Exploration of the roles of spoilage bacteria in degrading grass carp proteins during chilled storage: A combined metagenomic and metabolomic approach

Improving flavor quality in bighead carp (Aristichthys nobilis) fillets during chilled storage with chitosan-EGCG coating: Insights into its underlying regulatory mechanisms

Maintaining the flavor quality of aquatic products during storage is crucial for their market value and consumer acceptance. This study evaluated the effects of a chitosan-epigallocatechin gallate coating on the flavor profile of bighead carp fillets and explored its underlying regulatory mechanisms. Sensory evaluation, electronic nose, and analysis of volatile and ATP-related compounds revealed that the coating significantly reduced off-flavor compounds, improving flavor quality. The coating suppressed free amino acid and free fatty acid levels, inhibited flavor-converting enzyme activities, and slowed lipid metabolism. Correlation analysis highlighted positive links between key flavor compounds and flavor precursors, enzymes, and metabolites. High-throughput sequencing identified Lactococcus, Serratia, and Aeromonas as key microorganisms affecting flavor characteristics. These findings advance the understanding of flavor deterioration mechanisms and suggest potential strategies for preserving the flavor quality of bighead carp fillets during chilled storage.

The aprD-mutated strain modulates the development of Pseudomonas fragi population but has limited effects on the spoilage profiles of native residents

Extracellular enzymes produced by predominant bacteria exert important roles in inducing and accelerating spoilage, with their secretion regulated by specific genes. In Pseudomonas fragi, the aprD gene is a recognized regulator for secreting an alkaline extracellular protease. However, limited studies have focused on this gene in P. fragi population and its impact on meat microbial community structure and function. This study addressed this gap by monitoring the changes in biological properties of P. fragi populations and analyzing the discrepancies in spoilage phenotypes and microbial community structures of chilled chicken among groups differentiated by the initial prevalence of aprD-positive strains. The results showed that aprD-positive strains were disseminated in P. fragi populations, and its prevalence was associated with significant increases in swimming motility and biofilm formation capacities in specific groups. In situ contamination experiments revealed varying spoilage characteristics and community compositions among groups by day 3 of storage. Correlation analysis demonstrated a strong association between spoilage phenotypes and certain bacterial genera, such as Pseudomonadaceae_Pseudomonas and Carnobacterium. However, the microbial community structure and spoilage characteristics of samples from each group were not significantly different on the 5th day of storage. These findings suggest that even a small number of aprD mutants can significantly affect the assembly of the chilled meat microbial community. Nonetheless, the regulatory effect of aprD on spoilage at the strain and population levels of P. fragi is negligible in the context of complex natural microbiota. This work underscores the complex interactions between specific bacterial genes and the broader microbial ecology in refrigerated meat environments, providing deeper insights into the meat spoilage mechanisms.

Effects of atmospheric cold plasma treatment mode on muscle quality and bacterial community of red shrimp during cold storage

Atmospheric cold plasma (ACP), known for its safety, non-thermal processing, and energy efficiency, is especially effective for preserving perishable items such as seafood. However, excessive use of ACP may cause oxidation and sensory quality deterioration, which limits its application in the seafood industry. Thus, optimizing ACP treatment modes to balance sterilization efficiency with minimal oxidative effects is essential. This study aims to explore the impact of different ACP treatment modes (cyclical and one-time treatment) on the muscle quality and bacterial community of red shrimp during cold storage. The results indicated that on day 0 of storage, compared to the blank group and the one-time treatment group, the cyclical treatment significantly reduced the total viable count in red shrimp (p < 0.05). However, no significant differences were observed in centrifugal loss, cooking loss, textural properties, total sulfhydryl content, or Ca2+-ATPase activity (p > 0.05). By day 8, both ACP treatment modes significantly improved the protein quality of red shrimp. Compared with the one-time treatment, cyclical treatment reduced the abundance of Aliivibrio (57.24 %), Pseudoalteromonas (97.34 %), and Psychrobacter (59.07 %) in the bacterial community and delayed bacterial succession (especially Aliivibrio salmonicida, Psychrobacter cibarius, and Pseudoalteromonas nigrifaciens), slowing down the degradation of protein quality. Specifically, in the cyclical treatment group, cooking loss was reduced by 7.01 %, and improvements were observed in hardness, total sulfhydryl content, and Ca2+-ATPase activity, which increased by 8.93 %, 17.54 %, and 5.63 %, respectively. Overall, this study demonstrates that the ACP cyclical treatment mode has greater potential in preserving the freshness of seafood.

Protein degradation mechanisms during refrigerated storage of gazami crab (Portunus trituberculatus) at endogenous and microbial-derived enzyme levels

During storage, the proteins of gazami crab (Portunus trituberculatus) are prone to hydrolysis into amino acids and biogenic amines, in which enzymes play a critical role. However, studies exploring spoilage mechanisms from the perspective of enzymes are limited. This study identified 84 endogenous and 52 microbial-derived proteolytic enzymes and peptidases by proteomics and metagenomics. There are 7 endogenous amino acid deaminases, primarily degrade glutamate and aspartate. Additionally, 25 amino acid deaminases of microbial origin were identified, which mainly degrade serine. The formation of biogenic amines involved 14 enzymes, all of which were microbial in origin, primarily synthesizing putrescine from arginine. The main microbial contributors to these enzymes were Photobacterium, Vibrio, and Aliivibrio, accounting for 63.87 %, 15.51 %, and 8.69 % at the end of refrigeration, respectively. This study provides insights into the mechanisms of quality deterioration in gazami crab during refrigeration, from the perspectives of metabolic enzymes and microbial activity.

