Decarboxylation Of Amino Acids Research Articles

Improvement of the safety of artisanal Spanish fermented sausages: Spotlight on the role of bacteriocinogenic Lactiplantibacillus paraplantarum against a Companilactobacillus alimentarius histaminogenic strain

Biogenic amines (BA) in fermented sausages result from amino acid decarboxylation by microbial activity, either from technological or spoilage bacteria. Certain lactic acid bacteria typically found in fermented sausages are characterised for their ability to produce BA, especially histamine and tyramine. On the other hand, the bacteriocinogenic strain Lactiplantibacillus paraplantarum BPF2, isolated from a Spanish spontaneously dry-fermented sausages, has been characterized by good technological properties, production of leucocin K with antimicrobial activity against Listeria monocytogenes and ability to reduce the accumulation of BA in the final products. The antagonistic activity of leucocin K bacteriocin was tested in vitro against Companilactobacillus alimentarius SE14 (histamine producer), Enterococcus faecalis EF37 (tyramine producer), and L. monocytogenes Scott A. The inhibition of Comp. alimentarius SE14 by Lpl. paraplantarum BPF2 was assessed in traditional Spanish fermented sausages obtained in pilot plant, and chemico-physical parameters, microbial counts, and BA accumulation were monitored during fermentation and ripening. Leucocin K produced by Lpl. paraplantarum BPF2 was active in vitro against Comp. alimentarius SE14 and L. monocytogenes but was ineffective against E. faecalis EF37. The inoculation of the strain BPF2 as starter culture did not affect the expected chemico-physical (pH and colour) and microbial characteristics of the dry-fermented sausages. On the other hand, this strain was effective to significantly reduce the accumulation of histamine produced by the strain SE14, as well as putrescine and cadaverine. These findings demonstrated the relevant role of bacteriocin-producing strains as bio-protective starter cultures in improving the safety and quality of fermented meat products.

Pseudomonas fragi and Pseudomonas lundensis drove the co-spoilage in chilled pork: Insights from the metabolome

Pseudomonas fragi and Pseudomonas lundensis are key spoilage microorganisms in aerobically stored chilled meat, which had co-spoilage effect on chilled pork. However, the mechanism of co-spoilage interaction of P. fragi and P. lundensis has not been elucidated. The metabolism of nutrients in pork by mixed bacteria may differ from that by single strains. This study applied metabolomics and in vitro metabolite utilization experiment to assess the mechanism of that co-metabolize raw pork during storage. Results showed that co-spoilage group had 104 differential metabolites (histamine, N-methylhydantoin and D-gluconic acid, etc.) and 78 differential metabolites (putrescine, uracil acid and uracil, etc.) compared to P. fragi and P. lundensis group, respectively. These differential metabolites were mainly related to histidine metabolism, arginine biosynthesis, and purine. The co-spoilage effect of P. fragi and P. lundensis was related to the promotion of deamination and decarboxylation of histidine to produce histamine, the promotion of α-ketoglutarate and glutamate-mediated transamination, and the full utilization of the arginine deiminase pathway by the co-culture bacteria in the degradation of arginine to produce putrescine. In vitro experiment, co-cultures of these strains resulted in greater consumption of glucose, higher utilization activity, and promoted deamination and decarboxylation of amino acids. These findings reveal the complex and competitive interactions of co-culture of P. fragi and P. lundensis, providing insight into microbial spoilage mechanisms in chilled pork.

Ultrasensitive detection of histamine in spoiled meat employing silver nanoparticles decorated Perylene: An experimental-computational conjugation

Meat spoilage has been acquiring increasing attention recently and is directly associated with food safety and human health. Biogenic amines are the spying organic compounds fostered from the microorganism-mediated decarboxylation of amino acids during meat spoilage. Histamine, a biogenic amine acts as a model analyte and is toxic if consumed substantially. It is crucial to monitor histamine levels in meat due to its adverse effects. In this study, a simple and quick fluorescent sensor was fabricated for sensitive and selective detection of histamine. Citrate-capped silver nanoparticles (AgNP) were loaded onto Perylene (PER) to develop a sensing probe that was characterized using UV–visible, FTIR, XRD, and FESEM, and its optical behavior toward histamine was investigated. Moreover, the binding affinity between histamine and PER@AgNP was assessed using a DFT-based computer simulation. Under optimal conditions, the sensor showed linear relationships for histamine concentrations from 25 μM to 3200 μM with LOD 13.52 μM.

