Formation of the Heyns rearrangement products in dihydroxyacetone and glycine Maillard reaction: A computational study

Density functional theory computations at the standard state on the proposed mechanisms of dihydroxyacetone and glycine Maillard reaction under different pH conditions have revealed that dihydroxyacetone + deprotonated glycine and dihydroxyacetone + unprotonated glycine reactions are more favorable than dihydroxyacetone + protonated glycine and dihydroxyacetone + glycine zwitterion reactions for the formation of the Heyns rearrangement products (HRPs). The gaseous phase reaction is assumed more feasible than the aqueous phase reaction for the production of HRPs. Due to the possibility of the production of both of the enol and keto forms of HRPs, the rate of browning in the dihydroxyacetone + deprotonated glycine reaction is assumed higher than that of the others. Dihydroxyacetone + protonated glycine and dihydroxyacetone + glycine zwitterion reactions are not favorable for the formation of HRPs and, therefore, the reaction is assumed hindered under these conditions and the rate of browning is supposed to be lower than that of the others. Possibilities for the conversion of dihydroxyacetone to glyceraldehyde and formation of hydroxyacetaldehyde from dihydroxyacetone as a C2-fragmentation product have also been evaluated.     

果蔬制品的变色及其防止措施

分析了果蔬制品在加工贮存中变色的原因,综述了生产中常见的原料选择、热处理、添加化学试剂、驱除氧气等护色措施。     

Chemistry of Amadori rearrangement products: Analysis,synthesis, kinetics,reactions, and spectroscopic properties

The chemistry of the key intermediate in the Maillard reaction, the Amadori rearrangement product, is reviewed covering the areas of synthesis, chromatographic analyses, chemical and spectroscopic methods of characterization, reactions, and kinetics. Synthetic strategies involving free and protected sugars are described in detail with specific synthetic procedures. GC‐ and HPLC‐based separations of Amadori products are discussed in relation to the type of columns employed and methods of detection. Applications of infrared (IR) and nuclear magnetic resonance (NMR) spectroscopy for structural elucidation of Amadori products are also reviewed. In addition, mass spectrometry of free, protected, and protein‐bound Amadori products under different ionization conditions are presented. The mechanism of acid/base catalyzed thermal degradation reactions of Amadori compounds, as well as their kinetics of formation, are critically evaluated.     

赖氨酸Amadori和Heyns化合物热裂解产物对烟草风味的影响研究

  目的  比较赖氨酸Amadori和Heyns化合物的热解产物及对其烟草风味的影响。  方法  以赖氨酸和葡萄糖或果糖为原料,以偏重亚硫酸钠为催化剂、甲醇和冰醋酸为溶剂,分别合成赖氨酸的Amadori和Heyns化合物,采用在线热裂解-气相色谱/质谱联用技术(Py-GC/MS)对比了2种化合物的热解产物差异,并通过感官评吸实验比较了二者对卷烟风味的影响。  结果  （1）赖氨酸Amadori和Heyns化合物热解均能产生醛酮类、呋喃类、吡啶类、吡嗪类及吡咯类香味物质,同一类别产物的相对含量有较大差异。（2）赖氨酸Heyns化合物热解得到的风味成分数量更多。（3）赖氨酸Amadori化合物和Heyns化合物对卷烟的主要作用为增香、增浓和降低刺激,并使烟气更加流畅顺滑,赖氨酸Heyns化合物增加了卷烟白肋烟特征。  结论  赖氨酸Amadori化合物和Heyns化合物的热解产物不同,对卷烟风味的影响存在差异。      

Browning reactions in olives: Mechanism and polyphenols involved

The mechanism of the browning reaction in olives has been disclosed by following the polyphenol changes in healthy and bruised fruits and using “in vitro” models. It was later validated in independent experiments with active and denatured enzymatic extracts, treated or not with ascorbic acid to prevent oxidation. The proposed mechanism would consist of two steps. First, there is an enzymatic release of hydroxytyrosol, due to the action of the fruits’ β-glucosidases and esterases on oleuropein and hydroxytyrosol glucoside; additional hydroxytyrosol can also be produced (in a markedly lower proportion) by the chemical hydrolysis of oleuropein. In a second phase, hydroxytyrosol and verbascoside are oxidized by the fruits’ polyphenoloxidase (mainly) and by a chemical reaction, which occurs to a limited extent due to the olive flesh pH, ≈5.0.     

