Relative reactivity of amino acids with chlorine in mixtures

The relative reactivity of chlorine with amino acids is an important determinant of the resulting chlorination products in systems where chlorine is the limiting reagent, for example, in the human gastrointestinal tract after consumption of chlorine-containing water, or during food preparation with chlorinated water. Since few direct determinations of the initial reactivity of chlorine with amino acids have been made, 17 amino acids were compared in this study using competitive kinetic principles. The experimental results showed that (1) most amino acids have similar initial reactivities at neutral pH; (2) amino acids with thiol groups such as methionine and cysteine are exceptionally reactive and produce sulfoxides; (3) amino acids without thiol groups primarily undergo monochlorination of the amino nitrogen; and (4) glycine and proline are the least reactive. Dichlorination was estimated to occur with approximately 26% of the amino acid groups when the total amino acid: chlorine concentrations were equal.     

造纸法再造烟叶氨基酸、Amadori化合物含量分析及工艺影响研究

氨基酸、Amadori化合物与造纸法再造烟叶感官品质密切相关,本文研究国内外代表性造纸法再造烟叶产品中氨基酸、Amadori化合物含量差异,并结合再造烟叶生产过程中氨基酸、Amadori化合物含量变化趋势分析,以指导国产造纸法再造烟叶工业控制.研究结果表明,国内外造纸法再造烟叶产品中氨基酸、Amadori化合物含量有较...     

4-Hydroxynonenal and cholesterol oxidation products in atherosclerosis

4-Hydroxynonenal (HNE) is by far the most investigated aldehydic end-product of oxidative breakdown of membrane n-6 polyunsaturated fatty acids. Its potential involvement in the pathogenesis of atherosclerosis has been corroborated by its consistent detection in both oxidized LDL and fibrotic plaque in humans. HNE has been shown to activate both macrophage and smooth muscle cells, i.e. the two key cell types in chronic inflammatory processes characterized by excessive fibrogenesis. By signalling to the nucleus, the aldehyde may up-regulate in these cells both expression and synthesis of monocyte chemotactic protein 1 (MCP-1) and transforming growth factor beta1 (TGFbeta1). Oxysterols, namely 27 carbon atoms oxidation products of cholesterol, are found in relatively high amount in LDL from hypercholesterolemic individuals and are consistently detectable in foam cells and necrotic core of human atherosclerotic lesion. As for HNE, the challenge of cells of the macrophage lineage with a mixture of oxysterols like that detectable in hypercholesterolemic individuals led to a marked overexpression of TGFbeta1 and MCP-1. Both HNE and oxysterols then appear to be candidates for a primary role in the progression of the atherosclerotic process.     

Forty years of furosine - forty years of using Maillard reaction products as indicators of the nutritional quality of foods

The Maillard reaction products (MRPs) most widely used as markers of the nutritional quality of foods are furosine, N(epsilon)-carboxymethyllysine (CML), hydroxymethylfurfural, pyrraline, pentosidine and pronyl-lysine. One of the MRPs identified first was furosine, which was quantified in foods 40 years ago as a chemical indicator of the Amadori compound N(epsilon)-fructoselysine. Since then, furosine has gained broad attention by food chemists and biomedical researchers, as its formation upon heat treatment is well characterised. Moreover, it represents the Amadori products from early Maillard reactions in which amino acids react with reducing carbohydrates, resulting in a loss of their availability. This is of importance for the essential amino acid lysine, which is also the limiting amino acid in many proteins. In order to evaluate the nutritional quality of a protein, the concomitant analysis of free - and nutritionally available - lysine and the amount of lysine reacted to form the respective MRP is essential, even for mildly processed foods. The other chemical markers of heat treatment such as CML, pyrraline, pentosidine or pronyl-lysine seem to be useful markers of the advanced stages of Maillard reactions. Compared to the conditions in which furosine is formed, these compounds are generated under more severe conditions of heat treatment. However, the concentrations analysed are significantly lower than those of furosine. Therefore, the nutritional evaluation of a food protein should include not only furosine, but also other chemical markers of heat treatment such as, for example, CML, pyrraline and pentosidine.     

