aminobutyric Acid

In this study, α-dicarbonyl compounds consisting of a backbone with six carbon atoms resulting from the Maillard reaction of d-fructose with γ-aminobutyric acid were determined. The reaction was carried out under mild reaction conditions at 50 °C and water contents between 0 and 90%. A thus far unknown α-dicarbonyl compound was found as the main product in the first 24 h at water contents below 50%. After isolation of its stable quinoxaline derivative, it was possible to identify the compound as 2-deoxy-d- glycero-hexo-3,4-diulose (2-deoxyglucosone). For the first time, the four C₆-α-dicarbonyl compounds, 1-deoxyglucosone, 2-deoxyglucosone, 3-deoxyglucosone, and 4-deoxyglucosone, could be identified in the Maillard reaction of a hexose at the same time. This indicates the formation of a 2,3-eneaminol from the Schiff base of d-fructose and the formation of 2-amino-2-deoxy-3-ketose as an alternative to the Heyns product.

Sous-Vide Nonenzymatic Browning of Glucosamine at Different Temperatures

Sous-vide is an increasingly popular method of cooking under controlled conditions of temperature and time inside vacuumed pouches to preserve the nutritional and sensory qualities of food. Sous-vide nonenzymatic browning of glucosamine (GlcN) was investigated at 50, 60, and 70 °C for 12 h. Changes investigated were pH, color, level of browning, and the concentrations of the key Maillard and caramelization reaction products, including α-dicarbonyls and pyrazines. The concentrations of undesired 4-methylimidazole (4-MEI), 2-acetyl-4(5)-tetrahydroxybutyl imidazole (THI), and 5-hydroxymethylfurfural (5-HMF) were also determined. Six types of caramels were produced of unique composition with no detectable levels of 4-MEI. GlcN caramels produced under vacuum were more acidic and lighter in color, containing significantly less flavorful diacetyl, but more fructosazine (FR) as compared to nonvacuum caramels. THI concentration was well below the toxicity levels for all studied caramels. Principal component analyses showed that the incubation temperature played a key role in determining the composition of caramels.

Formation of Reactive Intermediates, Color, and Antioxidant Activity in the Maillard Reaction of Maltose in Comparison to d-Glucose

In this study, the Maillard reaction of maltose and d-glucose in the presence of l-alanine was investigated in aqueous solution at 130 °C and pH 5. The reactivity of both carbohydrates was compared in regards of their degradation, browning, and antioxidant activity. In order to identify relevant differences in the reaction pathways, the concentrations of selected intermediates such as 1,2-dicarbonyl compounds, furans, furanones, and pyranones were determined. It was found, that the degradation of maltose predominantly yields 1,2-dicarbonyls that still carry a glucosyl moiety and thus subsequent reactions to HMF, furfural, and 2-acetylfuran are favored due to the elimination of d-glucose, which is an excellent leaving group in aqueous solution. Consequently, higher amounts of these heterocycles are formed from maltose. 3-deoxyglucosone and 3-deoxygalactosone represent the only relevant C₆-1,2-dicarbonyls in maltose incubations and are produced in nearly equimolar amounts during the first 60 min of heating as byproducts of the HMF formation.

Browning Potential of C6-α-Dicarbonyl Compounds under Maillard Conditions

In this work, the three major C₆-α-dicarbonyl compounds glucosone (GLUC), 1-deoxyglucosone (1-DG), and 3-deoxyglucosone (3-DG) were synthesized and examined under Maillard conditions (aqueous solutions with the addition of l-alanine at 130 °C and pH 5/8). For the first time, the resulting color formation, antioxidant activity, and generation of short-chained α-dicarbonyls were investigated and compared to incubations of d-glucose and d-fructose. An additive effect on the formation of color, an antagonistic effect on the generation of α-dicarbonyl compounds, and a synergistic effect on the antioxidant activity could be observed for the 1-DG/GLUC combination. Despite their common degradation products, different extinctions could be measured, with 3-DG showing the strongest color formation, followed by GLUC and 1-DG. The analyzed α-dicarbonyl compounds have no direct impact on the formation of color but are precursors for most of the colored compounds. The main difference between the three substances is their ability to form different heterocyclic degradation products, such as pyranones (1-DG), furanones (1-DG), furans (GLUC and 3-DG), and the corresponding N-heterocycles in the presence of amino components. This seems to be the main reason for their varying browning potential and antioxidant activity.