Advances in High-Resolution Mass Spectrometry-Based Metabolomics: Applications in Food Analysis and Biomarker Discovery

Consumer concerns regarding food nutrition and quality are becoming increasingly prevalent. High-resolution mass spectrometry (HRMS)-based metabolomics stands as a cutting-edge and widely embraced technique in the realm of food component analysis and detection. It boasts the capability to identify character metabolites at exceedingly low abundances, which remain undetectable by conventional platforms. It can also enable real-time monitoring of the flux of targeted compounds in metabolic synthesis and decomposition. With the emergence of artificial intelligence and machine learning, it has become more convenient to process the vast data sets of metabolomics and identify biomarkers. The review summarizes the latest applications of HRMS-based metabolomics platforms in traditional foods, novel foods, and pharmaceutical-food homologous matrices. It compares the suitability of HRMS to nuclear magnetic resonance (NMR) in metabolomics across three dimensions and discusses the principles and application scenarios of various mass spectrometry technologies.

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.

Antibacterial mechanism of atmospheric cold plasma against Pseudomonas fluorescens and Pseudomonas putida and its preservation application on in-packaged red shrimp paste

This study aimed to investigate the antibacterial mechanism of atmospheric cold plasma (ACP) against Pseudomonas fluorescens and Pseudomonas putida and its preservation effect on red shrimp paste. A reactive species (RS) assay showed that O3, H2O2, and total nitric oxide were generated after ACP treatment, which possessed great potential for antibacterial and food preservation. In vitro antibacterial results showed that excess RS inhibited bacterial activity through cell membrane damage. Molecular docking predictions and enzyme activity assays indicated that ACP-induced RS might deactivate dehydrogenases (such as malic dehydrogenase) by oxidatively modifying the active sites. Fluorescence quantification experiments validated the damage of RS to dsDNA. Further preservation tests on shrimp paste demonstrated that ACP treatment significantly delayed the increase in total viable count, Pseudomonas count, and total volatile basic‑nitrogen during refrigeration. This study deepened the understanding of the antibacterial mechanism of ACP and highlighted its potential application as a new preservation method.

Investigating potential freshness indicators for packaged oysters through multivariate statistical analysis

Pacific oysters (Crassostrea gigas) are globally renowned shellfish. In South Korea, oysters are commonly packaged with filling water in polyethylene bags. Previous studies have proposed various freshness and quality parameters for oysters, including pH, volatile basic nitrogen content, glycogen content, and viable cell count. We aimed to identify the objective indicators of oyster freshness during storage and distribution using metabolomic analysis and multivariate statistical techniques. Packaged oyster samples were analyzed for metabolites using gas chromatography-mass-spectrometry during 9-days storage at 5 °C or 15 °C. Additionally, the pH, turbidity, and soluble protein content of the filling water were measured. Multivariate statistical analyses, including principal component analysis, partial least squares discriminant analysis, and orthogonal projections to latent structure-discriminant analysis revealed statistically significant results, demonstrating metabolite clustering based on storage duration. In conclusion, this study introduced crucial freshness indicators for stored or distributed oysters by utilizing metabolomic analysis and multivariate statistical techniques.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10068-024-01693-y.

Studies on Quality Deterioration and Metabolomic Changes in Oysters Induced by Spoilage Bacteria During Chilled Storage

The correlation between spoilage bacteria and the degradation of aquatic food quality during chilled storage is substantial. However, our understanding of the precise roles of spoilage bacteria in oyster spoilage remains incomplete. The aim of this study was to explore the role of three dominant spoilage bacteria strains in oyster spoilage. Subsequently, the metabolites of spoiled oyster meat after inoculation with bacteria were analyzed using LC-MS-based untargeted metabolomics. Combining the results from various biochemical indicators of spoilage, Psychrobacter immobilis, Shewanella putrefaciens, and Photobacterium swingsii are shown to be the main spoilage bacteria in spoiled oyster meat, and their effects on changes in oyster meat quality were evaluated through total volatile basic nitrogen (TVB-N), pH, thiobarbituric acid reactive substances (TBARSs), and weight loss, respectively. The results showed that Ps. immobilis and S. putrefaciens exhibited great spoilage capacity. P swingsii, although a dominant spoilage bacterium, exhibited lower spoilage competency than the above two bacterial strains but demonstrated activity in producing microbial lipases to oxidize fats. In addition, the results of the metabolomics of spoiled oyster meat suggest that 7, 8-Dimethoxy-3-(4-methoxyphenyl)-4-oxo-4H-chromen-5-yl-2-O-pentopyranosylhexopyranoside, 1,2,3,6-Tetrahydropyridine-4-carboxylic acid, Propionic acid, and L-phenylalanine are potential markers of spoilage in oysters. These findings extend our understanding of the roles that microorganisms play in the spoilage of oysters and offer valuable insights into the development of technologies for monitoring the freshness of oysters based on these potential spoilage markers.