加料发酵对茄芯烟叶化学成分及表面细菌多样性的影响

【目的】为探究茄芯烟叶在加料发酵方式下化学成分及表面细菌多样性的变化。【方法】以茄芯烟叶“印尼J/F/G”为试验材料,测定了加水（对照组）和加料（试验组）发酵烟叶主要化学成分的变化,并分析了随着发酵时间的延长烟叶的表面细菌群落结构和丰富度的变化。【结果】（1）工业发酵过程中烟叶表面细菌多样性发生明显变化,料液的添加提高了烟叶Operational taxonomicunit(OTU)数目并改变烟叶细菌群落结构与优势菌群。（2）烟叶蛋白含量在工业发酵过程中无明显变化,维持在16.45%～17.46%。（3）随着发酵进程的推进,对照组氨基酸总量呈现明显下降趋势,而料液在稳定烟叶氨基酸总量的同时,也有助于提升烟叶中苯丙氨酸、脯氨酸等Amadori氨基酸含量。（4）发酵开始时,试验组石油醚提取物含量高于对照组,对照组雪茄烟叶的石油醚提取物含量随发酵时间延长而显著增加,而试验组烟叶在工业发酵过程中的石油醚提取物含量增幅不明显。（5）工业发酵对烟叶中的豆蔻酸和月桂酸等饱和脂肪酸含量影响甚微,而料液的加入使发酵末期的烟叶油酸含量降低了52.37%。【结论】茄芯烟叶在工业发酵过程中,料液的添加改变了烟...     

Subcellular localization of fructosyl amino acid oxidases in peroxisomes of Aspergillus terreus and Penicillium janthinellum

Fructosyl amino acid oxidase (FAOD) is the enzyme catalyzing the oxidative deglycation of Amadori compounds, such as fructosyl amino acids, yielding the corresponding amino acids, glucosone, and H(2)O(2). In a previous report, we determined the primary structures of cDNAs coding for FAODs from two fungal strains Aspergillus terreus AP1 and Penicillium janthinellum and we found that both fungal FAODs included the putative peroxisome targeting signal 1 (PTS1) at the carboxyl terminal (Yoshida, N. et al., Eur. J. Biochem., 242, 499-505, 1996). In this study, we determined the intracellular localization of FAODs in these two fungi. Subcellular fractionation experiments and immuno-electronmicroscopic observations, together with the previous findings indicated that the FAODs were localized in peroxisomes of A. terreus AP1 and P. janthinellum. These FAODs were also found to belong to a new member of "peroxisomal sarcosine oxidase family protein" in eucaryotic cells.     

Formation of heterocyclic amine–amino acid adducts by heating in a model system

Although mutagenic and carcinogenic heterocyclic amines (HCAs) are known to be formed in cooked meat and fish, human HCA exposure and carcinogenic risk have not been elucidated in sufficient detail. In this work, we investigated the formations of HCA–amino acid adducts in a model system by using a liquid chromatography–mass spectrometry to elucidate another source of human HCA exposure. The 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) adduct with glycine was formed easily by heating at 200 °C within 5 min, which is probably based on the dehydration condensation of the amino group of PhIP and carboxyl group of glycine. PhIP and other HCAs such as 2-amino-3-methyl-3H-imidazo[4,5-f]quinolone, 2-amino-3,8-dimethylimidazo[4,5-f]-quinoxaline and 3-amino-1,4-dimethyl-5H-pyrido[3,4-b]indole, also bound with various amino acids by heating. Among these amino acids, proline tends to form adducts with HCAs, but serine, cysteine and lysine hardly bound with HCAs. These results provided a basic understanding of the formation of HCA adducts with amino acids during cooking.     

Model studies on the heating of food proteins. Amino acid composition of lysozyme, ribonuclease and insulin after dry heating

Lysozyme, ribonuclease and insulin were exposed to dry heating for 1 to 24 h at temperatures between 80 and 180 degrees C. Amino acid analyses of the heated samples showed that most of the amino acids are stable up to 120 degrees C. Initially, at higher temperatures, an almost rectilinear decrease took place which reached a critical stage at 160 degrees C. Nonpolar aliphatic, acidic and aromatic amino acids were all relatively stable (maximum loss less than 20% after 24 h at 180 degrees C). The lability of the other amino acids increased in the order proline, arginine, histidine, cysteine, threonine, lysine, tryptophan, serine, and methionine. Methionine was 86% decomposed after 24 h at 180 degrees C. Loss of trinitrobenzene sulfonic acid-reactive lysine ("available lysine") reached 20% at 100 degrees C and essentially 100% after 24 h at 180 degrees C. Maximum loss in weight during heating was 11%, although maximum protein loss was between 20 and 35%. Reaction orders and activation energies were estimated for some of the amino acid losses. Of the atypical amino acids ("hot spots") lysinoalanine, allo-isoleucine and ornithine that were detected, only lysinoalanine is useful as an indicator to detect amino acid damage after dry heating.     

