Application of capillary zone electrophoresis to the study of food and food-model melanoidins

Different water soluble melanoidins have been isolated from both heated (100 °C/24 h) carbohydrate/amino acid model systems and medium-roasted coffee. Capillary zone electrophoresis (50 mM sodium tetraborate, pH 9.3) has been applied to determine the saturated or aromatic character of the isolated melanoidins. Melanoidins obtained from different solutions after an equivalent heating treatment possess similar apparent molecular weight but different charge/mass ratio, suggesting differences in their degree of saturation. Melanoidins isolated from model systems containing lysine showed a lower saturation than those isolated from either coffee or other model systems containing glycine, alanine or tryptophan. Depending on the type of amino acid as reactant, melanoidins could be mainly constituted by a stable structure or common core which is changing according to the thermal conditions applied through a more saturated structure.     

ANTIMICROBIAL ACTIVITY OF MELANOIDINS

Melanoidins are high molecular weight compounds formed during the final stage of the Maillard reaction. Melanoidins have been studied in recent years because of their nutritional, biological and health implications, apart from their role on the stability during processing and shelf life of foods. A fast and robust microtiter plate‐based assay for a quantitative screening of the antimicrobial activity of melanoidins was applied. Oxytetracyclin was used as reference for assessing the antimicrobial activity of different melanoidins isolated from model systems. The minimum inhibitory concentration was calculated, and activity was related to the antimicrobial activity of an oxytetracyclin solution (100 µg/L). Glucose–lysine melanoidin exerted the highest antimicrobial activity, being at a concentration of 1 mg/mL, equivalent to an oxytetracyclin solution of 170 µg/L.     

Bread crust melanoidins as potential prebiotic ingredients

Melanoidins are the final products of the Maillard reaction. They are a heterogeneous mixture of compounds characterized by brown color and high molecular weight. The physiological properties of melanoidins have been widely investigated and there is a general consensus on their poor digestibility and bioavailability. In vitro studies on food melanoidins are in many cases limited by their poor water solubility. This problem was recently overcome for bread melanoidins using an enzymatic digestion procedure. Bread melanoidins are constituted by low-molecular-weight, colored compounds linked to the gluten polymer. In this work, melanoidins from different bread types were investigated for their potential prebiotic activity by a static batch culture. Results showed that anaerobic bacteria, particularly Bifidobacteria strains, are able to use bread melanoidins as carbon source. The bacterial growth is different for the various types of melanoidins samples indicating that starting materials and processing conditions have a strong influence on the prebiotic potential of bread melanoidins. In all cases the bacterial growth obtained using bread melanoidins is lower than that previously observed using melanoidins from other sources, such as coffee silverskin.     

烟道气饱充工艺吸附色素模型的建立

以粗糖浆中普遍存在的美拉德反应色素和蔗糖因高温焦化产生的色素一类黑精为研究模型,通过红外光谱定性分析了类黑精色素分子的分子特性,同时考察了类黑精色素分子的zeta电位分布情况,经烟道气饱充后,采用电子扫描电镜和聚焦光束反射测量仪（FBRM）分别分析并研究了不同分子量的类黑精色素对碳酸钙颗粒形貌以及粒径分布的影响,从理论上解释了类黑精分子模型对烟道气饱充效果的影响。     

Functional properties of melanoidins: In vitro antioxidant,antimicrobial and antihypertensive activities

Melanoidins formed at the last stage of the Maillard reaction have been pointed out to possess certain functional properties such as antioxidant, antimicrobial and antihypertensive activities. In order to gain more insights on these functional properties different soluble melanoidins and melanoidin fractions isolated from several amino acid–glucose model systems has been analysed In the case of antioxidant and antimicrobial properties, low molecular weight compounds bounded to melanoidins (BMC fraction) exerts antioxidant and antimicrobial activities usually higher than those of the pure melanoidins to whom they are linked. Contrary, in the case of antihypertensive activity it has been found that the main activity is related to the melanoidin core, not to BMC fraction. In addition it has been found no correlation, except for ABTS assay, among colour and antioxidant, antimicrobial or antihypertensive activity, supporting the idea that melanoidin chromophores are not responsible for these actions.     

