Volatile chemical spoilage indexes of raw Atlantic salmon ( Salmo salar ) stored under aerobic condition in relation to microbiological and sensory shelf lives

Effect of co-inoculation of Pseudomonas fragi and Pseudomonas putida on the spoilage of chilled pork after the screening of a variety of different combinations of two Pseudomonas species

This study preliminarily evaluated the effect of different combinations of two Pseudomonas species (P. fragi, P. lundensis, P. fluorescens, and P. putida) on the protein degradation capacity of meat and bacteria growth rules. Then P. fragi and P. putida, with the co-spoilage potential, were inoculated on pork to determine the ability of spoilage, and the potential spoilage genes further were revealed by whole genome sequencing. Results showed that, in the P. fragi + P. putida and P. fragi + P. fluorescens group, the diameter of Raw-pork Juice Agar (RJA) decomposition zone was significantly higher than that in the single-inoculated group, respectively. Furthermore, the results in situ showed that P. fragi and P. putida grew rapidly after co-culture, in which μmax was significantly higher than that in the single-inoculated group. In addition, at the end of storage, the pH and TVB-N values of pork after co-culture were significantly higher than those of the single-inoculated group, and the texture of pork was softer. Simultaneously, the contents of volatile organic compounds including 1-Octen-3-ol, 2-Nonanone, and Hexanal, were significantly increased after co-culture. Moreover, the genes of P. fragi and P. putida, identified by whole genome sequencing, related to amino acid metabolism, carbohydrate metabolism, and motor chemotaxis may be the primary reasons involved in the co-spoilage of pork. In conclusion, this study demonstrated that P. fragi and P. putida had a synergistic interaction to accelerate the spoilage of pork, which could provide a better understanding of co-spoilage of different Pseudomonas spp.

Flavor evolution and identification of the warmed-over flavor (WOF) in pre-cooked goose meat by means of HS-SPME-GC-MS and GC-IMS

This study explored the flavor evolution of pre-cooked goose meat during storage, focusing on lipid oxidation's impact on warmed-over flavor (WOF). Using electronic nose, GC-IMS, and SPME-GC-MS to characterize volatile organic compounds (VOCs), 60 VOCs were identified by GC-IMS. SPME-GC-MS and OAV analysis identified 15 key VOCs, with OPLS-DA and VIP analysis highlighting diisobutyl phthalate, 2-octenoic acid, octadecyl alcohol and 1-octeno-3-alcohol as potential indicators of storage time in pre-cooked goose meat. Pearson correlation analysis revealed a strong link between key VOCs and lipid oxidation, especially secondary oxidation and polyunsaturated fatty acids (C24:1, C22:6n3). These findings emphasize the role of lipid oxidation in flavor intensification, providing valuable insights for flavor profiling and oxidation control.

The possible inhibition mechanism of low salt dry-curing on volatile flavor deterioration in refrigerated grass carp (Ctenopharyngodon idella) blocks: Metabolomics and microorganisms

Complex microbial communities have an important impact on the flavor of low salt dry-curing (LSD)-pretreated grass carp blocks. Here, the flavors, metabolites, and bacterial diversity of LSD-pretreated fish during cold storage were analyzed using flavor analysis, metabolomics, and high-throughput sequencing to investigate their correlations in detail. LSD promoted the volatile flavor deterioration of grass carp blocks under 6 days of refrigeration but inhibited it under 15 days of refrigeration. Furthermore, 924 metabolites were identified in the refrigerated grass carp blocks, and LSD inhibited the growth of Psychrophilic dominant spoilage microorganisms (Proteobacteria) and promoted microbial abundance (Actinobacteriota, Firmicutes, Bacteroidota, and Cyanobacteria). Correlation analysis revealed that the degradation of phosphatidylcholine connected with the monomonas genus in LSD-pretreated fish blocks played a vital role in inhibiting the key volatile flavor (esters, aldehydes, and alcohols) deterioration. This information is useful for elucidating the inhibition mechanism of LSD on flavor deterioration in refrigerated fish blocks.

Microbiota diversity of three Brazilian native fishes during ice and frozen storage

This study aimed to assess the bacterial microbiota involved in the spoilage of pacu (Piaractus mesopotamics), patinga (female Piaractus mesopotamics x male Piaractus brachypomus), and tambacu (female Colossoma macropomum × male Piaractus mesopotamics) during ice and frozen storage. Changes in the microbiota of three fish species (N = 22) during storage were studied through 16S rRNA amplicon-based sequencing and correlated with volatile organic compounds (VOCs) and metabolites assessed by nuclear magnetic resonance (NMR). Storage conditions (time and temperature) affected the microbiota diversity in all fish samples. Fish microbiota comprised mainly of Pseudomonas sp., Brochothrix sp., Acinetobacter sp., Bacillus sp., Lactiplantibacillus sp., Kocuria sp., and Enterococcus sp. The relative abundance of Kocuria, P. fragi, L. plantarum, Enterococcus, and Acinetobacter was positively correlated with the metabolic pathways of ether lipid metabolism while B. thermosphacta and P. fragi were correlated with metabolic pathways involved in amino acid metabolism. P. fragi was the most prevalent spoilage bacteria in both storage conditions (ice and frozen), followed by B. thermosphacta. Moreover, the relative abundance of identified Bacillus strains in fish samples stored in ice was positively correlated with the production of VOCs (1-hexanol, nonanal, octenol, and 2-ethyl-1-hexanol) associated with off-flavors. 1H NMR analysis confirmed that amino acids, acetic acid, and ATP degradation products increase over (ice) storage, and therefore considered chemical spoilage index of fish fillets.