Effects of interactions between microorganisms and lipids on inferior volatile compound production during cold storage of grouper (Epinephelus coioides)

The interaction between microorganisms, proteins, and lipids plays a critical role in the odor production of fish. To explore the specific impact of the interaction between lipids and microorganisms on the overall odor of grouper, this study excluded the influence of proteins and assessed lipid (POV and TBARS) and microbial characteristics (biofilm mass and ATP content) in lipid solutions. The Results showed that microbial growth and lipid oxidation mutually promote each other. Lipidomics analysis identified 44 differential lipids, and microbial diversity analysis pinpointed five key microorganisms (Carnobacterium, Pseudomonas, Gluconacetobacter, Vagococcus, and Shewanella). Furthermore, 20 key volatile compounds (VOCs) related to odor changes in the grouper lipid solution were identified using HS-SPME-GC-MS. Correlation network analysis revealed potential microbial and lipid contributions to VOC categories, including alcohols, aldehydes, ketones, and nitrogen- and sulfur-containing compounds. This study provides new insights into the roles of microorganisms and lipids in flavor formation, offering valuable knowledge for improving seafood quality control.

Exploring the correlation of microbial community diversity and succession with protein degradation and impact on the production of volatile compounds during cold storage of grouper (Epinephelus coioides)

Microorganisms, proteins, and lipids play crucial and intricate roles in the aroma generation of aquatic products. To explore the impact of the interaction between microorganisms and proteins on the volatile compounds (VOCs) in grouper, this study employed whey protein isolate (WPI) to inhibit lipid oxidation and reduce mutual interference. Changes in bacterial profiles, metabolites, and VOCs were detected. Eighteen key VOCs associated with the overall flavor of grouper were identified, and the potential relationships among microorganisms, proteins, and VOCs were explored using a correlation network. Five microorganisms (Vibrio, Vagococcus, Pseudomonas, Psychrobacter, and Shewanella) closely related to characteristic flavor compounds were identified. Additionally, 30 differential metabolites related to proteins and six metabolic pathways were screened. Therefore, this study unveils the potential interaction between microorganisms and proteins in flavor formation and provides new insights into the relationships among microorganisms, proteins, and VOCs.

Insight into flavor changes in bighead carp (Aristichthys nobilis) fillets during storage based on enzymatic, microbial, and metabolism analysis

The flavor alterations in bighead carp subjected to varying storage temperatures and the underlying metabolic mechanism were elucidated. Analysis of volatile flavor compounds, electronic nose, free amino acids, ATP-related compounds, and sensory evaluations uncovered a progressive flavor deterioration during storage, especially at 25 °C. Metabolomics-based flavor relating component profiling analysis showed that free fatty acids formed various fatty aldehydes including (E, E)-2,4-heptadienal and nonanal under lipoxygenase catalysis. Alcohol dehydrogenase and alcohol acyltransferases were intimately involved in alcohol and ester generation, while alkaline phosphatase, 5'-nucleotidase, and acid phosphatase were closely associated with IMP, Hx, and HxR conversion, respectively. Aeromonas, Serratia, Lactococcus, Pseudomonas, and Peptostreptococcus notably influenced flavor metabolism and enzyme activities. The metabolism disparities of valine, leucine, isoleucine, lysine, and α-linolenic acid could be the primary factors contributing to flavor metabolism distinctions. This study offers novel insights into the flavor change mechanisms and potential regulation strategies of bighead carp during storage.

Enhancing bighead carp cutting: Chilled storage insights and machine vision-based segmentation algorithm development

To enhance market demand and fish utilization, cutting processing is essential for fish. Bighead carp were cut into four primary cuts: head, dorsal, belly, and tail, collectively accounting for 77.03% of the fish's total weight. These cuts were refrigerated at 4 °C for 10 days, during which the muscle from each cut was analyzed. Pseudomonas.fragi proliferated most rapidly and was most abundant in eye muscle (EM), while Aeromonas.sobria showed similar growth patterns in tail muscle (TM). Notably, EM exhibited the highest rate of fat oxidation. TM experienced the most rapid protein degradation. Furthermore, to facilitate the cutting applied in mechanical processing, a machine vision-based algorithm was developed. This algorithm utilized color threshold and morphological parameters to segment image background and divide bighead carp region. Consequently, each cut of bighead carp had a different storage quality and the machine vision-based algorithm proved effective for processing bighead carp.

Contribution of mono- and co-culture of Pseudomonas paralactis, Acinetobacter MN21 and Stenotrophomonas maltophilia to the spoilage of chill-stored lamb

Exploring the contribution of common microorganisms to spoilage is of great significance in inhibiting spoilage in lamb. This work investigated the extent of protein degradation and profile changes of free amino acids (FAAs), free fatty acids (FFAs) and volatile organic compounds (VOCs) in lamb caused by single- and co-culture of the common aerobic spoilage bacteria, P. paralactis, Ac. MN21 and S. maltophilia. Meanwhile, some key VOCs produced by the three bacteria during lamb spoilage were also screened by orthogonal partial least square discriminant analysis and difference value in VOCs content between inoculated groups and sterile group. Lamb inoculated with P. paralactis had the higher total viable counts, pH, total volatile base nitrogen and TCA-soluble peptides than those with the other two bacteria. Some FAAs and FFAs could be uniquely degraded by P. paralactis but not Ac. MN21 and S. maltophilia, such as Arg, Glu, C15:0, C18:0 and C18:1n9t. Co-culture of the three bacteria significantly promoted the overall spoilage, including bacterial growth, proteolysis and lipolysis. Key VOCs produced by P. paralactis were 2, 3-octanedione, those by Ac. MN21 were 1-octanol, octanal, hexanoic acid, 1-pentanol and hexanoic acid methyl ester, and that by S. maltophilia were hexanoic acid. The production of extensive key-VOCs was significantly and negatively correlated with C20:0, C23:0 and C18:ln9t degradation. This study can provide a basis for inhibiting common spoilage bacteria and promoting high-quality processing of fresh lamb.