Melanoidins produced by the Maillard reaction: Structure and biological activity

Melanoidins are compounds generated in the late stages of the Maillard reaction from reducing sugars and proteins or amino acids during food processing and preservation. Recently the effects of melanoidins on human health and the chemical characterisation of the beneficial components have gained a lot of attention. Food melanoidins have been reported to be anionic, coloured compounds and some of their key chromophores have been elucidated. The antioxidant activity and other biological effects of melanoidins from real foods and model systems have been widely studied. Despite this, very few different melanoidin structures have actually been described, and specific health effects have yet to be linked to chemically distinct melanoidins. The variety of different Maillard reaction products formed during the reaction, in conjunction with the difficulty in purifying and identifying them, makes a thorough analysis of melanoidins challenging. This review provides a comprehensive look at what is known to date about melanoidin structure, the formation mechanism for these compounds, and the biological properties related to the beneficial health effects of melanoidins.     

Influence of model melanoidins on calcium-dependent transport mechanisms in smooth muscle tissue

Melanoidins obtained from L-arginine and D-glucose (MW > 3500 Da) were tested for their ability to influence the contractility of gastric smooth muscles. A study within the range 0.1-10 mg/mL revealed that at low concentrations, the melanoidins provoked concentration-dependent contraction, whereas a muscle relaxation was registered at high concentrations. The contraction was preceded by changes in the calcium membrane current as measured by single sucrose-gap method and significantly attenuated by the calcium channel blockers D-600 and nifedipine. Measurements with Ca(2+)-selective electrode showed that the melanoidins decreased the concentration of ionized Ca(2+ )in tissue bath in concentration-dependent manner. Experiments carried out in solutions with lower than normal Ca(2+) concentration and using melanoidins preliminary saturated with Ca(2+ )confirmed that the calcium chelation by melanoidins was a key contributing cause for the development of relaxant response. The results obtained showed that the melanoidins could influence the contractility of smooth muscles through at least two pathways: at low concentrations they caused depolarization and activation of L-type calcium channels, stimulated the Ca(2+ )influx, and provoked contraction, whereas at high concentrations calcium binding by melanoidins led to significant depletion of extracellular calcium ions and contributed to the relaxation process observed.     

食品中类黑精的研究进展

类黑精是指碳水化合物与带有自由氨基的含氮化合物反应产生的棕色的高分子量美拉德反应产物,在烘培产品、啤酒、酱油、醋等食品中普遍存在。近年来,类黑精抗氧化、抗诱变、抗癌、抗菌、抗高血压等功能逐渐成为人们关注的焦点。本文综述了目前国内外关于类黑精结构、理化性质及分离纯化方法等方面的研究,并综述了其对人类健康有影响的生理活性,以期为进一步研究食品中类黑精的营养保健功能奠定基础,也为食品中类黑精的检测方法建立提供科学依据。     

Pro-oxidative effects of melanoidin–copper complexes on isolated and cellular DNA

High molecular weight Maillard reaction products (melanoidins) are described to possess metal-chelating properties. Whereas in food systems, this ability contributes to antioxidant properties, the consequences on biological systems are not quite clear. The study was aimed to evaluate the implication of metal complexation by melanoidins on DNA damage. Melanoidins prepared with d-glucose and different l-amino acids under water-free reaction conditions were charged with cupric ions. The effect on isolated DNA was investigated by the PM2 assay and on cellular systems in the human colon carcinoma cell line HCT-116 by alkaline unwinding. Independent of the amino acid composition, pure melanoidins (MW >14 kDa) did not cause significant DNA damage. By charging melanoidins with Cu²⁺ ions, a considerable DNA strand breaking activity was detectable, which was again amplified in an oxidative milieu (addition of hydrogen peroxide). Since Cu²⁺ normally does not provoke the formation of reactive oxygen species (ROS) via Fenton-type reaction, the results obtained have to be attributed to reducing properties of melanoidins. Thus, in melanoidin–copper complexes redox cycling may take place leading to Cu⁺ which subsequently undergoes Fenton-type and Haber–Weiss reactions. As a consequence, ROS are formed, which may explain the generation of DNA strand breaks.     

