Cyanogen chloride precursor analysis in chlorinated river water

Amino acids have been cited as potential precursors of the disinfection byproduct cyanogen chloride in chlorinated drinking water. Screening experiments with 17 amino acids were performed in this study to comprehensively identify important CNCl precursors. Among this set, only glycine was found to yield detectable CNCl (i.e., > 0.6% yields). Additional experiments were conducted to estimate the relative significance of glycine as a CNCI precursor in water samples collected from the Huron River, Michigan, by concurrently characterizing the amino acid content and monitoring CNCI yields after chlorination. Chlorine was added at slightly less than the sample breakpoint dose to optimize CNCl formation and stability in the samples. On the basis of previous determinations that glycine-nitrogen is stoichiometrically converted to CNCI-N at pH > 6, it was estimated that glycine may account for 42-45% of the CNCI formed in the river water samples (pH 8.2). The kinetic profile of CNCl formation in the sample, with a half-life of about 20 min, indicated that both rapid and slower formation pathways were important. Glycine formation of CNCl, with a half-life of 4 min, is likely to contribute significantly to the rapidly formed CNCI, while unidentified precursors must accountfor the slower pathway. Non-glycine-derived CNCl precursors in this water source were further examined to determine if they were largely proteinaceous in character using a technique known as immobilized metal ion affinity chromatography (IMAC). These experiments demonstrated that copper-loaded IMAC resins were much more effective in removing glycine than other CNCI precursor compounds in the sample matrix. The unidentified CNCI precursor components, therefore, are not likely to be proteinaceous and are more likely to be associated with the fulvic/humic fraction of organic matter.     

Reducing Acrylamide in Fried Snack Products by Adding Amino Acids

ABSTRACT: The aims of this study were to develop commercial methods for reducing the acrylamide content in processed foods and apply them to commercial snacks. The formation of acrylamide in fried foods was found to depend on the composition of raw materials as well as the frying time and temperature. In potato chips, acrylamide was rapidly formed at over 160°C, with the amount proportional to the heating duration and temperature. Free amino acids were used to reduce acrylamide, with lysine, glycine, and cysteine having the greatest effects in the aqueous system. Lysine and glycine were effective at inhibiting the formation of acrylamide in wheat-flour snacks. In potato snacks, the addition of 0.5% glycine to pallets reduced acrylamide by more than 70%. Soaking potato slices in a 3% solution of either lysine or glycine reduced the formation of acrylamide by more than 80% in potato chips fried for 1.5 min at 185°C. These results indicate that the addition of certain amino acids by soaking the uncooked products in appropriate solutions is an effective way of reducing acrylamide in processed foods.     

Formation of N-Substituted Pyrrole-2-Aldehydes in the Browning Reaction Between D-Xylose and Amino Compounds

SUMMARY– The formation of N -substituted pyrrole-2-aldehydes in the browning reaction between D-xylose and selected amino acids was investigated.
In order to facilitate the separation of the reaction products, the carbonyl compounds formed in the browning solution were converted into 2,4-dinitrophenylhydrazones (2,4-DNPs) and then esterified with diazomethane. Isolation of the esterified 2,4-DNP was accomplished by column chromatography with alumina. Chemical structures of the isolated 2,4-DNPs were confirmed by elementary analyses, ultraviolet and visible absorption spectra, and nuclear magnetic resonance spectra.
The following N -substituted pyrrole-2-aldehydes were isolated as methyl ester of 2,4-DNP, respectively: (2-formylpyrrol-I-ybacetic acid from the reaction mixture of D-xylose and glycine, 3-(2-formylpyrrol-1-y1)propionic acid from β-alanine, and 2-(2-formylpyrrol-1-y1)-4-methyl-valeric acid from L-leucine.
The extent of pyrrolealdehyde formation from D-xylose and selected alkylamine or amino acid was in the following order which corresponded to the extent of melanoidin formation: n-butylamine > methylamine, β-alanine > glycine > DL-alanine. N-substituted pyrrole-2-aldehyde was rather stable and was not considered to be an important intermediate of melanoidins. However, some correlationships between the formation of pyrrolealdehyde and that of melanoidins were demonstrated and discussed.     

