Elucidation of the chemical structure and determination of the production conditions for a bioactive Maillard reaction product, [5-(5,6-dihydro-4H-pyridin-3-ylidenemethyl)furan-2-yl]methanol, isolated from a glucose-lysine heated mixture

Antioxidant and Functional Activities of MRPs Derived from Different Sugar-Amino Acid Combinations and Reaction Conditions

The Maillard reaction (MR), or non-enzymatic browning, involves reducing sugars reacting with amino acids, peptides, or proteins when heated to produce an abundance of products that contribute to sensory, nutritional, and functional qualities of the food system. One example of an important functional quality of MR relates to antioxidant capacity, which has relevance to preserve food quality and also to extend a potential role that may promote gastrointestinal health. The addition of Alphacel (10%), a non-reactive polysaccharide, to MR reactants produced small significant (p < 0.05) reductions in yield of soluble Maillard reaction products (MRPs), sugar loss, and color change of products formed respectively, for reducing sugars. A similar effect was also noticed for different free-radical scavenging capacity (p < 0.05), using chemical (e.g., 2,2-diphenyl-1-picrylhydrazyl (DPPH)), Trolox equivalent antioxidant capacity (TEAC), and oxygen radical absorbance capacity (ORAC) assays. An inflamed Caco-2 cell model revealed nitric oxide (NO) inhibitory activity for Glu-amino acid MRPs, which contrasted the NO stimulatory activity obtained with Fru-amino acid MRPs, especially when glycine was used as the amino acid. Pre-treating Caco-2 cells with Fru-glycine MRPs protected against loss in trans-epithelial resistance (TEER) (p < 0.05) and reduced (p < 0.05) disruption of Caco-2 intestinal epithelial tight-junction (TJ) protein cells when exposed to 7.5% ethanol. A low molecular weight Fru-glycine (e.g., <1 kDa) fraction contributed to the protective effect, not observed with the corresponding high molecular weight MRP fraction. The presence of Alphacel had minimal effect on generating MRPs with relative modified protection against intestinal dysfunction in cultured Caco-2 cells. Rather, different types of sugar-amino acid combinations used to generate MRPs contributed more to mitigate injury in stress-induced Caco-2 cells. With the growing evidence that MRPs have a wide range of bioactive activities, this study concludes that specificity of substrate precursors that produce MRPs in heated foods is a critical factor for antioxidant and related cellular functions that represent a healthy gut.

Insights into melanoidin conversion into fluorescent nanoparticles in the Maillard reaction

Melanoidins are not the final product of the Maillard reaction, and they can be further converted to fluorescent nanoparticles after hydrothermal treatment.

A New Compound Isolated from the Reduced Ribose-Tryptophan Maillard Reaction Products Exhibits Distinct Anti-inflammatory Activity

In this study, a compound of 532.24 Da named BF-4 was separated from the ribose-tryptophan Maillard reaction products by solvent extraction and purified through reverse phase high performance liquid chromatography. The purified compound BF-4 was identified as 3-((1 H-indol-3-yl)methyl)-8-(5-((1 H-indol-3-yl)methyl)-6-oxomorpholin-2-yl)-9-hydroxy-1,7,4-dioxazecan-2-one in accordance with 1D- and 2D-NMR spectra and LC-ESI-MS/MS analysis. BF-4 significantly reduced the production of nitric oxide (NO), interleukin-6 (IL-6), and tumor necrosis factor α (TNF-α) in lipopolysaccharide-stimulated RAW 264.7 cells. It inhibited nuclear factor κB (NF-κB) activation and mitogen-activated protein kinase (MAPK) phosphorylation through suppressing phosphorylation of IκBα, P65, P38 and c-Jun N-terminal kinase (JNK). The anti-inflammatory activity of BF-4 was comparable to dexamethasone, and more importantly, BF-4 showed less cytotoxicity than dexamethasone on the normal human liver cell LO2. The results indicate that BF-4 is a promising anti-inflammatory agent with pharmaceutical potential.

Antioxidant activity and inhibitory effects of 2-hydroxy-3-methylcyclopent-2-enone isolated from ribose-histidine Maillard reaction products on aldose reductase and tyrosinase

This study aimed to better understand the functional properties of ribose and 20 amino acid Maillard reaction products (MRPs). The ABTS⁺ radical scavenging ability of the ribose-20 amino acid MRPs was evaluated. Among the MRPs, ribose-histidine MRPs (RH-MRPs) showed the highest inhibitory activities on the ABTS⁺ radical scavenging ability, aldose reductase (AR), and tyrosinase compared to other MRPs. Functional compounds with antioxidant and AR inhibitory activities have been recognized as an important strategy in the prevention and treatment of diabetic complications, and the search for tyrosinase inhibitors is important for the treatment of hyperpigmentation, development of skin-whitening agents, and use as preservatives in the food industry. On this basis, we sought to isolate and identify compounds with inhibitory activities against AR and tyrosinase. RH-MRPs were heated at 120 °C for 2 h and fractionated using four solvents: methylene chloride (MC), ethyl acetate, n-butanol, and water. The highest inhibitions were found in the MC fraction. The two compounds from this fraction were purified by silica gel column and preparative thin layer chromatography, and identified as 2-hydroxy-3-methylcyclopent-2-enone and furan-3-carboxylic acid. AR inhibition, tyrosinase inhibition, and ABTS⁺ scavenging (IC₅₀) of 2-hydroxy-3-methylcyclopent-2-enone were 4.47, 721.91 and 9.81 μg mL^-1, respectively. In this study, inhibitory effects of 2-hydroxy-3-methylcyclopent-2-enone isolated from RH-MRP were demonstrated on AR, tyrosinase, and its antioxidant activity for the first time. RH-MRP and its constituents can be developed as beneficial functional food sources and cosmetic materials and should be investigated further as potential functional food sources.

