Molecular characterization and functional roles for Vibrio alginolyticus resistance of an octopamine/tyramine receptor of the white shrimp, Litopenaeus vannamei

Octopamine and Tyramine are biogenic amines that have been demonstrated to play an important immunological role in white shrimp, Litopenaeus vannamei. G protein-coupled receptors, known as seven-transmembrane domain receptors, are a variety of neurotransmitter receptors which are sensitive to biogenic amines for initiating the cell signaling pathway. In present study, we cloned and characterized an octopamine/tyramine receptor (LvOA/TA-R) from the hemocytes of L. vannamei, with a 1194 b.p. open reading frame that encodes 398 amino acids. Several bioinformatics analyses indicated that LvOA/TA-R had seven conserved hydrophobic transmembrane domains. The phylogenetic analysis and multiple sequence alignment indicated that LvOA/TA-R was orthologous to the OA/TA receptor of tiger shrimp, P. monodon. LvOA/TA-R was expressed in hemocytes and nervous tissue including circumoesphageal connective tissue and the thoracic and abdominal ganglia. Significant increases in LvOA/TA-R occurred in hemocytes of L. vannamei under Vibrio alginolyticus infection within 30-60 min of infection. Here, we demonstrated that LvOA/TA-R expression is upregulated in response to Vibrio alginolyticus infection and appears to be functionally responsible for the observed immune response. These results suggest that LvOA/TA-R mediates regulation of immunity, which promotes the resistance of L. vannamei to V. alginolyticus.

Functional aspects of evolution in a cluster of salivary protein genes from mosquitoes

The D7 proteins are highly expressed in the saliva of hematophagous Nematocera and bind biogenic amines and eicosanoid compounds produced by the host during blood feeding. These proteins are encoded by gene clusters expressing forms having one or two odorant-binding protein-like domains. Here we examine functional diversity within the D7 group in the genus Anopheles and make structural comparisons with D7 proteins from culicine mosquitoes in order to understand aspects of D7 functional evolution. Two domain long form (D7L) and one domain short form (D7S) proteins from anopheline and culicine mosquitoes were characterized to determine their ligand selectivity and binding pocket structures. We previously showed that a D7L protein from Anopheles stephensi, of the subgenus Cellia, could bind eicosanoids at a site in its N-terminal domain but could not bind biogenic amines in its C-terminal domain as does a D7L1 ortholog from the culicine species Aedes aegypti, raising the question of whether anopheline D7L proteins had lost their ability to bind biogenic amines. Here we find that D7L from anopheline species belonging to two other subgenera, Nyssorhynchus and Anopheles, can bind biogenic amines and have a structure much like the Ae. aegypti ortholog. The unusual D7L, D7L3, can also bind serotonin in the Cellia species An. gambiae. We also show through structural comparisons with culicine forms that the biogenic amine binding function of single domain D7S proteins in the genus Anopheles may have evolved through gene conversion of structurally similar proteins, which did not have biogenic amine binding capability. Collectively, the data indicate that D7L proteins had a biogenic amine and eicosanoid binding function in the common ancestor of anopheline and culicine mosquitoes, and that the D7S proteins may have acquired a biogenic amine binding function in anophelines through a gene conversion process.

Probiotic potential of Tetragenococcus halophilus EFEL7002 isolated from Korean soy Meju

BACKGROUND

Probiotic starters can improve the flavor profile, texture, and health-promoting properties of fermented foods. Tetragenococcus halophilus is a halophilic lactic acid bacterium that is a candidate starter for high-salt fermented foods. However, the species is known to produce biogenic amines, which are associated with neurotoxicity. Here, we report a probiotic starter strain of T. halophilus, EFEL7002, that is suitable for use in high-salt fermentation.

RESULTS

EFEL7002 was isolated from Korean meju (fermented soybean) and identified as T. halophilus, with 99.85% similarity. The strain is safe for use in food as it is a non-hemolytic and non-biogenic amine producer. EFEL7002 is tolerant to gastrointestinal conditions and can adhere to Caco-2 cells. This strain showed antioxidant, anti-inflammatory, and protective effects against the human gut epithelial barrier. EFEL7002 grew well in media containing 0-18% NaCl showing maximum cell densities in 6% or 12% NaCl.

