Volatile components from the non-enzymic browning reaction of the cysteine/cystine-ribose system

Summary Volatile components from the Maillard reaction of the Cysteine/Cystine-ribose system of low water content were investigated. The reaction conditions were as follows: 0.01 mol ofl-cysteine andl-cystine each, 0.025 mol ofd-ribose and 35 ml of a phosphate buffer solution of pH 5.6 in 200 ml diethylene glycol. This mixture was heated for 24 h under reflux at 125° C. Analysis of the reaction mixture was performed by gas and thin-layer chromatography. Some 45 components, comprising thiophenes, thiazoles, a trithiane, pyrazines, pyrroles, pyridines, amines and furans, were identified. In the vapour above the reaction mixture 3 alkyl thiols, hydrogen sulphide and carbon disulphide were detected by flame photometric analysis. Possible pathways for the formation of 2-acylthiazoles, and of 3-methyl, and 5-methyl substituted 2-formylthiophenes are proposed.

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Zusammenfassung Die flüchtigen Verbindungen der Maillard-Reaktion des Cystein/Cystin-Ribose-Systems von niederigem Wassergehalt wurden untersucht. Die folgenden Reaktionsbedingungen wurden angewandt: 0,01 mol sowohl vonl-Cystein als vonl-Cystin, 0,025 mol vond-Ribose und 35 ml eines Phosphatpuffergemisches von pH 5,6 in 200 ml Diäthylenglycol. Dieses Gemisch wurde 24 Std unter Rückfluß bei 125° C erhitzt. Die Analyse des Reaktionsgemisches wurde mittels Gas- und Dünnschichtchromatographie durchgeführt. Etwa 45 Verbindungen, worunter Thiophene, Thiazole, ein Trithian, Pyrazine, Pyrrole, Pyridine, Amine und Furane, wurden identifiziert. In dem Dampf über dem Reaktionsgemisch wurden 3 Alkylthiole, Schwefelwasserstoff und Schwefelkohlenstoff mittels flammenphotometrischer Analyse vorgefunden. Mögliche Bildungswege für 2-Acylthiazole und für 3-Methyl, und 5-Methyl substituierten 2-Formylthiophene werden vorgeschlagen.

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Acknowledgement. The author is grateful to J. W. Marsman of the Institute of Organic Chemistry TNO, Utrecht, Netherlands, for the determination of the nmr spectra.

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The author is also indebted to R. Belz, J. Bouwman, J. Th. Heins, C. van Ingen, R. J. C. Kleipool and M. C. ten Noever de Brauw for assistance in obtaining and interpreting mass and infrared spectra, and to R. J. C. Kleipool and A. Tas for synthesizing components, without which it would not have been possible to arrive in all instances at positive identifications.     

Effect of antibrowning agents on browning and intermediate formation in the glucose-glutamic acid model

In this study, the inhibitory effects of antibrowning agents on browning and the formation of intermediates such as 3-deoxyglucosone (3-DG) and hydroxymethylfurfural (HMF) were evaluated with a glucose-glutamic acid model for soybean paste. The initial antibrowning capacity was measured in the following order: pentasodium tripolyphosphate < citric acid and oxalic acid < cysteine and glutathione < sodium sulfite. Our data showed that antibrowning agents, such as pentasodium tripolyphosphate, citric acid, and oxalic acid, were maintained antibrowning capacities during storage at both 4 and 30 °C, respectively. However, both cysteine and glutathione was reduced with storage time, especially in the air. A marked effect of nitrogen treatment was noted for 3 of the antibrowning agents after storage in air at 30 °C in the following order: sodium sulfite < cysteine < glutathione. The formation ratio of 3-DG and HMF was higher after storage at 30 °C than at 4 °C. These compounds were produced most abundantly in the presence of sodium sulfite, and the yields were not related significantly to the degree of browning. Citric acid and oxalic acid were identified as the most effective in inhibitors of browning and intermediates, even during storage in air at 30 °C.     

