Structure Of Melanoidins Research Articles

Differences in structure, stability and antioxidant activity of melanoidins from lager and ale beers

Beer melanoidins, the final products of the Maillard reaction (MR), play a critical role in determining the flavor stability of beer due to their antioxidant properties. This study investigated the structure, stability, and antioxidant activity of lager beer melanoidins (LBM) and ale beer melanoidins (ABM). The results revealed that ABM possessed a higher browning index and molecular weight, attribute to its relatively intense MR. However, this intensity also led to a more unfolded and disordered structure in ABM. Conversely, LBM outperformed ABM in the FAST index, thermal stability, and total antioxidant activity because the low alcohol content in lager beer reduced oxidation and thermal degradation while boosting the stability and antioxidant activity of melanoidins. As a result, it would offer a novel possibility to improve beer flavor stability by optimizing the brewing process to modify the structural and functional characteristics of melanoidins.

Comparison of characterization and composition of melanoidins from three different dried apple slices

The composition of melanoidins in dried apple that affects quality remains unclear. The composition and structure of melanoidins in dried apple slices by hot air drying (HAAM), instant controlled pressure drop drying (DICAM), and vacuum freeze-drying (FDAM) were investigated. It showed that the melanoidins were highly heterogeneous mixtures with a light-yellow color and blue-green fluorescence, belonging to polysaccharide-type melanoidins. Specifically, HAAM had a large molecular weight (929.5 g/mol) and wide molecular weight distribution, with more double-bond conjugated systems. DICAM (610.9 g/mol), possessing the strongest fluorescence intensity, was mainly composed of compounds with fewer π-conjugated structures and more electron-donating groups. As a control, the low level of Maillard reaction in FDAM resulted in the formation of the smallest molecular weight (458.6 g/mol) with weak fluorescence intensity. Moreover, 10 compounds were tentatively identified in apple melanoidins. This study provides the foundation for the future functional preparation of apple melanoidins.

Structure, spectral properties and antioxidant activity of melanoidins extracted from high temperature sterilized lotus rhizome juice

Melanoidins are complex macromolecular compounds closely associated with the browning phenomenon in high-temperature sterilized lotus rhizome juice (HTSL). This study aimed to preliminarily investigate the structural properties of melanoidins extracted from HTSL. Results showed that the average molecular weight of HTSL melanoidins ranged from 1.48 to 41.40 kDa. Medium and high molecular weight melanoidins were the main contributors to the brown color of HTSL. Sugars, proteins, and phenolics were present in HTSL, among which sugar was the most abundant, with glucose being the predominant monosaccharide in acid degradation products of melanoidins. Through fluorescence and ultraviolet spectral analysis, we found that the melanoidins contained carboxyl and carbonyl compounds, as well as furan and pyran heterocyclic compounds. The infrared spectra and nuclear magnetic resonance spectra revealed a prominent sugar absorption peak, indicating that sugar was the main component of the melanoidins of HTSL. Furthermore, in vitro antioxidant experiments showed that the antioxidant activity of melanoidins was significantly positively correlated with phenolic compounds. Our results indicated that there were differences in the structural properties of melanoidins fractions with different molecular weights. MW-H fraction significantly impacted the color and antioxidant activity of HTSL.

The Differences in the Composition of Maillard Components between Three Kinds of Sauce-Flavor Daqu

Sauce-flavor Daqu is a saccharifying and fermenting agent for sauce-flavor baijiu. Three kinds of Daqu (White Daqu (WQ), Yellow Daqu (YQ), and Black Daqu (BQ)) with different qualities are formed owing to the stacking fermentation. Maillard reaction is an important factor that causes significant differences among the three kinds of high-temperature Daqu, which is also an important source of flavor substances. However, there is a lack of research on the composition differences of Maillard reaction products in the three types of Daqu. In our study, HS-SPME-GC/MS, Py-GC/MS, and high-throughput sequencing were used to investigate the small molecule volatile Maillard substances, melanoidin (macromolecular Maillard substance) composition, and microbial community of three kinds of Daqu. The results showed that there were significant differences in the composition of Maillard products (furans, pyrazines, and melanoidin structure) between the three kinds of Daqu. The melanoidin was mainly composed of furans, pyrrolopyrazines, phenols, and indoles, the proportions of which were different in the three types of Daqu. BQ contained more Maillard products, making the melanoidin more complex. Kroppenstedtia, Monascus, and Thermoascus were the biomarkers of BQ, which contribute to the Maillard reaction. This study is of great significance to further deepen the understanding of the formation mechanism of BQ.

