Seafood Spoilage Research Articles

Heterostructures constructed by NiMoO4 functionalized 2D MoO3 nanosheets for ultrasensitive trimethylamine detection with ppb level detection

Trimethylamine (TMA) serves as an indicator for assessing seafood spoilage and a biomarker for kidney disease. Achieving this dual functionality necessitates the detection of TMA with a low detection limit and exceptional selectivity. Here, NiMoO4 functionalized MoO3 heterostructures were constructed and subjected to a systematic investigation of their sensing properties towards TMA. The 7 %-NiMoO4/MoO3 sensor could detect trace TMA at 200°C with a response value of 3.93 (0.1 ppm) and achieve detecting thresholds as low as 2.48 ppb (theoretical limit). Additionally, the sensor exhibits remarkable selectivity to TMA, an expansive adjustable concentration on detection range, and excellent long-term stability. The enhanced sensing properties may be ascribed to the forming p-n heterojunctions at the NiMoO4/MoO3 interface, effectively modulating the interfacial potential. Moreover, the NiMoO4/MoO3 heterostructures demonstrate excellent charge-transfer capability, high charge carrier density, and a substantial active surface area in electrochemical measurements, thereby enhancing the sensing ability of TMA. Additionally, the thin nanosheet structure facilitates efficient charge transportation along the length of the nanosheets, further enhancing the sensing response. These results indicate the potential of NiMoO4/MoO3 as a promising sensing material for TMA gas sensors.

Hierarchical 0D/1D/2D Au/PANI/WS2 ternary nanocomposite NH3 sensor with high performance and fast response/recovery for food spoilage detection

Ammonia (NH3) gas is regarded as a biomarker for clinical diagnosis of various diseases and a potential indicator for the spoilage of protein-rich foods. The acuate detection of the ammonia gas concentration depend on reliable gas sensor. In this paper, flexible room temperature ammonia gas sensor based on hierarchical Au/PANI/WS2 ternary composite was successfully prepared by in-situ polymerization, reduction and drop-coating process. The Au/PANI/WS2-based ammonia sensor was tested for its room temperature sensing property including response value, response/recovery time, selectivity, and long-term stability. The effects of flexible state, humidity and operating temperature on the sensor response were also investigated. The 0D/1D/2D Au/PANI/WS2-based sensor showed significantly enhanced ammonia sensing property both in response and response/recovery time as compared to that of pristine WS2. Gas sensing mechanism of the prepared sensor was investigated by complex impedance spectroscopy and in-situ fourier transform infrared spectroscopy analysis. Besides, the sensor was proved for its practical usability in seafood spoilage detection and warning. The construction of multidimensional materials into hierarchical structure may provide an instructive way for the sensibilization of layered two-dimensional nanomaterial of WS2.

Indicator Films Containing Dendrobium Orchid Flower Extract and TiO2 Nanoparticles for Monitoring Fish Fillet Spoilage

This work aimed to study a novel pH indicator film prepared from carboxymethyl cellulose (CMC)/tapioca starch (TS) incorporating Dendrobium orchid flowers and TiO2 nanoparticles for monitoring fish fillet freshness. The films were prepared based on carboxymethyl cellulose (CMC) and tapioca starch (TS) blend (CMC/TS) incorporated with TiO2 nanoparticles and Dendrobium orchid flower (DOF) extract. The result showed that the DOF extract contained peonidin-3,5-O-diglucoside and exhibited distinguishable color changes in different pH buffers. Likewise, the CMC/TS+TiO2+DOF film’s color changed corresponding to the extract. The X-ray diffraction analysis revealed the expansion of the film’s amorphous region, due to the intermolecular interactions. Analyzing scanning electron microscope images showed the effects of TiO2 and DOF extract on the surface morphology of films. The incorporation of TiO2 and DOF extract into the film formulation improved various film properties, such as redness, opacity, tensile strength, and water solubility. For the sensitivity testing, the color of the CMC/TS+TiO2+DOF film responded to ammonia vapor more than acetic acid vapor, suitable for monitoring seafood spoilage behavior. In addition, the application of film for monitoring the freshness of fish fillets was conducted. The CMC/TS+TiO2+DOF film color changed from purple to bluish-purple corresponding to the spoilage of samples. Indicating its potential as an indicator for monitoring fish fillets' freshness.

