Biogenic amines assessment during different stages of the canning process of skipjack tuna (Katsuwonus pelamis)

The present research focused on the biogenic amines (BAs) formation in skipjack tuna (Katsuwonus pelamis) throughout the whole canning process. In agreement with its wide employment on this species, on‐board brine immersion freezing (BIF) was tested as post‐mortem processing. The study included fish samples corresponding to different stages of the canning process such as frozen, thawed, cooked and canned; after cooking, two kinds of tuna muscles were considered, that is, whole fillets (main product) and grated muscle (off‐product arising from small pieces). For the BAs (tryptamine, putrescine, cadaverine, histamine, spermidine and spermine) assessment, an HPLC‐DAD method was developed and validated in skipjack tuna samples, in agreement with different parameters such as suitability, linearity, limits of detection and quantification, precision, accuracy and robustness. Tuna submitted on‐board to BIF procedure provided low levels of spermine and spermidine (up to 27.6 mg kg^?1), while contents on the remaining BAs maintained below the limit of detection. Throughout the different stages of the canning process, skipjack tuna showed a low formation of most BAs; interestingly, histamine content was found below 10.6 mg kg^?1 level. The highest values were obtained for spermidine, these related to cooked grated tuna (from 22.6 to 66.7 mg kg^?1) and canned grated tuna (from 70.6 to 104.4 mg kg^?1). Values for pH assessment in all kinds of tuna samples corroborated the results obtained for BAs determination. BIF procedure proved to be an amenable post‐mortem processing to guarantee the quality of canned skipjack tuna.     

Antifungal and antimycotoxigenic effects of Zingiber officinale,Cinnamomum zeylanicum and Cymbopogon martinii essential oils against Fusarium verticillioides

ABSTRACT

There is an increasing demand for fungi control in grains, especially toxigenic. Also, there is growing concern on the use of synthetic fungicides; thus alternatives are needed. The aim of this study was to evaluate the antifungal and antimycotoxigenic action of essential oils (EOs) from Zingiber officinale, Cinnamomum zeylanicum and Cymbopogon martinii against Fusarium verticillioides, a spoilage and toxigenic fungus. Essential oils were first chemically characterised by gas chromatography coupled to mass spectrometry, and their antioxidant potential was measured by the DPPH, ABTS and FRAP methods. Minimum inhibitory concentration (MIC) and disc diffusion were used to assess antifungal activity. Scanning electron microscopy was used to evaluate morphological changes in the fungus. Antimycotoxigenic activity of the EOs against the production of fumonisin B₁ and B₂ by F. verticillioides was evaluated using ultra-high-performance liquid chromatography system. Z. officinale, C. zeylanicum and C. martinii EOs were predominantly composed by zingiberene and geranial; eugenol; and geraniol, respectively. All the EOs had high antioxidant power, especially that from C. zeylanicum. The MICs were 250, 500 and 2,000 µg mL^?1 for C. zeylanicum, C. martinii and Z. officinale EOs, respectively. Mycelial reduction of F. verticillioides was observed when EOs were used, and the lowest activity was detected in the Z. officinale EO. Overall, the tested EOs promoted structural damage to the fungal cell wall, decreased conidia size and mycelial reduction. Antimycotoxigenic evaluation of the EOs evidenced a significant reduction (p < .05) in the production of fumonisins B₁ and B₂ with all the EOs evaluated in the study. These results suggest that especially C. zeylanicum and C. martinii EOs are highly useful for controlling F. verticillioides and fumonisins production.     

Teachers' work-related non-literature-known building-related symptoms are also connected to indoor toxicity: A cross-sectional study

A previous study showed that classical building-related symptoms (BRS) were related to indoor dust and microbial toxicity via boar sperm motility assay, a sensitive method for measuring mitochondrial toxicity. In this cross-sectional study, we analyzed whether teachers’ most common work-related non-literature-known BRS (nBRS) were also associated with dust or microbial toxicity. Teachers from 15 schools in Finland completed a questionnaire evaluating 20 nBRS including general, eye, respiratory, hearing, sleep, and mental symptoms. Boar sperm motility assay was used to measure the toxicity of extracts from wiped dust and microbial fallout samples collected from teachers’ classrooms. 231 teachers answered a questionnaire and their classroom toxicity data were recorded. A negative binomial mixed model showed that teachers’ work-related nBRS were 2.9-fold (95% CI: 1.2-7.3) higher in classrooms with highly toxic dust samples compared to classrooms with non-toxic dust samples (p = 0.024). The RR of work-related nBRS was 1.8 (95% CI: 1.1-2.9) for toxic microbial samples (p = 0.022). Teachers’ BRS appeared to be broader than reported in the literature, and the work-related nBRS were associated with toxic dusts and microbes in classrooms.     