Peroxyl radical scavenging activity of melanoidins in aqueous systems

Melanoidins are widely distributed in our diet, due to home or industrial processing of foods. Until recently, melanoidins were considered to be an inert, brown-coloured polymeric component. However, recent research into their nutritional, physiological, and functional properties has suggested that they have antioxidant properties, and we address this issue in this work. A sensitive procedure for assessing the inhibition of lipid peroxidation by melanoidins in watery media has been developed. Main drawbacks and critical steps of the procedure are discussed. Melanoidins can be classified according to the number of peroxyl radicals trapped per molecule. Coffee and sweet wine melanoidins show higher antioxidant activity than melanoidins isolated from beer. For the first time, a linear relationship between the peroxyl radical scavenging activity and the chromophore residues in the melanoidin skeleton responsible for browning has been established.     

Isolation and characterisation of a coffee melanoidin fraction

BACKGROUND: Melanoidins contribute to the colour and flavour of coffee brews and are also reported to be physiologically active components. However, structural information about coffee melanoidins is rare and current models are supported by few data. RESULTS: Using hydrophobic interaction chromatography (HIC), melanoidin fractions were isolated from different high‐molecular‐weight fractions of coffee brews obtained by ultrafiltration. Generally, melanoidin fractions isolated by HIC showed three‐ to fourfold higher antioxidant activities than the remaining high‐molecular‐weight material in the ultrafiltration fractions. Melanoidin fractions showed an intense brown colour: aqueous solutions with a concentration as low as 40 µg mL^?1 were distinguishable from pure water. The melanoidin fractions contained less than 6% each of releasable carbohydrates and amino acids. The molecular masses of the melanoidins were estimated to be between 3 and 22 kDa, irrespective of the ultrafiltration fraction from which they were obtained. Two‐dimensional nuclear magnetic resonance studies revealed an enrichment of phenolic/aromatic/olefinic structural units and did not support the idea of intact ferulate or caffeate moieties integrated into the melanoidin polymer. CONCLUSION: These studies support melanoidin models describing them as high‐molecular‐weight compounds themselves as opposed to models describing them as low‐molecular‐weight chromophores bound to polysaccharides or proteins. Phenolic constituents are more likely integrated into melanoidins as condensed phenolics than as intact hydroxycinnamates from chlorogenic acids. Copyright © 2008 Society of Chemical Industry     

Estimation of dietary intake of melanoidins from coffee and bread

Melanoidins are defined as polymeric high molecular weight, brown-coloured Maillard reaction end-products, containing nitrogen. They escape digestion and pass through the upper gastrointestinal tract and can interact with the different microbial species present in the colon. Major dietary sources of melanoidins are coffee and bread crust. Both coffee and bread crust melanoidins can be fermented by the human hindgut microflora thus sharing some of the properties attributed to dietary fibre. Despite the emerging positive physiological properties of such dietary constituents their intake has not been estimated yet. To this aim melanoidin content in different type of coffee brews, bread and dry biscuits was determined by sequential ultrafiltration and enzymatic digestion. Despite some drawbacks and limiting steps in the calculation, such as the lack of a reference material, an educated guess on the dietary intake of melanoidins has been put forward. Data indicated that the intake of coffee melanoidins ranged between 0.5 to 2.0 g per day for moderate and heavy consumers, respectively. For bread and dry biscuits an intake in the ranges of 1.8-15.0 and 3.2-8.5 g per day has been calculated. These figures suggest that a realistic estimation of melanoidins dietary intake for general population would be close to 10 g per day considering all the possible alimentary sources.     

Reactivity of acrylamide with coffee melanoidins in model systems

Coffee and its substitutes have been described as complex matrices for acrylamide (ACR) analysis due to both analytical interferences and ACR instability in the matrix. Melanoidins are multifunctional and biochemically active polymers which are formed in large extent during coffee roasting. Model systems composed of ACR (elimination studies) or glucose-asparagine (ACR formation/elimination studies) with/without melanoidins was heated at 180 °C. Washed sea sand and cellulose microcrystalline were used as matrix. Coffee melanoidins had a direct influence on the fate of ACR under heating, while the effect was not observed at room temperature. In addition, ACR decrease was also related to the reaction time and the initial amount of melanoidins in the media, where clearly a dose-response was observed. In contrast, pH (from 3.5 to 7.0) had no significant effect on ACR reactivity towards melanoidins. It is hypothesized that nucleophilic amino groups of amino acids from the proteinaceous backbone of melanoidins react via the Michael addition reaction with ACR, although the exact mechanism is unknown. Then, melanoidins could modulate the reaction pathways of ACR formation and elimination during coffee roasting and serve as acrylamide-mitigation substance.     

