Influence of α-dicarbonyl compounds to the molecular weight distribution of melanoidins in sucrose solutions: part 1

The correlations between formation of melanoidins and the content of α-dicarbonyl compounds and colour formation were studied in Maillard reaction model sucrose solutions at high treating temperatures (130 °C) corresponding to the industrial sucrose processing. Molecular weight distribution was determined by gel permeation chromatography (GPC) and α-dicarbonyls as high reactive intermediates of the Maillard reaction were detected by RP-HPLC and GC/MS. Referring to formation of melanoidins, new knowledge could be gained. The investigations clearly point out, that individual α-dicarbonyls are involved in formation of specific molecular weight fractions. 3-Deoxyhexosulose (3-DH) and methylglyoxal are the important α-dicarbonyl compounds in thermal-treated sucrose solutions. A low molecular weight fraction with a molecular weight range of <5,800 g/mol preferably occurs when 3-DH is formed in high concentrations. The high increase in intensity of a low molecular weight fraction is combined with a strong colour formation. In contrast to 3-DH, methylglyoxal promotes the formation of high molecular weight fractions between 6,600 g/mol and approximately 17,000 g/mol. Furthermore, model solutions with a high intensity of high molecular weight fractions show an early colour formation during the starting period of the reaction. Indeed, this early browning is not as intensive as the colour formation caused by the low molecular weight fraction during the later stage of the browning reaction. Out of this, 3-DH can be regarded as the most important intermediate for an intensive colour formation in sucrose solutions.     

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.     

Roasting of malt and xanthohumol enrichment in beer

The use of commercial roasted malts increases the content of the hop polyphenol xanthohumol (XN) in beer. This carrier effect is caused by high molecular melanoidins from roasted malt. Three roasting trials with different malts were performed in order to study the development of XN enrichment of wort and beer in laboratory and brewing trials. Different colour measurements, malt and flavour analysis, radical formation and antioxidative activity of selected samples were carried out. Furthermore, sensory tests of beers were conducted. During roasting the XN and isoxanthohumol enrichment in wort and beer rose with the roasting intensity of malt until it reached a maximum. The XN content in wort increased linearly with the colour of wort made from the malt samples. In PVPP-treated worts and in filtered beers, the XN content increased exponentially with the colour. After passing through a maximum, both the colour value and XN content in wort and beer decreased. Interestingly, the colour losses were more intensive than the losses of XN in worts and beers. The development of radical formation and the reducing power was linked during roasting. That means reducing groups of melanoidins are responsible for reducing power and prooxidative properties of malts. These functional groups of melanoidins are involved in the development of XN enrichment properties, because a linear correlation between these parameters was found. In conclusion, the roasting regimes showed potential for the development of special malt for the XN enrichment in beer- or malt-based beverages in late roasting stages. The use of this special malt brings more XN with less coloured malt in beer.     

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.     

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     

Characterization of melanoidins from a glucose-glycine model system

The properties of melanoidins prepared from glucose and glycine (GG) were investigated by a three step purification protocol consisting of dialysis, gel filtration at high ionic strength and ion metal affinity chromatography. The high molecular weight fraction obtained in the GG system is responsible for 80% of the total brown colour and its antioxidative ability was about 1/4 of that of Trolox measured by the inhibition of linoleic acid oxidation. GG melanoidins have good affinity towards Cu (II) (32% bound to the resin) while it is much lower towards Pb (II) (10%) and Fe (II) (5%). Capillary zone electrophoresis analysis suggests that GG melanoidins are positively charged, although no signal was observed analysing melanoidins by matrix-assisted laser desorption-ionisation time-of-flight mass spectrometry (MALDI-TOF/MS).     

L-丙氨酸和D-葡萄糖水溶性高分子棕色化反应产物的研究

本文报道了L-丙氨酸和D-葡萄糖水溶性高分子棕色化反应产物的制备与分离方法,研究了水溶性高分子棕色化反应产物的产率、元素组成、单位糖基脱水率、分子量分布随反应时间变化的规律,发现L-丙氨酸和D-葡萄糖水溶性高分子棕色化反应产物的数均分子量可高达6万以上。另外还对水溶性高分子产物在卷烟中的加香作用进行了探讨。      

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.     