Browning reactions during storage of low-moisture Australian sultanas: Evidence for arginine-mediated Maillard reactions

Browning during storage of low‐moisture dried Vitis Vinifera L. cv. Sultana (Thompson Seedless) grapes was examined in a multifactorial treatment and storage trial. Grapevines were subjected to two different levels of sun exposure, harvested fruit was dipped and subjected to different drying treatments to obtain a range of initial moisture contents (a_w= 0.419–0.558). The storage effects of temperature (10^oC and 30^oC), and the presence of oxygen on colour change (CIE L*a*b* tristimulus values, hue‐angle (h_ab*)) and chroma (C_ab*) over a fourteen‐month period were observed. The most significant changes in colour were measured for samples stored at 30^oC, both aerobically and anaerobically, although the largest changes occurred in the presence of oxygen. Initial a_w had a strong effect on colour changes; higher a_w non‐sunfinished samples underwent more significant browning compared to lower a_w sunfinished controls regardless of their oxygen status. Changes in the concentration of the free‐arginine and free‐proline, the most abundant free amino acids in sultanas, were monitored throughout the storage period. Free arginine decreased significantly at 30^oC in both the absence and presence of oxygen, whereas free proline increased (at both 10^oC and 30^oC), implying that free proline did not play a role in browning reactions at those temperatures. In addition to the decreases in free arginine, the concentration of 5‐hydroxymethyl furfural (5‐HMF), a marker of Maillard browning reactions, increased significantly in samples stored at 30^oC. Significant differences in the concentrations of 5‐HMF under the two oxygen conditions indicated sultana Maillard reactions, and possibly other non‐enzymatic browning processes, were oxygen sensitive.     

Nonenzymic browning. 4. Browning reactions of 2-furfuraldehyde with protein

Summary The binding of aldehyde on free amino groups of protein takes place during the heating of 2-furfuraldehyde with casein. The reaction is of the 1^st order, but becomes a 0 order reaction (with respect to amino groups) in the first reaction stage in case of sufficient excess of 2-furfuraldehyde. Multifold excess of 2-furfuraldehyde is necessary for the complete blocking of free amino groups. The condensation product is transformed by heating to higher temperatures, especially above 100° C, to deep brown coloured polymer products. A free amino group and also another functional group of protein are necessary for the formation of brown pigments. The reaction with other proteins is similar to that of casein.

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Zusammenfassung Während der Erhitzung von 2-Furfural mit Casein wird das Aldehyd an die freien Äminogruppen des Proteins gebunden. Die Reaktion ist 1. Ordnung, sie kann eine O. Ordnung werden (im Bezug mit Aminogruppen), wenn 2-Furfural in einem genügenden Über-schuß zu Beginn der Reaktion vorhanden ist. Ein mehrfacher Überschuß an 2-Furfural ist für die vollkommene Blockierung der Aminogruppen notwendig. Das Kondensationsprodukt wird durch Erhitzung unter höheren Temperaturen, besonders über 100° C, in tiefbraune Polymerderi vate überführt. Eine freie Aminogruppe und noch eine weitere Funktionsgruppe des Proteins sind für die Bildung der braunen Produkte notwendig. Die Reaktion verläuft mit anderen Eiweißstoffen in ähnlicher Weise wie mit Casein.

     

Monitoring of Maillard reactions in soy products

Chemical mechanism and the analytical methods suggested in the literature for the analysis of early Maillard reactions are summarised and critically evaluated. The applicability of our method for the measurement of the Maillard reactions - the soluble raffinose oligosaccharides and the basic amino groups of proteins - are illustrated by following early Maillard reactions in differently denaturated soya bean samples. The quantitative relations of Maillard reactions taking place in natural matrices could be clarified by monitoring both of the reactants by means of methods not requiring correction factors.     

Monitoring of Maillard reactions in soy products

Zusammenfassung Der chemische Mechanismus der Maillard-Reaktionen und die Literatur der für die Untersuchung der frühen Maillard-Reaktion vorgeschlagenen analytischen Methoden werden kritisch gesichtet. Wir belegen die Anwendbarkeit unseres Verfahrens für die Verfolgung der frühen Maillard-Reaktionen durch die Erfassung der daran Teilnehmenden, der löslichen Raffinose-Oligosaccharide und der basischen Aminogruppen der Proteine, und zwar am Beispiel der Analyse von unterschiedlich denaturierten Sojaprodukten. Hierbei ist es zum ersten Mal gelungen, die quantitativen Zusammenhänge zwischen den Maillard-Reaktanten in einer natürlichen Matrix mit numerischen Daten zu stützen, wobei mit dieser Methode keine Korrekturfaktoren benötigt werden.

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Monitoring of Maillard reactions in soy products

Summary Chemical mechanism and the analytical methods suggested in the literature for the analysis of early Maillard reactions are summarised and critically evaluated. The applicability of our method for the measurement of the Maillard reactions — the soluble raffinose oligosaccharides and the basic amino groups of proteins — are illustrated by following early Maillard reactions in differently denaturated soya bean samples. The quantitative relations of Maillard reactions taking place in natural matrices could be clarified by monitoring both of the reactants by means of methods not requiring correction factors.