Microbial consortia in commercial salmon products: A comparative study using cultivation-dependent and high-throughput sequencing approaches

Despite the widespread consumption of salmon products, an all-round microbiological survey on fresh salmon and smoked salmon products sold on the market directly to consumers remains to be undertaken. The present study conducted a comprehensive microbial investigation employing both conventional cultivation-based techniques and 16S rRNA amplicon sequencing. A total of 120 fresh salmon and 95 smoked salmon products were systematically collected across all four seasons (spring, summer, fall, and winter), accompanied by temperature assessments of each product's interior. The average aerobic plate counts for fresh salmon and smoked salmon were 3.63 log and 1.36 log CFU/g, respectively, and the highest seasonal concentrations occurred in summer. The average coliform count was higher in fresh salmon (1.50 log CFU/g) than in smoked salmon products (1.12 log CFU/g). Although smoked salmon exhibited CFU counts similar to those of fresh salmon according to culture-based methods, 16S sequencing unveiled a distinct microbial composition. Photobacterium and Pseudomonas, recognized as major spoilage-related microorganisms, were the predominant genera in all products, but especially in fresh salmon. Smoked salmon exhibited diverse variations in bacterial composition compared to fresh salmon. Three types of lactic acid bacteria-Leuconostoc, Lactobacillus, and Lactococcus-were found to be significantly more abundant in smoked salmon than in fresh salmon. The outcomes of this study contribute to an enhanced understanding of retail salmon products, shedding light on crucial areas for investigation and suggesting potential interventions regarding both sales and production of salmon products.

Optimization and Detection of Freshness Biomarkers of Atlantic Salmon Subjected to Different Vacuum Packaging Conditions during Storage at 0 °C by Metabolomics and Molecular Docking

The freshness of Atlantic salmon is influenced mainly by tissue metabolism, which in turn is affected by storage time and conditions. The alterations in taste profiles and nutritional values of salmon when packaged using vacuum methods have not been fully understood, and the factors contributing to these changes require further research. In this work, the extraction method for flavor nutrients from salmon was optimized via the Plackett-Burman (PB) test. A sensitive and rapid targeted metabolomics method for the simultaneous determination of 34 nutrients was successfully established via ultra-performance liquid chromatography-triple quadrupole/linear ion trap composite mass spectrometry (UHPLC-QTRAP/MS), and various nutritional compositions during storage at 0 °C under different vacuum conditions (0 kPa or -90 kPa) for 4 and 8 days were analyzed. Results showed that storage time had a significant effect on salmon metabolism. The total amino acids decreased by 62.95% and 65.89% at 0 kPa and -90 kPa, respectively. Notably, a marked reduction in histidine after 8 days at -90 kPa may have diminished bitterness, while decreased levels of umami-tasting amino acids like glutamine and aspartic acid affected the overall flavor profile. Overall, the packaging conditions at 0 °C and 0 kPa were more suitable for the preservation of most nutrients in salmon. Pathway enrichment analysis revealed that the reduction in substances was mainly related to the alanine, aspartate, and glutamate metabolism pathways. Alanine, inosine, and histidine, whose levels changed significantly, can bind to the typical umami taste receptor TIR1/TIR3 and can be biomarkers to monitor and determine the freshness or spoilage of salmon after 4-8 days of storage. This study revealed the changes in small-molecule nutrients in salmon during storage under different packaging conditions, which provides a reference for the packaging preservation technology of fresh salmon and new ideas for the evaluation of salmon quality and determination of freshness.

Chilled Pacu (Piaractus mesopotamicus) fillets: Modeling Pseudomonas spp. and psychrotrophic bacteria growth and monitoring spoilage indicators by 1H NMR and GC-MS during storage

This study aimed to assess the growth of Pseudomonas spp. and psychrotrophic bacteria in chilled Pacu (Piaractus mesopotamicus), a native South American fish, stored under chilling conditions (0 to 10 °C) through the use of predictive models under isothermal and non-isothermal conditions. Growth kinetic parameters, maximum growth rate (μmax, 1/h), lag time (tLag, h), and (Nmax, Log10 CFU/g) were estimated using the Baranyi and Roberts microbial growth model. Both kinetic parameters, growth rate and lag time, were significantly influenced by temperature (P < 0.05). The square root secondary model was used to describe the bacteria growth as a function of temperature. Secondary models, √μ = 0.016 (T + 10.13) and √μ =0.017 (T + 9.91) presented a linear correlation with R2 values >0.97 and were further validated under non-isothermal conditions. The model's performance was considered acceptable to predict the growth of Pseudomonas spp. and psychrotrophic bacteria in refrigerated Pacu fillets with bias and accuracy factors between 1.24 and 1.49 (fail-safe) and 1.45-1.49, respectively. Fish biomarkers and spoilage indicators were assessed during storage at 0, 4, and 10 °C. Volatile organic compounds, VOCs (1-hexanol, nonanal, octenol, and indicators 2-ethyl-1-hexanol) showed different behavior with storage time (P > 0.05). 1H NMR analysis confirmed increased enzymatic and microbial activity in Pacu fillets stored at 10 °C compared to 0 °C. The developed and validated models obtained in this study can be used as a tool for decision-making on the shelf-life and quality of refrigerated Pacu fillets stored under dynamic conditions from 0 to 10 °C.

Bioactivity of Microencapsulated Cell-Free Supernatant of Streptococcus thermophilus in Combination with Thyme Extract on Food-Related Bacteria

The bioactive properties of the combination of microencapsulated cell-free supernatant (CFS) from Streptococcus thermophilus and thyme extract on food-related bacteria (Photobacterium damselae, Proteus mirabilis, Vibrio vulnificus, Staphylococcus aureus ATCC29213, Enterococcus faecalis ATCC29212, and Salmonella Paratyphi A NCTC13) were investigated. The microencapsulated CFS of S. thermophilus, in combination with ethanolic thyme extract, had a particle size in the range of 1.11 to 11.39 µm. The microencapsulated CFS of S. thermophilus had a wrinkled, spherical form. In the supernatant, especially at 2% (v/w), the thyme extract additive caused a decrease in the wrinkled form and a completely spherical structure. A total of 11 compounds were determined in the cell-free supernatant of S. thermophilus, and acetic acid (39.64%) and methyl-d3 1-dideuterio-2-propenyl ether (10.87%) were the main components. Thyme extract contained seven components, the main component being carvacrol at 67.96% and 1,2,3-propanetriol at 25.77%. Significant differences (p < 0.05) were observed in the inhibition zones of the extracts on bacteria. The inhibitory effect of thyme extract on bacteria varied between 25.00 (P. damselae) and 41.67 mm (V. vulnificus). Less antibacterial activity was shown by the microencapsulated CFS from S. thermophilus compared to their pure form. (p < 0.05). As a result, it was found that microencapsulated forms of CFS from S. thermophilus, especially those prepared in combination with 2% (v/w) thyme extract, generally showed higher bioactive effects on bacteria.