Coculture of Acinetobacter johnsonii and Shewanella putrefaciens Contributes to the ABC Transporter that Impacts Cold Adaption in the Aquatic Food Storage Environment

Acinetobacter johnsonii and Shewanella putrefaciens were identified as specific spoilage organisms in aquatic food. The interactions among specific spoilage organisms under cold stress have a significant impact on the assembly of microbial communities, which play crucial roles in the spoilage and cold adaptation processes. The limited understanding of A. johnsonii and S. putrefaciens interactions in the cold adaptation mechanism hinders the elucidation of their roles in protein and metabolism levels. 4D quantitative proteomic analysis showed that the coculture of A. johnsonii and S. putrefaciens responds to low temperatures through ABC transporter proteins, resulting in phospholipid transport and inner membrane components. SapA and FtsX proteins were significantly upregulated, while LolC, LolD, LolE, PotD, PotA, PotB, and PotC proteins were significantly downregulated. Metabolome assays revealed that metabolites of glutathione and spermidine/putrescin were significantly upregulated, while metabolites of arginine/lysine/ornithine were significantly downregulated and involved in the ABC transporter metabolism. The results of ultramicroscopic analyses showed that the coculture of A. johnsonii and S. putrefaciens surface combined with the presence of the leakage of intracellular contents, suggesting that the bacteria were severely damaged and wrinkled to absorb metabolic nutrients and adapt to cold temperatures.

Revealing extracellular protein profile and excavating spoilage-related proteases of Aeromonas salmonicida based on multi-omics investigation

Aeromonas is a ubiquitous aquatic bacteria, and it is a significant factor contributing to meat spoilage during processing and consumption. The abilities of Aeromonas salmonicida 29 and 57, which exhibit spoilage heterogeneity, to secrete protease, lipase, hemolysin, gelatinase, amylase, and lecithinase were confirmed by plate method. A total of 3948 proteins were identified by ITRAQ in extracellular secretions of A. salmonicida, and 16 proteases were found to be potentially related to spoilage ability. The complete genome sequence of A. salmonicida 57 consists of one circular chromosome and three plasmids, while A. salmonicida 29 consists of one circular chromosome, without a plasmid. Transcriptomic analysis revealed a significant number of DEGs were up-regulated in A. salmonicida 29, which were mainly enriched in metabolic pathways (e.g., amino acid metabolism, carbohydrate metabolism), indicating that A. salmonicida 29 had better potential to decompose and utilize nutrients in meat. Six protease genes (2 pepB, hap, pepA, ftsI, and pepD) were excavated by combined ITRAQ with transcriptome analysis, which potentially contribute to bacterial spoilage ability and exhibit universality among other dominant spoilage bacteria. This investigation provides new insights and evidence for elucidating metabolic and spoilage phenotypic differences and provides candidate genes and strategies for future prevention and control technology development.

Study on preservation and monitoring effect of sodium alginate-konjac glucomannan films loaded with tea polyphenols and Lycium ruthenicum anthocyanins

To investigate the efficacy of sodium alginate-konjac glucomannan (SA-KGM) films with anthocyanins (LRA) and tea polyphenols (TP) in meat, beef and grass carp were selected as representative meat products for preservation and freshness monitoring experiments at 4 °C. Concurrently, storage experiments of the films were conducted in this controlled environment. The results of the storage experiment showed that the films delayed meat spoilage by 2-4 days, nearly doubling the preservation time compared to the blank control. Additionally, the film exhibited significant capability to monitor the spoilage process of beef and grass carp. It was revealed by curve fitting analysis that there was a significant correlation between the color change of the film and the spoilage index of the meat. Throughout the storage experiment with the film, it was observed that moisture significantly influenced the microstructure and bonding situation of the films, thereby impacting their mechanical and barrier properties. However, the films were still able to maintain satisfactory physicochemical properties in general. The above findings were crucial in guiding the promotion of the film within the food preservation industry.

Regulating effects of low salt dry-curing pre-treatment on microbiota, biochemical changes and flavour precursors of grass carp (Ctenopharyngodon idella) fillets during storage at 4 °C

Low salt dry-curing (LSD), as a healthier pre-treatment for the preservation of fishery products, is a potential technique substitute for excessively salty curing. The regulatory effects of 2 % and 3 % LSD on the quality evolution through an intrinsic correlation between microbiota succession and flavour precursors of refrigerated grass carp fillets were investigated in this study. The results showed that the LSD pre-treatment was effective in promoting proteolysis, free amino acid and fatty acid metabolism with the microbiota succession and quality evolution. Compared with unpre-treated samples, the 3 % LSD pre-treatment effectively extended the shelf life by 10 days within the acceptable quality attributes. Not only did the LSD pre-treatment lead to catalytic microbiota succession and inhibitive spoilage substance production but it also improved the flavour precursors, which are taste-active amino acids and polyunsaturated fatty acids (PUFAs). Moreover, considerable correlations between quality attributes, taste-active amino acids, PUFAs and microbiota were obtained.