The Strecker Degradation of Amino Acids: Newer Avenues for Flavor Formation

Newer aspects of the Strecker degradation related to foods are examined in terms of currently accepted mechanisms and isolated reaction intermediates. Emphasis is placed on Strecker and Strecker-like reactions between amino acids and lipid oxidation products, and terpenes or o-quinones as potential sources of novel flavor compounds. In addition, reactions are described in which Strecker aldehydes are formed directly from Amadori compounds instead of via amino acid/carbonyl reactions.     

Influence of fatty acids compositions and manufacturing type on the formation of 4-hydroxy-2-alkenals in food lipids

Correlations between 4-hydroxy-2-hexenal (HHE) or 4-hydroxy-2-nonenal (HNE) and fatty acids were statistically investigated in 73 kinds of commercially available food sources of n-3 or n-6 polyunsaturated fatty acids (PUFA). The analysis revealed that the level of HNE was obviously correlated with the contents of PUFA (r=0.462), n-6 PUFA (r=0.512), and saturated fatty acids (r=0.535). Significant correlation was also observed between HHE and HNE (r=0.486) although whose source fatty acids were different. Regarding the sesame oils and perilla oils currently available on the Korean markets, no appreciable difference in the levels of HHE or HNE was found depending on their manufacturing types.     

Volatiles from interactions of Maillard reactions and lipids.

This article provides current information on the production of volatile compounds from interactions of Maillard reactions and lipids. It includes a brief introduction outlining the Maillard reactions, the Strecker degradation of amino acids, and the oxidation of lipids. It highlights those compounds derived from these reactions that could interact to form volatile flavor components during the processing or cooking of food. The article discusses results obtained from model systems involving interactions between (1) Maillard reaction products and carbonyl compounds, (2) amino acids and carbonyl compounds, (3) amino acids and derivatives of fatty acids, and (4) Maillard reaction products, triglycerides and phospholipids. The qualitative and quantitative effects that triglycerides and phospholipids have on the formation of volatile Maillard products are also discussed. Particular attention is given to those long-chain alkyl heterocyclic compounds formed during these reactions, proposed methods for their formation, and their aromas. The role that such compounds play in food flavors is discussed with reference to those volatile compounds identified in certain cooked foods, such as meat (beef, lamb, and pork), chicken, potatoes (baked, French-fried, and crisps), and beverages (coffee, tea, and cocoa).     

Four permeases import proline and the toxic proline analogue azetidine-2-carboxylate into yeast

We have found that proline and the toxic proline analogue azetidine-2-carboxylate (AzC) are efficiently imported into Saccharomyces cerevisiae cells by four amino acid permeases, including two nitrogen-regulated permeases (PUT4 and GAP1) and two permeases that are regulated by the SPS sensor of extracellular amino acids (AGP1 and GNP1). In contrast to Agp1p, Gnp1p is not functionally expressed when cells are grown on media containing proline as sole nitrogen source. These findings have implications for the interpretation of studies using AzC to characterize nitrogen source-dependent regulation of amino acid uptake and of post-Golgi targeting and localization of amino acid permeases in yeast.     

陈窖豆豉粑类黑精提取及骨架肽段氨基酸组成分析

发酵期18个月的陈窖豆豉粑,其类黑精含量按Hashiba方法以干基计为4.76%。采用优化的常温分离提取工艺获得的类黑精组分经氨基酸分析表明,陈窖豆豉粑类黑精骨架由肽段构成,并且肽段中最具类黑精形成活性的氨基酸残基主要是天冬氨酸(Asp)、谷氨酸(Glu)、精氨酸(Arg)、赖氨酸(Lys)和脯氨酸(Pro)。     

Heat-induced decomposition of disaccharide Amadori compounds in quasi-water-free reaction conditions]

The thermally induced decomposition of disaccharide Amadori compounds has been compared to those of monosaccharide ones under almost water-free conditions. The structure of the synthesized maltulosyl compound has been proved to be 4C1-alpha-D-glucopyranosyl- (1----4)-2C5-beta-D-fructopyranosylglycine by 1H- and 13C-NMR spectroscopy. The decomposition of Amadori compounds has been used to study the kinetics of the browning reaction. Compared to fructosylglycine and maltotriulosylglycine, the browning of the disaccharide is faster. Curie point pyrolysis at 300 degrees C and investigation of the pyrolysate by gas chromatography/mass spectrometry have shown that the disaccharide component influences the thermal process. Furanes and furanones have been detected as predominant degradation products, the main one being 2(5H)-furanone. For the first time, we suggest a reaction pathway for the formation of these products via the Maillard reaction which includes 1,6-anhydroglucose.     