Chitosan coating with grape peel extract: A promising coating to enhance the freeze-thaw stability of beef

This study investigated the effect of chitosan coating with grape peel extracts (CH + GPE) on the physiochemical properties, protein and lipid oxidation, microstructure, and bacterial community diversity of beef during freeze-thaw (F-T) cycles. The results indicated that the CH + GPE groups had lower pH values, total aerobic count, total volatile base nitrogen, and thiobarbituric acid reactive substance values and better protection against color, water holding capacity, and sensory quality after five F-T cycles. The CH + GPE coating effectively inhibited beef microstructure destruction during the F-T cycles. High-throughput sequencing analysis revealed that the CH + GPE coating contributed to a decline in the bacterial diversity of beef and inhibited the growth of pathogenic bacteria. Interestingly, the CH + GPE coating affected the correlation between quality parameters and bacteria in beef. Consequently, the CH + GPE coating can be used as a novel packaging for preventing the loss of frozen meat quality due to temperature fluctuations.

Spoilage markers for freshwater fish: A comprehensive workflow for non-targeted analysis of VOCs using DHS-GC-HRMS

Changes of volatile organic compounds (VOCs) patterns during 6 days of storage at +4 °C were investigated in different freshwater fish species, namely carp and trout, using dynamic headspace gas chromatography time-of-flight mass spectrometry (DHS-GC-TOFMS). DHS parameters were systematically optimized to establish optimum extraction and pre-concentration of VOCs. Moreover, different sample preparation methods were tested: mincing with a manual meat grinder, as well as mincing plus homogenization with a handheld homogenizer both without and with water addition. The addition of water during sample preparation led to pronounced changes of the volatile profiles, depending on the molecular structure and lipophilicity of the analytes, resulting in losses of up to 98 % of more lipophilic compounds (logP > 3). The optimized method was applied to trout and carp. Trout samples of different storage days were compared using univariate (Mann-Whitney U test, fold change calculation) and multivariate (OPLS-DA) statistics. 37 potential spoilage markers were selected; for 11 compounds identity could be confirmed via measurement of authentic standards and 10 compounds were identified by library spectrum match. 22 compounds were also found to be statistically significant spoilage markers in carp. Merging results of the different statistical approaches, the list of 37 compounds could be narrowed down to the 14 most suitable for trout spoilage assessment. This study comprises a systematic evaluation of the capabilities of DHS-GC coupled to high-resolution (HR) MS for studying spoilage in different freshwater fish species, including a comprehensive data evaluation workflow.

Volatilome Analysis and Evolution in the Headspace of Packed Refrigerated Fish

Fresh fish is a perishable food in which chemical (namely oxidation) and microbiological degradation result in undesirable odor. Non-processed fish (i.e., raw fish) is increasingly commercialized in packaging systems which are convenient for its retailing and/or which can promote an extension of its shelf-life. Compared to fish sent to its retail unpackaged, fish packaging results in a modification of the gaseous composition of the atmosphere surrounding it. These modifications of atmosphere composition may affect both chemical and microbiological degradation pathways of fish constituents and thereby the volatile organic compounds produced. In addition to monitoring Total Volatile Basic Nitrogen (TVB-N), which is a common indicator to estimate non-processed fish freshness, analytical techniques such as gas chromatography coupled to mass spectrometry or techniques referred to as "electronic nose" allow either the identification of the entire set of these volatile compounds (the volatilome) and/or to selectively monitor some of them, respectively. Interestingly, monitoring these volatile organic compounds along fish storage might allow the identification of early-stage markers of fish alteration. In this context, to provide relevant information for the identification of volatile markers of non-processed packaged fish quality evolution during its storage, the following items have been successively reviewed: (1) inner atmosphere gaseous composition and evolution as a function of fish packaging systems; (2) fish constituents degradation pathways and analytical methods to monitor fish degradation with a focus on volatilome analysis; and (3) the effect of different factors affecting fish preservation (temperature, inner atmosphere composition, application of hurdle technology) on volatilome composition.

Effects of environmental pH on protein properties and flavor factors of hairtail (Trichiurus haumela) in thermal processing

The flavor and texture of hairtail (Trichiurus haumela) products easily change depending on the processing conditions including the programed temperature, environmental pH, and so on. In the present study, we aimed to explore the differences in the overall texture and flavor of hairtail under heat treatment with varied environmental pH. The results indicated that the secondary structure of the myofibrillar protein in thermal processed hairtail meat presented a transformation from α-helix to β-sheet structure with the decrease of solution pH. Moreover, heat treatment in an acidic solution environment effectively improved the sensory and flavor properties of hairtail. In addition, pH-mediated changes on protein characteristics of cooked hairtail meat showed significant correlation with the texture properties, while weakly correlated with the flavor.