Measurement of non-enzymic browning of dehydrated carrot

Non-enzymic browning of sulphited dehydrated carrot is measured by extracting brown materials with 2% acetic acid containing 1% formaldehyde, followed by precipitation of interfering pigments absorbing at 420 nm with 10% lead acetate and ethyl alcohol. The presence of sulphur dioxide is shown to reduce the absorption at 420 nm of a glucose—glycine browning solution and an extract of dehydrated carrot, the effect depending on time of incubation and exposure to light. The use of formaldehyde in the extraction solvent overcomes the effect of sulphur dioxide at concentrations up to 19 200 parts/million. The presence of carotenoids is shown to increase the absorption of browning extracts at 420 nm leading to high results. The interference from pigment materials is overcome by precipitation with lead acetate and ethyl alcohol. The use of both formaldehyde and lead acetate has no additional effect on browning determinations. Comparative tests of the proposed lead-alcohol precipitation method with an alcohol precipitation method, using both a glucose-glycine browning mixture and an extract of dehydrated carrot, shows only the lead-alcohol precipitation method to overcome errors due to carotenoid pigments either originally present in the extract or added as β-carotene, while the additional use of formaldehyde during extraction is necessary to overcome errors due to sulphur dioxide. Browning of dehydrated sulphited carrot stored for up to 20 days at 50 °C decreased with time of storage when measured by the alcohol precipitation method and in dehydrated non-sulphited carrot, browning showed only a slight increase with storage time. When measured by the lead-alcohol precipitation method, browning showed only a slight increase in stored dehydrated sulphited carrot, but a marked increase in stored dehydrated non-sulphited carrot, in agreement with visual observations.     

Role of amino acids in non-enzymic browning

Loss of nitrogen in the form of freeamino groups during browning of various aqueous sugar-glycine mixtures has been studied, and the results are reported. It has been found that such loss depends on the type of sugar (pentose, aldohexose, or ketose), and is initially accelerated in the presence of buffering agents. the results also indicate that all the free primary amino nitrogen present during browning of sugarglycine mixtures can be accounted for as glycine. Browning of various saturated and unsaturated aldehydes with glycine has been shown to lead to pigments containing no nitrogen, and the significance of this is discussed in relation to the browning reaction. It is suggested that monoketoseamines are a major intermediate in browning reactions involving loss of amino nitrogen, and an extended reaction-scheme for the browning of aldose-amino systems is presented. the significance of the low loss of amino nitrogen in ketose-glycine systems is discussed in relation to the mechanisms of browning of these systems. Consideration is given to methods used in colour measurement in non-enzymic browning and to the limitations of colour measurement as an index of the extent of reaction.     

Gas chromatographic determination of carbon dioxide in non-fat dry milk during non-enzymic browning reaction

Carbon dioxide formation in non-fat dry milk during accelerated non-enzymic browning reaction was determined by gas chromatography. Carbon dioxide content in the headspace of the sample bottle increased as the non-enzymic browning reaction increased. Non-fat dry milk containing added 0, 15 or 30 g kg^?1 lysine in the air-tight serum bottle was stored at 55, 65 or 75°C. The coefficients of variation for reflective spectroscopic brown colour measurement and GC carbon dioxide determination were 1.37% and 1.30%, respectively. The average correlation coefficient between brown colour development and carbon dioxide formation for the nine samples during storage was 0.96. The simple, fast and reproducible gas chromatographic carbon dioxide determination method could be used to study non-enzymic browning reactions in foods or to complement other analytical methods in measuring the non-enzymic browning reaction.     