CONCLUSIONS

T. halophilus EFEL7002 can be used as a health-promoting probiotic starter culture for various salty fermented foods.

Bioinformatics analysis of amino acid decarboxylases related to four major biogenic amines in pickles

Microbial amino acid decarboxylases (AADs) produce biogenic amines (BAs) in fermented food. However, a systematic comparison of the AADs' properties from different microorganisms in pickle fermentation remains unexplored. Here, we bioinformatically analyzed the amino acid sequences of AADs corresponding to four major BAs for common microorganisms in pickle fermentation. We showed that their sequences, besides tyrosine decarboxylase, differed among microorganisms. Overall, the AAD sequences varied lesser among bacterial species than between bacteria and fungi, with those in Lactobacillus sharing occasionally high similarity with other bacteria. Most AADs were predicted as stable cytosolic endoenzymes. Molecular docking showed that most commonly used spice components in pickle production, especially pepper, chili, and ginger, strongly bind to the AAD active sites, thus may inhibit the enzymes and reduce the BA accumulation. This study provides insights for deeply understanding the different microbial AAD properties in pickle fermentation and reducing BAs by appropriately using spices.

Effect of organic acids on the formation of biogenic amines in fermented anchovy sauce comprising raw anchovy materials with different levels of freshness

We investigated the effect of different levels of organic acids on the formation of biogenic amines in anchovy fish sauce. Fish sauce samples were prepared with fresh anchovies used immediately after being caught (F), and anchovies left at ambient temperature for 4 h (4 h), 18 h (18 h), or 24 h (24 h). Anchovies from each of the four groups were mixed with salt at a 4:1 ratio and then fermented at ambient temperature for varying periods of time. The F and 4 h anchovies contained higher levels of acetic acid, succinic acid, and lactic acid, and the levels increased during the fermentation process. The histamine content of the fish sauce samples prepared using F anchovies ranged from 44.0 to 9.2 mg/kg at 1 and 24 months of fermentation. The histamine content of fish sauce samples prepared using 4 h, 18 h, and 24 h anchovies was 111.5-37.0 mg/kg (4 h), 780.1-560.3 mg/kg (18 h), and 880.6-675.7 mg/kg (24 h). Our findings indicated that the histamine and other biogenic amine levels were closely associated with the degree of freshness of the raw anchovy material. These findings indicate that lower pH levels resulting from organic acids generated by the fresh raw material can effectively inhibit histamine formation.

Dietary administration of tyramine upregulates on immune resistance, carbohydrate metabolism, and biogenic amines in Macrobrachium rosenbergii

Survival rates of prawn, Macrobrachium rosenbergii, against Lactococcus garvieae, immune parameters, carbohydrate metabolism and biogenic amines were determined when the prawn were fed diets containing tyramine (TA) at the levels of 1 and 10 mg kg^-1. Results showed that prawn fed diets containing TA for 3 days, challenged with L. garvieae, and then continuously fed individually tested diets had a significantly higher survival rate than those fed the control diet at 168 h after the challenge, in a dose-dependent manner. Results included significant increases in total haemocyte count (THC), granular cells (GCs), semigranular cells (SGCs), phenoloxidase (PO) activity, respiratory bursts (RBs), RBs per haemocyte, phagocytic activity, and clearance efficiency to L. garvieae. Significantly lower plasma glucose and lactate were observed in prawn fed with TA-containing diets for 3 days, a result consistent with increases in the survival rate of the challenge test and the haemolymph octopamine (OA) level. Haemolymph dopamine (DA), norepinephrine (NE), TA, and OA levels of prawn that were fed TA-supplemented diets increased significantly after 1 day, and OA level increased continuously until the third day with a dose-effect relationship. It is therefore concluded that TA can be absorbed from a TA-containing diet to elevate haemolymph TA level, inducing the release of DA, NE, and OA to maintain homeostasis. The higher, more extensive OA expression promoted carbohydrate metabolism and immune resistance in M. rosenbergii.