Non-invasive measurement of spoilage of packed fish using halochromic sensor

Purpose This study aims to develop a pH-functional thin-film sensor for non-invasive measurement of spoilage of packed fish. Design/methodology/approach At first, polymers of natural origin such as hydroxy(propyl)methyl cellulose, potato dextrose agar and starch alongside a pH sensitive-mixed indicator formulation were used to produce thin film sensor. The developed thin film sensor was tested for monitoring the spoilage of seafood stored at 4°C. Using ultraviolet-visible and Fourier-transform infrared spectroscopy, the halochromic sensor was characterised. In addition, the halochromic response of the thin film was directly correlated to the total volatile base nitrogen emitted by the packaged fish, pH, microbial activity and sensory evaluation. Findings The results suggested the developed biopolymer-based thin film sensor showed different colours in line with the spoilage of the packed fish, which could be well correlated with the total volatile base nitrogen, microbial activity and sensory evaluation. In addition, the thin film sensors exhibited a high degree of biodegradability. The biopolymers-based thin film halochromic sensor has exhibited excellent biodegradability along with sensitiveness towards the spoilage of the packed fish. Originality/value In the future, consumers and retailers may prefer seafood containers equipped with such halochromic sensors to determine the degree of food deterioration as a direct indicator of food quality.

Bacterial biofilm formation in seafood: Mechanisms and inhibition through novel non‐thermal techniques

AbstractSeafoods are susceptible to microbial contamination due to their high moisture, nutrient contents and neutral pH. Among various microorganisms, biofilm‐forming bacteria pose a severe threat to the seafood supply chain as well as consumer health. Bacterial biofilm formation in seafood is primarily caused by Aeromonas hydrophila, Vibrio cholerae, V. vulnificus, V. parahaemolyticus, Salmonella spp., and Listeria monocytogenes. Biofilm formation is an important protective mechanism of microorganisms causing spoilage of seafood and disease threats to consumers. The attachment of microbes on the surface of seafood followed by the growth and proliferation of bacterial cells leads to the production of exopolymer compounds and the formation of biofilm. This biofilm is difficult to destroy or inhibit through conventional prevention/destruction techniques. The occurrence of bacterial strains/biofilms with more resistance to different preventive strategies is a big challenge for the seafood processing industry. This review covers the mechanisms of biofilm formation by bacteria and various non‐thermal processing approaches to prevent microbial contamination and biofilm formation in seafood products. The aforementioned non‐thermal processing techniques for the destruction of biofilm and quality control of seafood products include cold plasma treatment, irradiation, pulsed electric field technology, hydrostatic pressure processing, photosensitisation, natural bioactive compounds and so on. All these techniques effectively inhibit the bacterial biofilm and microbial growth without altering sensorial properties. However, further research validation and applications at the industry level are still required.

The full utilization of bagasse via deep eutectic solvent pretreatment for low-condensed lignin and cellulose smart indicator film

Full utilization of biomass after fractionation of its components is an effective way to maximize the value of biomass. Herein, in this study, a new acetal-mediated deep eutectic solvent (DES) was explored and its excellent performance in separating lignin from biomass as well as retarding lignin condensation has been observed. Subsequently, the separated lignin and cellulose-rich residue were used to prepare sunscreen and transparent food indicator films, respectively. The results showed that the acetal-mediated DES pretreatment can reduce the recalcitrance of bagasse, stabilize lignin (β-O-4 content of 68.6% in the lignin), and retain most of the cellulose (ie. 83.43%). Besides, the pretreatment enhanced the subsequent hydrogenolysis of lignin, and the higher β-O-4 content of the lignin contributed to the high yield of aromatic monomers (40.94%). In addition, regenerated lignin was attractive for sunscreen applications due to its lighter color and excellent UV-blocking properties. Furthermore, cellulose smart indicator film was highly sensitive, biodegradable, has excellent physical properties, and allows visual real-time monitoring of seafood spoilage using smartphones. Meanwhile, the yield of the removed hemicellulose converted to xylose in the pretreatment process reached 99.24%. In general, this work proposed a sustainable bio-refinery approach for the full upgrading of biomass.