Mechanisms of ammonia-like off-flavors formation in dried shrimp: Contribution of spoilage microbiota and their metabolism

Dried shrimp is susceptible to ammonia-like off-flavors (ALOF) during storage, yet the formation mechanisms are still not fully clear. This study analysed the contribution of different parts of dried shrimp to ALOF and characterised the formation mechanisms mainly from microbiological spoilage and amino acid metabolism points. Results showed that head viscera were the main contributors to ALOF, and visceral bacteria were the primary source of microorganisms in stored dried shrimp. The sensory scores of groups without head viscera kept at 0–1 during the storage, indicating no smellable ammonia odour. Analysis of off-flavor indicators showed that visceral bacteria promoted protein degradation and amino acid metabolism. Both amino acid deamination and decarboxylation activities of spoilage microbiota contributed to ALOF formation; however, deamination activities of visceral microbiota were more prominent, particularly for bitter amino acids metabolism. These results provide guidelines for controlling ALOF generation in dried shrimp products during storage.

A Comprehensive Review on the Biogenic Amines in Cheeses: Their Origin, Chemical Characteristics, Hazard and Reduction Strategies.

Most of the biogenic amines are naturally found in fermented foods as a consequence of amino acid decarboxylation. Their formation is ascribable to microorganisms (starters, contaminants and autochthonous) present in the food matrix. The concentration of these molecules is important for food security reasons, as they are involved in food poisoning illnesses. The most frequent amines found in foods are histamine, putrescine, cadaverine, tyramine, tryptamine, phenylethylamine, spermine and spermidine. One of the most risk-prone foods are cheeses, mostly ripened ones, which could easily accumulate amines due to their peculiar manufacturing process and ripening. Cheeses represent a pivotal food in our diet, providing for nutrients such as amino acids, calcium, vitamins and others; thus, since they are widely consumed, it is important to evaluate the presence of toxic molecules to avoid consumers' poisoning. This review aimed to gather general information on the role of biogenic amines, their formation, the health issues and the microorganisms and processes that produce/reduce them, with a focus on their content in different types of cheese (from soft to hard cheeses) and the biotic and abiotic factors that influence their formation or reduction and concentration. Finally, a multivariate analysis was performed on the biogenic amine content, derived from data available in the literature, to obtain more information about the factors influencing their presence in cheeses.

Lipid Nanoparticle mRNA Therapy Improves Survival and Reduces Serum Branched-Chain Amino Acids in Mouse Models of Maple Syrup Urine Disease.

Maple syrup urine disease (MSUD) is a rare, inherited, metabolic disorder characterized by dysfunction of the multi-subunit, mitochondrial enzyme complex branched-chain alpha-keto acid dehydrogenase (BCKDH). BCKDH catalyzes the oxidative decarboxylation of branched-chain amino acids (BCAAs). BCAAs and their neurotoxic alpha-keto intermediates can accumulate in the blood and tissues in the absence of functional BCKDH. We evaluated a lipid nanoparticle (LNP)-based treatment approach to address all possible genetic mutations that can cause MSUD (BCKDHA, BCKDHB, and DBT). In the intermediate MSUD mouse model, which harbors a mutation in the dihydrolipoamide branched-chain transacylase E2 (DBT) subunit of BCKDH, repeated administration of LNP-encapsulated mRNA therapy significantly extended survival and reduced serum leucine levels. We also evaluated our LNP approach in several models of classic MSUD, namely DBT knockout (KO) mice and the new BCKDHA KO and BCKDHB KO mice. The latter two were generated by CRISPR/Cas9 gene editing and contain the highly prevalent classic MSUD-causing mutations seen in the Mennonite and Costa Rican populations. Intravenous LNP-encapsulated mRNA administration extended survival and increased body weight in the DBT KO and BCKDHA KO models of classic MSUD but was not effective in BCKDHB KO mice. Our data provide a promising proof-of-concept that a universal, mutation-independent approach to treating MSUD is possible and viable.

