N-Benzylazacyclophane synthesis via aromatic Mannich reaction

A new method for synthesizing phenolic N-benzylazacyclophanes starting from tyramine is presented here. Computational calculations showed that macrocyclization is favored by the formation of hydrogen bond-based templates; these templates are not affected by including benzyl groups in the nitrogen atom of the tyramine moiety. The results showed that N-benzyl groups with electron-donating substituents have more nucleophilic nitrogen atoms, thereby favoring macrocyclization, while electron-withdrawing groups favor polymerization.     

基于酪胺信号放大的新型免疫传感器

将酪胺应用于酶联免疫分析,建立了一种新的高灵敏伏安型免疫传感器。利用纳米金的静电吸咐和己二硫醇、巯基乙胺的自组装,将羊抗人IgG抗体固定到金电极表面上,以辣根过氧化物酶标记羊抗人IgG抗体为酶标抗体,以生物素化酪胺为酶底物,利用催化酪胺沉积反应,在传感界面沉积大量生物素,使原始信号得到几何级数的放大。结果表明,通过生物素化酪胺催化放大后,制得的免疫传感器对H2O2的催化能力增大近20倍,检测hIgG在1.5μg/L～22 mg/L范围内有良好的线性关系,检出限为0.1μg/L。用于实际试样的回收率的测定,结果良好。     

Enzymatic determination of biogenic amines with transglutaminase

Tyramine, histamine, putrescine and cadaverine, the most common biogenic amines indicating the food quality, were studied in the transglutaminase-catalyzed reaction. Transglutaminase (protein-glutamine gamma-glutamyltransferase EC 2.3.2.13) catalyzes an acyl transfer reaction between a donor substrate and an acceptor substrate (e.g. biogenic amine) and forms a cross-linkage between substrates with a release of ammonia. The reaction can be monitored by measuring the ammonia produced in the reaction. The concentration of produced ammonia was found to be proportional to the concentration of biogenic amine and could hence be used to determination of biogenic amines in food matrixes.     

VUV Photoionization and Dissociation of Tyramine and Dopamine: the Joint Experimental and Theoretical Studies

Photon induced dissociation investigations of neutral tyramine and dopamine are carried out with synchrotron vacuum ultraviolet photoionization mass spectrometry and theoretical calculations. At low photon energy, only molecular ions are measured by virtue of near-threshold photoionization. While increasing photon energy to 11.7 eV or more, four distinct fragment ions are obtained for tyramine and dopamine, respectively. Besides, the ioniza-tion energies of tyramine and dopamine are determined to be 7.98±0.05 and 7.67±0.05 eV by measuring the photoionization efficiency curves of corresponding molecular ions. With help of density function theory calculations, the detailed fragmentation pathways are es-tablished as well. These two molecular cations have similar aminoethyl group elimination pathways, C₇H₈O₂^+·(m/z=124) and C₇H₈O^+·(m/z=108) are supposed to be generated by the McLafferty rearrangement via γ-hydrogen (γ-H) shift inducing β-fission. And CH₂NH₂⁺ is proposed to derive from the direct fission of C7-C8 bond. Besides, the McLafferty rear-rangement and the C7-C8 bond fission are validated to be dominant dissociation pathways for tyramine and dopamine cations.     

Recent trends in the determination of biogenic amines in fermented beverages – A review

Biogenic amines (BA) are generally considered as a food hazard, even though there is not a threshold for these biomolecules in the European legislation, except for histamine in fishery products. These compounds are formed during the storage and processing of certain foods through microbiological activity, and when present in high concentrations, could have toxicological effects, causing health problems in consumers, especially to sensitive persons. This fact, in addition to the economical concern involved, makes it necessary to control the amounts of biogenic amines in foods. For all these reasons, literature on biogenic amines in different food products, especially in fermented beverages, is extensive. This review provides an overview of the most recent trends in the determination of biogenic amines in fermented beverages focusing on novelty, improvement and optimization of analytical methods. Hence, the different sample treatment procedures (including derivatization), the most important analytical techniques and the most frequent applications are described and discussed. Although biogenic amines have been determined in wine and other fermented beverages for decades, new advancements and technical possibilities have allowed to increase the accuracy and sensitivity of analytical methods, in order to overcome the challenges posed by the complex matrices and their high intrinsic variability. Thus, the different purposes of BA determination (food safety, production process or food microbiology research) and the most widely employed analytical techniques have been reviewed.     