Porous starch embedded with anthocyanins-CMC coating as bifunctional packaging with seafood freshness monitoring properties

In line with the growing demand for more sustainable and efficient materials for food packaging, new bifunctional pH-responsive composites were developed with the dual purpose of packaging and indicating seafood spoilage. Within this study, a fully bio-based composite based on porous starch (PS) was prepared via microwave irradiation (∼1 g/cm3) followed by functionalization via dip-coating with an active solution of anthocyanins-carboxymethyl cellulose (CMC). Here, the edible anthocyanins (Ath) endowed excellent antioxidant and pH-sensing properties to the resulting bifunctional composite (PS-ACMC), covering a pH range of 6–11.5, making it compelling for developing smart food-packaging materials. Moreover, results indicated that the coating scarcely altered the excellent mechanical properties developed by the PS sample, which were comparable with the commercial expanded polystyrene foams. Concurrently, to enhance the competitive properties of the starch component, bifunctional PS-CMC systems were devised crosslinking starch with citric acid. The obtained citrate-starch specimens exhibited a superior porous structure with lower density (∼0.61 g/cm3), antioxidant properties, and about 40% less solubility in water compared to the neat starch sample. Remarkably, this functionalization hindered the colour-switching properties when the active coating was added, likely due to a strong fixation of the CMC with the natural dye. However, PS-ACMC composites exhibited a rapid and effective colour response, transitioning from violet to greenish-blue, facilitating visual and real-time assessment of the freshness when using shrimp as test specimens. The results reported underscored the high potential of such bifunctional biocomposites in obtaining sustainable and smart freshness-monitoring packaging for seafood.

Comprehensive shotgun proteomic characterization and virulence factors of seafood spoilage bacteria

This article summarizes the characterization, by shotgun proteomics, of 11 bacterial strains identified as responsible for seafood spoilage. A total of 4455 peptide spectrum matches, corresponding to 4299 peptides and 3817 proteins were identified. Analyses of data determined the functional pathways they are involved in. The proteins identified were integrated into a protein-protein network that involves 371 nodes and 3016 edges. Those proteins are implicated in energy pathways, peptidoglycan biosynthesis, spermidine/putrescine metabolism. An additional 773 peptides were characterized as virulence factors, that participates in bacterial pathogenesis; while 14 peptides were defined as biomarkers, as they can be used to differentiate the bacterial species present. This report represents the most extensive proteomic repository available in the field of seafood spoilage bacteria; the data substantially advances the understanding of seafood decay, as well as provides fundamental bases for the recognition of the bacteria existent in seafood that cause spoilage during food processing/storage.

Insight to the diversity of Photobacterium spp. isolated from European plaice (Pleuronectes platessa) based on phylogenetic analysis, phenotypic characterisation and spoilage potential