Biogenic Amines in Seafood

Biogenic amines (BAs) are organic compounds naturally formed in foods through the microbial decarboxylation of amino acids. These compounds are particularly significant in seafood due to the high susceptibility of these products to microbial contamination and improper storage conditions. Biogenic amines, including histamine, tyramine, putrescine, and cadaverine, are often indicators of food freshness and spoilage. Their presence at high levels can pose serious health risks to consumers, making the study of their formation, types, and control methods crucial for food safety. This comprehensive review examines the mechanisms underlying the formation of biogenic amines in seafood. The primary sources of these compounds are bacteria from the families Enterobacteriaceae, Lactobacillaceae, and Pseudomonadaceae. Factors such as temperature, pH, and oxygen availability significantly influence bacterial activity and, consequently, biogenic amine production. Histamine is highlighted as one of the most toxic biogenic amines, capable of causing histamine poisoning, which presents symptoms such as flushing, headaches, nausea, and vomiting. Control and prevention strategies for biogenic amine formation are critically discussed, including the maintenance of the cold chain, hygienic processing techniques, salting, fermentation, and the use of starter cultures. Additionally, innovative microbial inactivation methods such as high hydrostatic pressure and UV radiation are explored for their efficacy in reducing biogenic amine levels. The review also addresses current regulations and standards set by international health authorities, particularly focusing on histamine levels in fish and fish products. These regulations ensure regular monitoring and compliance to protect consumer health. Future research directions are proposed, emphasizing the need for developing new detection methods for rapid and sensitive identification of biogenic amines, improving bacterial inactivation techniques, and advancing genetic and molecular biology studies to better understand the production mechanisms of these compounds. Furthermore, raising consumer awareness about the health impacts of biogenic amines through educational programs is highlighted as a critical area for public health promotion. In conclusion, the review underscores the importance of biogenic amines in seafood quality and safety. Effective control and prevention measures, combined with ongoing research and regulatory compliance, are essential to minimize health risks associated with these compounds. Ensuring proper handling, storage, and processing conditions, along with increasing consumer awareness, will contribute significantly to managing and mitigating the risks posed by biogenic amines in seafood.

Constructing Ultra-Strong SERS Tags in the Cellular Raman-Silent Region by Orthogonal Array Testing Strategy.

Surface-enhanced Raman spectroscopy (SERS) tags have the advantages of unique fingerprint vibration spectrum, ultranarrow spectral line widths, and weak photobleaching effect, showing great potential for bioimaging. However, SERS imaging is still hindered for further application due to its weak spontaneous Raman scattering, biomolecular signal interference, and long acquisition times. Here, we develop a novel SERS tag of the core (Au)-shell (N-doped graphene) structure (Au@NGs) with ultrastrong and stable Raman signal (2180 cm-1) in the cellular Raman-silent region (1800-2800 cm-1) through base-promoted oxidative decarboxylation of amino acids. Exploring the factors (metal salts, amino acids, catalysts, temperature, etc.) to obtain Au@NGs with the strongest Raman signal commonly requires more than 100,000 separate experiments, while that using an orthogonal array testing strategy is reduced to 56. The existence of deep charge transfer between the Au surface and C≡N-graphene is proved by theoretical calculations, which means the ultrastrong signal of Au@NGs is the joint effect of electromagnetic and chemical enhancement. The Au@NGs have a detection sensitivity down to a single-nanoparticle level, and high-speed and high-resolution cellular imaging (4453 pixels) is obtained within 10 s by global Raman imaging. The combination of Au@NGs-based tags with ultrastrong intrinsic Raman imaging capability and global imaging technology holds great promise for high-speed Raman imaging.