     

Effect of Amadori rearrangement products on the non-enzymic browning in model systems

The Amadori product was prepared from D-glucose and L-alanine after Hashiba. The browning process was investigated by determining the absorbance at 520 nm, in aqueous solutions at 110 °C for 5–8 h. Because of the limited access of oxygen and its low solubility in the reaction medium, the browning proceeded after zeroth order kinetics with the maximum browning rate at pH = 8–9. The browning rate remained unaffected by additions of sodium sulphite, rutin. propyl gallate (except when present at high levels), iron(III)chloride or copper(II)chloride but decreased in presence of L-cysteine or iron(II)chloride. Hydrogen peroxide bleached the pigment but did not inhibit the subsequent browning of reaction products. Under experimental conditions the solution of Amadori product did not darken with substantially greater rate than the solution of D-glucose and L-alanine. Lower additions of D-glucose to the solution of Amadori product moderately increased the reaction rate while additions of L-alanine or L-hydroxyproline moderately decreased the browning rate.     

Nonenzymatic browning reactions of retro-aldol degradation products of carbohydrates

 Methylglyoxal and glyceraldehyde were used to demonstrate the involvement of retro-aldol degradation products of carbohydrates in browning (A ₄₂₀), the formation of hydroxymethylfurfural (HMF), and the extent to which the mechanism of browning proceeds by homolytic or heterolytic pathways in the caramelization and Maillard reactions of mono- and disaccharides. The amino component of Maillard systems is required for the retro-aldol cleavage of D-glucose. The short-chain α-dicarbonyl compounds so formed appear to dominate not only the formation of brown products but also the mechanism of the browning of D-glucose under these conditions, even if only small amounts are formed. Evidence is presented to link the formation of free radicals in the browning of glucose to reactions of the retro-aldol products. A novel reaction pathway is suggested for the formation of HMF from glyceraldehyde. Received: 9 October 1998 / Revised version: 15 December 1998     

Enzymatic browning reactions in apple and apple products

This review examines the parameters of enzymatic browning in apple and apple products that is, phenolic compounds, polyphenoloxidases, and other factors (ascorbic acid and peroxidases), both qualitatively and quantitatively. Then the relationships between intensity of browning and the browning parameters are discussed, including a paragraph on the methods used for browning evaluation. Finally, the different methods for the control of browning are presented.     

Some formaldehyde reaction products in non-enzymatic browning reactions

Summary The volatiles isolated from the glycine-glyoxal model system were analysed and two compounds derived from formaldehyde (arising from the Strecker degradation of glycine) were identified. The structure of the two compounds, i.e., 2,4,6-trioxaheptane and 2,4,6,8-tetraoxanonane, was confirmed by the analysis of the reference compounds isolated from the commercial formaldehyde solution and analysed by gas chromatography/mass spectrometry and¹H-NMR spectrometry. The above compounds (the reaction products of formaldehyde oligomers with methanol) are described, for the first time, as minor volatiles in non-enzymatic browning reactions.

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Einige Reaktionsprodukte von Formaldehyd in nicht-enzymatischen Bräunungsreaktionen

Zusammenfassung Es wurden aus einem Modellsystem Glycin-Glyoxal flüchtige Stoffe isoliert und zwei Verbindungen, abgeleitet vom Formaldehyd (der durch die Streckersche Reaktion der Degradierung von Glycin entsteht) identifiziert. Die Struktur dieser zwei Verbindungen 2,4,6-Trioxaheptan und 2,4,6,8-Tetraoxanonan wurde durch die Analyse der Referenzverbindungen aus der Lösung von Formaldehyd des Handels bestätigt. Die Analyse wurde mit der Methode MGC/MS and¹H-NMR Spektrometrie vorgenommen. Die oben angeführten Verbindungen (Reaktionsprodukte von Oligomeren von Formaldehyd mit Methanol) wurden zum erstenmal als flüchtige Stoffe in den Reaktionen der nicht-enzymatischen Bräunung beschrieben.

     

鲜麻山药酚类物质酶促褐变的研究

对鲜麻山药酚类物质的分布,酚类物质的种类进行研究,从而确定一种酶促褐变的底物,对PPO酶的活性及其与褐变底物的亲和力进行分析和研究。表明鲜麻山药是由于酚类物质在PPO下进行的酶促褐变。并筛选出抑制麻山药PPO酶活力的最佳温度、酸碱环境和抑制剂。     

Nonenzymic browning. 3. Browning reactions during heating of fish oil fatty acid esters with protein

Summary During heating of mixtures of methyl esters of polyunsaturated fish oil fatty acids and albumen under simulated conditions of roasting and frying of fish, peroxides present in the lipidic fraction are rapidly decomposed and form both liposoluble and insoluble brown pigments with free amino groups of albumen. Small amounts of lipids in the mixture have already great effect on the development of colour. The reaction is very rapid at the temperatures above 100° C, and the brown pigments are not decomposed by prolonged heating.