Amino acid-dependent formation pathways of 2-acetylfuran and 2,5-dimethyl-4-hydroxy-3[2H]-furanone in the Maillard reaction

The formation pathways of two furanoids, 2-acetylfuran and 2,5-dimethyl-4-hydroxy-3[2H]-furanone (DMHF) were studied by GC–MS in the Maillard-type model system based on glucose and selected amino acids. The reaction was performed in 0.01 M phosphate buffer by heating a 1:1 mixture of [¹³C6] glucose and [¹²C6] glucose with amino acid. There is only one major formation pathway for DMHF in which the glucose carbon skeleton stayed intact. Formation pathways for 2-acetylfuran were more complicated. They formed either from glucose or from glucose and glycine. In the presence of glycine, the [C-5] unit of glucose combined with formaldehyde from glycine leads to 2-acetylfuran. For other amino acids, either cyclisation of intact glucose or recombination of glucose fragments can lead to 2-acetylfuran formation. These results indicate a competitive trend in controlling Maillard reaction. Therefore, besides changing Miallard reaction impact factors (temperature, time, pH etc.), inhibiting or preventing the competitive reaction cascade may direct desired pathways of Maillard reaction.     

Metabolomics reveals the effect of garlic on antioxidant- and protease-activities during Cheonggukjang (fermented soybean paste) fermentation

We performed mass spectrometry (MS)-based metabolite profiling of Cheonggukjang (CGJ) and three types of garlic (normal, sprouted, and fermented) added CGJ (G-CGJ). Metabolite profiling suggested that the major distinguishing factor between the four types of CGJ lay in whether garlic was added, although different metabolic states were observed in G-CGJ. Among the discriminant metabolites between CGJ and G-CGJ, the levels of four amino acids such as l-valine, l-isoleucine, l-leucine, and glycine were decreased in G-CGJ compared to CGJ because garlic inhibited the protease activity of Bacillus subtilis during fermentation. In addition, the relative contents of l-cysteine, s-allyl-cysteine, s-allyl-cysteine sulfoxide, soyasaponin βg, and soyasaponin γg, which showed positive correlation with antioxidant activities, were high in G-CGJ. These results suggest that MS-based metabolite profiling could be a useful tool for understanding the metabolic differences of fermented foods according to the additives, and their relationship with antioxidant activity.     

Nucleation of amino acid‐rich crystals on the surface of dried scallop (Chlamys farreri) during storage: formation mechanism and influence of environmental relative humidity

Formation of crystals on the surface of dried scallop (Chlamys farreri) adductor muscle is often observed during storage. The composition of these white crystals was determined, and the effect of relative humidity (RH) during storage on their formation was also studied. The white crystals were determined as the crystal of free amino acids, mainly composed of taurine (Tau) and glycine (Gly). The main polymorphic form of glycine in the crystals was further confirmed as the γ‐form. Besides free amino acids, another major part of the crystal composition was ions, such as Na⁺, NH₄⁺, K⁺, PO₄^3? and Cl^?. The presence of various free amino acids and Na⁺ and K⁺ might contribute to the crystallisation of γ‐glycine. RH particularly at 65% and above significantly increased the amount of crystals. RH of 43% and below was recommended to prevent the formation of amino acid‐rich crystals on dried scallops during storage.     

氨基酸对葡萄糖、半乳糖模型产生呋喃的影响

为研究氨基酸对葡萄糖和半乳糖模型产生呋喃的影响,通过向葡萄糖模型和半乳糖模型中加入不同含量的甘氨酸、丝氨酸、苏氨酸、谷氨酸,模拟密封罐装食品的灭菌条件（121 ℃条件下油浴30 min）,采用顶空气相色谱-质谱（headspace-gas chromatography-mass spectrometry,HS-GC-MS）法检测呋喃的含量。结果表明：低含量（≤5 mg）的甘氨酸、极低含量（1 mg）的丝氨酸、高含量（50 mg）的苏氨酸和谷氨酸的添加能够明显促进葡萄糖模型产生呋喃,而对于半乳糖模型,所有高含量（50 mg）氨基酸的添加都能够导致呋喃的大量产生。苏氨酸对葡萄糖模型产生呋喃的促进作用明显强于其余3 种氨基酸（P＜0.05）;对于半乳糖模型,甘氨酸、苏氨酸对其产生呋喃的促进作用最强,且它们之间无明显差异。     