1T/2H Mixed-phase MoS2 with enlarged interlayer spacing induced via bacteria-derived carbon for long-lifespan pseudocapacitors

Pseudocapacitors (PCs) are considered prospective candidates for large-scale aqueous energy storage systems due to their high power density. However, the poor cycling stability resulting from sluggish metal ion transport kinetics and the instability of the electrode structure hinders their further applications. To address this issue, an effective strategy of 1T/2H mixed-phase MoS2 directly grown on the electrochemically activated carbon (EC) induced via bacteria-derived carbon (BC) from bacillus subtilis is proposed to achieve efficient anodes for potassium ion capacitors. The inherent nitrogen elements found in the bacteria-derived carbon, along with a trace amount of amines and their derivatives generated from amino acid decarboxylation, act as support by inserting into the MoS2 interlayer. Amines and their derivatives as intercalators could suppress the MoS2 layer stacking and mitigate structure damage, which is responsible for preventing rapid capacity fading. Thus, the mixed-phase MoS2 with an expanded interlayer spacing of 0.94 nm achieves a remarkable durability with a capacitance retention of 110.2 % after 40,000 cycles at 10 A g−1. Density Functional Theory (DFT) reveals that the mixed-phase MoS2 could improve electron transfer ability and cyclic stability, in which the rich vacancies introduced by bacteria-derived carbon could enhance the K+ adsorption. To highlight, the asymmetric capacitor device (ASC) adopting mixed-phase MoS2 anode shows a long lifespan (88 % capacitance retention over 10,000 cycles). This work will provide a green approach to boost cycling performance of MoS2 anodes and shed light on developing high-performance MoS2-based materials for electrochemical energy storage.

Trace Amine-Associated Receptors' Role in Immune System Functions.

Trace amines are a separate, independent group of biogenic amines, close in structure to classical monoamine neurotransmitters such as dopamine, serotonin, and norepinephrine that include many products of the endogenous or bacteria-mediated decarboxylation of amino acids. A family of G protein-coupled trace amine-associated receptors (in humans, TAAR1, TAAR2, TAAR5, TAAR6, TAAR8, and TAAR9) that senses trace amines was discovered relatively recently. They are mostly investigated for their involvement in the olfaction of volatile amines encoding innate behaviors and their potential contribution to the pathogenesis of neuropsychiatric disorders, but the expression of the TAAR family of receptors is also observed in various populations of cells in the immune system. This review is focused on the basic information of the interaction of trace amines and their receptors with cells of the general immune systems of humans and other mammals. We also overview the available data on TAARs' role in the function of individual populations of myeloid and lymphoid cells. With further research on the regulatory role of the trace amine system in immune functions and on uncovering the contribution of these processes to the pathogenesis of the immune response, a significant advance in the field could be expected. Furthermore, the determination of the molecular mechanisms of TAARs' involvement in immune system regulation and the further investigation of their potential chemotactic role could bring about the development of new approaches for the treatment of disorders related to immune system dysfunctions.

Dopamine-Functionalized Gold Nanoparticles for Colorimetric Detection of Histamine.

Histamine, a primary biogenic amine (BA) generated through the decarboxylation of amino acids, concentration increases in protein-rich foods during deterioration. Thus, its detection plays a crucial role in ensuring food safety and quality. This study introduces an innovative approach involving the direct integration of dopamine onto gold nanoparticles (DCt-AuNP), aiming at rapid histamine colorimetric detection. Transmission electron microscopy revealed the aggregation of uniformly distributed spherical DCt-AuNPs with 12.02 ± 2.53 nm sizes upon the addition of histamine to DCt-AuNP solution. The Fourier-transform infrared (FTIR) spectra demonstrated the disappearance of the dicarboxy acetone peak at 1710 cm-1 along with the formation of well-defined peaks at 1585 cm-1, and 1396 cm-1 associated with the N-H bending modes and the aromatic C=C bond stretching vibration in histamine molecule, respectively, confirming the ligand exchange and interactions of histamine on the surface of DCt-AuNPs. The UV-vis spectra of the DCt-AuNP solution exhibited a red shift and a reduction in surface plasmon resonance (SPR) peak intensity at 518 nm along with the emergence of the 650 nm peak, signifying aggregation DCt-AuNPs with increasing histamine concentration. Notably, color transitions from wine-red to deep blue were observed in the DCt-AuNP solution in response to histamine, providing a reliable colorimetric signal. Dynamic Light Scattering (DLS) characterization showed a significant increase in the hydrodynamic diameter, from ∼15 to ∼1690 nm, confirming the interparticle cross-linking of DCt-AuNPs in the presence of histamine. This newly developed DCt-AuNP sensor provides colorimetric results in less than a minute that exhibits a remarkable naked-eye histamine detection threshold of 1.57 μM and a calculated detection limit of 0.426 μM, making it a promising tool for the rapid and sensitive detection of histamine.