Unusual Inner-Salt Guaiazulene Alkaloids and bis-Sesquiterpene from the South China Sea Gorgonian Muriceides collaris

Three new guaiazulene alkaloids muriceidines A–C (1–3) and one new bis-sesquiterpene muriceidone A (4), were isolated from the South China Sea gorgonian Muriceides collaris. Muriceidines are the first examples structurally architected by guaiazulene coupling with an inner-salt Δ¹-pipecolic acid via a unique sp² methine-bridged linkage, and the bis-sesquiterpene was comprised by a guaiazulene and a indene units linked through a unprecedented carbon-carbon σ-bond between the high steric bridgehead carbon C-10 of guaiazulene moiety and C-2′ of indene moiety. The chiral compounds 2–4 were obtained initially as racemates and further separated by chiral HPLC methods. The inner-salt structures of 1–3 and absolute configurations of 2–4 were fully elucidated by calculated ¹³C NMR, ECD and OR with quantum chemical calculation methods. Compound 1 showed cytotoxicity against K562 cell lines with IC₅₀ value of 8.4 μM and antifouling activity against the larvae of the barnacle Balanus albicostatus with EC₅₀ value of 11.9 μg/mL and potent therapeutic index (LC₅₀/EC₅₀ = 3.66). Also the racemic (±)-3 showed cytotoxicities against both HL-60 and K562 cell lines with IC₅₀ values of 2.2 and 3.7 μM, respectively. A semisynthetic trial was performed to validate the proposed biosynthetic hypotheses.

Anti-inflammatory effect of sugar-amino acid Maillard reaction products on intestinal inflammation model in vitro and in vivo

The Maillard reaction is a nonenzymatic reaction between an amino acid and a reducing sugar that usually occurs upon heating. This reaction occurs routinely in cooking, generates numerous products, which are collectively referred to as Maillard reaction products (MRPs) contributing to aroma and color features. Advanced glycation end-products (AGEs) transformed from MRPs are participated in many types of inflammation reaction. In this study, various sugar-amino acid MRPs were prepared from three different amino acids (lysine, arginine, and glycine) and sugars (glucose, fructose, and galactose) for 1 h with heating at 121 °C. Treatment of lipopolysaccharide-stimulated RAW264.7 macrophages with the MRPs decreased nitric oxide (NO) expression compared to control without MRPs treatment. MRPs derived from lysine and galactose (Lys-Gal MRPs) significantly inhibited NO expression. The retentate fraction of Lys-Gal MRPs with cut-off of molecular weight of 3-10 kDa (LGCM) suppressed NO expression more effectively than did Lys-Gal MRPs. The anti-inflammatory effect of LGCM was evaluated using a co-culture system consisting of Caco-2 (apical side) and RAW264.7 or THP-1 (basolateral side) cells to investigate the gut inflammation reaction by stimulated macrophage cells. In this system, LGCM prevented a decreased transepithelial electrical resistance, and decreased both tumor necrosis factor-α production in macrophages and interleukin (IL)-8 and IL-1β mRNA expression in Caco-2 cells. In co-culture and in vivo dextran sulfate sodium (DSS)-induced colitis model study, we also observed the anti-inflammatory activity of LGCM.

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.

Detection of Maillard Reaction Product [5-(5,6-Dihydro-4H-pyridin-3-ylidenemethyl)furan-2-yl]methanol (F3-A) in Breads and Demonstration of Bioavailability in Caco-2 Intestinal Cells

[5-(5,6-Dihydro-4H-pyridin-3-ylidenemethyl)furan-2-yl]methanol, also called F3-A, has been isolated from hexose-lysine Maillard reaction (MR) models. Here we report on optimized conditions for the recovery of F3-A and concentrations found in bread. Recovery of F3-A was best achieved when samples were extracted with dichloromethane (DCM) at a solvent to sample ratio of 2:1 (v/v) after adjustment of the pH to 12. The amount of F3-A in whole wheat bread was significantly (P < 0.05) higher than that in white bread; bread crust contained a significantly (P < 0.05) higher amount of F3-A (0.9-7.8 μg/100 g) than the bread crumb (not detectable-3.5 μg/100 g); and toasting increased F3-A concentration with a range of not detectable to 6.0 μg/100 g in the control bread and 4.0 and 17.7 μg/100 g in the dark-toasted white sandwich bread and 100% whole wheat sandwich bread, respectively. The in vitro permeability of F3-A was measured using Caco-2 cell monolayer. The apparent permeability coefficient (P_app) of F3-A is (6.01 ± 0.35) × 10^-5 cm/s, which is similar to that of propranolol, a highly passive transcellular absorbed drug. In conclusion, the concentration of F3-A recovered in bread varies with the type of bread and degree of toasting, and F3-A is bioavailable.