The yield of 3-deoxy-4-sulphopentosulose in the sulphite inhibited non-enzymic browning of ascorbic acid

The ion exchange behaviour of 3-deoxy-4-sulphopentosulose is markedly influenced by the presence of hydrogen sulphite ion, the dihydroxysulphonate being held more firmly on a strongly basic resin than the free dicarbonylic product. The apparent formation of other sulphonates in model ascorbic acid/glycine/HSO₃- reactions is explained in terms of this ion exchange behaviour and the major reaction product is 3-deoxy-4-sulphopentosulose in 75 % yield. In foods, the yields of this sulphonate and also of 3-deoxy-4-sulphohexosulose are now regarded as true indicators of the extent of the fate of sulphur dioxide by way of its inhibition of non-enzymic browning reactions.     

Measurement of non-enzymic browning of dehydrated and intermediate moisture meat

Non-enzymic browning (NEB) of a traditional intermediate moisture meat (den-deng) and dehydrated meat was measured by both aqueous trypsin digestion and lead acetate-ethanol precipitation methods. Trypsin digestion did not interfere with NEB determination, and the addition of a glucose-glycine NEB mixture to dendeng had no effect on NEB measured by the lead acetate-ethanol precipitation method. Comparison of NEB measurements by the lead acetate-ethanol precipitation method and an aqueous trypsin digestion method on dendeng containing added myoglobin and/or haem pigments showed that only the lead acetate-ethanol precipitation method overcame errors which were due to the presence of these pigments. Spice pigments present in dendeng also interfered and led to high NEB values, while NEB increased markedly in the presence of coconut sugar. Results for NEB of dendeng and dehydrated meat stored for up to 12 weeks at 50°C were lower when measured by the lead acetate-ethanol precipitation method compared to results by the aqueous trypsin digestion method, although both methods showed that NEB increased with storage time.     

贮藏条件等对番茄粉非酶褐变的影响

对番茄粉在不同的贮藏条件下（贮藏温度、湿度、包装材料以及不同的添加物）的非酶褐变动力学进行了研究。研究显示;亚硫酸氢钠对番茄粉的褐变影响很大,抗坏血酸在一定程度上也可抑制番茄粉的褐变,但氯化钠对番茄粉的褐变没有影响。番茄粉贮藏的温度和贮藏环境的湿度以及包装材料对番茄粉的褐变也有较大的影响。番茄粉的褐变遵循零级动力学反应。     

Effects of reaction parameters on generation of volatile compounds from the Maillard reaction between L‐ascorbic acid and glycine

The formation of volatiles from the reaction between L‐ascorbic acid (ASA) and glycine (Gly) at different reaction parameters, such as temperature, time and pH, were reported and 20 different volatile compounds were identified using solid‐phase microextraction–gas chromatography–mass spectrometry (SPME‐GC‐MS). The results showed that the reaction parameters had the different effects on formation of volatiles, while the effect of pH was the most remarkable. When the initial solution pH was 4.5, the major volatiles were found to be furfural or derivatives of furan; while when pH ranged from 6.8 to 9.5, the major volatiles were found to be derivatives of pyrazines, including 2,5‐dimethyl‐pyrazine, 2‐ethyl‐5‐methyl‐pyrazine, trimethyl‐pyrazine, 3‐ethyl‐2,5‐dimethyl‐pyrazine and 2,3‐diethyl‐5‐methyl‐pyrazine. The quantity of 2,5‐dimethyl‐pyrazine and 2‐ethyl‐5‐methyl‐pyrazine reached the maximum when pH was 8.0. Finally, a possible reaction mechanism of ASA and Gly and the pathway for the formation of the various kinds of volatile products were proposed.     

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.     

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.

     

The reactivity of intermediates in non-enzymic browning reactions towards nitrite ion

The intermediates of non-enzymic browning reactions, 4, 5-dihydroxy-2-oxopentanal and 2-oxo-4,5,6-trihydroxyhexanal, show significant reactivity towards nitrite ion at pH 4.7 and 7.0, respectively.     