Dynamic Changes of the Microbial Community and Volatile Organic Compounds of the Northern Pike (Esox lucius) during Storage

In this study, the quality (sensory evaluation, microbial enumerate, color, tvb-n (total volatile basic nitrogen), tca-soluble peptide (trichloroacetic acid-soluble peptide), muscle glucose, lactate, total sugar, Bas (Biogenic amines), VOCs (volatile organic compounds) and the microbial dynamic structure in samples stored at 4 °C were evaluated, and the relationship between VOCs and the diversity structure of microorganisms was also discussed. It was determined by sensory evaluation that the shelf life of samples was around 8 days. Protein and sugar were detected in large quantities by microorganisms in the later stage. At the same time, this also caused a large amount of Bas (biogenic amines) (tyramine, cadaverine, and putrescine). According to high-throughput amplicon sequencing, the initial microbiota of samples was mainly composed of Pseudomonas, Acinetobacter, Planifilum, Vagococcus, Hafnia, Mycobacterium, Thauera, and Yersinia. Among them, Pseudomonas was the most advantageous taxon of samples at the end of the shelf life. The minor fraction of the microbial consortium consisting of Vagococcus, Acinetobacter and Myroides was detected. The substances 3-methyl-1-butanol, ethyl acetate, and acetone were the main volatile components. The glucose, lactic acid, and total sugar were negatively correlated with Yersinia, Hafnia-Obesumbacterium, Thauera, Mycobacterium, and Planifilum; the proportion of these microorganisms was relatively high in the early stage. TVB-N and TCA-soluble peptides were positively correlated with Pseudomonas, Shewanella, Brochothrix, Vagococcus, Myroides, and Acinetobacter, and these microorganisms increased greatly in the later stage. The substance 3-methyl-1-butanol was positively correlated with Pseudomonas and negatively correlated with Mycobacterium. Ethyl acetate was associated with Hafnia-Obesumbacterium, Thauera, and Yersinia. Acetone was positively correlated with Acinetobacter.

Chlorogenic Acid Inhibits Rahnella aquatilis KM25 Growth and Proteolytic Activity in Fish-Based Products

This work verified the antiproliferative and antiproteolytic activities of chlorogenic acid against Rahnella aquatilis KM25, a spoilage organism of raw salmon stored at 4 °C. Chlorogenic acid limited the growth of R. aqatilis KM25 in vitro at a concentration of 2.0 mg/mL. The dead (46%), viable (25%), and injured (20%) cell subpopulations were identified by flow cytometry following treatment of R. aquatilis KM25 with the examined agent. The exposure of R. aquatilis KM25 to chlorogenic acid altered its morphology. Changes in cell dimensions, mostly in length parameters from 0.778 µm to 1.09 µm, were found. The length of untreated cells ranged from 0.958 µm to 1.53 µm. The RT-qPCR experiments revealed changes in the expression of genes responsible for the proliferation and proteolytic activity of cells. Chlorogenic acid caused a significant reduction in the mRNA levels of the ftsZ, ftsA, ftsN, tolB, and M4 genes (-2.5, -1.5, -2.0, -1.5, and -1.5, respectively). In situ experiments confirmed the potential of chlorogenic acid to limit bacterial growth. A similar effect was noted in samples treated with benzoic acid, where the growth inhibition of R. aquatilis KM25 was 85-95%. Reduction of microbial R. aquatilis KM25 proliferation significantly limited total volatile base nitrogen (TVB-N) and trimethylamine (TMA-N) formation during storage, extending the shelf life of model products. The TVB-N and TMA-N parameters did not exceed the upper levels of the maximum permissible limit of acceptability. In this work, the TVB-N and TMA-N parameters were 10-25 mg/100 g and 2.5-20.5 mg/100 g, respectively; for samples with benzoic acid-supplemented marinades, the parameters TVB-N and TMA-N were 7.5-25.0 mg/100 g and 2.0-20.0 mg/100 g, respectively. Based on the results of this work, it can be concluded that chlorogenic acid can increase the safety, shelf life, and quality of fishery products.

Nanoemulsion-based approach to preserve muscle food: A review with current knowledge

Muscle foods are regarded as nutritionally dense foods while they are prone to spoilage by action of microorganism and oxidation. Recently, the consumer's preference is mostly toward minimally processed foods as well as preserved with natural preservatives. However, natural extract directly to the food matrix has several drawbacks. Hence development and applications of nanoemulsion has gained importance for the preservation of muscle foods to meet consumer requirements with enhanced food safety. Nanoemulsion utilizes natural extracts at much lower concentration with higher preservative abilities over original components. Nanoemulsions offer protection to the active component from degradation and ensure longer bioavailability. Novel techniques used for formulation of nanoemulsion provide stability to the emulsion with desirable qualities to improve their impacts. The application of nanoemulsion is known to enhance the preservative action of nanoemulsions by improving the microbial safety and oxidative stability in nanoform. This review provides recent updates on different methods used for formulation of nanoemulsions from different sources. Besides, successful application of nanoemulsion derived using natural agents for muscle food preservation and shelf life extension are reviewed. Thus, the application of nanoemulsion to extend shelf life and maintain quality is suggested for muscle foods.

Study on Volatile Chemicals as Spoilage Indexes of Salmon by HS-SPME-GC-MS Technique during Non-Frozen Storage

Freshness is the most fundamental and important factor to assess raw fish quality. The purpose of our study was to determine the potential spoilage indexes of salmon during non-frozen storage by using headspace solid-phase microextraction (HS-SPME) followed by gas chromatography-mass spectrometry (GC-MS). More than 300 volatile compounds in salmon were detected when sensory scores declined gradually following the quality changes of salmon at different temperatures. And there were 27 and 31 compounds that showed concentration variations when stored at 4 °C and 25 °C, respectively. Among them, the contents of 1,3-di-tert-butylbenzene, acetic acid, and 3-methyl-1-butanol increased significantly in the later storage period and were in accordance with the salmon's qualities. The present study provides valuable information on the volatile chemical spoilage indexes that are closely related to the freshness of salmon, which may provide an efficient alternative way for quality evaluation of salmon.