Effect of low-voltage electrostatic field-assisted partial freezing on large yellow croaker protein properties and metabolomic analysis during storage

BACKGROUND

Large yellow croaker is highly perishable during storage because of high protein and moisture content. The degradation of the fish is mainly attributed to microbial growth and enzyme activity, so it is important to find an efficient storage method to extend its shelf life.

METHODOLOGY

This study investigated the effect of a low-voltage electrostatic field combined with partial freezing treatment on the physicochemical properties of myofibrillar protein (MP) and metabolomic analysis of large yellow croaker during preservation. The samples in chilled storage (C), partial freezing storage (PF) and 6 kV/m low-voltage electrostatic field partial freezing storage (LVEF-PF) were analyzed during an 18 day storage period.

RESULTS

In comparison with the C and PF groups, LVEF-PF delayed the oxidation of MP by inhibiting the formation of carbonyl groups (2.25 nmol/mg pro), and maintaining higher sulfhydryl content (29.73 nmol/mg pro). Fourier transform infrared (FTIR) spectroscopy and fluorescence spectroscopy analysis also demonstrated that the LVEF-PF treatment maintained the stability of the protein structure by increasing the a-helix ratio (19.88%) and reducing the random coil ratio (17.83%). Scanning electron microscopy showed that, compared with the LVEF-PF group, there was more degeneration and aggregation of MP in the C and PF groups after 18 days' storage. The results of untargeted metabolomic analysis showed that 415 kinds of differential metabolites were identified after storage, and the difference levels of differential metabolites were least between the samples treated with LVEF-PF stored on the ninth day and the fresh samples. The main differential metabolic pathways during storage were amino acid metabolism and lipid metabolism.

CONCLUSION

The LVEF-PF treatment could maintain the stability of myofibrillar protein in large yellow croaker during storage. These results showed a potential application of the LVEF-PF method for aquatic product preservation. © 2023 Society of Chemical Industry.

Effect of chlorogenic acid grafted chitosan on microbiological compositions of sea bass (Lateolabrax japonicus) fillets: Dominant spoilage bacteria, inhibition activity and membrane damage mechanisms

This study investigated the effect of chlorogenic acid grafted chitosan (CS-g-CA) on the microbiota composition of sea bass (Lateolabrax japonicus), isolated and identified the specific spoilage organisms (SSOs) in the late stage of refrigerated fillets and evaluation of their spoilage potential. Moreover, antibacterial activity and membrane damage mechanism of CS-g-CA against spoilage bacteria was also investigated. Illumina-MiSeq high throughput sequencing results showed that CS-g-CA retarded the growth of Pseudomonas spp., which largely contributed to delaying the quality degradation of sea bass during storage. Then nine spoilage bacteria were isolated and identified from the fillets at the end of storage and inoculated into sterile fish fillets to determine their spoilage capacity. Results showed that fish fillets inoculated with spoilage bacteria exhibited a significant increase in TVB-N, TBA and putrescine content and decreased sensory quality during storage. Subsequently, the inhibitory activity of CS-g-CA against spoilage bacteria was investigated and strains that were more sensitive to the CS-g-CA with a strong spoilage capacity were selected for the study of the inhibition mechanism. Results suggested that CS-g-CA had strong inhibitory activity and led to bacterial death through the mechanism of membrane damage. Overall, this study analyzed the effect of CS-g-CA on the preservation of fish fillets from a microbiological point of view to provide a reference for the anti-bacterial preservation of aquatic products.

Effect of oxygen supplement on post-mortem metabolic profile of shrimp during cold storage

Shrimp, renowned for its exceptional nutritional value, holds a pivotal position within the realm of aquatic products. The supplementation of extra oxygen to shrimp throughout the entire supply chain has found application within the commercial seafood market. In this study, a dual-platform metabolic analysis, coupled with multivariate data analysis, was employed to discern the impact of supplementary oxygen. Furthermore, this approach facilitated the construction of the post-mortem metabolic profile of shrimp during cold storage. A noticeable decrease of alcohols, ketones and carbohydrates which are related to the energy metabolism in shrimp has been found during cold storage, compared to the fresh shrimp. The degradation of nutritional amino acids was alleviated in shrimp after 4 h of extra oxygen supplement. Furthermore, a higher concentration of identified fatty acids, integral to lipid metabolism and functioning as flavor compounds was observed in shrimp subsequent to oxygen supplementation. Therefore, the additional oxygen supplementation exerted influence on multiple metabolic pathways, including nitrogen metabolism, amino acid and peptide metabolism, nucleotide metabolism, carbohydrate metabolism, and lipid metabolism. This study has constructed a comprehensive post-mortem metabolic profile of shrimp during cold storage, thereby establishing a theoretical foundation for the utilization of oxygen supplements in the preservation of seafood.