Investigation on the extractability of melanoidins in portioned espresso coffee

Coffee melanoidins have attracted interest as a result of its potential health benefits. This investigation aims to elucidate the extraction behavior of melanoidins and their populations during the preparation of portioned espresso coffee and its relationship with the antioxidant activity of the coffee brew. Filter-paper pods, FAP capsule, and clone capsule containing light roasted coffee have been investigated. An accumulative fractionation approach has applied to model the extraction kinetics of melanoidins, melanoidin populations, browning, chlorogenic acids (CGA), and antioxidant activity. Melanoidins were very efficiently extracted in clone capsules since less than 9 s was necessary to extract the 50% of the melanoidin content as compared with pods and FAP capsules, and the kinetic of extraction is slower than CGA. The extraction profile of melanoidins and browning fitted better with the antioxidant capacity than CGA and total solids profile. Melanoidin populations were obtained according to ethanol solubility. Total melanoidin content and the ratio between melanoidin populations did not change during extraction volume for espresso coffee. Melanoidin populations soluble at 75% ethanol showed the highest antioxidant activity. However, melanoidins with higher antioxidant activity are extracted at higher volumes. This investigation could make possible the adjustment of the technological requirements of espresso coffeemakers to produce an espresso coffee with high levels of beneficial compounds.     

Fermentation of heated gluten systems by gut microflora

The Maillard reaction causes changes to protein structure and occurs in foods mainly during thermal treatment. Melanoidins, the final products of the Maillard reaction, may enter the gastrointestinal tract, which is populated by different species of bacteria. In this study, melanoidins were prepared from gluten and glucose. Their effect on the growth of faecal bacteria was determined in culture with genotype and phenotype probes to identify the different species involved. Analysis of peptic and tryptic digests showed that low molecular mass products are formed from the degradation of melanoidins. Results showed a change in the growth of bacteria. This in vitro study demonstrated that melanoidins, prepared from gluten and glucose, affect the growth of the gut microflora.     

Biological Properties of Melanoidins: A Review

Melanoidins are brown, high molecular weight products of Maillard reaction, which takes place during thermal processing of food. They are formed in a multistage reaction between reducing sugars and compounds possessing free amino groups and found in roasted coffee, bakery products, cooked meat, beer, honey, sweet wine, processed tomatoes, and fiber. Nowadays, melanoidins have attracted a lot of attention, not only as a functional food ingredient, but also as a potential pro-healthy dietary supplement. In this field, their antioxidant, antimicrobial, anticancer, and detoxifying activity have been described. Based on recent research developments, an overview of the biological properties of melanoidins with implications for human health is presented.     

美拉德反应产物类黑精的研究进展

美拉德反应是食品加工、贮藏及烹饪过程中普遍存在的重要反应,其终产物类黑精是一类结构复杂的高分子量化合物,其不但赋予食品色泽和风味品质,且具有多种功能活性,多年来始终是食品科学领域研究的热点。因此,本文在阐述美拉德反应过程的基础上,综述了类黑精的来源、制备过程、分离纯化、理化特性与结构表征以及功能活性的研究进展,并对其研究价值进行了展望,以期为食品类黑精的相关研究及应用开发提供参考。     

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

Melanoidins, 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.     

食品类黑精的研究进展

类黑精是美拉德反应后期形成的一类棕褐色的、结构复杂的大分子化合物，在食品中普遍存在。大量的研究显示，食品类黑精具有明显的抗氧化、抗诱变、抗癌、抗菌以及结合风味物质等功能。本文就近年来国内外有关食品类黑精的研究成果作一简单介绍。     

蛋白黑素的研究进展

蛋白黑素是美拉德反应的终产物,在食品烹制及生产加工过程中生成,广泛分布于饮食当中。本文对蛋白黑素的结构、安全性、呈味机制、检验方法以及消除等方面的研究进展做以全面论述。