Comparative Proteomics Reveals the Spoilage-Related Factors of Shewanella putrefaciens Under Refrigerated Condition

Combined Effect of Cold Atmospheric Plasma and Chitooligosaccharide-EGCG Conjugate on Quality and Shelf-Life of Depurated Asian Green Mussel

The combined effects of chitooligosaccharide-epigallocatechin gallate conjugate (CEC) at different concentrations (1, 2, and 3%, w/w) and cold atmospheric plasma (CAP) on the depurated Asian green mussel edible portion (AGM-EP) were investigated during refrigerated storage for 15 days. Among all the treatments, the microbial counts, total volatile bases (TMA-N and TVB-N), and lipid oxidation of AGM-EP-treated 3% CEC in conjunction with CAP (CEC-3-CAP) were lower than the other samples during 15-day storage (p < 0.05). Total viable bacteria (6.16 log CFU/g sample), psychrotrophic bacteria (3.24 log CFU/g sample), Vibrio spp. (2.47 log CFU/g sample), presumptive Pseudomonas (5.93 log CFU/g sample), and H2S-producing bacteria (5.05 log CFU/g sample) counts of the CEC-3-CAP were lower than samples treated with 1 and 2% (w/w) CEC on day 15, as well as samples solely treated using CAP during refrigerated storage, irrespective of storage time. Additionally, CEC-3-CAP had significantly lower lipid oxidation (PV: 8.36 mg cumene hydroperoxide/kg sample and TBARS: 2.65 mg MDA/kg sample) as compared to those without CEC added and other samples (p < 0.05). The incorporation of CEC effectively mitigated lipid oxidation as supported by lower reduction of PUFAs in AGM-EP. Moreover, on day 0, no significant differences were observed in cooking loss or textural parameters (firmness and toughness) among the treatments (p > 0.05). However, as storage progressed, cooking loss increased in the CEC-3-CAP sample, while a noticeable decline in firmness and toughness was recorded (p < 0.05). This further attributed to the lower likeness attained for CAP-3-CAP on day 12, but the score was higher than the acceptable limit (5.0). Therefore, CAP together with CEC is a promising technology to prolong the shelf-life of depurated AGM-EP by at least 9 days as compared to the control (3 days), but it certainly needs further studies for the retention of textural properties and sensorial attributes.

Correlation between quality change and hydrogen sulfide in aquatic product: Detection of hydrogen sulfide and its potential applications using bigeye tuna (Thunnus obesus) model during cold storage

Hydrogen sulfide (H2S) is an metabolic product of tuna during the spoilage, and relationship between H2S and tuna quality has not been specifically studied. This study detected changes in H2S content, H2S precursor substances, and related enzymes based on the formation pathway of H2S. H2S content increased of tuna resulted in significant increases in contents of cystathionine β-synthase, cystathionine γ-lyase, 3-mercapto pyruvate sulfotransferase, cysteine aminotransferase and methionine, while content of cysteine decreased which provided H2S formation. Cysteine and methionine metabolism, sulfur metabolism and histidine metabolism were metabolic pathways to assess H2S accumulation. Canonical correlation analysis showed that H2S content was significantly correlated with total volatile base nitrogen, total viable count (p < 0.05). This study elucidates the universality of H2S as an index for assessing seafood quality, utilizing quality indicators and modeling. Our findings offer a theoretical foundation and potential practical applications for improving the quality control of aquatic products.

Antimicrobial activity of chitosan /corn starch film incorporated with starch nanocrystals /nettle essential oil nanoemulsion for Eleutheronema tetradactylum fillet preservation

This study aimed to estimate the effects of chitosan/ corn starch (CH/ CS equal 62:38) film in combination with nettle essential oil nanoemulsions (0.41 wt% NEONEs) and starch nanocrystals (6 wt% SNCs) on the microbial and qualitative characteristics of the Eleutheronema tetradactylumfillets during refrigeration storage (4 ± 1 °C). The fillets were covered by biopolymeric films (CH/CS, CH/CS/SNCs, CH/CS/ NEONEs, CH/CS/SNCs/NEONEs). The qualitative analysis of refrigerated fillets was performed on days 1, 7, and 10. The incorporation of NEONEs and SNCs into CH/CS made an active film with antimicrobial effects. The decrease in pH (5.89 %), PV (44.72 %), FFA (10.41 %), TVB-N (35.01 %), TBA (27.07 %) and increase in moisture (5.38 %) were observed in the covered fillets by CH/CS/SNCs/NEONEs film in compared to uncovered fillets at 4 °C on day 10. The results revealed that incorporating SNCs (6 %) and NEONEs (0.41 %) into CH/CS could increase the storage time of the refrigerated fish fillets.

A longitudinal study on the bacterial quality of baby spinach cultivated in Arizona and California

In the U.S., baby spinach is mostly produced in Arizona (AZ) and California (CA). Characterizing the impact of growing region on the bacterial quality of baby spinach can inform quality management practices in industry. Between December 2021 and December 2022, baby spinach was sampled after harvest and packaging for microbiological testing, including shelf-life testing of packaged samples that were stored at 4°C. Samples were tested to (i) determine bacterial concentration, and (ii) obtain and identify bacterial isolates. Packaged samples from the Salinas, CA, area (n = 13), compared to those from the Yuma, AZ, area (n = 9), had a significantly higher bacterial concentration, on average, by 0.78 log10 CFU/g (P < 0.01, based on aerobic, mesophilic plate count data) or 0.67 log10 CFU/g (P < 0.01, based on psychrotolerant plate count data); the bacterial concentrations of harvest samples from the Yuma and Salinas areas were not significantly different. Our data also support that an increase in preharvest temperature is significantly associated with an increase in the bacterial concentration on harvested and packaged spinach. A Fisher's exact test and linear discriminant analysis (effect size), respectively, demonstrated that (i) the genera of 2,186 bacterial isolates were associated (P < 0.01) with growing region and (ii) Pseudomonas spp. and Exiguobacterium spp. were enriched in spinach from the Yuma and Salinas areas, respectively. Our findings provide preliminary evidence that growing region and preharvest temperature may impact the bacterial quality of spinach and thus could inform more targeted strategies to manage produce quality.