This study aimed to explore the diversity of fifty-four Photobacterium strains isolated from muscle tissue of European plaice (Pleuronectes platessa) caught at different fishing seasons and stored 14-days under various conditions. Single phylogenetic markers (16S rRNA, gapA, gyrB and recA) and multilocus sequence analysis (MLSA) were employed to classify isolates at species level. Furthermore, intra- and interspecies variability in the phenotypic traits, maximum specific growth rate (μmax) and spoilage potential of the Photobacterium isolates were investigated. The isolates were classified into the P. iliopiscarium (53.7 %), P. phosphoreum (40.7 %) and P. piscicola (5.6 %) clades using MLSA. Two housekeeping genes, gyrB and recA, exhibited a consistent phylogenetic relationship with MLSA, suggesting that they might be used as individual phylogenetic markers for the Photobacterium genus. Intra- and interspecies variability in the expression of phenotypic characteristics and the production of trimethylamine (TMA), inosine (HxR), and hypoxanthine (Hx) were observed. A growth optimum temperature for P. iliopiscarium was approximately 20 °C, while those for P. phosphoreum and P. piscicola were closer to 15 °C. All isolates exhibited the highest growth density at 1.5 % NaCl, followed by 0.5 %, 3 %, and 6 % NaCl. However, P. phosphoreum demonstrated a higher NaCl tolerance than the other two species. Although, the high CO2 atmosphere significantly inhibited the growth of all strains at 4 °C, P. phosphoreum and P. piscicola showed higher growth density at 15 °C than P. iliopiscarium. Notably, all strains demonstrated H2S production. The μmax varied considerably within each species, highlighting the significance of strain-level variability. This study demonstrates that P. iliopiscarium and P. piscicola, alongside P. phosphoreum, are efficient TMA-, HxR-, Hx-, and H2S-producers, suggesting their potential contribution to synergistic off-odour generation and spoilage. Moreover, the Photobacterium isolates seem to exhibit diverse adaptations to their environments, resulting in fluctuated growth and spoilage potential. Understanding intra- and interspecies variability will facilitate modelling seafood spoilage in microbial risk assessments and developing targeted hurdles to prolong products' shelf-life.

The design and application of xylose-lysine based time-temperature indicators for visually monitoring the shelf-life of chilled large yellow croaker

The spoilage of seafood is highly dependent on temperature changes during cold chain. To visually reflect the shelf-life of large yellow croakers (0–25 °C), the xylose-lysine based time-temperature indicator (TTI) label was designed and applicated. The ultraviolet (UV) spectrum, and color response of Maillard reaction (MR) indicated that the color changes of TTI was related to the formation of melanoidins of MR. The color changes of TTI, and the quality degradation of large yellow croakers were described by kinetics analysis, which showed that Ea of TVB-N (70.45 kJ/mol) was closer to that of TTI (83.51 kJ/mol). Under fluctuating temperatures, the difference of the effective temperature (Teff) between TVB-N (15.95 °C) and TTI (16.84 °C) was less than 1 °C, and the relative error of shelf-life was −8.33%. Briefly, this novel TTI label as an environmentally friendly system could be attached to sample surface for real-time reflecting shelf-life of seafood in cold chain.

Determination of seafood spoilage by digital colorimetry of indicator test systems

A simple and affordable colorimetric procedure for determination of the seafood spoilage (e.g., shrimp, squid, catfish and herring) using a smartphone and chemometric analysis is considered. The proposed colorimetric sensor consists of 12 zones, i.e., disks of cellulose paper 4 mm in diameter impregnated with acid-base indicators with a color change in the pH range of 3 – 8.8. Spoiling of the seafood is accompanied with a release of volatile biogenic amines that change the color of the indicator zones. A device and a method for measuring the colorimetric parameters of a test system using a smartphone as a recording device equipped with a specialized RGBer product are described. Processing of the data array (the sum of the R, G, and B channel values for each indicator, or the R, G, and B values for individual indicators) was performed using the XLSTAT software. Patterns of the degradation of food products identified in the study made it possible to propose a method for assessing the quality of seafood in real time. The optimal time regime of heat treatment of the sample was determined, which is necessary for the isolation of biogenic amines and the formation of an analytical signal. The parameters for identification of the seafood spoilage are the values of the main component F1 (or the position of the images on the canonical function projection graph) after evaluating the colorimetric data using the principal component method. The results obtained with a colorimetric sensor match the data for determination of the total microbial number of the analyzed products. The considered method for assessing spoilage of the seafood is distinguished by the simplicity of hardware design, the availability of the materials and software resources used, the rapidity of the procedure, and the mobility of the means for recording the analytical signal.