4-hydroxy-2-alkenals in polyunsaturated fatty acids-fortified infant formulas and other commercial food products.

4-Hydroxy-2-hexenal (HHE) and 4-hydroxy-2-nonenal (HNE) were determined using selected ion-monitoring gas chromatography-mass spectrometry (GC-MS) in 56 kinds of commercially available PUFA-fortified foods including infant formulas and baby foods. HHE and HNE, each specifically coming from the oxidation of n-3 and n-6 polyunsaturated fatty acids (PUFA), were observed at <10-77 and 41-132 microg kg(-1) in the infant formulas (n = 12) and at <10-52 and 36-116 microg kg(-1) in the baby foods (n = 7), respectively. 4-Hydroxy-2-alkenals in infant formulas and baby foods were further determined at 10 and 30 days after opening in an attempt to examine the time dependence of the levels of 4-hydroxy-2-alkenals. The values of HHE and HNE had increased appreciably to <10-220 and 79-792 microg kg(-1) in infant formulas and to <10-112 and 135-572 microg kg(-1) in baby foods, respectively, at 10 days and decreased, although statistically not significant, in most of the tested samples after 30 days, which suggested that the reactive compounds might interact with other constituents like proteins in the samples to form adducts or be decomposed with time. Based on the current study, it was calculated that 3-month to 1-year-old babies maintained exclusively on these commercially available PUFA-fortified infant formulas or baby foods could be exposed to a maximum of 20.2 microg kg(-1) body weight day(-1) of 4-hydroxy-2-alkenals, which is two orders of magnitude higher than the exposure of Korean adults estimated in a previous study of the authors' (2005). The present study may trigger future studies investigating the physiological influence of 4-hydroxy-2-alkenals originating from the diet on man at an early stage of development.     

Verhalten von Amadori-Verbindungen w?hrend der Kakaoverarbeitung 1. Bildung und Abbau von Amadori-Verbindungen

Zusammenfassung Es konnte nachgewiesen werden, daß sowohl in geröstetem als auch in ungeröstetem Kakao Amadori-Verbindungen vorkommen. Sie werden aus reduzierenden Zuckern (Aldosen) und Aminosäuren gebildet. Sie stellen Vorstufen der bei Röstprozessen ablaufenden und zur Aromabildung führenden Maillard-Reaktion dar. Amadori-Verbindungen treten zwar bereits bei der Aminosäureanalyse von Kakaoextrakten in Erscheinung, werden hier aber nur unvollständig getrennt und können daher nicht zugeordnet werden. Eine vollständige Auftrennung der in Kakao enthaltenen Amadori-Verbindungen war erst durch Capillargaschromatographie nach erfolgter Oximierung und Silylierung möglich. Es treten für jede der Einzelverbindungen Doppelpeaks auf, die der syn- und anti-Form der Oxime entsprechen. Die Untersuchungen ergaben, daß Amadori-Verbindungen bereits in fermentierten und im Erzeugerland getrockneten Kakaobohnen vorliegen. Ihre von den jeweiligen Mengen der freien Aminosäuren abhängigen Konzentrationen nehmen bei einer der Röstung vorgeschalteten Vortrocknung weiter zu. Im Verlauf der Röstung erfolgt anfangs eine gewisse Zunahme, später jedoch eine Abnahme. Auch während des bei der Schokoladenherstellung sich anschließenden Conchierprozesses werden Amadori-Verbindungen weiter abgebaut.

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The role of Amadori compounds during cocoa processing1. Formation and decomposition of Amadori compounds

Summary Amadori compounds formed by the reaction of reducing sugars (aldoses) and amino acids occur in both roasted and unroasted cocoa. They are precursors of the Maillard reaction leading to the formation of aroma compounds during the roasting processes. Amadori compounds appear during the amino acid analysis of cocoa extracts. However, they cannot be separated completely and therefore cannot be identified. Prior to gas chromatographic separation, the Amadori compounds isolated from cocoa were oximated and trimethylsilylized. By capillary gas chromatography double peaks for each compound corresponding to the syn- and anti-forms of the oximes were obtained. It was shown that Amadori compounds already occur in fermented cocoa beans dried in the producer country. Depending on the amounts of the individual free amino acids, their concentrations increase during pre-drying prior to roasting. Furthermore during the roasting process an increase in the amount of these compounds Was observed which was later followed by a decrease. Amadori compounds also decompose during the conching process performed during chocolate processing.