Elucidating the structure of melanoidins derived from biscuits: A preliminary study.

Melanoidins present important physiological activities, but their structure is largely unknown. The objective of the present work was to reveal the physicochemical characteristics of biscuit melanoidins(BM) prepared under high temperature(HT) and low temperature(LT) conditions (150°C/25min-100°C/80min respectively). BM were characterised and analysed by differential scanning calorimetry, X-ray and FT-IR. Moreover, the antioxidant capacity and the zeta potential were determined. The phenolic content of HT-BM was higher than that of LT-BM (19.5±2.6% vs 7.8±0.3% respectively, p≤0.05) and the antioxidant capacity determined by ABTS/DPPH/FRAP (p≤0.05) was greater. Also, HT-BM presented a 30% increase in crystal structure compared to LT-BM according to X-ray analysis. The magnitude of the negative net charge was significantly higher in HT-BM (-36.8±0.6) than in LT-BM (-16.8±0.1)(p≤0.05). FT-IR analysis confirmed the presence of phenolic and intermediate Maillard reaction compounds bound to the HT-BM structure. In conclusion, the different heating treatments applied to biscuits led to differences in the melanoidin structure.

Formation of Recalcitrant Compounds during Anaerobic Digestion of Thermally Pre-Treated Sludge: A Critical Macromolecular and Structural Study.

Thermal hydrolysis, when used as pre-treatment, enhances the anaerobic digestion of sewage sludge; moreover, due to the high temperature normally applied, undesirable recalcitrant compounds via Maillard reactions may also be formed. However, although the appearance of these recalcitrant compounds is widely reported, more information on the formation, structure, and fate of these compounds is still needed. This study was focused on understanding the amount and whereabouts of such compounds during the anaerobic digestion process with thermal pre-treatment in soluble and total phase and advance in its structural identification by analyzing their infrared (IR) spectra. It was found that, even with the improved methane production and COD degradation, at 165 °C for 30 min, humic-like compounds are formed which could not be degraded at the anaerobic digestion step. These compounds account for 25% of the original sludge. Infrared spectroscopy proved to be a powerful technique, permitting their differentiation from the natural humic-like compounds. This research provides new information about the structure of melanoidins at every stage of the thermal hydrolysis pre-treatment and how they contribute to the dissolved organic nitrogen.

Method development for the identification, extraction and characterization of melanoidins in thermal hydrolyzed sludge

Melanoidins, the brown late-stage Maillard reaction products, are responsible for color development and refractoriness in thermal hydrolyzed sludge (THS), causing negative effects on wastewater treatment. This study aimed to develop a methodology for the identification, isolation and preliminary characterization of the THS melanoidins. After thermal hydrolysis, the formation of melanoidins were confirmed by physicochemical indicators and excitation-emission matrix fluorescence analysis. The macroporous resin adsorption method was adopted to successfully extract melanoidins from THS with high recovery and selectivity. The main chemical components of the extracted melanoidins were carbohydrate (23.1 %), protein (43.8 %) and phenol (13.7 %), and the C/N was 4.5. In addition, furans, alcohols and sulfur-containing volatile substances were detected by pyrolysis-gas chromatography–mass spectrometry. Fourier transform infrared spectroscopy determined that functional groups such as CO, CN, NH, C-O-C, amide I and phenyl were present in the structure of THS melanoidins, and nuclear magnetic resonance spectroscopy indicated the formation of heterocyclic macromolecular structures. Their formation pathways were speculated to involve the cross-linkage of low-molecular-weight components (e.g. proteins, Amadori and Schiff base compounds) and the polymerization of heterocyclic units (e.g. furans, pyroles and pyrazines). The above results clarify the fundamental characteristics of the melanoidins formed during sludge thermal hydrolysis and will help improve subsequent research on melanoidins control.

Structure and functional characterization of melanoidins from crystal malt

Structure and functional characterization of melanoidins from crystal malt

Structure, chemical stability and antioxidant activity of melanoidins extracted from dark beer by acetone precipitation and macroporous resin adsorption