Reducing biogenic amine in seriflux and huangjiu by recycling of seriflux inoculated with Lactobacillus plantarum JN01

High content of biogenic amine (BA) in huangjiu could pose serious quality concerns. More than 71% of BA in huangjiu were carried over from seriflux (rice soaking wastewater), which were produced by some BA producing bacteria during rice soaking process. A BA non-producing strain, Lactobacillus plantarum JN01, was introduced to rice soaking process, which decreased BA content in seriflux by 93.8% by niche competition at bench scale. Recycling of seriflux inoculated with L. plantarum JN01 at pilot run scale for ten batches demonstrated that BA in seriflux and huangjiu were reduced by 78.4% and 87.7%, respectively. The safety of huangjiu was enormously improved without affecting on the profiles of flavor compounds. Our results demostrated that seriflux recycling technology could reduce 50% of water consumption and achieve "zero effluents" in rice soaking process, which might potentially be a "green technology" not only for huangjiu brewing industry, but also for other related traditional fermented food industries.

Simultaneous derivatization and liquid-solid phase transition microextraction of six biogenic amines in foods followed by narrowbore liquid chromatography-ultraviolet detection

Biogenic amines are quality control criteria for foods that are potentially toxic to humans. In this study, amidation derivatization for biogenic amines and liquid-solid phase transition microextraction were carried out simultaneously for food sample pretreatment. The derivatization reaction was executed in one pot with coumarin-3-carboxylic acid as the derivatizing reagent and (1-cyano-2-ethoxy-2-oxoethylidenaminooxy)dimethylamino-morpholino-carbenium hexafluorophosphate as the coupling agent. Liquid-solid phase transition microextraction was achieved by the salting-out effect, using a phase change salt (1 M disodium hydrogen phosphate) solution. The combined derivatization and microextraction process was completed within 3 min at 30 °C, and the liquid top phase was easily obtained by placing the tube in an ice bath. Finally, a narrowbore liquid chromatograph coupled with a UV detector was used to determine the levels of six biogenic amines. The coupling agent-assisted derivatization and liquid-solid phase transition microextraction parameters were also investigated. The quantitative linear ranges were 3-400 μM for histamine, putrescine, spermidine, cadaverine, and tyramine and 5-400 μM for spermine, and the detection limit was 1 μM. The relative standard deviations of the intra- and inter-batches were <5.3% and 8.4%, respectively, while the relative error was <4.5% for both. We successfully applied this simultaneous derivatization-microextraction method to determine the biogenic amines in fermented foods.

Bacterial Diversity of Sun-Dried Spanish Mackerel in Dalian and Application of Lactobacillus plantarum X23 as a Biopreservative

ABSTRACT

Sun-dried Spanish mackerel is a common food in Dalian and made by adding salt and sun drying, which has special physical, chemical, and microbiological properties. In this study, the physicochemical properties and microbial composition of commercially available sun-dried Spanish mackerel in Dalian were assessed, and some Lactobacillus strains were screened as a biopreservative for sun-dried Spanish mackerel preparation. The results showed that the total volatile base nitrogen content in the traditional sun-dried Spanish mackerel samples from Dalian was within 30 mg/100 g, the histamine content was 7 to 17 mg/kg, and the dominant bacteria at the genus level were Lactobacillus, Psychrobacter, and Ralstonia. A strain with biopreservative potential was isolated from a sun-dried Spanish mackerel sample, identified as L. plantarum species by 16S rDNA sequencing, and assigned as L. plantarum X23. Fresh Spanish mackerel flesh was treated with 16% brine and L. plantarum X23 at a dose of 107 CFU/mL and then dried in the sun. The sun-dried Spanish mackerel flesh treated with 16% brine and L. plantarum X23 showed a decreased histamine and acid value, increased free amino acid content, and a higher sensory score compared with the sun-dried Spanish mackerel without L. plantarum X23 treatment (P < 0.05). In conclusion, the sun-dried Spanish mackerel purchased from the supermarkets in Dalian were safely edible, and L. plantarum X23 can significantly reduce the content of histamine and putrescine in self-made, low-salt, sun-dried Spanish mackerel and has potential as a biopreservative for sun-dried Spanish mackerel preparation.