Off-Pathway-Sensitive Protein-Splicing Screening Based on a Toxin/Antitoxin System

Protein-splicing domains are frequently used engineering tools that find application in the in vivo and in vitro ligation of protein domains. Directed evolution is among the most promising technologies used to advance this technology. However, the available screening systems for protein-splicing activity are associated with bottlenecks such as the selection of pseudo-positive clones arising from off-pathway reaction products or fragment complementation. Herein, we report a stringent screening method for protein-splicing activity in cis and trans, that exclusively selects productively splicing domains. By fusing splicing domains to an intrinsically disordered region of the antidote from the Escherichia coli CcdA/CcdB type II toxin/antitoxin system, we linked protein splicing to cell survival. The screen allows selecting novel cis- and trans-splicing inteins catalyzing productive highly efficient protein splicing, for example, from directed-evolution approaches or the natural intein sequence space.     

Uncertainties in the determination of pyrrolizidine alkaloid levels in naturally contaminated honeys and comparison of results obtained by different analytical approaches

The contamination of honey with hepatotoxic pyrrolizidine alkaloids (PAs) is a well-known hazard for food safety. While management strategies and controls of the honey industry aim to reduce the PA levels, uncertainties remain with regard to the safety of regionally produced and marketed honey. In addition, a previous study showed large differences of results obtained after various periods of storage and apparent differences between the analytical results of different laboratories. Therefore, this study aimed at examining these uncertainties by monitoring the impact of storage on the PA and PA N-oxide (PANO) content of two freshly harvested honeys and on possible demixing effects caused by pollen settling. Additionally, three analytical approaches – target analysis with matrix-matched calibration or standard addition and a sum parameter method – were applied for a comparative analysis of 20 honeys harvested in summer 2016. All samples originated from Schleswig-Holstein in Northern Germany where the PA plant Jacobaea vulgaris is currently observed on a massive scale. The results of the time series analyses showed that PANO levels markedly decreased within a few weeks and practically reached the LOD 16 weeks after harvest. Tertiary PAs, by contrast, remained stable and did not increase as a consequence of PANO decrease. The experiments on a putative demixing, which may result in a heterogeneous distribution of PAs/PANOs, revealed that there was no such effect during storage of up to 12 weeks. A comparison of the PA/PANO levels obtained by different analytical approaches showed that in some cases the sum parameter method yielded much higher levels than the target approaches, whereas in other cases, the target analysis with standard addition found higher levels than the other two methods. In summary, the results of this study highlight uncertainties regarding the validity and comparability of analytical results and consequently regarding health risk assessment.     

Silage review: Animal and human health risks from silage

Silage may contain several agents that are potentially hazardous to animal health, the safety of milk or other animal food products, or both. This paper reviews published literature about microbial hazards, plant toxins, and chemical hazards. Microbial hazards include Clostridium botulinum, Bacillus cereus, Listeria monocytogenes, Shiga toxin-producing Escherichia coli, Mycobacterium bovis, and various mold species. High concentrations of C. botulinum in silage have been associated with cattle botulism. A high initial concentration of C. botulinum spores in forage in combination with poor silage fermentation conditions can promote the growth of C. botulinum in silage. The elevated pH level that is generally associated with aerobic deterioration of silage is a major factor influencing concentrations of L. monocytogenes, Shiga toxin-producing E. coli, and molds in silage and may also encourage survival and growth of M. bovis, the bacterium that causes bovine tuberculosis. Soil is a major source of B. cereus spores in silage; growth of this bacterium in silage appears to be limited. Hazards from plant toxins include pyrrolizidine, tropane and tropolone alkaloids, phytoestrogens, prussic acid, and mimosine, compounds that exist naturally in certain plant species that may contaminate forages at harvesting. Another group of toxins belonging to this category are ergot alkaloids, which are produced by endophytic fungal species in forages such as tall fescue grass, sorghum, and ryegrass. Varying effects of ensiling on the degradation of these plant toxins have been reported. Chemical hazards include nitrate, nitrite, and toxic oxide gases of nitrogen produced from nitrate and high levels of butyric acid, biogenic amines, and ammonia. Chemical and microbiological hazards are associated with poorly fermented silages, which can be avoided by using proper silage-making practices and creating conditions that promote a rapid and sufficient reduction of the silage pH and prevent aerobic deterioration.     