Radical Mediated Decarboxylation of Amino Acids via Photochemical Carbonyl Sulfide (COS) Elimination.

Herein, we present the first examples of amino acid decarboxylation via photochemically activated carbonyl sulfide (COS) elimination of the corresponding thioacids. This method offers a mild approach for the decarboxylation of amino acids, furnishing N-alkyl amino derivatives. The methodology was compatible with amino acids displaying both polar and hydrophobic sidechains and was tolerant towards widely used amino acid-protecting groups. The compatibility of the reaction with continuous-flow conditions demonstrates the scalability of the process.

Peeling the onion: additional layers of regulation in the acid stress response.

Bacteria are capable of withstanding large changes in osmolality and cytoplasmic pH, unlike eukaryotes that tightly regulate their pH and cellular composition. Previous studies on the bacterial acid stress response described a rapid, brief acidification, followed by immediate recovery. More recent experiments with better pH probes have imaged single living cells, and we now appreciate that following acid stress, bacteria maintain an acidic cytoplasm for as long as the stress remains. This acidification enables pathogens to sense a host environment and turn on their virulence programs, for example, enabling survival and replication within acidic vacuoles. Single-cell analysis identified an intracellular pH threshold of ~6.5. Acid stress reduces the internal pH below this threshold, triggering the assembly of a type III secretion system in Salmonella and the secretion of virulence factors in the host. These pathways are significant because preventing intracellular acidification of Salmonella renders it avirulent, suggesting that acid stress pathways represent a potential therapeutic target. Although we refer to the acid stress response as singular, it is actually a complex response that involves numerous two-component signaling systems, several amino acid decarboxylation systems, as well as cellular buffering systems and electron transport chain components, among others. In a recent paper in the Journal of Bacteriology, M. G. Gorelik, H. Yakhnin, A. Pannuri, A. C. Walker, C. Pourciau, D. Czyz, T. Romeo, and P. Babitzke (J Bacteriol 206:e00354-23, 2024, https://doi.org/10.1128/jb.00354-23) describe a new connection linking the carbon storage regulator CsrA to the acid stress response, highlighting new additional layers of complexity.

Facile Synthesis of PEGylated Gold Nanoparticles for Enhanced Colorimetric Detection of Histamine.

Histamine is among the biogenic amines that are formed during the microbial decarboxylation of amino acids in various food products, posing a significant threat to both food safety and human health. Herein, we present a one-step synthesis of PEGylated gold nanoparticles (PEG-AuNPs) for rapid, simple, and cost-effective colorimetric histamine detection. PEG-AuNPs' surface plasmon resonance (SPR) range at 520-530 nm with a hydrodynamic size distribution of 20-40 nm. Fourier transform infrared (FT-IR) spectra confirmed the reduction of AuNPs at 1645 cm-1 along with the other observed peaks at 2870, 1350, and 1100 cm-1 as a strong evidence for the presence of PEG. Upon the addition of histamine to the PEG-AuNP solution, transmission electron microscopy (TEM) highlighted the aggregation of nanoparticles. In addition, red shifting and a decrease in the absorbance of the SPR peak along with the appearance of an additional peak at ∼690 nm was observed in the PEG-AuNP absorption spectra in the presence of histamine. Increasing the PEG concentration in the gold colloids leads to the formation of a protective barrier around the surface of nanoparticles, which influences the colloidal stability by impeding the aggregation of PEG-AuNPs upon histamine addition. The minimum colorimetric response of PEG-AuNPs to histamine concentration is 30 ppm, as assessed by the naked eye. The absorption ratio (A690/A526) showed a linear dynamic range from 20 to 100 ppm with a limit of detection of 9.357 μM. Additionally, the assay demonstrates a commendable selectivity toward histamine analyte.