Ppb-level detection of trimethylamine as biomarker in exhaled gas based on MoO3/V2O5 hierarchical heterostructure

The toxic gas trimethylamine (TMA) with fishy odor can not only be used as an indicator for evaluating seafood spoilage, but also as a biomarker for trimethylaminuria and kidney disease. This paper constructs a ppb-level trimethylamine gas sensor that operates at room temperature based on MoO3/V2O5 nanocomposites, which were fabricated by hydrothermal synthesis process. The adsorption energy of TMA on sensitive materials was calculated through the density functional theory, and the sensing mechanism was explored by simulating the adsorption process of TMA on the sensitive materials. The response (11.37%) of MoO3/V2O5 composites to ultra-low concentration (20 ppb) TMA was better than that of pure MoO3 nanorods (5.49%) and V2O5 nanospheres (6.36%) at room temperature. Compared with pure MoO3 sensors, an n-n heterojunction is formed between MoO3 and V2O5, which enhances the sensing performance of pure sensing material for TMA. In addition, the detection of exhaled gas in simulated kidney disease patients indicates that this sensor has great potential as an effective TMA detection tool in the field of non-invasive disease diagnosis.

Biphenyl-based AIE-active turn-on fluorescent probes for simultaneous sensing of biothiols and amine vapors and visual real-time monitoring of seafood spoilage

Abnormal level of biothiols content in living organisms and volatile vapor amines could cause severe injury to human health, development of convenient and portable detecting devices for the biothiols and amines recognition is bound to scientific significance as well as practical application. Up to now, mainly confined by aggregation caused quenching (ACQ) effect, the potential application of traditional fluorescent sensing were extremely restricted. In this contribution, two biphenyl-based “turn-on” type fluorescent probes FCH-NBSC and FCH-AC were designed and constructed for biothiols and vapor amines quantitative detection respectively, which were consisted of a common fluorophore FCH–OH with AIE properties and two sensitive recognition segments nitrobenzene sulfonyl chloride (NBSC) and acetyl (AC). Date from experiments demonstrated that probe FCH-NBSC and FCH-AC exhibited excellent linearity and low detection limits for detection of biothiols (Cys, 0.228 μM, GSH, 0.212 μM, Hcy, 0.315 μM, vapor amine, 7.6 ppm), respectively. Sensing mechanism demonstrated that this fluorescent characteristics variation could be ascribed to biothiols and vapor amines caused cleavage of NBSC segment of FCH-NBSC and AC group of FCH-AC respectively to form a common ESIPT compound FCH–OH, which opened aggregation induced emission (AIE) property promoted by intra/intermolecular H-bonds. Furthermore, FCH-NBSC can successfully achieve rapid biothiols recognition inside biological cells via difference in fluorescent signals due to its low toxicity and high sensitivity. Meanwhile, probe FCH-AC have been applied in visual real-time monitoring of seafood spoilage field due to its unique recognition effect for amine vapor.

Changes in the physicochemical properties of grouper (Epinephelus coioides) fillets stored under vacuum packaging at chilly temperature contributing with the spoilage bacteria

Microbial activity is the primary and inevitable factor contributing to seafood spoilage. To assess the spoilage potential of dominant bacteria (Hafnia paralvei and Aeromonas allosaccharophila) isolated from spoiled vacuum-packed grouper fillets under cold storage. In this study, the total viable count (TVC), total volatile basic nitrogen (TVB-N), pH, trichloroacetic acid (TCA)-soluble peptides, water-holding capacity (WHC), nucleotide catabolism, free amino acids (FAAs), and volatile compounds (VOCs) of grouper fillets in vacuum packaging under cold storage with different bacteria inoculated (H. paralvei inoculated, A. allosaccharophila inoculated, and H. paralvei &A. allosaccharophila inoculated) were characterized. The results revealed that H. paralvei exhibited stronger degradation activity, leading to decreased water-holding capacity and increased levels of TVB-N and TCA-soluble peptides. Amino acid analysis showed distinct metabolic patterns for H. paralvei and A. allosaccharophila, with H. paralvei showing a high potential for utilizing FAAs. Both H. paralvei and A. allosaccharophila caused nucleotide catabolism, but A. allosaccharophila produced more hypoxanthine riboside and hypoxanthine. In addition, the analysis of VOCs indicated that H. paralvei produces large content of aldehydes in the middle of storage, particularly benzaldehyde. In addition, the grouper fillets inoculated with H. paralvei &A. allosaccharophila showed similar physicochemical changes to that inoculated with H. paralvei. In conclusion, H. paralvei emerged as the key bacteria responsible for spoilage in vacuum-packed grouper. This study is helpful in further understanding the relationship between spoilage microorganisms and the quality of grouper fillets, thereby providing valuable information for their preservation.