Microbial Control of Raw and Cold-Smoked Atlantic Salmon (Salmo salar) through a Microwave Plasma Treatment

The control of the pathogenic load on foodstuffs is a key element in food safety. Particularly, seafood such as cold-smoked salmon is threatened by pathogens such as Salmonella sp. or Listeria monocytogenes. Despite strict existing hygiene procedures, the production industry constantly demands novel, reliable methods for microbial decontamination. Against that background, a microwave plasma-based decontamination technique via plasma-processed air (PPA) is presented. Thereby, the samples undergo two treatment steps, a pre-treatment step where PPA is produced when compressed air flows over a plasma torch, and a post-treatment step where the PPA acts on the samples. This publication embraces experiments that compare the total viable count (tvc) of bacteria found on PPA-treated raw (rs) and cold-smoked salmon (css) samples and their references. The tvc over the storage time is evaluated using a logistic growth model that reveals a PPA sensitivity for raw salmon (rs). A shelf-life prolongation of two days is determined. When cold-smoked salmon (css) is PPA-treated, the treatment reveals no further impact. When PPA-treated raw salmon (rs) is compared with PPA-untreated cold-smoked salmon (css), the PPA treatment appears as reliable as the cold-smoking process and retards the growth of cultivable bacteria in the same manner. The experiments are flanked by quality measurements such as color and texture measurements before and after the PPA treatment. Salmon samples, which undergo an overtreatment, solely show light changes such as a whitish surface flocculation. A relatively mild treatment as applied in the storage experiments has no further detected impact on the fish matrix.

Halochromic Inks Applied on Cardboard for Food Spoilage Monitorization

Control of food spoilage is a critical concern in the current world scenario, not only to ensure the quality and safety of food but also to avoid the generation of food waste. This paper evaluates a dual-sensor strategy using six different pH indicators stamped on cardboard for the detection of spoilage in three different foods: beef, salmon, and strawberries. After function validation and formulation optimizations in the laboratory, the halochromic sensors methyl orange and bromocresol purple 2% (w/v) were stamped on cardboard and, in contact with the previously mentioned foods, were able to produce an easily perceptible signal for spoilage by changing color. Additionally, when it comes to mechanical characterization the inks showed high abrasion (>100 cycles) and adhesion resistance (>91%).

Edible Xanthan/Propolis Coating and Its Effect on Physicochemical, Microbial, and Sensory Quality Indices in Mackerel Tuna (Euthynnus affinis) Fillets during Chilled Storage

Worldwide aquaculture production is increasing, but with this increase comes quality and safety related problems. Hence, there is an urgent need to develop potent technologies to extend the shelf life of fish. Xanthan gum is commonly used in the food industry because of its high-water solubility, stability of its aqueous solutions in a wide pH range, and high viscosity. One of its modern food applications is its use as a gelling agent in edible coatings building. Therefore, in this study, the effect of xanthan coating containing various concentrations (0, 1, 2%; w/v) of ethanolic extract of propolis (EEP) on physicochemical, microbial, and sensory quality indices in mackerel fillets stored at 2 °C for 20 days was evaluated. The pH, peroxide value, K-value, TVB-N, TBARS, microbiological and sensory characteristics were determined every 5 days over the storage period (20 days). Samples treated with xanthan (XAN) coatings containing 1 and 2% of EEP were shown to have the highest level of physicochemical protection and maximum level of microbial inhibition (p < 0.05) compared to uncoated samples (control) over the storage period. Furthermore, the addition of EEP to XAN was more effective in notably preserving (p < 0.05) the taste and odor of coated samples compared to control.

Changes in Volatile Composition of Cape Hake Fillets under Modified Atmosphere Packaging Systems during Cold Storage

Fresh ready-to-cook fish fillets are susceptible to loss of freshness and accumulation of off-odour due to accelerated microbial spoilage. Suboptimal storage temperature and packaging conditions accelerate this process, limiting the economic potential. This study investigated the effects of modified atmosphere packaging (MAP) and storage temperature (0 °C and 4 °C) on the volatile compounds (VOCs) of Cape hake (Merluccius capensis) fish fillets as a predictor of shelf life and quality. Fresh Cape hake fillets were packaged under active modified atmosphere (40% CO2 + 30% O2 + 30% N2) and passive modified atmosphere (0.039% CO2 + 20.95% O2 + 78% N2) with or without an absorbent pad and stored at 0 °C and 4 °C for 12 d. The results obtained demonstrated that changes in VOCs and concentration were significantly (p < 0.05) influenced by MAP conditions, storage temperature and duration. A total of 16 volatiles were identified in the packaged Cape hake fillets: 4 primary VOCs and 12 secondary VOCs. The spoilage VOCs identified include tri-methylamine (TMA) (ammonia-like), esters (sickeningly sweet) and sulphur group (putrid). The concentration of secondary VOCs increased continuously during storage. Active-MA-packaged fillets performed better and had lower TMA values of 0.31% at 0 °C on day 12 in comparison to 7.22% at 0 °C under passive on day 6. Ethyl acetate was detected in passive-MA-packaged fillets stored at 0 °C on day 3, and the levels increased to 3.26% on day 6, while active-MA-packaged fillets maintained freshness. This study showed that in conjunction with TMA, VOCs such as esters and sulphur-related compounds could be used as spoilage markers for Cape hake fish fillets.

Spoilage of tilapia by Pseudomonas putida with different adhesion abilities

Four Pseudomonas putida strains isolated from spoiled tilapia were divided into three adhesion abilities—high, medium, and low—by an in vitro mucus model. Four strains had no significant difference in spoilage ability to the inoculated fish fillets. However, according to the in vivo experiment, the spoilage caused by the four P.putida was positively correlated with their adhesion abilities. High adhesion strains not only caused more TVB-N in chilled fish, but also activated the spoilage activity of intestinal flora. The diversity of intestinal flora and the changes in volatile components in fish were detected by high-throughput sequencing and SPME-GC/MS. The strains with high adhesion abilities significantly changed the intestinal flora, which led to a significant increase in low-grade aldehydes, indole, and esters in flesh of fish, as well as the production of a fishy and pungent odor. The intestinal adhesion ability of spoilage bacteria was considered the key factor in spoilage of chilled fish.

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A positive correlation between the intestinal adhesion ability of P.putida and the spoilage ability in vivo.

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P.putida affected the intestinal microflora and led to increase in fishy and pungent odor.

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The intestinal adhesion ability of P.putida was considered as a key factor in spoilage.