The rôle of buffer salts in non-enzymic browning

A technique of heat-processing solutions in sealed jars has been used to study non-enzymic browning, particularly with regard to the effect of added buffer salts. This technique facilitates the simultaneous examination of a larger number of solutions and permits the use of higher temperatures than would otherwise be possible. It has been shown that systems containing a reducing sugar, an amino-acid and a buffer salt in solution must be regarded as triple systems, there being in most cases a well defined optimum ratio of any two components of the system. It also appears that salts of carboxylic acids have no unique browning properties, the effects of both organic and inorganic buffer salts being approximately additive provided that direct reaction with the sugar cannot occur. The importance of buffer salts as general acid-base catalysts is stressed. Their buffering action against acid reaction products is also discussed.     

The chemistry of non-enzymic browning in foods and its control by sulphites

Non-enzymic browning involves a complex of chemical reactions with few identifying common features other than the involvement of carbonylic intermediates, the production of brown pigments (melanoidins) and the effect of sulphites in either inhibiting or retarding the development of the melanoidins. In general, amine compounds (amines, amino acids, peptides, proteins) are important in reactions, usually with carbohydrates, which (a) produce highly reactive carbonylic intermediates and (b) involve condensation with these intermediates to produce highly coloured pigments. These reactions occur in many foods and, where they are undesirable, may usually be controlled more or less successfully by the addition of sulphites. This effectiveness of a single additive in controlling a variety of chemical pathways is probably due to the number of different reactions which sulphite can enter into with, for example, reducing sugars, simple carbonyls, αβ-dicarbonyls, β-hydroxycarbonyls, αβ-unsaturated carbonyls and with the melanoidins. It is known that in exerting its anti-browning effect in food, the amount of measurable sulphite decreases and there is some evidence that amongst the products derived from sulphite in a rat diet there is at least one toxic factor. Information is only recently available about the nature of some of the more stable products (e.g. sulphonated deoxyosuloses) arising from sulphite-loss and further investigation of the biological properties of these products seems necessary. With increasing concern about the total dietary intake of sulphite it is becoming more necessary to identify the uses of this additive where there is no adequate alternative and the most effective ways of employing it where it is essential in food processing; further advances in the chemistry of sulphites in relation to food will be important in achieving this.     

Studies on non-enzymic browning in orange juice using a model system based on freshly squeezed orange juice

An orange juice based model system was set up wherein variables such as the addition of glucose, lysine, sorbitol and L -ascorbic acid and changes in pH and storage temperature were introduced to study their effects on L -ascorbic acid degradation and on browning. The addition of glucose, lysine and sorbitol did not have a significant effect on L -ascorbic acid degradation, whereas added L -ascorbic acid acted solely as a reserve material. In terms of browning, a change in pH and storage at elevated temperature produced a synergistic effect in the development of brown colour which was enhanced by the introduction of additives. Based on the results obtained, L -ascorbic acid appears to be the precursor in the non-enzymic browning occurring in this type of sample due to the formation of reactive carbonyl compounds produced upon its degradation which tend to polymerise, or to react with nitrogenous compounds, to give brown pigments.     

温度对鸡骨酶解液美拉德反应产物光谱特性和挥发性风味成分的影响

以鸡骨酶解液和木糖进行美拉德反应,研究不同温度下鸡骨酶解液-木糖美拉德反应产物光谱特性和挥发性风味成分的变化规律。结果表明,随着温度的增加,鸡骨酶解液美拉德反应产物褐变程度增加,中间产物的生成与荧光光谱具有很好的一致性;鸡骨酶解液美拉德反应产物中醛酮酯类化合物增加,且鉴定出酸类物质和杂环类化合物,其中3-乙基呋喃、2,6-甲基吡嗪等杂环类化合物对产物整体肉香风味形成有着重要的贡献。     