The recognition of high molecular weight melanoidins as the main components responsible for radical-scavenging capacity of unheated and heat-treated Canadian honeys

As the Maillard reaction is known to occur in heat-treated foods, unheated and heated honey samples were subjected to the activity-guided fractionation and size-exclusion chromatography to compare the degree of browning, radical scavenging activity (ORAC) and molecular size of the fractions obtained. Heat-treatment increased browning in the fractions of light- and medium-coloured honeys (p < 0.002), accelerated the formation of high molecular weight melanoidins (85–232 kDa) and significantly increased ORAC values (p < 0.0001). In contrast, melanoidin content and ORAC decreased in the fractions of heat-treated dark buckwheat honey (p < 0.001). Unheated dark honey contained a significantly higher amount of melanoidins than other honeys (p < 0.007). Together, results showed that at low initial concentration of melanoidins, heat-treatment accelerated formation of new melanoidins and increased ORAC, while at high concentration it caused decrease and a reduction of radical scavenging activity. This study emphasises the importance of non-enzymatic browning in the prediction of the antioxidant pool in thermally processed honeys.     

Honey melanoidins: Analysis of the compositions of the high molecular weight melanoidins exhibiting radical-scavenging activity

Size-exclusion chromatography (SEC) and activity-guided fractionation of honeys allowed the isolation of high molecular weight brown compounds, ranging in size from 66 to 235 kDa that exhibited peroxyl radical-scavenging activity. Their concentrations, antioxidant activity and degree of browning increased after heat-treatment of honeys, suggesting that they represent melanoidins. Chemical analysis of melanoidins demonstrated the presence of proteins, polyphenols and oligosaccharides. Heat-treatment caused an increased incorporation of phenolics into high molecular weight melanoidins and drastically decreased the protein content in these fractions with a concomitant appearance of high molecular weight protein–polyphenol complexes of reduced solubility. LC–ESI–MS demonstrated the presence of oligosaccharide moieties, supporting the postulated origin of melanoidins. The changes in the phenolic content of melanoidins from heated honeys were strongly correlated with their oxygen radical absorbance capacity (ORAC) values (R = 0.75, p < 0.0001), indicating that polyphenols contribute to the antioxidant activity of melanoidins. In summary, honey melanoidins are multi-component polymers consisting of protein–polyphenol–oligosaccharide complexes. A direct interaction between polyphenols and melanoidins resulted in a loss or gain of function for melanoidin antioxidant activity.     

How Does Roasting Process Influence the Retention of Coffee Aroma Compounds by Lyophilized Coffee Extract?

ABSTRACT:  The aims of this study were (1) to study the effect of lyophilized coffee extract on the retention of aroma compounds and (2) to study if aroma compounds selected are differently affected by the lyophilized coffee extracts obtained from conventional and Torrefacto coffee brews prepared by filter coffeemaker and by espresso coffee machine. Variable amounts of lyophilized coffee extracts, relative to coffee powder, containing different percentages of high molecular weight compounds, mainly melanoidins (value given in parentheses), were obtained: 20.9% (14.8) and 24.9% (23.3), respectively, for conventional and Torrefacto coffee brew prepared by filter coffeemaker and 18.1% (18.8) and 20.7% (57.5), respectively, for conventional and Torrefacto coffee brew prepared by espresso coffee machine. The retention of aroma compounds increased by increasing the lyophilized coffee extract concentration and was found to be dependent on the aroma compounds. The retention of aroma compounds was found to be slightly different depending on the brewing procedure employed, showing lyophilized coffee extracts obtained with espresso coffee machine had higher retention values that those extracted by filter coffeemaker. Retention capacity of lyophilized coffee extracts obtained from the conventional and the Torrefacto roasted coffee did not show differences except in the case of ethyl nonanoate.     

乌贼墨抑制海洋鱼体腐败菌活性成分的分离

对乌贼墨中抑制海洋鱼体腐败菌活性成分进行了分离,并初步探讨了抑菌成分的理化特性。结果表明:乌贼墨粗提物经DEAE-纤维素和Sepharose 4B分离后获得具有较高活性的抑菌活性物质,分子量约为83589u,对四种海洋鱼体腐败菌(气单胞菌、黄杆菌、芽孢杆菌、肠杆菌)的平均抑菌率为62.36%。经紫外扫描(UV)和红外光谱(IR)分析,抑菌物质的主要成分为多糖。     