     

Isolation and characterization of proline iminopeptidase from Propionibacterium freudenreichii ATCC 9614

A dimeric, 90 kDa subunit intracellular proline iminopeptidase from Propionibacterium freudenreichii ATCC 9614 was purified to homogeneity by chromatography on hydroxyapatite, Sephacryl 200, Phenyl Superose and Mono Q. The enzyme was specific on Pro-p-nitroanilide and Pro-X dipeptides. It hydrolyzed 2 fragments of hormone oligopeptides with an N-terminal proline: bradykinin, f2-7 and substance P, f4-11. A number of oligopeptides containing 5-11 amino acids residues and proline at the penultimate position from N-terminus or other internal position were not hydrolyzed. The enzyme was most active at pH 7-7.5 and at 37-40 degrees C but it retained 9% of maximal activity at pH 5.5 and >12% of maximal activity at 10 or 60 degrees C. The enzyme was inhibited strongly by the serine protease inhibitor 3,4-dichloroisocoumarin, and stimulated markedly by 1 mol/l of NaCl. The results indicate that the enzyme may lead to the accumulation of proline from dipeptides and oligopeptides during the ripening of cheese.     

“中国苦水玫瑰”氨基酸含量及其代谢香气组分与种植区域的相关性

采集甘肃永登不同地域种植的“中国苦水玫瑰”花瓣和种植土壤样品，采用氨基酸自动分析仪、固相微萃取联合气相色谱-质谱联用仪和离子色谱仪检测花瓣中氨基酸含量、氨基酸代谢香气组分构成及土壤理化指标。结果显示，“中国苦水玫瑰”花瓣中含有丰富的氨基酸，不同种植区域氨基酸含量差异显著，谷氨酸、丙氨酸、赖氨酸、脯氨酸是影响不同地区玫瑰样品氨基酸构成的主要组分，除了丙氨酸，其余3种氨基酸均在大同地区含量最高。在样品中共检出氨基酸代谢类香气物质11种，其含量在3个地区存在一定的差异，大同地区玫瑰样品中含有较多的氨基酸代谢类香气物质。不同地区“中国苦水玫瑰”种植的土壤理化指标无明显相似性，SO₄^2-、有效磷、HCO₃^-是受地域影响最大的3个组分，且土壤性质与氨基酸含量及其代谢香气组分均存在着不同程度的相关性。     

The Free Amino Acids of Israel Orange Juice

SUMMARY— Twenty-two Israel orange juice samples were analyzed chromatographically, and 16 free amino acids were identified with seven different solvent systems. Aspartic acid, glutamic acid, lysine, alanine, and proline were identified with all 7 solvent systems; asparagine with 6; serine with 5; arginine, valine and leucine with 4; γ-amino-butyric acid with 3; glycine, methionine and phenylalanine with 2; and threo-nine and tyrosine with 1. The presence of isoleucine in Israel orange juice appears doubtful.
A quantitative estimation of the free amino acids indicates that amounts of aspartic acid, serine, and alanine are high compared with California orange juice, but glutamic acid and lysine are low.     

A Kinetic Study of the Reaction of Aqueous Chlorine and Chlorine Dioxide with Amino Acids, Peptides and Proteins

Reactions involving aqueous chlorine and ClO₂ with amino acids in 0.1M sodium phosphate buffer at pH 3, 6, and 9 were studied using iodometric and spectrophotometric techniques. The N,N-diethyl-p-phenylene-diamine (DPD) titrimetric technique was used to differentiate the chlorinated species formed in the reaction mixture. Chlorinated derivatives of amino acids were readily formed and then decomposed. Except in the mixtures with proline, hydroxyproline and glycine, the rate of loss of available chlorine in the reaction mixtures followed first order kinetics and was found to be pH dependent. Only a few amino acids reacted with aqueous ClO₂. The reaction also followed pseudo-first order kinetics. Reactions of three peptides and two proteins with aqueous chlorine and ClO₂ at pH 6.0 were also studied. Except for aspartame, they reacted rapidly with both chlorine compounds.