Maillard模式反应牛肉香精挥发性风味成分分析

应用同时蒸馏萃取（SDE）和固相微萃取（SPME）两种预处理方法，GC-MS分析Maillard模式反应牛肉香精的挥发性风味成分，共分离鉴定出87种挥发性化合物，其中2-甲基-3-呋喃硫醇、四氢-2-甲基-3（2H）-呋喃酮、双二（2-甲基-3-呋喃基）二硫醚、3-甲基-2-乙酰基噻吩等为特征型牛肉香味化合物。两种提取方法互为补充，较为全面的反映了牛肉香精的风味轮廓组成。     

The Maillard reaction. 18. Radical inhibition of browning by sulfur compounds

ESR spectroscopic investigations on the mechanism of Maillard-reactions using the model D-glucose/glycine show radical formation in some of the reaction steps. These are possibly due to competitive reactions against ionic mechanism. The formation of radicals depends on the concentration of reactants and reaches a maximum in thermically induced browning reactions. The addition of L-cysteine leads to a decrease in the radical concentration to about 60%. It can be indirectly proven that the radicals are involved in the formation of browning products. The hyperfine structures of ESR spectra are supposed to be similar to pyrazine cation radicals.     

Changes in the profile of volatile compounds in wines stored under oxygen and their relationship with the browning process

 Eight young white wines produced in Aragon from Macabeo and Chardonnay grapes were stored under an oxygen atmosphere in the dark at room temperature. Changes in the colour and volatile compound composition were recorded over a period of 13 weeks. Significant changes in the volatile compound composition were detected through analysis of variance (ANOVA) of repeated measures, considering both grape variety and browning tendency as discriminant categories. The amounts of fatty acids and fermentation esters in the wine were significantly changed by the oxidative storage. Some of these changes can be attributed to acid-ester hydrolysis equilibria, but not others, such as the decrease in concentrations of octanoic and decanoic acids. The oxidative storage also affected most of the unsaturated fatty-acid-derived compounds: trans-2-octenal, trans-2-nonenal, trans-2-decenal and 1-octen-3-ol were all found to increase in the first stages of storage, while hexanol decreased slightly. Volatile phenols behaved very differently: while phenol and 4-ethylphenol initially increased and later decreased, eugenol increased through the process and 4-vinyl-guaiacol disappeared. Benzaldehyde and furfural increased while methionol and terpenols disappeared. Only furfural was found to be linked with the tendency of the wine to brown, while only linalool and benzaldehyde were found to be linked whith the grape variety. The levels of some odorants previously isolated by sniffing detection were temptatively monitored, and significant changes in their concentrations were found to occur during the process. Received: 16 December 1996 / Revised version: 27 March 1997     

Changes in the profile of volatile compounds in wines stored under oxygen and their relationship with the browning process

 Eight young white wines produced in Aragon from Macabeo and Chardonnay grapes were stored under an oxygen atmosphere in the dark at room temperature. Changes in the colour and volatile compound composition were recorded over a period of 13 weeks. Significant changes in the volatile compound composition were detected through analysis of variance (ANOVA) of repeated measures, considering both grape variety and browning tendency as discriminant categories. The amounts of fatty acids and fermentation esters in the wine were significantly changed by the oxidative storage. Some of these changes can be attributed to acid-ester hydrolysis equilibria, but not others, such as the decrease in concentrations of octanoic and decanoic acids. The oxidative storage also affected most of the unsaturated fatty-acid-derived compounds: trans-2-octenal, trans-2-nonenal, trans-2-decenal and 1-octen-3-ol were all found to increase in the first stages of storage, while hexanol decreased slightly. Volatile phenols behaved very differently: while phenol and 4-ethylphenol initially increased and later decreased, eugenol increased through the process and 4-vinyl-guaiacol disappeared. Benzaldehyde and furfural increased while methionol and terpenols disappeared. Only furfural was found to be linked with the tendency of the wine to brown, while only linalool and benzaldehyde were found to be linked whith the grape variety. The levels of some odorants previously isolated by sniffing detection were temptatively monitored, and significant changes in their concentrations were found to occur during the process. Received: 16 December 1996 / Revised version: 27 March 1997