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Zusammenfassung Gemische der Methylester von polyungesättigten Fischölfettsäuren mit Albumin wurden unter simulierten Bedingungen des Röstens und Fritürens erhitzt. Die in der lipidischen Fraktion anwesenden Peroxide werden schnell zersetzt und bilden fettlösliche sowie auch unlösliche stickstoffhaltige braune Produkte mit den freien Aminogruppen des Albumins. Geringe Lipidmengen haben schon einen merkbaren Einfluß auf die Farbentwicklung. Die Reaktion tritt sehr schnell bei Temperaturen > 100° C ein und die braunen Produkte ändern sich auch während einer längeren Erhitzung nicht wesentlich.

     

Formation of volatile pyrrole products from epoxyalkenal/protein reactions

The production of volatile compounds in the reaction of the lipid peroxidation product (E)-4,5-epoxy-(E)-2-heptenal with lysine or bovine serum albumin was studied in order to characterise alternative mechanisms for production of volatile pyrrole derivatives in foods. A mixture of the lipid and the ammo acid or the protein was stirred overnight at 31°C and the volatiles formed were collected using a Tenax TA trap. Several aldehydes, ketones, alkylfurans, alkyl- and acyl-pyrroles, and alkylpyridines were identified by GC/MS. Formation of pyrrole derivatives in these reactions suggested the existence of alternative mechanisms for production of these flavour-associated compounds, previously considered to be formed mainly via Maillard reactions. This new route does not need the presence of sugars, and might contribute significantly to volatile pyrrole production in foods under conditions unfavourable for classic Maillard reactions.     

Browning reactions during storage of low-moisture Australian sultanas: Further evidence for arginine-mediated Maillard reactions during storage, and some effects of vine-shading and harvest date

Sultana grapevines (Vitis Vinifera L. cv. Sultana syn. Thompson Seedless) were subjected to four shading regimes: 50% shading (1), 25% shading (2), fully exposed‐top of canopy (3) and beneath canopy (4) and harvested early (21 February) and late (13 March) in the 1996/1997 sultana season. Grapes from each of the eight field‐treatment combinations represented a range of maturities (14.4 to 23.50^oBrix). Grape samples from each of the treatments were dipped and dried to 18% moisture, with half of each of the sultana samples further reduced in moisture by sunfinishing on plastic sheets in direct sun. These field treatments resulted in sixteen unique dried sultana bulk samples with a range of initial chemico‐physical properties; a_w (0.481–0.691), skin‐polyphenoloxidase (PPO) activity (4.40–9.05 μmol O₂/g.minute) free arginine in skin tissues (1.0–5.10 mg/g) and protein (16.40–27.18 mg/g). Sultanas were stored at 10^oC and 30^oC in either the presence or absence of oxygen for 10 months, and changes in CIE L*a*b* tristimulus values, hue‐angle (h_ab*) and chroma (C_ab*) were monitored. Significant changes in sultana colour occurred in samples stored at 30^oC, especially in higher a_w non‐sunfinished sultanas. Although browning was more intense in the presence of oxygen, significant browning also occurred in the absence of oxygen. Lower concentrations of 5‐hydroxy methylfurfural, a key marker of Maillard browning in samples stored at 30^oC in the presence of oxygen, indicated that the non‐enzymatic reactions were sensitive to oxygen. Changes in the concentration of trans‐caftaric acid, the main substrate of grape PPO, were also measured during sultana drying. Storage browning (changes in L*, b*, h_ab*, C_ab*)in dried sultanas could be predicted by regression models using pre‐storage a_w, free‐skin arginine or Kjeldahl protein after 10 months' storage between 10^oC and 30^oC. Non‐enzymatic and Maillard‐type reactions (sensitive to both oxygen and a_w), made an important contribution to sultana storage browning. We provide only weak evidence that either shaded (immature) or green fruit was more susceptible to storage browning.     

Synthesen verzweigter MonosaccharideHerrn Professor K. Heyns zum 65. Geburtstag gewidmet.

Syntheses of Branched-Chain Monosaccharides The occurence and the significance of branchedchain sugars is described. A method is outlined for the synthesis of complex branched-chain sugars with functionalized side-chain, which fo the first time makes the class of these substances accessible. The synthesis of L-streptose, D-hamamelose, D-aldgarose is described. By the synthesis of D-aldgarose interesting stereochemical problems and, whose solutions are discussed.