HIGHLIGHTS

Metagenomic insights into the bacteria responsible for producing biogenic amines in sufu

Harmful levels of biogenic amines (BAs) are frequently identified in sufu. The microorganisms and mechanisms responsible for BA production in sufu, however, are not well documented. In this study, sufu samples were randomly obtained from various regions of China. Putrescine, tyramine, and histamine were quantitated as the most abundant BAs. According to the metagenome sequencing, the abundances and diversities of genes encoding the critical enzymes in BA production were acquired. The results showed that genes encoding arginine-, ornithine-, tryptophan-, and histidine decarboxylases were the predominant amino acid decarboxylase genes. Furthermore, 34 metagenome-assembled genomes (MAGs) were generated, of which 23 encoded at least one gene involved in BA production. Genetic analysis of MAGs indicated genera affiliated with Enterococcus, Lactobacillus-related, and Lactococcus were the major histamine-synthesizing bacteria, and tyrosine may be utilized by Bacillus, Chryseobacterium, Kurthia, Lysinibacillus, Macrococcus, and Streptococcus to product tyramine. The critical species involved in two putrescine-producing pathways were also explored. In the ornithine decarboxylase pathway, Lactobacillus-related and Veillonella were predicted to be the main performers, whereas Sphingobacterium and unclassified Flavobacteriaceae were the dominant executors in the agmatine deiminase pathway. The present study not only explained the BAs formation mechanism in sufu but also identified specific bacteria used to control BAs in fermented soybean products.

Evaluation and prediction of the biogenic amines in Chinese traditional broad bean paste

Biogenic amines (BAs) are a threat to the safety of broad bean paste, and biosynthetic mechanism of BA and its regulation are unknown. This study aimed to assess microbial BA synthesis in Chinese traditional broad bean paste and determine favorable fermentation conditions for BA regulation. The BAs content in 27 pastes was within the safe range. 64 strains with potential decarboxylation were screened in Luria-Bertani Glycerol medium and identified as Bacillus spp. Although Bacillus amyloliquefaciens produced highest levels of BAs (70.14 ± 2.69 mg/L) in LBAA, Bacillus subtilis produced 6% more BAs than B. amyloliquefaciens. Meanwhile, temperature was the most remarkable factor affecting BAs production by B. amyloliquefaciens 1-13. Furthermore, the fermented broad bean paste model revealed that BA content increased by 61.2 mg/kg every 10 days at 45 °C, which was approximately threefold of that at 25 °C. An ARIMA prediction model of BAs content was constructed, and the total BAs content of 40 mg/100 g was set as the critical value. This study not only contributed to understanding the BAs formation mechanism, but also provided potential measures to control the BAs in fermented soybean products.

Regulation of dopamine production in the brains during sexual maturation in male honey bees

To explore the physiological mechanisms that underlie age-related dopamine increases during sexual maturation in the brains of male honey bees, we focused on the expression of genes encoding the enzymes tyrosine hydroxylase (Amth) and DOPA decarboxylase (Amddc), which are involved in dopamine biosynthesis in the brain. We hypothesized that juvenile hormone in hemolymph and tyrosine intake from food known as factors enhancing brain dopamine levels might both control the expression of genes related to dopamine production, and we tested this hypothesis in experiments. The brain levels of tyrosine and DOPA, which are precursors of dopamine, decreased as males aged, whereas the dopamine levels increased, suggesting active metabolism of dopamine precursors. The relative expression levels of Amth and Amddc were significantly higher in the brains of 4-day-old males compared with 0-day-old males, and the higher level of Amddc was maintained after 8 days. Topical application of the juvenile hormone analog methoprene enhanced the expression levels of Amth and Amddc in the brains according to the methoprene concentration. Oral intake of tyrosine enhanced the tyrosine, DOPA and dopamine levels in the brain, and activated Amddc expression in the brain, suggesting that tyrosine intake can increase both substrates and enzyme for dopamine biosynthesis. These results support our hypothesis that juvenile hormone and tyrosine intake may enhance the expression levels of genes encoding enzymes involved in dopamine biosynthesis in male honey bee brains during sexual maturation.