Amino Acid Profiles of Common Cultivated Mushrooms Including the Identification of N-(N-γ-L-Glutamyl-3-Sulfo-L-Alanyl)Glycine in Flammulina velutipes

Amino acid profiles of nonprotein nitrogen (NPN) and protein nitrogen (PN) fractions of common cultivated mushrooms were determined. Free amino acids in the NPN fractions were generally characterized by the predominant occurrence of alanine and amino acids metabolically related to the glutamic acid family and also by the common presence of unique nonprotein amino acids, such as saccharopine, cystathionine and ethanolamine. A novel glutathione analog, N-(N-γ-L-glutamyl-3-sulfo-L-alanyl)glycine, was found in Flammulina velutipes. The proportion of the NPN to the total nitrogen was relatively high and large amounts of the NPN were made up of free amino acids and related compounds. Protein amino acids in the NPN and PN fractions accounted for about 65% of the total nitrogen, suggesting that a practical nitrogen-protein conversion factor for the mushrooms may be considered to be about 4 on the average.     

Cyclocondensation of 2,3-butanedione in the presence of amino acids and formation of 4,5-dimethyl-1,2-phenylendiamine

The chemical interaction of 2,3-butanedione with amino acids through Strecker reaction has been studied extensively. However, the formation of previously reported 4,5-dimethyl-1,2-benzoquinone from 2,3-butanedione/amino acid model systems has not been investigated in detail. In this study such model systems containing 2,3-butanedione were investigated under pyrolytic conditions using glycine, sodium glycinate and glycine hydrochloride as amino acids able to modulate acid/base catalytic activity of the reaction medium. The analysis of the data indicated that replacing glycine with its corresponding salts promoted significantly the generation of 2,3,6,7-tetramethylquinoxaline relative to tetramethylpyrazine, the indicator compound for the Strecker reaction. The origin of the 2,3,6,7-tetramethylquinoxaline was traced back to the formation of 4,5-dimethyl-1,2-benzoquinone through isotope labelling studies. Furthermore, these studies have also indicated the ability of glycine not only to catalyse the cyclocondensation of butanedione into 4,5-dimethyl-1,2-benzoquinone but also its conversion into 4,5-dimethyl-1,2-phenylenediamine through Strecker-type transformations. The trapping of 2,3-butanedione by this in situ generated 4,5-dimethyl-1,2-phenylenediamine gave rise to the observed 2,3,6,7-tetramethylquinoxaline.     

The potential of dairy lactic acid bacteria to metabolise amino acids via non-transaminating reactions and endogenous transamination

The metabolism of amino acids by 22 starter and 49 non-starter lactic acid bacteria (LAB) was studied in a system consisting of amino acids and non-growing cells without added amino acceptors such as alpha-ketoglutarate. There were significant inter- and intra-species differences in the metabolism of amino acids. Some amino acids such as alanine, arginine, aspartate, serine and branched-chain amino acids (leucine, isoleucine and valine) were utilised, whereas other amino acids such as glycine, ornithine and citrulline were produced. Alanine and aspartate were utilised by some LAB and accumulated during the incubation of other LAB. Arginine was degraded not only by Lactococcus lactis subsp. lactis (the lactococcal subspecies known to catabolise arginine), but also by pediococci, heterofermentative lactobacilli (Lactobacillus brevis and Lb. fermentum) and some unidentified homofermentative lactobacilli. Serine was utilised predominantly by homofermentative Lb. paracasei subsp. paracasei, Lb. rhamnosus and Lb. plantarum. Of the LAB studied, Lb. brevis and Lb. fermentum were the most metabolically active, utilising alanine, arginine, aspartate, glutamate and branched-chain amino acids. Leuconostocs were the least metabolically active, showing little potential to metabolise amino acids. The formation of ammonia and acetate from amino acid metabolism varied both between species and between strains within species. These findings suggest that the potential of LAB for amino acid metabolism via non-transaminating reactions and endogenous transamination will impact both on the physiology of LAB and on cheese ripening, especially when transamination is rate-limiting in the absence of an exogenous amino acceptor such as alpha-ketoglutarate.     