Antioxidant Properties of Heterocyclic Intermediates of the Maillard Reaction and Structurally Related Compounds

It is well established that a wide range of reductones is formed in the course of the Maillard reaction and that these substances contribute to the oxidative stability of food. The aim of this study was to analyze 12 important heterocyclic intermediates with and without reductone structure as well as structurally related substances under equal conditions to compare their antioxidant properties in detail. For this purpose, five methods were selected including photometrical methods such as the trolox equivalent antioxidant capacity assay and an electron paramagnetic resonance spectroscopic method. Reductones with furan-3-one structure and 2,3-dihydro-3,5-dihydroxy-6-methyl-4H-pyran-4-one were reducing in all assays, whereas isomaltol and maltol did not react in assays based on the reduction of metal ions because of their complexing abilities. The introduction of protecting groups to the free hydroxyl functions of selected reductones could nearly eliminate their reducing abilities. In addition, the oxidation products of the different reductive heterocycles were compared after treatment with iodine. Mainly short-chained organic acids such as lactic, glycolic, and glyceric acid are formed as result of the degradation, which indicates 1,3-dicarbonyl cleavage reactions of corresponding tricarbonyl compounds as intermediates of the oxidation.

Structure-reactivity relationship of Amadori rearrangement products compared to related ketoses

Structure-reactivity relationships of Amadori rearrangement products compared to their related ketoses were derived from multiple NMR spectroscopic techniques. Besides structure elucidation of six Amadori rearrangement products derived from d-glucose and d-galactose with l-alanine, l-phenylalanine and l-proline, especially quantitative (13)C selective saturation transfer NMR spectroscopy was applied to deduce information on isomeric systems. It could be shown exemplarily that the Amadori compound N-(1-deoxy-d-fructos-1-yl)-l-proline exhibits much higher isomerisation rates than d-fructose, which can be explained by C-1 substituent mediated intramolecular catalysis. In combination with a reduced carbonyl activity of Amadori compounds compared to their related ketoses which results in an increased acyclic keto isomer concentration, the results on isomerisation dynamics lead to a highly significant increased reactivity of Amadori compounds. This can be clearly seen, comparing approximated carbohydrate milieu stability time constants (ACuSTiC) which is 1 s for N-(1-deoxy-d-fructos-1-yl)-l-proline and 10 s for d-fructose at pD 4.20 ± 0.05 at 350 K. In addition, first NMR spectroscopic data are provided, which prove that α-pyranose of (amino acid substituted) d-fructose adopts both, (2)C5 and (5)C2 conformation.

Maillard reaction products and potatoes: have the benefits been clearly assessed?

Cooking foods affords numerous food safety benefits. During heating, Maillard reaction products (MRPs) are formed. MRPs contribute sensory aspects to food, including color, taste, and texture. One MRP, acrylamide, has been implicated in negative health outcomes; however, emerging data suggests MRPs may also deliver certain health benefits. The food industry has taken steps to decrease acrylamide formation, but the perception that high levels of acrylamide compromise the nutritional benefit of certain foods has continued. Potatoes are susceptible to MRP formation during cooking but also are considered an affordable, high nutrient content food. In particular, potatoes contribute significantly to fiber and potassium intakes in the U.S. population, two nutrients of need. How, then, should potatoes be judged for effects on health? A structured evidence assessment was conducted to identify literature, specifically clinical trials, on MRPs from potatoes and health, as well as nutritional contribution of potatoes. The results indicate limited human clinical data are available on negative health outcomes of potato-based MRPs, whereas potatoes are important contributors of key nutrients, such as fiber and potassium. Therefore, a balanced benefit-risk approach is warranted in order to assure that decreasing consumption of certain foods, like potatoes, does not lead to unintended consequences of nutrition inadequacies.

Rapid Myoglobin Aggregation through Glucosamine-Induced α-Dicarbonyl Formation

The extent of glycation and conformational changes of horse myoglobin (Mb) upon glycation with N-acetyl-glucosamine (GlcNAc), glucose (Glc) and glucosamine (GlcN) were investigated. Among tested sugars, the rate of glycation with GlcN was the most rapid as shown by MALDI and ESI mass spectrometries. Protein oxidation, as evaluated by the amount of carbonyl groups present on Mb, was found to increase exponentially in Mb-Glc conjugates over time, whereas in Mb-GlcN mixtures the carbonyl groups decreased significantly after maximum at 3 days of the reaction. The reaction between GlcN and Mb resulted in a significantly higher amount of α-dicarbonyl compounds, mostly glucosone and 3-deoxyglucosone, ranging from and 27 to 332 mg/L and from 14 to 304 mg/L, respectively. Already at 0.5 days, tertiary structural changes of Mb-GlcN conjugate were observed by altered tryptophan fluorescence. A reduction of metmyoglobin to deoxy-and oxymyoglobin forms was observed on the first day of reaction, coinciding with the greatest amount of glucosone produced. In contrast to native α-helical myoglobin, 41% of the glycated protein sequence was transformed into a β-sheet conformation, as determined by circular dichroism spectropolarimetry. Transmission electron microscopy demonstrated that Mb glycation with GlcN causes the formation of amorphous or fibrous aggregates, started already at 3 reaction days. These aggregates bind to an amyloid-specific dye thioflavin T. With the aid of α-dicarbonyl compounds and advanced products of reaction, this study suggests that the Mb glycation with GlcN induces the unfolding of an initially globular protein structure into amyloid fibrils comprised of a β-sheet structure.