Spoilage Investigation of Chill Stored Meagre (Argyrosomus regius) Using Modern Microbiological and Analytical Techniques

Spoilage status of whole and filleted chill-stored meagre caught in January and July was evaluated using sensory, microbiological, 16S metabarcoding and Volatile Organic Compounds (VOCs) analysis. Based on the sensory analysis, shelf-life was 15 and 12 days for the whole fish taken in January and July, respectively, while 7 days for fish fillets of both months. For the whole fish, Total Viable Counts (TVC) at the beginning of storage was 2.90 and 4.73 log cfu/g for fish caught in January and July respectively, while it was found about 3 log cfu/g in fish fillets of both months. The 16S metabarcoding analysis showed different profiles between the two seasons throughout the storage. Pseudomonas (47%) and Psychrobacter (42.5%) dominated in whole meagre of January, while Pseudomonas (66.6%) and Shewanella (10.5%) dominated in fish of July, at the end of shelf-life. Regarding the fillets, Pseudomonas clearly dominated at the end of shelf-life for both months. The volatile profile of meagre was predominated by alcohols and carbonyl compounds. After univariate and multivariate testing, we observed one group of compounds (trimethylamine, 3-methylbutanoic acid, 3-methyl-1-butanol) positively correlating with time of storage and another group with a declining trend (such as heptanal and octanal). Furthermore, the volatile profile seemed to be affected by the fish culturing season. Our findings provide insights into the spoilage mechanism and give information that helps stakeholders to supply meagre products of a high-quality level in national and international commerce.

Investigation of fermentation-induced changes in the volatile compounds of Trachinotus ovatus (meixiangyu) based on molecular sensory and interpretable machine-learning techniques: Comparison of different fermentation stages

Fermented golden pomfret (Trachinotus ovatus) is appreciated by local consumers owing to its distinct flavor. Electronic nose (E-nose) and gas chromatography-ion mobility spectrometry (GC-IMS) technologies were used to analyze the changes in volatile compounds responsible for evolution of the golden pomfret odor profile during fermentation. Forty-five ion peaks were detected using GC-IMS. Although aldehydes represented the major initial volatile compound group, their levels decreased as fermentation proceeded. Between 3 and 15 days, increased levels of esters contributed to a stable volatile organic compounds profile. After 18 days, high levels of indole and pyrazines were detected. Eleven key volatile compounds were screened based on partial least squares discriminant analysis (PLS-DA). Back propagation artificial neural network (BP-ANN) predicted the fermentation stage enabling the development of better strategies to regulate golden pomfret fermentation. This study provided a theoretical basis for real-time monitoring and quality control of Chinese fermented golden pomfet.

Hermetia illucens (L.) (Diptera: Stratiomyidae) Odorant Binding Proteins and Their Interactions with Selected Volatile Organic Compounds: An In Silico Approach

The black soldier fly (BSF), Hermetia illucens (Diptera: Stratiomyidae), has considerable global interest due to its outstanding capacity in bioconverting organic waste to insect biomass, which can be used for livestock, poultry, and aquaculture feed. Mass production of this insect in colonies requires the development of methods concentrating oviposition in specific collection devices, while the mass production of larvae and disposing of waste may require substrates that are more palatable and more attractive to the insects. In insects, chemoreception plays an essential role throughout their life cycle, responding to an array of chemical, biological and environmental signals to locate and select food, mates, oviposition sites and avoid predators. To interpret these signals, insects use an arsenal of molecular components, including small proteins called odorant binding proteins (OBPs). Next generation sequencing was used to identify genes involved in chemoreception during the larval and adult stage of BSF, with particular attention to OBPs. The analysis of the de novo adult and larval transcriptome led to the identification of 27 and 31 OBPs for adults and larvae, respectively. Among these OBPs, 15 were common in larval and adult transcriptomes and the tertiary structures of 8 selected OBPs were modelled. In silico docking of ligands confirms the potential interaction with VOCs of interest. Starting from the information about the growth performance of H. illucens on different organic substrates from the agri-food sector, the present work demonstrates a possible correlation between a pool of selected VOCs, emitted by those substrates that are attractive for H. illucens females when searching for oviposition sites, as well as phagostimulants for larvae. The binding affinities between OBPs and selected ligands calculated by in silico modelling may indicate a correlation among OBPs, VOCs and behavioural preferences that will be the basis for further analysis.

Cold plasma for the preservation of aquatic food products: An overview

Cold plasma (CP) is an upcoming technology implemented for the preservation of highly perishable foods, especially aquatic food products (AFPs). The high moisture content, high-quality protein with all essential amino acids and unsaturated fatty acids makes AFP more susceptible to microbial spoilage and oxidation of lipids and proteins. Spoilage lowers the nutritive value and could generate toxic components, making it unsafe for consumption. In recent times, the rising demand for food products of aquatic origin with preserved quality and extended shelf-life has been recorded. In addition, minimally or nonthermally processed and preserved foods are gaining great attention. CP technology has demonstrated an excellent ability to inactivate microorganisms without promoting their resistance and triggering some deteriorative enzymes, which are typical factors responsible for the spoilage of AFP. Consequently, CP could be recommended as a minimal processing intervention for preserving the quality of AFP. This review focuses on different mechanisms of fish spoilage, that is, by microorganisms and oxidation, their inhibition via the application of CP, and the retention of quality and shelf-life extension of AFP.

Changes in the Microbial Communities of Tiger Frog (Rana tigrina) Meat during Refrigerated Storage

ABSTRACT

Microbial activity is the major cause of the spoilage of aquatic meat products during storage. This study investigated the changes of the microbial compositions of the tiger frog (Rana tigrina) meat stored aerobically at 4°C for 12 days using 16S rRNA amplicon high-throughput sequencing analysis. The microbial diversity and species richness of the frog meat were abundant at the initial phase of storage but decreased substantially with prolongation of the storage time. Proteobacteria was the prevalent phylum identified from the frog meat, with a relative abundance of 40.29% at day 0 increasing to 96.77% at day 6 and 95.41% at day 12. At the genus level, Shewanella, Pseudomonas, and Acinetobacter were the three dominant genera in the spoiled samples and contributed to frog meat spoilage. Their proportions were 41.67, 28.48, and 5.94% at day 6 and 29.94, 23.48, and 18.44% at day 12, respectively. The present study is conducive to understanding the pattern and process of frog meat spoilage during refrigeration and could be used to develop efficient control measures to mitigate the predominant psychrotrophic spoilers in aerobically stored frog meat.