Rapid simultaneous determination of amines and organic acids in citrus using high-performance liquid chromatography

Rapid analytical method for the simultaneous separation and determination of amines and organic acids is a vital interest for quality control of citrus and their products. In the present study, a simultaneous high performance liquid chromatography (HPLC) method for the rapid separation of three amines and two organic acids was developed. Chromatographic separation of compounds was achieved using Xbridge C₁₈ column at ambient temperature, with an isocratic mobile phase of 3 mM phosphoric acid at a flow rate of 1.0 mL min⁻¹. A photodiode array (PDA) detector was used to monitor the eluent at 223 nm and 254 nm with a total analysis time of 10 min. Extraction of amines and organic acids from citrus juice was optimized. The method was validated by tests of linearity, recovery, precision and ruggedness. The limit of detection (LOD) and limit of quantification (LOQ) for amines and ascorbic acid were determined to be 5 ng and 9.8 ng, respectively. All calibration curves showed good linearity (R² ≥ 0.9999) within the test ranges. The recoveries of the amines and organic acids ranged between 84% and 117%. The identity of each peak was confirmed by mass spectral (MS) analysis. The developed method was successfully applied to analyze the content of amines and organic acids in six different species and two varieties of citrus. Results indicate that mandarin and Marrs sweet orange contain high level of amines, while pummelo and Rio Red grapefruit had high content of ascorbic acid (137-251 μg mL⁻¹) and citric acid (5-22 mg mL⁻¹). Synephrine was the major amine present in Clementine (114 μg mL⁻¹) and Marrs sweet orange (85 μg mL⁻¹). To the best of our knowledge, this is the first report on simultaneous separation and quantification of amines and organic acids in Marrs sweet orange, Meyer lemon, Nova tangerine, Clementine, Ugli tangelo and Wekiwa tangelo.     

Disposable Horseradish Peroxidase Biosensors for the Selective Determination of Tyramine

This work reports the development of horseradish peroxidase based biosensors using screen‐printed carbon electrodes for the determination of tyramine (tyr). A novel procedure based on the insertion of the enzyme in the screen‐printing process (SPC_HRPEs) has been compared with the cross‐linked immobilization into the carbon working electrode (HRP/SPCEs). Both biosensors were characterized obtaining good capability of detection (2.1±0.2 and 0.2±0.01 µM for SPC_HRPEs and HRP/SPCEs, respectively). The reproducibility was 3.4 % and 6.8 % for SPC_HRPEs and HRP/SPCEs, respectively. The repeatability was 2.2 % and 7.1 % for SPC_HRPEs and HRP/SPCEs, respectively. The specificity towards different biogenic amines was analyzed. The developed biosensors were applied to the determination of tyr content in cheese samples.     

Preparation and characterization of sensing membranes for the detection of glucose, lactate and tyramine in microtiter plates

In this work, sensing membranes for the detection of glucose, lactate and tyramine were successfully prepared by immobilizing enzymes and fluorophore on sol-gels. The membranes were fabricated on the bottom of the wells in a microtiter plate. Glucose oxidase (GOD), lactate oxidase (LOD) and tyramine oxidase (TOD) were immobilized on individual sol-gels or a mixture of different sol-gels (3-glycidoxypropyl-trimethoxysilane (GPTMS), methyl-triethoxysilane (MTES), aminopropyl-trimethoxysilane (APTMS)). The oxidation of the analytes specifically catalyzed by the enzymes resulted in the reduction of the oxygen concentration, which changed the fluorescence intensity (FI) of the oxygen sensitive ruthenium complex acting as the transducer. The linear calibration graphs were in the ranges of 0.0-5.0 g/l for glucose, 0.0-9.0 mg/l for lactate and 0.0-100 mg/l for tyramine. The values of the detection limit were found to be 0.10-0.52 g/l for glucose, 7.77 mg/l for lactate and 6.30-8.73 mg/l for tyramine. The covalent binding between the epoxy and amine groups of the sol-gels and enzymes, respectively, prevented the enzymes from being washed out and preserved the high stability of the sensing membranes. The different ratios of silanes in the sol-gels, which were used as the supporting matrix for the immobilization of the enzymes led to different responses of the sensing membranes to various concentrations of glucose, lactate and tyramine. The kinetic parameters of the enzymatic reactions, and the stability and other parameters for the sensing membranes were also investigated.     

Determination of histamine and some other amines by high-performance capillary electrophoresis with on-line mode in-capillary derivatization

We have developed a method for the determination of histamine (His), tyramine (Tyr) and cadaverine (Cad) using high-performance capillary electrophoresis with fluorescence detection and an on-line mode in-capillary derivatization with o-phthalaldehyde (OPA)/N-acetylcysteine (NAC) as derivatization reagent. HPCE separation of His, Tyr, Cad and Spermidine (Spd) was influenced by sodium dodecyl sulfate (SDS) and phosphate–borate buffer (pH 10) concentration. After optimization of the method, a 4-component amine solution containing His, Tyr, Cad and Spd could be separated and detected by using 2 mM OPA/NAC–20 mM SDS–20 mM phosphate–borate buffer (pH 10) as a run buffer at an applied voltage of 25 kV, with detection at 340 nm. Although a practical sensitivity level can be obtained by using fluorescence detection (λ_ex=340 nm, λ_em=450 nm) instead of ultraviolet–visible detection, Spd was not detected at all. The precision (relative standard deviation; n=15) of this method for within- and between-days is less than 2.9% (peak area) and 1.3% (migration time), respectively. Linearity for these analytes, except for Spd, was established over a concentration range of 0.02 to 1.00 μmol/ml and detection limits (S/N=3) range from 1 nmol/ml for His and Tyr to 5 nmol/ml for Cad. The determination of His and some amines in aging raw fish meat samples (room temperature, 48 h) was carried out using the described method with fluorescence detection.