Changes in biogenic amines, biochemical and microbial attributes of three spotted crab (Portunus sanguinolentus) during iced and refrigerated storage

Three spotted crab (Portunus sanguinolentus) is a preferred variety of crab among seafood consumers. Biochemical, microbial and sensory characters along with formation of biogenic amines of whole crabs stored under iced and refrigerated condition was evaluated. Cadaverine, putrescine and spermidine were the major amines formed during spoilage and a strong correlation between cadaverine and psychrotrophs was observed in refrigerated (0.92) and iced storage (0.86) respectively. Histamine was at lower level and not likely to cause any toxicological problems to consumers. Although TVB-N and TMA-N increased significantly (p < 0.01), TVBN was observed as a good indicator of spoilage than TMA-N. Mesophilic and psychrotrophic bacteria crossed 7 log CFU/g on 8th day, rejection day of refrigeration, while it was below spoilage limit in iced storage. A shelf life of 6 and 10 days were observed in storage under refrigeration and icing respectively based on microbiological, biochemical and sensory attributes.

A narrative review on biogenic amines in fermented fish and meat products

Biogenic amines (BAs) are organic nitrogenous compounds, formed mostly by decarboxylation of corresponding amino acids. BAs are responsible for several biological events. However, if the concentration of BAs reached the threshold level, it causes mild to serious health problems in human. The objective of this manuscript was to summarize the prevalence and prevention of Bas formation, detection methods and factors affecting the BAs formation in fermented fish and meat products. Meat sausages are the fermented meat product that contains high BAs. Fish sauces are reported to have high BAs compared to other fish products. Several chemosensors and chromatography methods are available to screen and detect BAs in foods. The prevention measures are vital to avoid toxic outbreaks. The use of starter culture, application of physical factors, control of environmental factors, and use of polyphenols could prevent or diminish the formation of BAs in fermented foods. The literature survey warrants that the development of potent starter with desirable characters, maintenance of hygienic food production and regular monitoring of commercial products are necessary to ensure the quality and safety of fermented fish and meat product.

Heterologous Expression and Application of Multicopper Oxidases from Enterococcus spp. for Degradation of Biogenic Amines

BACKGROUND

Biogenic amines are harmful to human health at a certain extent. As a kind of biogenic amine oxidase, multicopper oxidase can be used to degrade them. Currently, the literature about enzyme from Enterococcus spp. are limited, and recombinant multicopper oxidase might be an effective way to degrade biogenic amines.

OBJECTIVE

(i) Select and identify strains that can degrade biogenic amines, (ii) overexpress enzyme from Enterococcus spp., (iii) measure gene expression and probe amine-degradation differences among strains (native, E. coli DH5α, and L. delbruckii), and (iv) examine the biochemical properties of recombinant multicopper oxidase, (v) apply the recombinant enzyme into smoked horsemeat sausage.

METHODS

Reverse transcription PCR and high-performance liquid chromatography were performed to examine gene expression and amine degradation rate.

RESULTS

The results demonstrated that target enzymes were successfully overexpressed, accompanied by increased amine-degrading activity (P <0.05). Gene from E. faecalis M5B was expressed in L. delbrueckii resulted in degradation rates for phenylethylamine, putrescine, histamine and tyramine of 54%, 52%, 70% and 40%, respectively, significantly higher than achieved by other recombinant strains.

CONCLUSION

In this work, gene expression levels were higher in recombinant M5B than recombinant M2B, regardless of host. E. coli is more stable to express multicopper oxidase. Besides, the amine-degrading ability was markedly increased in the two recombinant strains. After prolonged incubation, the recombinant enzyme could degrade three amines, and it displayed high alkali resistance and thermostability.

Biochemical characterization and synthetic application of aromatic L-amino acid decarboxylase from Bacillus atrophaeus