氨基酸对葡萄糖-天冬酰胺模拟体系中丙烯酰胺形成的抑制作用研究

目的 研究4种氨基酸对已建立的葡萄糖-天冬酰胺模拟体系中丙烯酰胺生成的影响。方法 以葡萄糖-天冬酰胺组为对照组,在此基础上分别加入半胱氨酸、甘氨酸、赖氨酸和谷氨酸4种氨基酸为实验组,于140℃反应5～30min,测定反应后模拟体系的褐变程度、色差值、生成丙烯酰胺含量和剩余葡萄糖含量。结果 4种氨基酸中,半胱氨酸和谷氨酸对模拟体系中的褐变度和色差值的抑制作用较好;半胱氨酸和赖氨酸对底物葡萄糖的消耗作用较快;半胱氨酸对丙烯酰胺的抑制效果最好,抑制率为(76.00±0.73)%,其他氨基酸的抑制率分别为甘氨酸(38.39±0.44)%、赖氨酸(51.03±3.09)%和谷氨酸(28.76±2.43)%;进一步研究发现,当添加4.2mmol半胱氨酸时,丙烯酰胺抑制率达(95.32±0.47)%。结论 4种氨基酸相比,半胱氨酸对丙烯酰胺形成的抑制效果最好,且对于降低葡萄糖-天冬酰胺模拟体系的褐变度、色差值、葡萄糖含量有较好的效果。     

Effect of glucose and glycine addition to cocoa mass before roasting on Maillard precursor consumption and pyrazine formation

Cocoa mass was treated with glucose and/or glycine before roasting. For glucose‐treated samples the reductions in reducing sugars and free amino acids were 41.1 and 56.9% respectively, whereas for glycine‐treated samples the respective reductions were 16.2 and 37.4%. The combination of glucose plus glycine treatment led to 39.0 and 48.9% reductions in reducing sugars and free amino acids respectively. For free amino acids the reductions in control and glucose‐treated samples were similar, 56.2 and 56.9% respectively, indicating that the added glucose did not significantly (P < 0.05) influence the free amino acid uptake. When glycine was added, the consumption of free amino acids (37.4%) was lower than for the control and glucose treatments. When glucose and glycine were added, the reduction in free amino acids (48.9%) was lower than for the control and glucose treatments but higher than for the glycine treatment. Apparently, glycine addition inhibited the reducing sugar and free amino acid consumption, whereas glucose addition enhanced the reducing sugar and free amino acid consumption. The glucose plus glycine treatment was similar to the glycine treatment in the contents of 2,5‐dimethyl‐ and trimethylpyrazines. For 2‐methylpyrazine the value for glucose‐treated samples was lower than for control and glycine‐treated samples but almost equal to the value for the glucose plus glycine treatment. It is concluded that the addition of glucose and/or glycine does not affect pyrazine production. © 2002 Society of Chemical Industry     

Liposome encapsulation protects bacteriocin-like substance P34 against inhibition by Maillard reaction products

Bacteriocins are biopreservatives with potential to be used in heat processed foods, and liposome encapsulation may offer a protective effect against interaction of these peptides with food compounds. In this work, Maillard reaction products (MRPs) were prepared by heating (90 °C for 7 h) different combinations of sugars and amino acids, and their inhibitory capacity against free and liposome-encapsulated bacteriocin-like substance (BLS) P34 was evaluated. MRPs formed by fructose and glycine had the highest inhibitory capacity against free and encapsulated BLS P43, remaining 50% of initial activity. Liposome encapsulation increased stability of BLS P34 when it was confronted to glucose/glycine, galactose/glycine, sucrose/glycine and glucose/alanine MRPs. Inhibition mostly occurs within the first 24 h of incubation of BLS P34 and MRPs. Inhibitory activity seems to be associated to melanoidin formation and antioxidant capacity of MRPs. The results show that liposome encapsulation of BLS P34 may be an interesting technique to increase the stability of antimicrobial peptides in heat treated foods.     

