Fructosazine, a Polyhydroxyalkylpyrazine with Antimicrobial Activity: Mechanism of Inhibition against Extremely Heat Resistant Escherichia coli

Effect and Mechanism of Eliminating Staphylococcus aureus by Electron Beam Irradiation and Reducing the Toxicity of Its Metabolites

The purpose of this study was to evaluate the mechanism of sterilization of Staphylococcus aureus by electron beam irradiation (0.5-, 1-, 2-, 4-, and 6-kGy treatments) and whether it reduces the toxicity of its fermentation supernatant. In this study, we investigated the mechanism of sterilization of S. aureus by electron beam irradiation using colony count, membrane potential, intracellular ATP, and UV absorbance measurements; we used hemolytic, cytotoxic, and suckling mouse wound models to verify that electron beam irradiation reduced the toxicity of the S. aureus fermentation supernatant. The results showed that 2 kGy of electron beam irradiation treatment completely inactivated S. aureus in suspension culture, and 4 kGy inactivated cells in S. aureus biofilms. This study suggests that the bactericidal effect of electron beam irradiation on S. aureus may be attributed to reversible damage to the cytoplasmic membrane, resulting in its leakage and the significant degradation of genomic DNA. The combined results of hemolytic, cytotoxic, and suckling mouse wound models demonstrated that the toxicity of S. aureus metabolites was significantly reduced when the electron beam irradiation dose was 4 kGy. In summary, electron beam irradiation has the potential to control S. aureus and reduce its toxic metabolites in food. IMPORTANCE Electron beam irradiation of >1 kGy damaged the cytoplasmic membrane, and reactive oxygen species (ROS) penetrated the cells. Electron beam irradiation of >4 kGy reduces the combined toxicity of virulent proteins produced by Staphylococcus aureus. Electron beam irradiation of >4 kGy can be used to inactivate Staphylococcus aureus and biofilms on milk.

Fishery waste valorization: Sulfated ZrO2 as a heterogeneous catalyst for chitin and chitosan depolymerization

Chitin and chitosan are abundant unique sources of biologically-fixed nitrogen mainly derived from residues of the fishery productive chain. Their high potential as nitrogen-based highly added-value platform molecules is still largely unexploited and a catalytic way for their valorization would be strongly desirable within a biorefinery concept. Here we report our results obtained with a series of heterogeneous catalysts in the depolymerization of chitosan and chitin to acetylglucosamine. Copper catalysts supported on SiO2, SiO2–Al2O3, SiO2-ZrO2, ZrO2 and the corresponding bare oxides/mixed oxides were tested, together with a sulfated zirconia system (ZrO2-SO3H) that revealed to be extremely selective towards glucosamine, both for chitosan and chitin, thus giving pretty high yields with respect to the values reported so far (44% and 21%, respectively). The use of a heterogeneous catalyst alone, without the need of any additives or the combination with a mineral acid, makes these results remarkable.

Improved bactericidal capacity of UV-B radiation against E. coli strains by photosensitizing bacteria with fructosazine - An advanced Maillard reaction product

This study investigated the effect of UV-B irradiation and the combinational effect with glucosamine caramel, fructosazine and riboflavin on the antimicrobial activities against Bacillus subtilis (ATCC 6633) and two strains of Escherichia coli (AW 1.7 and ATCC 25922). The quantum yield of fructosazine was two times less than that of tryptophan, indicating its ability to emit fluorescent light but less efficiently than tryptophan. UV-B treatment alone was efficient to achieve a bactericidal effect for both E. coli stains tested, however no effect was found for Bacillus subtilis for up to 80 mJ/cm² UV-B. The combination of UV-B with photosensitizers fructosazine, glucosamine caramel and riboflavin enhanced the UV-B efficacy against E. coli strains at lower UV-B doses, while Bacillus subtilis ATCC 6633 was more resistant to the treatment combinations. High-performance liquid chromatography showed the production of different fructosazine reaction products occurred during irradiation, including the possible formation of endoperoxides.

Practical Three-Minute Synthesis of Acid-Coated Fluorescent Carbon Dots with Tuneable Core Structure

We report a one-pot, three-minute synthesis of carboxylic acid-decorated fluorescent carbon dots (COOH-FCDs) with tuneable core morphology dependent on the surface passivating agent. Mechanism investigations highlighted the presence of key pyrazine and polyhydroxyl aromatic motifs, which are formed from the degradation of glucosamine in the presence of a bifunctional linker bearing acid and amine groups. The novel COOH-FCDs are selective Fe3+ and hemin sensors. Furthermore, the FCDs are shown to be non-toxic, fluorescent bioimaging agents for cancer cells.

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.

Inhibitory activity of a Concanavalin-isolated fraction from a glucosamine-peptides reaction system against heat resistant E. coli

Alcalase-derived gelatin hydrolysates were glycated with glucosamine in the presence (+) or absence (−) of transglutaminase (TGase), and their antimicrobial activities toward Escherichia coli AW 1.7 were studied. Glycation treatments were subjected to concanavalin A affinity chromatography to selectively collect the glycopeptide-enriched fractions and the changes in antimicrobial activity were determined. The minimum inhibitory concentration of glycated hydrolysates decreased by 1.2 times compared to the native hydrolysate, with no differences between (+) or (−) TGase treatments. No difference was observed in the dicarbonyl compound concentration between the two glycation methods except that 3-deoxyglucosone was greater in the TGase-mediated reaction. Concanavalin A-retentate, but not the flow-through fractions, significantly improved the antimicrobial activity, however there was no difference between +TGase and −TGase glycated treatments. Purification of the retentate fraction from fluorescent compounds did not improve its antimicrobial activity.

Transport of the Glucosamine-Derived Browning Product Fructosazine (Polyhydroxyalkylpyrazine) Across the Human Intestinal Caco-2 Cell Monolayer: Role of the Hexose Transporters

The transport mechanism of fructosazine, a glucosamine self-condensation product, was investigated using a Caco-2 cell model. Fructosazine transport was assessed by measuring the bidirectional permeability coefficient across Caco-2 cells. The mechanism of transport was evaluated using phlorizin, an inhibitor of sodium-dependent glucose cotransporters (SGLT) 1 and 2, phloretin and quercetin, inhibitors of glucose transporters (GLUT) 1 and 2, transcytosis inhibitor wortmannin, and gap junction disruptor cytochalasin D. The role of hexose transporters was further studied using downregulated or overexpressed cell lines. The apparent permeability (P_a,b) of fructosazine was 1.30 ± 0.02 × 10^-6 cm/s. No significant (p > 0.05) effect was observed in fructosazine transport by adding wortmannin and cytochalasin D. The presence of phlorizin, phloretin, and quercetin decreased fructosazine transport. The downregulated GLUT cells line was unable to transport fructosazine. In human intestinal epithelial Caco-2 cells, GLUT1 or GLUT2 and SGLT are mainly responsible for fructosazine transport.