Mechanism and degradation pathways of photo-Fenton system using Fe(III)-EDDS for Microcystis aeruginosa and microcystin-LR removal

Harmful algal blooms is a global problem of water pollution causing great economic losses to countries. Microcystis aeruginosa, as a dominant algal species in cyanobacterial blooms, has attracted extensive attention. However, most of the current studies on the treatment of alga-containing waters focus on the removal of algal cells or microcystins, lacking the exploration of the degradation pathways and analyses of the toxicity of the products. In this paper, we constructed a photo-Fenton system using Fe(III)-EDDS (EDDS: Ethylenediamine-N,N’-disuccinic acid) complex as an iron source for the simultaneous removal of Microcystis aeruginosa as well as microcystin-LR (MC-LR). The results showed that adding 0.1 mM of Fe(III)-EDDS complex and 1.0 mM of H2O2 achieved 83.3% algal cell removal in 240 min under neutral pH conditions and also degraded 72.5% of MC-LR. Moreover, the degradation products of MC-LR and EDDS were analyzed by LC-MS, which showed that the toxicity of the MC-LR molecule was greatly reduced by benzene ring removal and decarboxylation of partial amino acids, while its degradation resulted from the destruction of amino acids in the MC-LR molecule. The toxicity analyses provide a basis for the practical application of the system, hence consideration can be given to combining or improving it with the existing UV disinfection technologies in water supply plants for potential algal bloom outbreaks. This study was the first time to apply the Fe(III)-EDDS system to the field of microalgae removal and MC-LR detoxication, aiming to provide new development ideas for water purification and photochemical algae removal technology.

Microbial contribution to 14 biogenic amines accumulation in refrigerated raw and deep-fried hairtails (Trichiurus lepturus)

Biogenic amines (BAs) produced by microbial decarboxylation of amino acids are crucial toxic nitrogenous compounds in fish. An optimized ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC–MS/MS) method with simple pretreatment was established to detect 14 BAs in both raw (control check, CK) and deep-fried (DF) hairtails. This method exhibited a good linear relationship with average recoveries of 73.3–120.0 % and relative standard deviations of 2.5–10.0 %, respectively. The total BAs in CK and DF hairtails decreased sharply to 338.2 and 25.3 mg/kg on the 9th day, respectively. Four BAs, including cadaverine (CAD), histamine (HIS), tyramine (TYR), and putrescine (PUT) accounted for 92.5–99.9 % of total BAs were selected as the dominant BAs. Bacterial analysis showed that the abundance of DF was relatively low. Further correlation analysis proved that Vibrio had a significant (p < 0.05) positive correlation with total BAs and could be the main BA-producing bacterium in DF hairtail. This work provides new evidence of the accumulation of BAs in refrigerated hairtail.

Inhibition of Food-Borne Pathogen Growth and Biogenic Amine Synthesis by Spice Extracts

Food-borne pathogens and their toxins cause significant health problems in humans. Formation of biogenic amines (BAs) produced by microbial decarboxylation of amino acids in food is undesirable because it can induce toxic effects in consumers. Therefore, it is crucial to investigate the effects of natural additives with high bioactivity like spice extracts to inhibit the growth of these bacteria and the formation of BAs in food. In the present study, the antibacterial effects of diethyl ether spice (sumac, cumin, black pepper, and red pepper) extracts at doses of 1% (w/v) on Gram-positive (Staphylococcus aureus and Enterococcus faecalis) and Gram-negative (Klebsiella pneumoniae, Pseudomonas aeruginosa, Campylobacter jejuni, Aeromonas hydrophila, Salmonella Paratyphi A, and Yersinia enterocolitica) food-borne pathogen bacterial strains (FBP) were established. In addition, the accumulation of ammonia (AMN), trimethylamine (TMA), and biogenic amines (BAs) in tyrosine decarboxylase broth (TDB) was investigated by using high performance liquid chromatography (HPLC). Sumac extract exhibited the highest antibacterial potential against all FBPs, followed by cumin and peppers. AMN (570.71 mg/L) and TMA (53.66 mg/L) production were strongly inhibited by sumac extract in the levels of 55.10 mg/L for Y. enterocolitica and 2.76 mg/L for A. hydrophila, respectively. With the exception of S. aureus, black pepper dramatically reduced the synthesis of putrescine, serotonin, dopamine, and agmatine by FBP especially for Gram-negative ones. Furthermore, sumac extracts inhibited histamine and tyramine production by the majority of FBP. This research suggests the application of sumac extracts as natural preservatives for inhibiting the growth of FBPs and limiting the production of AMN, TMA, and BAs.