Optimization of nutrient-induced germination of Bacillus sporothermodurans spores using response surface methodology

Spores of Bacillus sporothermodurans are known to be contaminant of dairy products and to be extremely heat-resistant. The induction of endospore germination before a heat treatment could be an efficient method to inactivate these bacteria and ensure milk stability. In this study, the nutrient-induced germination of B. sporothermodurans LTIS27 spores was studied. Testing the effect of 23 nutrient elements to trigger an important germination rate of B. sporothermodurans spores, only d-glucose, l-alanine, and inosine were considered as strong independent germinants. Both inosine and l-alanine play major roles as co-germinants with several other amino acids. A central composite experimental design with three factors (l-alanine, d-glucose, and temperature) using response surface methodology was used to optimize the nutrient-induced germination. The optimal rate of nutrient-induced germination (100%) of B. sporothermodurans spores was obtained after incubation of spore for 60 min at 35 °C in presence of 9 and 60 mM of d-glucose and l-alanine, respectively. The results in this study can help to predict the effect of environmental factors and nutrients on spore germination, which will be beneficial for screening of B. sporothermodurans in milk after induction their germination. Moreover, the chosen method of optimization of the nutrient-induced germination was efficient in finding the optimum values of three factors.     

食品中D-氨基酸的形成机制及生理功能研究进展

自然界构成蛋白质的20种氨基酸中，除甘氨酸外，其他19种氨基酸均具有两个互为镜像的立体异构体（D型和L型）。传统观点认为L-氨基酸是参与生命活动的主体，而D-氨基酸在生物体内的存在及生理活性未被重视。随着氨基酸手性分析技术的发展，从包括人类在内的哺乳动物、植物、微生物等有机体中发现大量D-氨基酸及含有D-氨基酸的生物活性肽。D-氨基酸具备独特的生理活性，主要表现在神经信号传导、激素调节、抗菌、免疫调节等方面。日常膳食是人体D-氨基酸的主要来源，其为人类日均提供约100 mg D-氨基酸。食品中的D-氨基酸主要在发酵、高温及一定的p H值等加工条件下产生，少量来自食品原料本身。目前市场上已开始出现以D-氨基酸为主要成分的新兴功能性食品，其蕴含的巨大潜力仍有待深入挖掘，并有望成为未来新型功能性食品的重要原料。     

Effect of amino acids on Maillard reaction product formation and total antioxidant capacity in white pan bread

Maillard reaction products (MRPs) can be an important dietary antioxidant source. Bread is the most popular bakery product; however, limited information is available on the antioxidant activities of MRPs generated during bread-baking. This paper reports the effect of different amino acids on bread properties, melanoidin formation and antioxidant activities. Totally six amino acids at four different levels were evaluated. Increasing the amount of amino acid led to darker bread crust, higher melanoidin content and stronger antioxidant activity. Among the six amino acids, bread with glycine had the highest melanoidin content and ABTS radical scavenging activity up to 1079.77 ± 8.43 μmol TE mg⁻¹. Bread with lysine had the highest DPPH radical scavenging activity up to 281.97 ± 10.52 μmol TE mg⁻¹. Bread with alanine had the highest crust metal chelating activity compared with others. Adding certain dietary amino acids is a potential approach to enhance the antioxidant capacity of bread products.     