粮油食品防霉微生物筛选及其活性物质初步研究

为开发新型防霉剂，降低粮油食品储藏、运输、流通等过程中霉变对其品质和食用安全的影响，研究筛选获得具有强防霉活性的微生物。采用抑菌圈法，以禾谷镰刀菌（Fusarium graminearum）为指示菌筛选具有防霉活性的菌株。利用形态学观察、生化特征鉴定和16S rDNA基因序列比对进行菌株鉴定；通过不同温度、pH和蛋白酶K处理对防霉活性物质进行初步分析。结果显示：通过初筛获得33株对禾谷镰刀菌具有强抑制活性的菌株，复筛后选择的7株菌归属为芽孢杆菌属（Bacillus）；活性物质分析发现7株菌的活性物质均不耐高温和强酸碱，同时蛋白酶K处理对其防霉效果没有明显影响，初步推断为肽类；通过抑菌谱测定发现菌株ASAG 62对常见霉菌（产黄青霉Penicillium flavum、黑曲霉Aspergillus Niger、赭曲霉Aspergillus ochre、黄曲霉Aspergillus flavus、禾谷镰刀菌F. graminearum）均具有良好的抑制效果。     

Growth inhibition of Fusarium graminearum and deoxynivalenol detoxification by lactic acid bacteria and their application in sourdough bread

Eight lactic acid bacteria (LAB) strains were screened for their ability to inhibit Fusarium graminearum (F. graminearum) growth and remove deoxynivalenol (DON). Furthermore, the selected LAB strains were applied as starter cultures to evaluate their performance during the breadmaking process. Lactobacillus plantarum (L. plantarum) AR524 exhibited strong inhibitory activity against F. graminearum growth in a pH-dependent manner and removed up to 40.9% of DON, mainly through cell wall binding. Compared with the control, L. plantarum AR524 inhibited 60.19% of F. graminearum growth and removed 50.53% of DON during breadmaking. The texture properties of the bread were also remarkably improved by L. plantarum AR524, and its shelf life was extended from 3 days to 6 days without the application of any chemical preservatives. Therefore, L. plantarum AR524 shows excellent potential for application as a bioprotective starter culture in bakery products.     

Structure–Activity Relationship Study of Spider Polyamine Toxins as Inhibitors of Ionotropic Glutamate Receptors

The spider polyamine toxins Joro spider toxin‐3 (JSTX‐3) and Nephila polyamine toxins‐1 and ‐8 (NPTX‐1 and NPTX‐8) are isolated from the venom of the orb‐weaver spider Nephila clavata (Joro spider). They share a high degree of structural resemblance, their aromatic head groups being the only difference, and were recently found to be very potent open‐channel blockers of ionotropic glutamate (iGlu) receptors. In this study we designed and synthesized a collection of 24 analogues of these toxins using a recently developed solid‐phase synthetic methodology. Systematic variation in two regions of the toxins and subsequent evaluation of biological activity at AMPA and NMDA subtypes of iGlu receptors provided succinct information on structure–activity relationships. In particular, one set of analogues were found to display exquisite selectivity and potency for AMPA receptors relative to the natural products. Thus, this systematic SAR study has provided new pharmacological tools for studies of iGlu receptors.     

Photobleaching Reveals Heterogeneous Stoichiometry for Equinatoxin II Oligomers

Equinatoxin II (EqtII), a sea anemone cytolysin, is known to oligomerize to form pores that spontaneously insert into membranes. Crystallographic and cryo‐EM studies of structurally similar cytolysins offer contradictory evidence for pore stoichiometry. Here we used single‐molecule photobleaching of fluorescently labeled EqtII to determine the stoichiometry of EqtII oligomers in supported lipid bilayers. A frequency analysis of photobleaching steps revealed a log‐normal distribution of stoichiometries with a mean of 3.4±2.3 standard deviations. Comparison of our experimental data with simulations of fixed stoichiometries supports our observation of a heterogeneous distribution of EqtII oligomerization. These data are consistent with a model of EqtII stoichiometry where pores are on average tetrameric, but with large variation in the number of subunits in individual pores.