IMPORTANCE

In the U.S., most spinach is produced in Arizona (AZ) and California (CA) seasonally; typically, spinach is cultivated in the Yuma, AZ, area during the winter and in the Salinas, CA, area during the summer. As the bacterial quality of baby spinach can influence consumer acceptance of the product, it is important to assess whether the bacterial quality of baby spinach can vary between spinach-growing regions. The findings of this study provide insights that could be used to support region-specific quality management strategies for baby spinach. Our results also highlight the value of further evaluating the impact of growing region and preharvest temperature on the bacterial quality of different produce commodities.

Inter-facility characterization of bacteria in seafood processing plants: Exploring potential reservoirs of spoilage organisms and the resistome

A study was conducted in fish processing facilities to investigate the microbial composition, microbial metabolic potential, and distribution of antibiotic resistance genes. Whole metagenomic sequencing was used to analyze microbial communities from different processing rooms, operators and fish products. Taxonomic analyses identified the genera Pseudomonas and Psychrobacter as the most prevalent bacteria. A Principal Component Analysis revealed a distinct separation between fish product and environmental samples, as well as differences between fish product samples from companies processing either Gadidae or Salmonidae fish. Some particular bacterial genera and species were associated with specific processing rooms and operators. Metabolic analysis of metagenome assembled genomes demonstrated variations in microbiota metabolic profiles of microbiota across rooms and fish products. The study also examined the presence of antibiotic-resistance genes in fish processing environments, contributing to the understanding of microbial dynamics, metabolic potential, and implications for fish spoilage.

Phylogenetic analysis of Shewanella spp. isolated from fish

Different species of Shewanella spp. widely inhabit freshwater and marine environments. Some of them are opportunistic fish pathogens. The application of high-throughput sequencing enabled the characterization and taxonomic reclassification of many Shewanella spp. species. Still, some strains collected from fish need to be better recognized. The aim of the present study was to classify and determine the phylogenetic relationships of Shewanella spp. collected from fish. The complete genomes of 94 strains of Shewanella spp. from different fish species were sequenced using Illumina platform (MiSeq). The 16S rRNA gene, genomic features and whole-genome relationships of those bacteria were comprehensively analysed in comparison to reference strains. Whole-genome analysis showed that the tested Shewanella spp. strains were clustered into six groups similar to reference strains of S. xiamenensis, S. oneidensis, S. glacialipiscicola, S. hafniensis, S. baltica and S. oncorhynchi. Our study indicates that the whole-genome sequence analysis enabled taxonomic classification and assessment of the diversity of the Shewanella spp. strains, as opposed to recently the gold standard method of 16S rRNA amplicon sequencing. The high genetic diversity and low similarity to the reference genome of S. oneidensis indicate that the group of strains may be a subspecies or even new species. Furthermore, we showed that the most frequent Shewanella spp. species occurring in freshwater fish in our study is the recently described species S. oncorhynchi.

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.

Quorum-quenching enzymes: Promising bioresources and their opportunities and challenges as alternative bacteriostatic agents in food industry

The problems of spoilage, disease, and biofilm caused by bacterial quorum-sensing (QS) systems have posed a significant challenge to the development of the food industry. Quorum-quenching (QQ) enzymes can block QS by hydrolyzing or modifying the signal molecule, making these enzymes promising new candidates for use as antimicrobials. With many recent studies of QQ enzymes and their potential to target foodborne bacteria, an updated and systematic review is necessary. Thus, the goals of this review were to summarize what is known about the effects of bacterial QS on the food industry; discuss the current understanding of the catalytic mechanisms of QQ enzymes, including lactonase, acylase, and oxidoreductase; and describe strategies for the engineering and evolution of QQ enzymes for practical use. In particular, this review focuses on the latest progress in the application of QQ enzymes in the field of food. Finally, the current challenges limiting the systematic application of QQ enzymes in the food industry are discussed to help guide the future development of these important enzymes.

The Characteristics and Function of Internalin G in Listeria monocytogenes

In order to clarified characteristics and function of internalin G (inlG) in Listeria monocytogenes ATCC®19111 (1/2a) (LM), the immune protection of the inlG was evaluated in mice, the homologous recombination was used to construct inlG deletion strains, and their biological characteristics were studied by the transcriptomics analysis. As a result, the immunization of mice with the purified protein achieved a protective effect against bacterial infection. The deletion strain LM-AinlG was successfully constructed with genetic stability. The mouse infection test showed that the virulence of LM was decreased after the deletion of the inlG gene. The deletion strain showed enhanced adhesion to and invasion of Caco-2 cells. Compared to the wild strain, 18 genes were up-regulated, and 24 genes were down-regulated in the LM-AinlG. This study has laid a foundation for further research on the function of inlG and the pathogenesis of LM. In this study, immunization of mice with the purified inlG protein achieved a protective effect against Listeria monocytogenes infection. The virulence of LM-ΔinlG was decreased by mouse infection. However, the adhesion and invasion ability to Caco-2 cell were enhanced. Compared to the wild strain, 18 genes were up-regulated, and 24 genes were down-regulated in the LM-ΔinlG. This study has laid a foundation for further study of the function of the inlG and the listeriosis.