Melanoidins contribute to the sensory and functional properties of dark beers. The structure, stability, and antioxidant activity of acetone precipitation extracted melanoidins (APE-M) and macroporous resin adsorption extracted melanoidins (MAE-M) from dark beer were investigated. The structural properties of melanoidins were characterized using Fourier transform infrared spectroscopy (FTIR), circular dichroism (CD), scanning electron microscopy (SEM), and the solution storage stability, thermal behavior and antioxidant activity of melanoidins in dark beers were evaluated. MAE-M revealed more sophisticated structures than APE-M, including more concrete characteristics of Maillard reaction (MR) products in FTIR (1550–1500 cm−1), more ordered secondary structure in CD spectra, and thinner slices as well as more microspheres in SEM. The solution storage stability assay showed that certain factors, including 55 °C, 5 % v/v ethanol, UV light, and H2O2 solution, accelerated the degradation of melanoidins. The moderate extraction process of MAE-M performed a minor enthalpy change (−92.28 Jg−1) in the DSC-TG test than that of APE-M (−319.41 Jg−1). Furthermore, the ABTS and DPPH radical scavenging activities and the FRAP assay demonstrated that the antioxidant activity of MAE-M was almost twice that of APE-M. In general, MAE was more effective in extracting beer melanoidins while maintaining its accurate structure and profitable antioxidant activity than APE.

Dietary Melanoidins from Biscuits and Bread Crust Alter the Structure and Short-Chain Fatty Acid Production of Human Gut Microbiota.

Melanoidins are the products of the Maillard reaction between carbonyl and amino groups of macromolecules and are readily formed in foods, especially during heat treatment. In this study we utilized the three-stage Human Gut Simulator system to assess the effect of providing melanoidins extracted from either biscuits or bread crust to the human gut microbiota. Addition of melanoidins to the growth medium led to statistically significant alterations in the microbial community composition, and it increased short-chain fatty acid and antioxidant production by the microbiota. The magnitude of these changes was much higher for cultures grown with biscuit melanoidins. Several lines of evidence indicate that such differences between these melanoidin sources might be due to the presence of lipid components in biscuit melanoidin structures. Because melanoidins are largely not degraded by human gastrointestinal enzymes, they provide an additional source of microbiota-accessible nutrients to our gut microbes.

Interest of Coffee Melanoidins as Sustainable Healthier Food Ingredients.

Coffee melanoidins are generated by the Maillard reaction during the thermal processes occurring in the journey of coffee from the plant to the cup (during drying and roasting). Melanoidins, the brown pigments formed as the end products of this reaction, have been reported in cascara, silverskin, spent coffee grounds, and coffee brew. The latter is one of the main natural sources of melanoidins of the daily diet worldwide. However, their presence in coffee by-products has been recently described. These complex macromolecules possess multiple health-promoting properties, such as antioxidant, anti-inflammatory, dietary fiber effect, and prebiotic capacity, which make them very interesting from a nutritional point of view. In addition, they have a great impact on the sensory profile of foods and their acceptance by the consumers. The present study is a descriptive, narrative, mini-review about the nature, structure, digestibility, properties (sensory, nutritional, and health-promoting), safety and regulatory status of melanoidins from the coffee brew and its by-products with a special emphasis on the latter.

Browning and pigmentation in food through the Maillard reaction.

The Maillard reaction was discovered in 1912 by Louis C. Maillard when he observed the browning phenomena with aroma formation in a heated solution containing a sugar and an amino acid. The Maillard reaction starts from the reactions between carbonyl groups of various sugars and amino groups of amino acids/ proteins, following the formation of intermediate compounds or poly-carbonyl compounds, which further react with each other and amino acids/proteins. Through various chemical reactions such as condensation, polymerization, degradation, cyclization etc., color and aroma are formed. The imparting of brown color is mainly attributed to melanoidins. However, the chemical structure of melanoidins remains unclear because melanoidins are complex and heterogeneous polymers. On the other hand, various kinds of low-molecular-weight pigments formed through the Maillard reaction have been isolated and their structures have been identified. Even though the contribution of each pigment is small, the recognition of color is cumulative. In some case, these pigments form brown polymers or significantly contribute to the total color of a model solution. These chemically clear information gives us a novel aspect for an overview of browning or pigmentation through the Maillard reaction. Graphical abstract.

Characterisation of melanoidins derived from Brewers' spent grain: new insights into their structure and antioxidant activity

SummaryMelanoidins, formed at the final stages of Maillard reaction (MR), present important physiological activities, but their structure and reaction pathways are largely unknown in real food systems. In the present work, these bioactive compounds derived from Brewers' spent grain (BSG) with different roasting degrees were analysed. Results showed that BSG could be considered a more important source of bioavailable antioxidants than what it was reported in previous studies. During MR development, proteinic structures are partially lost while a carbohydrate skeleton is formed. The crystallinity is reduced and the structure sets into a conformation with a peak centred at 20° (2θ), stable with the increasing thermal treatment. While MR continues the development of browning compounds increases, the antioxidant activity rises and phenolic compounds are bind to the melanoidin structure (P ≤ 0.05). Moreover, FTIR analysis showed a dominance of α‐glyosidic linkage and the presence of furanose rings in the melanoidins structure.