Aromatic L-amino acid decarboxylases (AADCs) are ubiquitously found in higher organisms owing to their physiological role in the synthesis of neurotransmitters and alkaloids. However, bacterial AADC has not attracted much attention because of its rather limited availability and narrow substrate range. Here, we examined the biochemical properties of AADC from Bacillus atrophaeus (AADC-BA) and assessed the synthetic feasibility of the enzyme for the preparation of monoamine neurotransmitters. AADC-BA was expressed in Escherichia coli BL21(DE3) and the purified enzyme showed a specific activity of 2.6 ± 0.4 U/mg for 10 mM L-phenylalanine (L-Phe) at 37 °C. AADC-BA showed optimal pH and temperature ranges at 7-8 and 37-45 °C, respectively. The K_M and k_cat values for L-Phe were 7.2 mM and 7.4 s^-1, respectively, at pH 7.0 and 37 °C. Comparison of the kinetic constants at different temperatures revealed that the temperature dependency of the enzyme was mainly determined by catalytic turnover rather than substrate binding. AADC-BA showed a broad substrate scope for various aromatic amino acids, including L-Phe, L-tryptophan (610% relative to L-Phe), L-tyrosine (12%), 3,4-dihydroxyphenyl-L-alanine (24%), 5-hydroxy-L-tryptophan (L-HTP, 71%), 4-chloro-L-phenylalanine (520%), and 4-nitro-L-phenylalanine (450%). Homology modeling and docking simulations were carried out and were consistent with the observed substrate specificity. To demonstrate the synthetic potential of AADC-BA, we carried out the production of serotonin by decarboxylation of L-HTP. The reaction yield of serotonin reached 98% after 1 h at the reaction conditions of 50 mM L-HTP and 4 U/mL AADC-BA. Moreover, we carried out preparative-scale decarboxylation of L-Phe (100 mM in 40-mL reaction mixture) and isolated the resulting 2-phenylethylamine (51% recovery yield). We expect that the broad substrate specificity of AADC-BA can be exploited to produce various aromatic biogenic amines. KEY POINTS: • AADC-BA showed broad substrate specificity for various aromatic amino acids. • The substrate specificity was elucidated by in silico structural modeling. • The synthetic potential of AADC-BA was demonstrated for the production of biogenic amines.

Simple and rapid determination of biogenic amines in fish and fish products by liquid chromatography-tandem mass spectrometry using 2,4,6-triethyl-3,5-dimethyl pyrylium trifluoromethanesulfonate as a derivatization reagent

A simple and rapid analytical method was developed for determination of four biogenic amines [histamine (Him), cadaverine (Cad), tyramine (Tym), 2-phenylethylamine (Pea)] in fish and fish products. This method uses a new derivatization reagent, 2,4,6-triethyl-3,5-dimethyl pyrylium trifluoromethanesulfonate (Py-Tag). The four biogenic amines in the samples were extracted with trichloroacetic acid. The diluted extract was derivatized with Py-Tag (15 min at 50°C) and then subjected to liquid chromatography-tandem mass spectrometry (LC-MS/MS). The limits of quantification for the method were 2 mg/kg for Him, Tym, and Pea and 10 mg/kg for Cad. The matrix effects derived from the tested fish and fish products were negligible in the LC-MS/MS analysis. The impact of the sample matrices on the Py-Tag derivatization was also negligible. The trueness and repeatability of the method were assessed by performing replicate analyses (n = 5) of five samples of fish and fish products, each spiked with the four biogenic amines at three different concentration levels. Analysis of the samples found 87%-104% of the spiked concentrations and the relative standard deviations were <6.1%. A reference sample and quality control canned fish samples were analyzed by the method, and the concentrations of the Him were within acceptable limits. The developed method was successfully used to determine concentrations of the four biogenic amines in 48 fish and fish products on the Japanese market. The developed method does not require cleanup using a solid-phase extraction column or similar, and the derivatization reaction time was only 15 min. The results suggested that the present method is reliable and suitable for rapid analysis of the four biogenic amines in fish and fish products.

Thermoplastic electrodes as a new electrochemical platform coupled to microfluidic devices for tryptamine determination

This study reports a new electrochemical method for tryptamine determination using a paper-based microfluidic device and a thermoplastic electrode (TPE) as an amperometric detector. Tryptamine (Tryp) is a biogenic amine present in drinks and foods. Even though this compound has some beneficial effects on human health, the ingestion of foods with high concentrations of Tryp may be detrimental, which justifies the need for monitoring the Tryp levels. The TPEs were made from 50% carbon black and 50% polycaprolactone and characterized by cyclic voltammetry, demonstrating enhancement in the analytical response compared to other carbon composites. TPEs also showed a better antifouling effect for Tryp compared to conventional glassy carbon electrodes. Once characterized, the electrodes were incorporated into the microfluidic device to determine Tryp in water and cheese samples using amperometry. A linear range was achieved from 10 to 75 μmol L^-1 with limits of detection and quantification of 3.2 and 10.5 μmol L^-1, respectively. Therefore, this work shows promising findings of the electrochemical determination of Tryp, bringing valuable results regarding the electrochemical properties of thermoplastic composites.