Advancements in nonthermal physical field technologies for prefabricated aquatic food: A comprehensive review

Aquatic foods are nutritious, enjoyable, and highly favored by consumers. In recent years, young consumers have shown a preference for prefabricated food due to its convenience, nutritional value, safety, and increasing market share. However, aquatic foods are prone to microbial spoilage due to their high moisture content, protein content, and unsaturated fatty acids. Furthermore, traditional processing methods of aquatic foods can lead to issues such as protein denaturation, lipid peroxidation, and other food safety and nutritional health problems. Therefore, there is a growing interest in exploring new technologies that can achieve a balance between antimicrobial efficiency and food quality. This review examines the mechanisms of cold plasma, high-pressure processing, photodynamic inactivation, pulsed electric field treatment, and ultraviolet irradiation. It also summarizes the research progress in nonthermal physical field technologies and their application combined with other technologies in prefabricated aquatic food. Additionally, the review discusses the current trends and developments in the field of prefabricated aquatic foods. The aim of this paper is to provide a theoretical basis for the development of new technologies and their implementation in the industrial production of prefabricated aquatic food.

Exploring the humification process of municipal sludge in hyperthermophilic composting through metagenomic and untargeted metabolomic

Hyperthermophilic composting (HC) has been widely recognized for the advantage of high treatment efficiency for organic wastes. However, the humification process is still unclear. In this study, the humification process of HC was investigated, compared to conventional composting (CK). The results showed that the highest composting temperature, organic matter degradation rate, and humification index in HC were 92.62 °C, 23.98%, and 1.59, while those in CK were 70.23 °C, 14.49 %, and 1.04, indicating HC accelerated humification process. Moreover, the results of metagenomic and untargeted metabolomic showed that the genes and metabolisms related to carbohydrate, lipid, amino acid, fatty acid, and nucleotide were more abundant in HC. Consequently, the metabolic pathways regarding organic matter degradation and microbial reproduction were enhanced in the high temperature stage of HC, further accelerating the humification reaction in the low temperature stage. This work contributes to the comprehension of the humification mechanism in HC.

Integrated volatile compounds and non-targeted metabolomics analysis reveal the characteristic flavor formation of proteins in grouper (Epinephelus coioides) during cold storage

Microorganisms, lipids, and proteins always interact in a complex way in the fish matrix, which becomes a hindrance to evaluate the quality of the individual factors affecting them. In order to investigate the relationship between protein deterioration and volatile compounds (VOCs) in grouper during cold storage, the myofibril protein (MP) was used as a single-factor study to exclude microorganisms and lipids effects. The oxidation and degradation of MP during storage at 4 ℃ were evaluated, including MP content, total sulfhydryl content, carbonyl content, spatial structure and microstructure. Headspace-solid phase microextraction- gas chromatography-mass spectrometry (HS-SPME-GC-MS) was used to analyze the VOCs of grouper MP, and a total of 7 key VOCs were selected, including three ketones (2-nonanone, 2-undecanone and 2-tridecanone), three esters (methyl butyrate, methyl palmitate and methyl ester 9-octadecenoic acid) and one alcohol (3-methyl-1-butanol). At the same time, a non-targeted metabolomics method based on UPLC-Q-Extractive Orbitrap was used to investigate the changes in metabolites during MP storage. A total of 107 up-regulated differential metabolites and 7 down-regulated metabolites were annotated, and 6 metabolic pathways highly related to proteins were screened. Spearman correlation analysis showed that 7 key VOCs are associated with the biosynthesis and metabolism of ornithine and lysine. And a possible solution to protein deterioration in grouper was proposed, which provided a reference for improving protein quality and regulating flavor formation during cold storage of grouper at source.

Degradation and evaluation of myofibril proteins induced by endogenous protease in aquatic products during storage: a review

Myofibril proteins degradation constitutes an important factor in quality deterioration, procedural activation or inhibition of endogenous protease potential regulates autolytic proteolysis-induced softening of post mortem fish muscle. Based on the brief introduction of myofibril proteins degradation in fish skeletal muscle, a detailed description of the main myofibril degradation properties and the distinct role played by endogenous proteases were proposed, which reflects the limitations and challenges of the current research on myofibril hydrolysis mechanisms based on the varied surrounding conditions. In addition, the latest researches on the evaluation method of myofibril proteins degradation were comprehensively reviewed. The potential use of label-free proteomics combined with bioinformatics was also emphasized and has become an important means to in-depth understand protein degradation mechanism.

Effects of combined treatment of electrolytic water and chitosan on the quality and proteome of large yellow croaker (Pseudosciaena crocea) during refrigerated storage

The labeled quantitative proteomic method was used to study the changes in muscle proteins of large yellow croaker (Pseudosciaena crocea) treated with electrolytic water (EW) and chitosan (CHI) combined preservation during 12 days of refrigeration storage (4 °C). The analysis indicated that the freshness instructed by total viable count (TVC), total volatile basic nitrogen (TVB-N) and K value was significantly maintained after combined preservation during storage at 4 °C for 12 days (CS12). Furthermore, 46 differentially abundant proteins (DAPs) were detected in storage at 4 °C for 12 days (S12) compared to the freshness group (F), which bioinformatics confirmed were mainly skeletal proteins and enzymes. Correlation analysis showed that 19 highly correlated DAPs could be used as potential protein markers of freshness. Changes in the relation of freshness and protein were shown in further correlative analysis of F and CS12, which were caused by combined preservation. Therefore, combined preservation is promising in the quality and stability of large yellow croakers.