Kurozu melanoidin, a novel oligoglucan-melanoidin complex from Japanese black vinegar, suppresses adipogenesis in vitro

• This study identifies an anti-adipogenic factor in the black vinegar kurozu. • The factor, kurozu melanoidin (KZM), consists of an oligoglycan and a melanoidin. • KZM inhibits adipocyte differentiation of 3 T3-L1 cells in vitro . • KZM may, in part, account for anti-obesity effects of kurozu. The black vinegar “kurozu” has an anti-obesity potential, but its active principle is unknown. Here, we isolate and characterize a novel oligoglucan-melanoidin complex, designated kurozu melanoidin (KZM), that suppresses adipogenesis in vitro . KZM was isolated by organic solvent extraction, followed by size-exclusion chromatography. Its average molecular mass was estimated to be 1,090 ± 30 Da using polyethylene glycols as standards. The combination of spectroscopic and chemical analyses revealed the presence of an oligoglucan and a melanoidin structures in KZM. The glucan moiety consisted mainly of 1 → 4 linkage. The MALDI-TOF-MS analysis identified an array of ion peaks that differed in m / z by ~ 162.055 [C 6 H 12 O 6 − H 2 O], indicating a variation of glucan chain length. Prominent signals around m / z 500–600 that were unassignable to glucan units suggested ion peaks for the melanoidin moiety. KZM significantly suppressed adipogenesis of 3T3-L1 preadipocytes at 100 μM.

Use of NMR techniques to investigate the changes on the chemical composition of coffee melanoidins

We aimed to investigate the effect of roasting time on the chemical structure of coffee melanoidins and how the incorporation of chlorogenic acids (CGA) occurs using one-dimensional and two-dimensional Nuclear Magnetic Resonance spectroscopy (1D and 2D NMR). 1H NMR spectra showed large signals suggestive of proteins and polysaccharides due to their reduced intrinsic mobility. The spectra also revealed that melanoidins molecular weight increased during intermediate times of roasting and slightly decrease thereafter. In roasted samples, HSQC 2D NMR spectra showed 1H,13C cross-peaks from aromatic and olefinic groups of CGA. COSY 2D NMR experiments without and with enrichment of 5-caffeoylquinic acid standard allowed the detection of all 1H,1H cross-peaks from CGA, suggesting their intact incorporation, which was confirmed by a 1H NMR experiment using a T2-filter to remove large signals from macromolecules. Together, our results show that CGA are linked to coffee melanoidins by strong chemical bonds.

In Vitro Antioxidant Activity and FTIR Characterization of High-Molecular Weight Melanoidin Fractions from Different Types of Cocoa Beans.

Melanoidins from real foods and model systems have received considerable interest due to potential health benefits. However, due to the complexity of these compounds, to date, the exact structure of melanoidins and mechanism involved in their biological activity has not been fully elucidated. Thus, the aim of this study was to investigate the total phenolic content, antioxidant properties, and structural characteristics of high-molecular weight (HMW) melanoidin fractions isolated by dialysis (>12.4 kDa) from raw and roasted cocoa beans of Criollo, Forastero, and Trinitario beans cultivated in various area. In vitro antioxidant properties of all studied HMW cocoa fractions were evaluated by four different assays, namely free radical scavenging activity against DPPH• and ABTS•+ radicals, ferric reducing antioxidant power (FRAP), and metal-chelating ability. Additionally, the structure–activity relationship of isolated HMW melanoidin fractions were analyzed using attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). The results show that roasting at a temperature of 150 °C and a relative air humidity of 0.3% effectively enhances the total phenolics content and the antioxidant potential of almost all HMW cocoa melanoidin fractions. The ATR-FTIR analysis revealed that the various mechanisms of action of HMW melanoidins isolates of different types of cocoa beans related to their structural diversity. Consequently, the results clearly demonstrated that HMW cocoa fractions isolated from cocoa beans (especially those of Criollo variety) roasted at higher temperatures with the lower relative humidity of air possess high antioxidant properties in vitro.

Melanoidins from Chinese Distilled Spent Grain: Content, Preliminary Structure, Antioxidant, and ACE-Inhibitory Activities In Vitro.