山西老陈醋类黑精的分离及其抑菌活性

为探究老陈醋类黑精的抑菌作用,采用超滤和尺寸排阻色谱法将山西老陈醋冻干粉（Shanxi aged vinegarextract,SAVE）分离成不同分子质量的水提物和类黑精部分,采用NaCl解离法将醋类黑精解离为类黑精骨架和小分子复合物两部分,用比浊法测定各组分对大肠杆菌、金黄色葡萄球菌和枯草芽孢杆菌的抑菌活性。结果表明：SAVE中的类黑精具有显著的抑菌活力（P＜0.05）,类黑精对SAVE的抑菌性发挥了主要作用;类黑精中分子质量在3～5 kD的组分抑菌活力最强,其对3 种受试菌的最低抑菌浓度（minimal inhibitory concentration,MIC）均为5 mg/mL;类黑精组成中的小分子复合物比类黑精骨架部分具有更强的抑菌活性。     

Protective Effect of Melanoidins from Fructose–Glutamic Acid on Polyphenol Oxidase Inactivation by Ultraviolet–Visible Irradiation

Ultraviolet irradiation has been proved to be effective for inactivating polyphenol oxidase in some fruit derivatives. However, some compounds that may be found in these products, such as melanoidins, can protect the enzyme during the irradiation process. In this piece of work, the protective effect of melanoidins synthesized from fructose and glutamic acid on Agaricus bisporus polyphenol oxidase inactivation by ultraviolet–visible irradiation has been assessed. The polymers with molecular mass lower than 150 kDa had a greater protective effect than those molecules higher than 150 kDa. If the obtained melanoidins are not fractioned by their molecular mass, the protective effect that they exert is lower. It was found that the most effective radiation to inactivate this polyphenol oxidase is that between 260 and 310 nm.     

Relationship between the chemical composition and the biological activities of food melanoidins

The relationship between the chemical composition and the biological activities of food melanoidin-rich fractions was investigated. Melanoidin-rich fractions were extracted using ultrafiltration (a 10 kDa cut-off) from coffee, barley coffee, dark beer, and traditional balsamic vinegar. All the food melanoidin-rich fractions were formed mainly of carbohydrates, phenolic compounds, and proteins. In dark beer, barley coffee, and traditional balsamic vinegar melanoidins, glucose was the most abundant sugar incorporated into melanoidins. Coffee melanoidins contained the largest amount of phenolic groups, followed by traditional balsamic vinegar melanoidins. The radical scavenging, Fe²⁺-chelating, and heme binding abilities of food melanoidins were investigated under gastric conditions. The melanoidinrich fraction extracted from coffee was the most active, showing the highest radical scavenging, Fe²⁺-chelating, and heme binding activities, compared to barley coffee, dark beer, and traditional balsamic vinegar. The radical scavenging and Fe²⁺-chelating abilities were assigned to the phenolic groups present in food melanoidins.     

Formation and characterisation of melanoidin-like polycondensation products from amino acids and lipid oxidation products

Various coloured water-soluble high molecular weight and water-nonsoluble reaction products were isolated from model reactions of an amino acid (glycine or lysine) and a lipid oxidation product (hexanal, (2E)-hexenal, (2E, 4E)-decadienal) with or without glucose. They were characterised by UV–visible absorbance measurements, elementary analysis, and thermal degradation followed by SPME–GC–MS analysis. The UV–visible absorbance spectra before and after dialysis indicated that the most important contributors to the formation of water-soluble coloured material were constituents of the low molecular fraction. Elementary analysis data indicated that a higher amount of nitrogen was incorporated in the high molecular weight fractions as compared to the water-nonsoluble fractions, except for the water-nonsoluble reaction products from amino acid/(2E, 4E)-decadienal interactions, which showed the lowest C/N ratio found. Volatile carbonyl compounds, furans, aliphatic compounds, pyridines, pyrroles and benzene derivatives were the main groups identified in the thermal degradation profile of each fraction tested. Especially pyridines seem typical indicators of amino acid–lipid oxidation product interactions.     

Molecular Weight Affected Antioxidant,Hypoglycemic and Hypotensive Activities of Cold Water Extract from Pleurotus citrinopileatus