Epilepsy in inherited neurotransmitter disorders: Spotlights on pathophysiology and clinical management

Inborn errors of neurotransmitter metabolism are ultrarare disorders affecting neurotransmitter biosynthesis, breakdown or transport or their essential cofactors. Neurotransmitter dysfunctions could also result from the impairment of neuronal receptors, intracellular signaling, vesicle release or other synaptic abnormalities. Epilepsy is the main clinical hallmark in some of these diseases (e.g. disorders of GABA metabolism, glycine encephalopathy) while it is infrequent in others (e.g. all the disorders of monoamine metabolism in exception for dihydropteridine reductase deficiency). This review analyzes the epileptogenic mechanisms, the epilepsy phenotypes and the principle for the clinical management of epilepsy in primary and secondary inherited disorders of neurotransmitter metabolism (disorders of GABA, serine and glycine metabolism, disorders of neurotransmitter receptors and secondary neurotransmitter diseases).

Beer spoilage lactic acid bacteria from craft brewery microbiota: Microbiological quality and food safety

Craft beer is more susceptible to microbial spoilage because it does not have a pasteurization or filtration process, with lactic acid bacteria (LAB) being the most common beer spoilage microorganism. The aim of this study was to isolate LAB in a craft brewery and their characterization from a food safety and microbiological quality perspective, with a special focus on their abilities to produce biogenic amines (BA) and spoil the beer. The results of 60 monitored points inside the craft brewery showed that LAB associated with the craft brewing processes belonged to Lactobacillus, Pediococcus, and Leuconostoc genera, and most of them were detected in the filling area, which can lead to secondary contamination. Two isolates of L. brevis showed the most significant beer spoilage ability because they could grow in more acidic conditions, at a higher hop and alcohol content, and they displayed horA, horC, and hitA genes, which spoiled the vast majority of the tested beers. In addition, the aforementioned L. brevis isolates showed the highest BA production.

Effects of Different Salt Concentrations on Several Freshness Indicators of North Pacific Squid (Ommastrephes sloani pacificus) during Storage at 4°C

ABSTRACT

The effects of salt treatment (2% [w/w] low salt and 6% [w/w] high salt) and storage time (0 to 12 days) on two biogenic amines (histamine and tyramine), total volatile base nitrogen (TVB-N), pH, and volatile compounds of the North Pacific squid during storage at 4°C were evaluated. The freshness of squid muscle was evaluated by monitoring the changes in these indicators during storage. Results showed that histamine and tyramine contents increased with storage time (4.29 to 22.47 mg/kg for histamine and 28.10 to 135.78 mg/kg for tyramine) and that, in samples treated with salt, formation of these amines can be effectively inhibited (P < 0.05) compared with untreated samples. The overall pH level initially decreased and then increased during storage (ranging from 6.49 to 7.13), and the pH level of the two salt treatment groups was a little lower than that of the control group. The TVB-N value increased with time and was effectively inhibited by salt (P < 0.05). The number and content of the volatile components in squid varied during the entire storage time. The main volatile components detected in North Pacific squid were aliphatic hydrocarbons, alcohols, aldehydes, ketones, acids, esters, aromatic hydrocarbons, phenols, nitrogenous compounds, sulfo compounds, and esters. Several compounds, such as trimethylamine, butyric acid, and sulfureted hydrogen, can be used to determine the quality of aquatic products, and salt treatment can inhibit their formation. The TVB-N value was significantly correlated with pH level and with the concentrations of histamine, tyramine, and several volatile compounds in all samples (P < 0.05). In summary, salt concentration had a positive effect on extending the shelf life of North Pacific squid, and multiple indicators should be used to determine the quality of squid.