Paper-based fluorescent materials containing on-demand nanostructured brain-cells-inspired AIE self-assembles for real-time visual monitoring of seafood spoilage

Biogenic amines containing NH3 are important indicators for conducting full-scale appraisal of food spoilage and disease diagnosis. However, the currently-used detection methods of NH3 have several limitations such as time-consuming high cost, and inability to provide visual real-time monitoring. Therefore, researchers have attempted to explore strategies for quantitative real-time monitoring of NH3 for food spoilage has attracted widespread attentions. Herein, we developed sustainable, fast response, hypersensitized, user-friendly and molecular-level light-emitting biomass-based materials (AFP-FP) containing on-demand nanostructured brain-cells-inspired aggregation-induced-emission (AIE) self-assembles for real-time visual monitoring of seafood spoilage. The 2-hydroxy-5-methyl-isophthalaldehyde-based AIE probe (AFP) was synthesized using a simple “one-step” route. AFP-FP exhibited high selectivity, sensitivity, repeatable and quantitative recognition (y = 7.292×103x + 7.621×104, R = 0.990) of NH3 with a low detection limit (246 ppb) and fast response (<1 s). Furthermore, we integrated AFP-FP into a user-friendly smartphone color recognition app, enabling its practical application in visual, real-time daylight monitoring of food spoilage.

Facilely Processable Dual-Color Ratiometric Fluorescent Sensors for Highly Sensitive Detection of Food Spoilage

Spoiled food, especially seafood, poses a huge challenge to food safety and human health, which should be addressed through early monitoring and warning of freshness. Despite the fact that several food colorimetric sensors have been reported recently, only a small number of them can match the demands of easy manufacturing, high sensitivity, and satisfactory reliability. Herein, we report a type of dual-color ratiometric composites as fluorescent sensors (DUCS) with good processability, which offers the superior real-time and visual detection of seafood spoilage. A visually detectable colorimetric sensitivity under portable UV light irradiation has been achieved for seafood stored at room temperature for 4–6 h (response time variable with different food ingredients). Moreover, the ease and versatility of our formulation, composed of organic fluorophores, polymers, and additives as composites, has enabled facile processing, including drop-coating and stamp-patterning, which would facilitate a broad scope of applications for food sensing and beyond.

Purification and characterizations of a novel extracellular protease from Shewanella putrefaciens isolated from bigeye tuna

Shewanella putrefaciens is one of the common spoilage microorganisms in aquatic products, and its extracellular protease is the main cause of seafood spoilage. The characteristics of the extracellular protease produced by S. putrefaciens YZ08 and its hydrolytic properties on fish proteins were studied. After purification, an extracellular protease of 18.78 kDa was obtained and identified as a metalloprotease of the M23 family. The gene encoding this enzyme was cloned and purified by expression in E. coli to obtain a recombinant protease. YZ08 protease showed optimum enzymatic activity at 40 °C and pH 9.0 and was stable at pH 7.0–10.0 and low temperature (<40 °C). The kinetic parameters and thermal inactivation parameters of the enzyme were determined. S. putrefaciens YZ08 protease can degrade fish myofibrillar and sarcoplasmic proteins, breaking them down into small particles and low molecular peptides. The three-dimensional structure of the protease was simulated by homology modeling and revealed a correlation between the active site in the protein and substrate specificity. This work provides a foundation for characterizing the properties of S. putrefaciens YZ08 protease and for controlling the quality and safety of seafood.

