Reduction mechanism of tetrazolium salt XTT by a glucosamine derivative

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.

Development and validation of a selective and effective pressurized liquid extraction followed by liquid chromatography-mass spectrometry method for the determination of fructosazine analogues in the ammonia treated extract of Eugenia jambolana Lamarck seeds

This study describes a selective and effective pressurized liquid extraction (PLE) coupled with HPLC-DAD-ESI/MS method for the identification and quantification of three fructosazine analogues (FZAs), fructosazine, 2,6- and 2,5-deoxyfructosazine in Madeglucyl^® (MG) which is an ammonia treated extract of Eugenia jambolana Lamarck seeds, and is the world's first anti-diabetic phytodrug. FZAs were extracted from MG by PLE using methanol as extraction solvent. The PLE extract was then analyzed directly by HPLC-DAD-ESI/MS without cleanup step. Chromatographic separation of these highly related structures was achieved on a porous graphic carbon (PGC) column. The identification of the target FZAs was confirmed by the similar retention time, similar UV and MS spectra to the corresponding pure standards. The quantification was performed by using an electrospray positive ionization mass spectrometry in the selected ion monitoring (SIM) mode. The PLE procedure was optimized and overall method was validated in terms of sensitivity, linearity, selectivity and matrix effect, precision, accuracy and recovery, and stability of the target FZAs in the aqueous solution and in the PLE extracts solution of MG. The developed method was proved to be selective, sensitive, precise, accurate for the quantification of FZAs in MG.

Iron (Fe(2+))-Catalyzed Glucosamine Browning at 50 °C: Identification and Quantification of Major Flavor Compounds for Antibacterial Activity

Glucosamine browning at 50 °C with (GlcN/Fe(2+)) or without iron (GlcN) was studied over time from 0 to 48 h. Generation of reactive oxygen species (ROS), H2O2, and (1)O2, along with α-dicarbonyls, fructosazine, and deoxyfructosazine, was evaluated. Singlet oxygen generation increased over time and was greater in GlcN/Fe(2+) caramel solution. The presence of iron significantly increased the concentration of α-dicarbonyls at an early incubation time (3 h). Fructosazine and deoxyfructosazine were the major degradation products at 48 h comprising together up to 37 and 49% in GlcN and GlcN/Fe(2+), respectively. GlcN/Fe(2+) (48 h) exhibited a MIC50 against highly heat-resistant Escherichia coli AW 1.7 at pH 5, but not at pH 7. Despite several antimicrobial compounds being produced during browning, GlcN/Fe(2+) created a synergistic environment for the fructosazine-organic acids to confer their antimicrobial activity. GlcN caramel solutions have the potential to serve as both flavoring compounds and antimicrobial agents in formulated food systems.

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.

Studies on the Formation of Maillard and Caramelization Products from Glucosamine Incubated at 37 °C

This experiment compared the in vitro degradation of glucosamine (GlcN), N-acetylglucosamine, and glucose in the presence of NH3 incubated at 37 °C in phosphate buffer from 0.5 to 12 days. The reactions were monitored with UV-vis absorption and fluorescence emission spectroscopies, and the main products of degradation, quinoxaline derivatives of α-dicarbonyl compounds and condensation products, were determined using UHPLC-UV and Orbitrap mass spectrometry. GlcN produced two major dicarbonyl compounds, glucosone and 3-deoxyglucosone, ranging from 709 to 3245 mg/kg GlcN and from 272 to 4535 mg/kg GlcN, respectively. 3,4-Dideoxyglucosone-3-ene, glyoxal, hydroxypyruvaldehyde, methylglyoxal, and diacetyl were also detected in lower amounts compared to glucosone and 3-deoxyglucosone. Several pyrazine condensation products resulting from the reaction between dicarbonyls and GlcN were also identified. This study determined that GlcN is a significantly unstable molecule producing a high level of degradation products at 37 °C.