Cold water extract of P. citrinopileatus (CWEPC) was fractioned into 4 fractions, PC‐I (<1 kDa), PC‐II (1‐3.5 kDa), PC‐III (3.5‐10 kDa), and PC‐IV (>10 kDa), by ultrafiltration. The antioxidant activities, the inhibition of pancreatic α‐amylase, intestinal α‐glucosidase, and hypertension‐linked angiotensin converting enzyme (ACE), as well as the contents of polysaccharides, protein, and phenolic compounds of 4 fractions were determined. The results showed that lower MW fractions exerted a higher antioxidant activity, which was correlated to phenolic contents. The high molecular fraction (PC‐IV) exhibited significantly higher inhibitory activity on α‐amylase, α‐glucosidase, and ACE compared to CWEPC and the other 3 lower MW fractions (<10 kDa), which was more related to protein contents. The inhibition capability of CWEPC and PC‐IV on α‐amylase activity was 1/13.4 to 1/2.7 relative to that of acarbose, respectively. Kinetic data revealed that PC‐IV fraction followed a noncompetitive inhibition pattern on α‐glucosidase activity. The study demonstrated that various MW fractions and types of components contribute to different biological functions of P. citrinopileatus and it is protein constituents but not peptides responsible for the hypoglycemic potential of CWEPC.     

Influence of high molecular weight polypeptides on the mouthfeel of commercial beer

Low malt beers have high sales volumes in Japan, but improving their mouthfeel, including softness, smoothness and decreasing astringency, is challenging because the compounds responsible remain unclear. In this study, beer was fractionated by preparative size‐exclusion chromatography, with the polypeptide and maltodextrin fractions purified using solid‐phase extraction and ion‐exchange resin. Sensory data from a spike test showed that the mouthfeel (softness, smoothness, and reduced astringency) of low malt beer was improved both by the degree of polymerisation (DP) of maltodextrins (DP of 2‐10; at increased concentration of 40 to 60%; P < 0.01) and by 10 ‐ 20 kilodalton (kDa) high molecular weight (HMW) polypeptide and 2‐3 kDa low molecular weight polypeptide fractions (at a 50% increase in concentration; P < 0.01). Furthermore, highly purified 10 to 20 kDa HMW polypeptides improved the softness and smoothness and decreased the astringency (at a 25% increase in concentration). This report is the first to provide experimental sensory data indicating that HMW polypeptides improve the mouthfeel of beer. Based on these findings, a new low malt beer was developed that showed significantly higher levels of the 10‐20 kDa HMW polypeptides with an overall improved mouthfeel. Mass spectrometric analysis of the 10 to 20 kDa proteins identified several unique foam positive proteins, including barley dimeric alpha‐amylase inhibitor‐1 and non‐specific lipid‐transfer protein 1. These 10‐20 kDa HMW proteins are likely to be responsible for the improved mouthfeel of beer. © 2020 Kirin Holdings Kabushik Kaisha Co. Ltd. Journal of the Institute of Brewing published by John Wiley & Sons Ltd on behalf of The Institute of Brewing & Distilling     

Transglutaminase treatment of brown rice flour: A chromatographic, electrophoretic and spectroscopic study of protein modifications

Recently, it was shown that transglutaminase (TGase) treatment of brown rice (BR) flour results in textural improvements of gluten-free bread. In this study, changes in the protein profiles of BR flour and protein fractions induced by TGase treatment were investigated to better understand the activity and specificity of the enzyme. Size-exclusion HPLC (SE-HPLC) profiles of flour extracts, under reducing conditions, revealed the presence of macromolecular protein complexes, as well as low molecular weight proteins. After TGase treatments (10 U/g of proteins) a general reduction in peak intensities indicated the polymerisation of BR proteins into larger, insoluble complexes. Microchip capillary electrophoresis and two-dimensional (2D) gel electrophoresis revealed that the α and β glutelin subunits were primary substrates for the polymerisation reaction, whereas albumins and globulins were only slightly affected. SE-HPLC of the protein fractions revealed glutelins’ polymerisation into high molecular weight structures after TGase treatment. Dynamic light scattering measurements showed that new supramolecular aggregates of glutelins co-existed with the macromolecular complexes already present in the untreated fraction. Front-face fluorescence approaches indicated that TGase treatment caused a decrease in protein surface hydrophobicity of BR flour, but not of the glutelin suspensions. It is concluded that the large protein complexes resulting from glutelin polymerisation and the stronger hydrophobic interactions among proteins result in the improved textural properties of TGase-treated BR bread.     

黑木耳多糖的酶法提取、纯化及性质研究

本文以双酶法提取黑木耳粗多糖,利用DEAE-Cellulose 52和Sepharose CL-4B柱层析对其进行纯化,以Sephadex G-100凝胶柱层析测定了多糖的分子量。结果表明黑木耳多糖含有两个主要组分APE Ⅰ和APE Ⅱ,分子量分别为31.7×104和18.3×104,均为非淀粉类多糖,不含单糖、蛋白质、核酸及多酚类物质。