Atmospheric cold plasma: A potential technology to control Shewanella putrefaciens in stored shrimp

This work aimed to investigate the inactivation mechanism of atmospheric cold plasma (ACP) against Shewanella putrefaciens both in PBS and sterile shrimp juice (SSJ). Reductions in cell density, cell viability, and biofilm formation activity were observed after ACP treatment. ACP cyclical treatment (1 min, 5 times) was more efficient than a one-time treatment (5 min, 1 time). After ACP cyclical treatment, the cell counts and cell viability of S. putrefaciens in PBS were decreased by 3.41 log CFU/mL and 85.30 %, respectively. As for SSJ group, the antibacterial efficiency of ACP declined, but the antibacterial effect of ACP cyclical treatment was still stronger than that of ACP one-time treatment. The biofilm formation activity of S. putrefaciens in PBS was almost completely inhibited, while it gradually returned to normal level with the prolonged of storage time for the SSJ counterpart. The rapid decrease in AKP activity after ACP treatment indicated the damage to cell wall integrity, which was also demonstrated by TEM. In addition, cell membrane and DNA damage of the strain also occurred after ACP treatment. The ROS fluorescence intensity in PBS was higher for the one-time treatment group, while the cyclical treatment group exhibited higher and more stable ozone levels. It was also detected that the total nitric oxide concentration in bacterial suspension depended on the dose of ACP treatment time. ACP treatment (35 kV) for 5 min, especially cyclical treatment, displayed its antibacterial properties on packaged shrimp contaminated with high concentration of S. putrefaciens. ACP cyclical treatment reduced surface bacterial counts of whole shrimps by 0.52 log CFU/mL, while ACP one-time treatment only achieved a decrease of 0.18 log CFU/mL. Therefore, ACP treatment could be considered as a potential alternative to enhance microbial control in food processing.

Exploring the effect of Lactiplantibacillus plantarum Lac 9-3 with high adhesion on refrigerated shrimp: Adhesion modeling and biopreservation evaluation

Lactic acid bacteria (LAB) have recently become ideal candidates for developing food biopreservatives. Adhesion is critical for LAB to perform biocontrol functions in food processing and preservation. In this study, we innovatively proposed an effective adhesion evaluation model related to the surface properties of LAB to excavate a LAB strain with high adhesion on the surface of shrimp. Then, the biocontrol potential regarding the quality of refrigerated shrimp was explored, especially for protein quality. The screening of highly adherent LAB was performed using 54 LAB strains tolerant to the low temperature (4 °C) and present antimicrobial activity. Based on surface hydrophobicity, autoaggregation, and biofilm formation, a new method for predicting LAB adhesion was established by stepwise multiple linear regression. The most relevant relationship between adhesion and biofilm formation was derived from the model. Lactiplantibacillus plantarum Lac 9-3 stood out for the strongest adhesion on the shrimp surface and the highest antimicrobial activity. The preservation results showed that Lac 9-3 significantly (p < 0.05) retarded the accumulation of total volatile basic nitrogen (TVB-N) and the growth of spoilage bacteria. The damage to the texture properties of shrimp was inhibited. Meanwhile, the degradation of myofibrillar protein was alleviated, including a significant delay (p < 0.05) in sulfhydryl (SH) group reduction, surface hydrophobicity increases, and protein conformation changes. This research optimized the evaluation of the bacteria adhesion potential, providing a new idea for developing biocontrol strategies to extend the commercial life of aquatic products.

Metabolomics insights into the potential of encapsulated essential oils as multifunctional food additives

Growing consumer concern about foodborne disease outbreaks and health risks associated with chemical additives has propelled the usage of essential oils (EOs) as novel food additives, but are limited by instability. In this regard, a series of EOs nano/micro-capsules have been widely used to enhance their stability and improve food quality. However, classical food quality assessment methods are insufficient to fully characterize the effects of encapsulated EOs on food properties, including physical, biochemical, organoleptic, and microbial changes. Recently, the rapid development of high-throughput sequencing is accelerating the application of metabolomics in food safety and quality analysis. This review seeks to present the most recent achievements in the application of non-targeted metabolomics to identify and quantify the overall metabolite profile associated with food quality, which can guide the development of emerging food preservation technologies. The scientific findings confirm that metabolomics opens up exciting prospects for biomarker screening in food preservation and contributes to an in-depth understanding of the mechanisms of action (MoA) of EOs. Future research should focus on constructing food quality assessment criteria based on multi-omics technologies, which will drive the standardization and commercialization of EOs for food industry applications.

Effects of Modified Atmosphere Packaging with Varied CO2 and O2 Concentrations on the Texture, Protein, and Odor Characteristics of Salmon during Cold Storage

The effect of gas ratio on the growth of bacteria has been well demonstrated, but some adverse effects of modified atmosphere packaging (MAP) on seafoods have also been found. To provide a better understanding of the effects of CO₂ and O₂ concentrations (CO₂ from 40% to 100% and O₂ from 0% to 30%) in MAP on the texture and protein contents and odor characteristics of salmon during cold storage, the physiochemical, microbial, and odor indicators were compared with those without treatment (CK). Generally, MAP treatments hindered the increase of microbial counts, total volatile basic nitrogen, and TCA-soluble peptides, and decreased the water-holding capacity, hardness, springiness, and sarcoplasmic and myofibrillar protein contents. The results also indicated that 60%CO₂/10%O₂/30%N₂ was optimal and decreased the total mesophilic bacterial counts by 2.8 log cfu/g in comparison with CK on day 12. In agreement, the concentration of CO₂ of 60% showed the lowest myofibrillar protein degradation, and less subsequent loss of hardness. The electronic nose characteristics analysis indicated that 60%CO₂/20%O₂/20%N₂ and 60%CO₂/10%O₂/30%N₂ had the best effect to maintain the original odor profiles of salmon. The correlation analysis demonstrated that microbial growth had a strong relationship with myofibrillar and sarcoplasmic protein content. It can be concluded that 60%CO₂/10%O₂/30%N₂ displayed the best effect to achieve the goal of preventing protein degradation and odor changes in salmon fillets.