Distilled spent grain (DSG), as the major by-product of baijiu making, contains melanoidins generated via the Maillard reaction. In this study, four melanoidin fractions (RF1‒RF4) were isolated successively from dried DSG (DDSG) using sodium hydroxide solution and water as extractants, and the content, preliminary structure, and ACE-inhibitory activities in vitro of melanoidins were first investigated. The antioxidant activity was also evaluated. The results indicated that the total content of melanoidins was 268.60 mg/g DDSG dry weight (dw) using a model system of glucose and serine as standard, and RF4 showed the highest content of melanoidins (174.30 mg/g DDSG dw). Functional groups like C=O, N‒H, C‒N, O‒H, C‒H, C‒O, C-C, and ‒C‒CO‒C‒ were present in the structure of melanoidins from RF4, as determined by Fourier transform infrared (FT-IR) assay. The highest antioxidant activities, as assessed by 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS•+), ferric-reducing antioxidant power (FRAP), and 1,1-diphenyl-2-picrylhydrazyl radical (DPPH) assays, and the highest angiotensin-converting enzyme (ACE) inhibitory activity (95.92% at 2 mg RF4/mL) were also exhibited by RF4. The RF4 was further fractionated by ultrafiltration based on molecular weight (MW). The more than 100 kDa melanoidins (RF4-6) exhibited the highest yield and antioxidant activity. The 3‒10 kDa melanoidins (RF4-2) were more efficient in ACE-inhibitory activity. Our study could raise awareness of the DDSG as a value-added resource.

High Hydrostatic Pressure-Assisted Extraction of High-Molecular-Weight Melanoidins from Black Garlic: Composition, Structure, and Bioactive Properties

Melanoidin is one of the most important ingredients in black garlic due to the high nutritional values and biological functions. High hydrostatic pressures from 200 to 500 MPa were employed to extract the melanoidins from black garlic for improving the extraction efficiency and enhancing the activities. The results indicated that total phenolics, flavonoids, and sugar yields were all increased when pressure was applied and the antioxidant and overall reducing power was maximized. The bioactive properties of protein tyrosine phosphatase 1B, angiotensin-converting enzyme, and trypsin inhibitory activities were also enhanced compared with the control. Moreover, FT-IR spectroscopy indicated high pressure altered the melanoidin structures to different degrees. It was found that an application of 300 MPa for 5 min was the optimal treatment protocol under all operating conditions.

Basic Structure of Melanoidins Formed in the Maillard Reaction of 3-Deoxyglucosone and γ-Aminobutyric Acid.

Melanoidins are formed in foods during processing through the Maillard reaction between carbohydrates and amino compounds. The aim of this study was to draw conclusions about the formation mechanism and the structure of melanoidins formed at low water contents and low temperatures. In the Maillard reaction of d-glucose and γ-aminobutyric acid at low water contents 3-deoxyglucosone is the most important intermediate. Therefore, we used the reaction of 3-deoxyglucosone with γ-aminobutyric acid or β-alanine as a simplified model system. The degradation of 3-deoxyglucosone and the color formation of the formed melanoidins were determined. In addition, the reaction mixture was analyzed with high-resolution mass spectrometry and a Kendrick analysis was applied. Oligomers consisting of up to four molecules of 3-deoxyglucosone and three amino acids and their respective dehydration products with furanoidic structure were detected. The melanoidin structure of C-C linked monomeric units postulated by Kroh et al. could be confirmed.

Chlorogenic acid–arabinose hybrid domains in coffee melanoidins: Evidences from a model system

Arabinose from arabinogalactan side chains was hypothesized as a possible binding site for chlorogenic acids in coffee melanoidins. To investigate this hypothesis, a mixture of 5-O-caffeoylquinic acid (5-CQA), the most abundant chlorogenic acid in green coffee beans, and (α1→5)-l-arabinotriose, structurally related to arabinogalactan side chains, was submitted to dry thermal treatments. The compounds formed during thermal processing were identified by electrospray ionization mass spectrometry (ESI-MS) and characterized by tandem MS (ESI-MSn). Compounds composed by one or two CQAs covalently linked with pentose (Pent) residues (1–12) were identified, along with compounds bearing a sugar moiety but composed exclusively by the quinic or caffeic acid moiety of CQAs. The presence of isomers was demonstrated by liquid chromatography online coupled to ESI-MS and ESI-MSn. Pent1–2CQA were identified in coffee samples. These results give evidence for a diversity of chlorogenic acid–arabinose hybrids formed during roasting, opening new perspectives for their identification in melanoidin structures.