Role of amino acids and glucose in development of burnt off-flavours in liver sausage during heat processing

The effect of amino acids and glucose on the development of burnt off-flavours was investigated in meat model systems for liver sausage. At a constant glucose concentration, the burnt flavour was intensified by addition of an amino acid mixture. In a batter without liver, the development of burnt off-flavours, similar to those in liver sausage, could be induced through addition of exogenous amino acids and glucose. The endogenous amino acids from liver reacted more intensely than the exogenous amino acids in the formation of the burnt flavour components. After heating batches with added exogenous amino acids and glucose the free amino acid contents (73–89% of initial content) were higher than in batches to which liver was added (42–53% of initial content). The differences in the free amino acid content of glycine, glutamic acid and threonine were linearly related to the intensity of burnt flavour. Results indicate that burnt flavour is due to the Maillard reaction.     

Effect of amino acids on the formation of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) in creatinine/phenylalanine and creatinine/phenylalanine/4-oxo-2-nonenal reaction mixtures

2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) formation in mixtures of creatinine, phenylalanine, amino acids and 4-oxo-2-nonenal was studied, to analyse the role of amino acids on the generation of this heterocyclic aromatic amine. When oxidised lipid was absent, cysteine, serine, aspartic acid, threonine, asparagine, tryptophan, tyrosine, proline, and methionine increased significantly (p < 0.05) the amount of PhIP formed in comparison to the control. When lipid was present, only the addition of methionine, glycine, and serine increased significantly (p < 0.05) the amount of PhIP produced, while histidine, cysteine, lysine, tryptophan, tyrosine, and alanine reduced significantly (p < 0.05) PhIP. These results may be a consequence of the different competitive reactions that occur. Thus, in the absence of lipids, thermal decomposition of the amino acids produced reactive carbonyls that converted phenylalanine into phenylacetaldehyde as a key step in the formation of PhIP. When oxidised lipid was present, amino acids competed with phenylalanine for the lipid, and amino acid degradation products were formed, among which alpha-keto acids seemed to play a role in these reactions. These results suggest that PhIP can be produced by several alternative reaction pathways from all major food components, including amino acids and lipids, in addition to carbohydrates.     

不同氨基酸和糖对美拉德反应产物的影响

利用半胱氨酸、甘氨酸、谷氨酸3 种氨基酸和木糖、葡萄糖2 种还原糖作为反应底物,模拟美拉德反应制备香精,并对其香气成分和有害物质进行综合分析。结果表明：参与反应的氨基酸种类越多,所测得的挥发性物质种数也越多,反应产物的风味越丰富;甘氨酸参与的美拉德反应中丙烯酰胺的生成量较少,而谷氨酸的参与反应中丙烯酰胺的生成量较多;还原糖种类对丙烯酰胺的产生影响不大;谷氨酸参与的美拉德反应产物中,5-羟甲基糠醛（5-hydroxymethylfurfural,5-HMF）含量高,而半胱氨酸和甘氨酸参与的反应产物中,5-HMF的含量较低;木糖可减少产物中的5-HMF的含量。利用本实验条件制备香精,产物中的丙烯酰胺和5-HMF含量在安全范围内。     

Intermediate role of α-keto acids in the formation of Strecker aldehydes

The ability of α-keto acids to covert amino acids into Strecker aldehydes was investigated in an attempt to both identify new pathways for Strecker degradation, and analyse the role of α-keto acids as intermediate compounds in the formation of Strecker aldehydes by oxidised lipids. The results obtained indicated that phenylalanine was converted into phenylacetaldehyde to a significant extent by all α-keto acids assayed; glyoxylic acid being the most reactive α-keto acid for this reaction. It has been proposed that the reaction occurs by formation of an imine between the keto group of the α-keto acid, and the amino group of the amino acid. This then undergoes an electronic rearrangement with the loss of carbon dioxide to produce a new imine. This final imine is the origin of both the Strecker aldehyde and the amino acid from which the α-keto acid is derived. When glycine was incubated in the presence of 4,5-epoxy-2-decenal, the amino acid was converted into glyoxylic acid, and this α-keto acid was then able to convert phenylalanine into phenylacetaldehyde. All these results suggest that Strecker aldehydes can be produced by amino acid degradation initiated by different reactive carbonyl compounds, included those coming from amino acids and proteins. In addition, α-keto acids may act as intermediates for the Strecker degradation of amino acids by oxidised lipids.