Exploration of the roles of microbiota on biogenic amines formation during traditional fermentation of Scomber japonicus

The influence of microbiota composition and metabolisms on the safety and quality of fermented fish products is attracting increasing attention. In this study, the total viable count (TVC), pH, total volatile base nitrogen (TVB-N) as well as biogenic amines (BAs) of traditional fermented Scomber japonicus (zaoyu) were quantitatively determined. To comprehend microbial community variation and predict their functions during fermentation, 16S rRNA-based high-throughput sequencing (HTS) and phylogenetic investigation of communities by reconstruction of unobserved states (PICRUSt) were employed, respectively. The fresh samples stored without fermentation were used as controls. TVC and TVB-N values increased rapidly, and the content of BAs exceeded the permissible limit on day 2 in the controls, indicating serious spoilage of the fish. In contrast, a slower increase in TVC and TVB-N was observed and the content of BAs was within the acceptable limit throughout the fermentation of zaoyu. Significant differences in microbiota composition were observed between zaoyu and the controls. The bacterial community composition of zaoyu was relatively simple and Lactobacillus was identified as the dominant microbial group. The accumulation of histamine was inhibited in zaoyu, which was positively correlated with the relative abundance of Vibrio, Enterobacter, Macrococcus, Weissella, et al. based on Redundancy analysis (RDA), while Lactobacillus showed a positive correlation with tyramine, cadaverine, and putrescine. Functional predictions, based on Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways analysis, revealed that the relative abundance of metabolic function exhibited a decreasing trend with prolonged fermentation time and the abundance of metabolism-related genes was relatively stable in the later stage of fermentation. Those metabolisms related to the formation of BAs like histidine metabolism and arginine metabolism were inhibited in zaoyu. This study has accompanied microbiota analysis and functional metabolism with the accumulation of BAs to trace their correspondences, clarifying the roles of microorganisms in the inhibition of BAs during fermentation of Scomber japonicus.

Dual bacterial strains TTI for monitoring fish quality in food cold chain

Most microbial time-temperature indicators (TTIs) considered only one spoilage strain. This research compared single and dual spoilage strains-based microbial TTI for quality changes of chilled grouper fish (Epinephelus fuscoguttatus x E. lanceolatus) fillet products during distribution. The next-generation sequencing (NGS) and traditional plate count approach showed that Pseudomonas fragi and Vibrio parahaemolyticus were specific spoilage bacteria at 7 and 15°C. A dual-strain TTI response provides more accurate results than a single-strain TTI and provides an irreversible color change from yellow to reddish-brown, showing levels of fish freshness. The microbial TTI comprises fish spoilage bacteria strains with 3 log CFU/ml, a nutrient broth supplemented with 2% NaCl as a medium, and phenol red with 0.25 mg/ml as a pH indicator. Overall, this study points to the applicability of a dual-strain microbial TTI as a valuable tool for monitoring fish quality changes during cold chain break condition.

Unraveling the Effects of Biochemical Drivers on the Bacterial Communities and Volatile Profiles in Refrigerated Sturgeon Filets at 4°C

Spoilage bacteria seriously influence the flavor and quality of fish meat. In this study, we investigated the quality characteristics, bacterial community, and volatile profiles of refrigerated (4°C) sturgeon filets during 10-day storage. On day 10, the refrigerated samples showed the lowest bacterial diversity and the largest difference in microbiota and biochemistry. The dominant genera in the fresh samples were Macrococcus, Acinetobacter, Moraxella, Brucella, and Pseudomonas, while the dominant bacteria changed into Acinetobacter, Carnobacterium, Macrococcus, Pseudomonas, and Psychrobacter at the end of storage. Our results suggest that these dominant taxa contribute to the spoilage of the refrigerated sturgeon filets. Meanwhile, during the storage, total viable counts, total volatile basic nitrogen, thiobarbituric acid-reactive substances, and trichloroacetic acid-soluble peptide significantly increased (P &lt; 0.05), while the sensory score decreased steadily. Additionally, the ATP-related compounds and the K-value showed similarly increasing trends. The shelf-life of the refrigerated sturgeon filets was less than 8 days. The gas chromatography–ion mobility spectrometry results suggest that hexanal, ethyl acetate, ethanol, butanal, 1-propanol, isopentyl alcohol, 2-pentanone, 2-heptanone, ethyl propanoate, and propyl sulfide are potential chemical spoilage markers. The predicted metabolic pathways indicated an abundant carbohydrate metabolism and amino metabolism in the refrigerated sturgeon filets. This study provides insight into the determinants of sturgeon shelf-life and the spoilage process involved in refrigerated fish.