HIGHLIGHTS

Analysis of decomposition in 23 seafood products by liquid chromatography with high-resolution mass spectrometry with sensory-driven modeling

Samples of 23 seafood products were obtained internationally in processing plants and subjected to controlled decomposition to produce seven discrete quality increments. A sensory expert evaluated each sample for decomposition, using a scale of 1-100. Samples were then extracted and analyzed by liquid chromatography with high-resolution mass spectrometry (LC-HRMS). Untargeted data processing was performed, and a sensory-driven Random Forest model in the R programming language for each product was created. Five samples of each quality increment were analyzed in duplicate on separate days. Scores analogous to those obtained through sensory analysis were calculated by this approach, and these were compared to the original sensory findings. Correlation values (r) were calculated from these plots and ranged from 0.971 to 0.999. The finding of decomposition state of each sample was consistent with sensory for 548 of 550 test samples (99.6%). Of the two misidentified samples, one was a false negative, and one false positive (0.2% each). One additional sample from each of the 1st, 4th, and 7th increments of each product was extracted and analyzed on a third separate day to evaluate reproducibility. The range of these triplicate calculated scores was 15 or less for all samples tested, 10 or less for 63 of the 69 triplicate tests (91%), and five or less for 41 (59%). From the models, the most predictive compounds of interest were selected, and many of these were identified using MS2 data with standard or database comparison, allowing identification of compounds indicative of decomposition in these products which have not previously been explored for this purpose.

Probabilistic topic modelling in food spoilage analysis: A case study with Atlantic salmon (Salmo salar)

Probabilistic topic modelling is frequently used in machine learning and statistical analysis for extracting latent information from complex datasets. Despite being closely associated with natural language processing and text mining, these methods possess several properties that make them particularly attractive in metabolomics applications where the applicability of traditional multivariate statistics tends to be limited. The aim of the study was thus to introduce probabilistic topic modelling - more specifically, Latent Dirichlet Allocation (LDA) - in a novel experimental context: volatilome-based (sea) food spoilage characterization. This was realized as a case study, focusing on modelling the spoilage of Atlantic salmon (Salmo salar) at 4 °C under different gaseous atmospheres (% CO₂/O₂/N₂): 0/0/100 (A), air (B), 60/0/40 (C) or 60/40/0 (D). First, an exploratory analysis was performed to optimize the model tunings and to consequently model salmon spoilage under 100% N₂ (A). Based on the obtained results, a systematic spoilage characterization protocol was established and used for identifying potential volatile spoilage indicators under all tested storage conditions. In conclusion, LDA could be used for extracting sets of underlying VOC profiles and identifying those signifying salmon spoilage, giving rise to an extensive discussion regarding the key points associated with model tuning and/or spoilage analysis. The identified compounds were well in accordance with a previously established approach based on partial least squares regression analysis (PLS). Overall, the outcomes of the study not only reflect the promising potential of LDA in spoilage characterization, but also provide several new insights into the development of data-driven methods for food quality analysis.

Evaluation of Salmon, Tuna, and Beef Freshness Using a Portable Spectrometer

There has been strong demand for the development of an accurate but simple method to assess the freshness of food. In this study, we demonstrated a system to determine food freshness by analyzing the spectral response from a portable visible/near-infrared (VIS/NIR) spectrometer using the Convolutional Neural Network (CNN)-based machine learning algorithm. Spectral response data from salmon, tuna, and beef incubated at 25 °C were obtained every minute for 30 h and then categorized into three states of “fresh”, “likely spoiled”, and “spoiled” based on time and pH. Using the obtained spectral data, a CNN-based machine learning algorithm was built to evaluate the freshness of experimental objects. In addition, a CNN-based machine learning algorithm with a shift-invariant feature can minimize the effect of the variation caused using multiple devices in a real environment. The accuracy of the obtained machine learning model based on the spectral data in predicting the freshness was approximately 85% for salmon, 88% for tuna, and 92% for beef. Therefore, our study demonstrates the practicality of a portable spectrometer in food freshness assessment.

Growth and spoilage metabolites production of a mesophilic Aeromonas salmonicida strain in Atlantic salmon (Salmo salar L.) during cold storage in modified atmosphere

AIMS

The aim of the study was to quantify the growth kinetic parameters and spoilage-associated metabolites of an inoculated strain of Aeromonas salmonicida in pre-rigor filleted Atlantic salmon (Salmo salar L.) stored in vacuum (VP) or modified atmosphere (MAP 60/40% CO₂ /N₂ ) at 4 and 8°C.

METHODS AND RESULTS

The maximum growth rate of A. salmonicida in VP salmon stored at 4°C was 0·56 ± 0·04 day^-1 with no detectable lag-phase and the concentration of Aeromonas reached 8·33 log CFU per g after 10 days. The growth rates and maximum population density of Aeromonas in MAP salmon were lower but the applied atmosphere did not inhibit the growth. A selection of metabolites associated with fish spoilage were quantified using ¹ H nuclear magnetic resonance (NMR) spectroscopy. The concentration of trimethylamine (TMA) was significantly affected by storage time and temperature, packaging atmosphere and inoculation with A. salmonicida (General Linear Model (GLM), P < 0·001 for all factors).

CONCLUSION

The study presents preliminary results on A. salmonicida as a potential spoilage organism in vacuum-packaged salmon during cold storage. The combination of refrigeration and a packaging atmosphere consisting of 60/40 % CO₂ /N₂ did not completely inhibit the growth but prevented the formation of TMA.

SIGNIFICANCE AND IMPACT OF THE STUDY

Little information is available on the spoilage potential of Aeromonas spp. in minimally processed salmon products under different packaging conditions. The study clearly demonstrates the importance of hurdle technology and provides data to further elucidate the significance of Aeromonas spp. as a spoilage organism.