Optical dِِِِiscrimination of histamine and ethylenediamine in meat samples using a colorimetric affordable test strip (CATS): introducing a novel lab-on paper sensing strategy for low-cost ensuring food safety by rapid and accurate monitoring of biogenic amines.

Biogenic amines (BAs) are a group of organic compounds that are produced through the decarboxylation of amino acids by microorganisms. These compounds are commonly found in a variety of foods and are known to cause adverse health effects if consumed in high concentrations. Therefore, the development of sensitive and rapid detection methods for detection and determination of BAs is essential for ensuring food safety. In this study, a novel colorimetric affordable test strip (CATS) was developed for the colorimetric and naked-eye detection of two BAs of ethylenediamine (EDA) and histamine (HIS) in meat samples. Also, triangular silver nanoparticles (AgNPrs) were used as a diagnostic optical probe, and CATS used as a simple, environmentally friendly, inexpensive diagnostic substrate for on-site recognition of meat spoil. The AgNPrs-based optosensor demonstrated high sensitivity and selectivity towards EDA and HIS, allowing for the detection of low concentrations of the BAs in real food samples such as raw chicken and beef. The system presented a UV-vis technique for HIS and EDA analysis in the linear range of 0.1 μM to 0.01 mM, with an LLOQ of 0.1 μM, and 0.05 to 1 μM, with an LLOQ of 0.05 μM, respectively. Additionally, the performance of the designed CATS in the analysis of produced gases was evaluated, highlighting the potential of this simple and cost-effective strategy for the development of BAs diagnostic kits. This approach provides a simple and cost-effective method for detecting BAs in food, which could be beneficial for ensuring food safety and preventing the harmful effects associated with their consumption.

Redesigning transamination and decarboxylation characteristics of L-aspartate aminotransferase by site directed mutation of non-active site

Aspartate aminotransferase (L-AspAT) is a highly substrate-specific biocatalyst for chiral amino acid splitting and unnatural amino acid synthesis, with both transamination and decarboxylation functions, but it is frequently interfered with each other in the catalytic process. The characterized mutant strains for the isolation of transamination and decarboxylation were obtained by bioinformatics analysis and site-directed mutagenesis in this research. The results showed that the mutants T296D and C180I enhanced decarboxylation by hydrogen bonding to α-ketoglutarate. In contrast, the mutants W130S and W130P increased the transamination activities to 157 % and 144 % of the WT respectively, which improved the binding efficiency through the expansion of the substrate binding pocket of the mutations. In addition, the catalytic efficiency of W130P for o-chlorobenzoylformate was also increased to 226 % of the WT, and the size of the binding pocket with o-chlorobenzoylformate was increased from 9.2 Å to 11.5 Å, a big change improved the probability of the substrate's entry. These results provided an extremely important idea and theoretical basis for changing the preference of bifunctional enzymes by mutating.

Development and evaluation of a gas chromatography-mass spectrometry method for biogenic amines to assess decomposition in seafood

Biogenic amines (BAs) are low molecular mass compounds formed by the microbial-induced decarboxylation of specific amino acids. These molecules are markers of quality index and can indicate potential spoilage of a product. Currently, the FDA relies on sensory analysis as well as indole and histamine levels to evaluate the degree of seafood decomposition. However, there is a need for alternative analytical methods to corroborate those analyses. An optimized dispersive liquid-liquid microextraction (DLLME) method was developed for the extraction of four BAs (putrescine, cadaverine, histamine and tyramine) from various decomposition stages of nine seafood species previously tested by the FDA Seafood Sensory Experts. The BAs depicted very different concentration patterns between species and were able to distinguish within-species decomposition stages classified by the organoleptic analysis as “borderline increments”. The results suggest that all four analyzed BAs can be potentially used as biomarkers of seafood decomposition, but the choice of biomarker is species dependent. Some of the prominent associations were putrescine in shrimp, cadaverine in weakfish, histamine in canned tuna, and tyramine in scallops. The differentiation between “borderline” stages of decomposition also demonstrates the suitability of the method to support the FDA sensory analyses of seafood, ultimately leading to improved consumer protection.