Changes in texture, rheology and volatile compounds of golden pomfret sticks inoculated with Shewanella baltica during spoilage

Shewanella baltica has a high spoilage ability to decompose nutrients in fish. To investigate the role of S. baltica in fish protein and flavour during spoilage, the texture, rheology, protein patterns and volatile compounds of golden pomfret inoculated with S. baltica during 10-day storage were tested. During storage, S. baltica reduced the hardness of fish sticks by 29.73–49.24 %. Compared to the control (G0′: 20.27 ± 2.15 kPa), inoculated samples showed lower moduli (G0′: 16.71 ± 0.82–17.50 ± 1.80 kPa). Their myosin heavy chains, myosin-binding protein C and actin were decomposed into smaller proteins, which was validated by the lower intensities of molecules with Mw 160–176 kDa. Furthermore, S. baltica generated volatile spoilage markers, including dimethyl sulfide, 2-methyl-butanal and 3-methyl-butanal. This study reveals the mechanism of fish texture and flavour changes induced by S. baltica, and provides insights into controlling bacterial spoilage of seafood.

Biomass-based indole derived composited with cotton cellulose fiber integrated as sensitive fluorescence platform for NH3 detection and monitoring of seafood spoilage

Herein, an indole-derived water-soluble fluorescence nanomaterial and biomass-based cellulose filter paper integrated as solid-state fluorescence platform (H2-FP) for seafood spoilage detection was prepared. H2 exhibits high fluorescence stability and good biocompatibility with green beans, onion tissues, blood and zebrafish, which proving that H2 has a wide range of application scenarios. Further, H2-FP with effective, solid-state fluorescence, portable, and reusable characteristics is nanoengineered for NH3 quantitative and qualitative detection (DOL = 2.6 ppm). Then, H2-FP has been successfully used to monitor NH3 release in the seafood spoilage process at various storage time (4 °C and 25 °C). More importantly, fluorescence color of H2-FP is integrated smartphone are converted to digital values through RGB channels and successfully used to visualize semi-quantitative recognition of NH3. This sensing fluorescence platform integrated with smartphone furnishes an effective fabrication strategy and broad prospects for explore various biomass-based materials for sensing NH3 change in biological and environmental samples.

Sigma factor RpoS positively affects the spoilage activity of Shewanella baltica and negatively regulates its adhesion effect.

Shewanella baltica is the dominant bacterium that causes spoilage of seafood. RpoS is an alternative sigma factor regulating stress adaptation in many bacteria. However, the detailed regulatory mechanism of RpoS in S. baltica remains unclear. This study aims to investigate the regulatory function of RpoS on spoilage activity and adhesion ability in S. baltica. Results revealed that RpoS had no effect on the growth of S. baltica, but positively regulated the spoilage potential of S. baltica accompanied by a slower decline of total volatile basic nitrogen, lightness, and the sensory score of fish fillets inoculated with rpoS mutant. RpoS negatively regulated the adhesion ability, which was manifested in that the bacterial number of rpoS mutant adhered to stainless steel coupon was higher than that of the S. baltica in the early stage, and the biofilm formed on glass slide by rpoS mutant was thicker and tighter compared with S. baltica. Transcriptomic analysis showed that a total of 397 differentially expressed genes were regulated by RpoS. These genes were mainly enrichment in flagellar assembly, fatty acid metabolism/degradation, and RNA degradation pathways, which were associated with motility, biofilm formation and cold adaptation. This study demonstrated that RpoS is a primary regulator involved in flagellar assembly mediated biofilm formation and cold adaptation-related spoilage activity of S. baltica. Our research will provide significant insights into the control of microbiological spoilage in seafood.