Characterization of the Volatiles and Quality of Hybrid Grouper and Their Relationship to Changes of Microbial Community During Storage at 4 °C

To investigate the effects of spoilage bacteria on aquatic product quality and volatile organic compounds (VOCs) in hybrid grouper (Epinephelus fuscoguttatus ♀×Epinephelus lanceolatus ♂), the physical conditions were evaluated, the chemical changes including color, total volatile base nitrogen (TVB-N), VOCs, and free amino acids (FFAs) were determined, and biological profiles were made through microbial community (total viable counts (TVC), 16S rRNA gene amplification sequencing, and next-generation sequencing (NGS) technology on hybrid grouper, which were stored at 4 °C for 10 days. The results showed that the whiteness and TVB-N of grouper increased throughout the storage period. The contents of glycine, alanine, and total free amino acid decreased with the microbial activity towards the end of the study period. At the end of storage, the TVC reached 9.0 log10 (CFU/g). Seventy eight strains of bacteria were isolated from the hybrid grouper, most of which were shown to be Pseudomonas spp., after 16S rRNA sequencing. The results of the NGS test showed that the diversity of dominant bacteria decreased with time; Pseudomonas azotoformans was the dominant spoilage bacteria at the end of storage. The VOCs of fish and bacteria in the grouper's spoilage process were presented in headspace solid-phase microextraction gas chromatography-mass spectrometry (HS-SPME-GC-MS). Twenty eight compounds were identified in hybrid grouper, among which alcohol and aldehyde were used to characterize freshness, both of which were not only related to the overall flavor of the grouper, but were also affected by microbial activity. However, due to the complexity of microbial communities in aquatic products, the correlation between community changes and VOCs needs further research. This study provides insights into the correlation between VOCs and specific spoilage organisms (SSOs) through the analysis of the microbial community and VOCs.

Understanding spoilage microbial community and spoilage mechanisms in foods of animal origin

The increasing global population has resulted in increased demand for food. Goods quality and safe food is required for healthy living. However, food spoilage has resulted in food insecurity in different regions of the world. Spoilage of food occurs when the quality of food deteriorates from its original organoleptic properties observed at the time of processing. Food spoilage results in huge economic losses to both producers (farmers) and consumers. Factors such as storage temperature, pH, water availability, presence of spoilage microorganisms including bacteria and fungi, initial microbial load (total viable count-TVC), and processing influence the rate of food spoilage. This article reviews the spoilage microbiota and spoilage mechanisms in meat and dairy products and seafood. Understanding food spoilage mechanisms will assist in the development of robust technologies for the prevention of food spoilage and waste.

Relevant Aspects of Clostridium estertheticum as a Specific Spoilage Organism of Vacuum-Packed Meat

Clostridium estertheticum is a psychrotolerant, gram-positive, motile, anaerobic, spore-forming, rod-shaped bacteria that causes blown pack spoilage (BPS). Spoilage occurs in vacuum-packed meat without temperature abuse. Having been reported in the last 30 years in several countries, BPS by Cl. estertheticum is a major issue around the world and presents a huge economic impact on the meat industry. Despite being an important spoilage microorganism, studies on Cl. estertheticum are challenged by numerous aspects. These include, lack or poor growth in laboratory media, long culturing periods, and unpredictable isolation on the media. These factors hamper the detection of Cl. estertheticum before occurrence of BPS, which further undermines efforts to prevent the occurrence of BPS. Nevertheless, considerable developments have taken place with regard to culture-independent methods. Although information on Cl. estertheticum is available, it is limited and remains highly fragmented. Therefore, this review collates the available information and discusses relevant aspects of Cl. estertheticum as a specific spoilage organism of BPS in vacuum-packed meat.

Spoilage evaluation of raw Atlantic salmon (Salmo salar) stored under modified atmospheres by multivariate statistics and augmented ordinal regression

The development of quality monitoring systems for perishable food products like seafood requires extensive data collection under specified packaging and storage conditions, followed by advanced data analysis and interpretation. Even though the benefits of using volatile organic compounds as food quality indices have been recognized, few studies have focused on real-time quantification of the seafood volatilome and subsequent systematic identification of the most important spoilage indicators. In this study, spoilage of Atlantic salmon (Salmo salar) stored under modified atmospheres (% CO₂/O₂/N₂) and air was characterized by performing multivariate statistical analysis and augmented ordinal regression modelling for data collected by microbiological, chemical and sensory analyses. Out of 25 compounds quantified by selected-ion flow-tube mass spectrometry, ethanol, dimethyl sulfide and hydrogen sulfide were found characteristic under anaerobic conditions (0/0/100 and 60/0/40), whereas spoilage under air was primarily associated with the production of alcohols and ketones. Under high-O₂ MAP (60/40/0), only 3-methylbutanal fulfilled the identification criteria. Overall, this manuscript presents a systematic and widely applicable methodology for the identification of most potential seafood spoilage indicators within the context of intelligent packaging technology development. In particular, parallel application of statistics and modelling was found highly beneficial for the performance of the quality characterization process and for the practical applicability of the obtained results in food quality monitoring.

In Vivo Sampling: A Promising Technique for Detecting and Profiling Endogenous Substances in Living Systems

Endogenous substances, naturally occurring in living organisms, are critical components with physiological and biological functions. Discovery and quantitative measurement of endogenous substances in living biotas are important for food analysis, crop cultivation, and quality assessment. Low or non-invasive in vivo sampling techniques offer the advantages of minimal perturbation to the investigated system and potentially obtain more accurate feedback compared to in vitro sampling. In this perspective, we summarize the up-to-date progress in the development of microdialysis and solid-phase microextraction as valuable tools for in vivo sampling of endogenous substances in food and agriculture chemistry. We discuss their feasibility for on-site and real-time in vivo monitoring and highlight the prospects in searching for highly specific coatings, miniaturized sampling devices, and instruments that well meet the trend for high-efficient and high-throughput analyses.