HIGHLIGHTS

Evaluation of the physicochemical, biochemical and microbiological characteristics of three Serbian traditional dry-fermented sausages

Three Serbian traditional dry-fermented sausages, Sremski kulen (S), Lemeški kulen (L) and Petrovačka kobasica (P), were compared for physicochemical, biochemical and microbiological properties, in order to provide complex overview of their quality and safety. The sausages were produced and analyzed within two production seasons in traditional practice. Water activity, color, texture and proximate composition varied significantly (P < 0.05), particularly due to moisture, protein and fat content, what indicated differences in basic formulation of raw sausage mixture, type of casing and some technological procedures. Based on the fatty acid profile the most favorable PUFA/SFA ratio was obtained in sausage P (0.68), while the obtained results for acid value (15.2-22.4 mg KOH/g lipid) and TBARS value (0.27-0.55 mg malondialdyde/kg) indicated low level of lipid degradation and oxidation in all samples. Regarding the microbial and biogenic amines (BA) analysis, positive outcome of this research is the total absence of all pathogenic microorganisms examined, while the registered levels of BA showed a great variability among the sausages. In particular, total BA content in L attained level that is approx. 50% higher than the recommended one. Hence, special care should be implemented regarding the future production and consumption of this type of sausage. Overall results of this study may be useful to define complete distinctive features of these sausages, to determine relations among them, as well as to improve some phases of traditional manufacturing process.

Modelling biogenic amines in fish meat in Central Europe using censored distributions

The aim of the study is to model concentrations of selected biogenic amines in various fish species (Atlantic salmon, Atlantic cod, striped catfish) bought in retail stores in Central Europe. Since the data contains non-detectable values, statistical methods for left-censored values from the exponential and Weibull distributions are applied and used to evaluate and compare the amount of biogenic amines in fish samples. Moreover, a risk of exceeding certain limits of biogenic amine concentrations to protect human health is determined. There are relatively high concentrations of putrescine, cadaverine and histamine in almost all fish species. Moreover, there was a significant difference in mean concentrations (distributions of concentrations, respectively) of histamine, tyramine and spermidine among the species.

Timing of male territorial flight and foraging of the large carpenter bee Xylocopa appendiculata related to serotonin in the brain

To determine how males of the large carpenter bee, Xylocopa appendiculata, maximize access to females while minimizing energy cost and acquiring energy for territorial flights, we investigated the times of territorial flights by males and foraging by males and females. Males were present continuously in territories from 8:00 to 12:00. They approached, chased, and excluded conspecific males from their territories. In the laboratory, males showed higher locomotor and flight activities in the morning and lower activities in the afternoon. Both males and females visited flowers from 8:00 to 16:00, but the most frequent visits were earlier in females (10:00-12:00) than in males (12:00-13:00). Relative body weights in territorial males often increased. These results indicate that the males time their territorial flights to maximize contact with females and obtain nectar as fuel between and after the territorial flights. The time-related territorial flight in males might be based on a time-keeping system in the brain. Brain levels of serotonin and its precursor tryptophan were significantly higher in males collected at 16:00 than at 11:00, suggesting a relation between time-related territorial flight and serotonin synthesis in the brain.

Optical sensors for determination of biogenic amines in food

This review presents the state-of-the-art of optical sensors for determination of biogenic amines (BAs) in food by publications covering about the last 10 years. Interest in the development of rapid and preferably on-site methods for quantification of BAs is based on their important role in implementation and regulation of various physiological processes. At the same time, BAs can develop in different kinds of food by fermentation processes or microbial activity or arise due to contamination, which induces toxicological risks and food poisoning and causes serious health issues. Therefore, various optical chemosensor systems have been devised that are easy to assemble and fast responding and low-cost analytical tools. If amenable to on-site analysis, they are an attractive alternative to existing instrumental analytical methods used for BA determination in food. Hence, also portable sensor systems or dipstick sensors are described based on various probes that typically enable signal readouts such as photometry, reflectometry, luminescence, surface-enhanced Raman spectroscopy, or ellipsometry. The quantification of BAs in real food samples and the design of the sensors are highlighted and the analytical figures of merit are compared. Future instrumental trends for BA sensing point to the use of cell phone-based fully automated optical evaluation and devices that could even comprise microfluidic micro total analysis systems.