Acinetobacter as a potentially important producer of urocanic acid in chub mackerel, a histidine metabolite of emerging health concern

Histamine and Scombrotoxins

Histamine intoxications result when histamine-metabolizing enzymes are compromised or overwhelmed by dietary histamine in the human body. This can occur either due to metabolic enzyme deficiencies, such as in histamine intolerance to wines, aged cheese and other foods or from high concentrations of histamine following ingestion of decomposed fish. The presence of histamine in decomposed fish and fish products results from bacterial decarboxylation of free L-histidine following product mishandling. Consequently, histamine intoxications from mishandled fish, commonly referred to as scombrotoxin fish poisoning (SFP) or scombroid poisoning, require high levels of free L-histidine only found in certain species of pelagic fish. Differential diagnosis is required of clinicians since dietary histamine intoxications produce the same symptoms typical of release of endogenous histamine due to IgE -mediated seafood allergies or anisakiasis. Although high levels of dietary histamine are responsible for SFP, histamine has important physiological functions and tends to exert toxic effects only at doses beyond the physiological range. Endogenous histamine is essential to local immune responses, regulation of gastric acid secretion in the gut, and neurotransmission in the central nervous system. Scombrotoxins, postulated to explain histamine's augmented toxicity in scombrotoxic fish, are a milieu of histamine and other bioactives. Since time-and-temperature abuse is required to produce high levels of histamine in fish, management consists of ensuring proper handling by identifying hazards and critical control points (HACCP) and maintaining a "cold chain" from catch to consumption. Reference methods for detecting histamine have received increased attention and the European Commission has validated a popular precolumn dansylation-based HPLC method through inter-laboratory collaboration and studied method equivalence with the AOAC fluorescence method 977.13 recognized by Codex Alimentarius. Much progress has been made during the last decade in the development and validation of rapid screening methods for detecting histamine in food and especially in fish products. These include many innovative sensors and several validated commercial test kits, many of them based on a recombinant form of the enzyme histamine dehydrogenase (HD).

High-throughput sequence analysis of bacterial communities and their predictive functionalities in traditionally preserved fish products of Sikkim, India

Traditionally preserved fish products viz. suka ko maccha, a smoked fish product, sidra and sukuti, sun-dried fish products are commonly consumed in Sikkim state in India. Bacterial communities in these fish products were analysed by high-throughput sequence (HTS) method supported by bioinformatics tool. Metataxonomic of the overall bacterial communities in samples revealed the abundance of phylum Firmicutes followed by Proteobacteria. Psychrobacter was abundant genus in all traditionally preserved fish products of Sikkim, followed by Bacillus, Staphylococcus, Serratia, Clostridium, Enterobacter, Pseudomonas, Rummeliibacillus, Enterococcus, Photobacterium, Myroides, Peptostreptococcus, Plesiomonas and Achromobacter. Product-wise distribution showed that Bacillus was abundant in suka ko maacha and sidra samples, whereas Psychrobacter was abundant in sukuti samples. Unique genus to each product was observed on the basis of analysis of shared operational-taxonomic-unit (OTU) contents, Alpha diversity indices showed significantly differences among the samples, and also showed maximum coverage as per Good's coverage (0.99). Beta diversity showed clustering of bacterial compositions between suka ko maacha and sidra, whereas sukuti showed scattering pattern among the other samples, indicating a diverse population in suka ko maacha and sidra samples. Non-parametric analysis of abundant genera and predictive functionalities showed the complex bacterial inter-dependencies with predictive functionalities mostly in metabolism (79.88%).

Metabolite Profile Differences Among Different Storage Time in Beef Preserved at Low Temperature

Storage temperature influences meat color stability and quality. This study was performed to quality change-associated metabolites profiles using a nontargeted liquid chromatography-mass spectrometry (LC-MS/MS)-based method. Beef longissimus dorsi samples were purchased immediately after slaughter, and then stored at room temperature, 4 °C and 0 °C. Water holding capacity (WHC), moisture content and pH value of the muscle samples were detected. Muscle samples and quality control samples were then prepared for nontargeted LC-MS/MS system, followed by identification of distinct metabolites. Pearson correlation coefficients between metabolites and quality indexes were calculated. Storage reduced pH values of beef, and room temperature and 4 °C displayed the lowest pH value. Moisture content and WHC in beef muscles, especially WHC declined obviously during the first 24 hr. The significantly altered metabolites profiles in meat samples at 0, 3.5, and 7 days during 4 °C storage were identified using LC-MS/MS. Most metabolites showed linear changes during storage (0 to 7 days). Using Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis, we found 1(α)-naphthol, urocanic acid, tyramine, guanine, histamine, picolinic acid, 4-hydroxybenzaldehyde, and hypoxanthine were increased, and 2-(S-glutathionyl)acetyl glutathione and glutathione were decreased in beef during 4 °C storage. Correlation analysis showed there were significantly correlations between metabolites and meat quality indexes (WHC, moisture content, and pH). In summary, 1(α)-naphthol, urocanic acid, tyramine, guanine, histamine, picolinic acid, 4-hydroxybenzaldehyde, and hypoxanthine, proved to be harmful to human body, accumulated gradually, especially after 3.5 days during storage at 4 °C. While the contents of beneficial substances, including 2-(S-glutathionyl)acetyl glutathione and glutathione, were decreased, which provided reference for the nutrition guidance of using beef meat.

Dietary methionine restriction improves the gut microbiota and reduces intestinal permeability and inflammation in high-fat-fed mice

Dietary methionine restriction improved the intestinal microbiota composition, barrier function, oxidative stress, and inflammation in high-fat-fed mice.