Application of Biotechnology in Specific Spoilage Organisms of Aquatic Products

Effect of Near-Freezing Storage Combined with High-Voltage Electric Fields on the Freshness of Large Yellow Croaker

Seafood is highly perishable after being caught, making effective preservation technology essential. A few studies have explored the mechanisms of near-freezing storage combined with high-voltage electric fields for seafood preservation. This study uses near-freezing storage at -1 °C in conjunction with three high-voltage electric fields (5 kV/m, 8 kV/m, and 16 kV/m) to store large yellow croakers for 21 days and assesses their quality through sensory evaluation, pH values, malondialdehyde, total volatile basic nitrogen, and total viable counts. The results indicate that high-voltage electric fields effectively inhibit endogenous enzyme activity and microbial growth while reducing lipid oxidation in large yellow croakers. The preservation effect is optimal at an electric field strength of 16 kV/m, extending their shelf life by 9 days. These findings offer valuable theoretical and data-driven insights for applying near-freezing storage and electric field preservation technology in cross-regional fish transportation.

Bimetallic Fe/Ni metal organic framework-based hypoxanthine biosensor for early monitoring of freshness changes of aquatic products

The timely detection of freshness changes of aquatic products is crucial. In this study, we have developed a reliable, cost-effective, and user-friendly method for rapidly detecting hypoxanthine using a xanthine oxidase (XOD)/nanozyme enzymatic cascade system. The nanozyme, derived from the Fe7/Ni3 metal-organic framework (Fe7Ni3MOF), exhibited good peroxidase-mimetic activity and stability. Our proposed XOD/Fe7Ni3MOF enzymatic cascade system demonstrated a linear response to hypoxanthine in the range of 3-70 μM, with a low detection limit of 1.39 μM. We also analyzed hypoxanthine in actual aquatic products, achieving spiked recoveries ranging from 90.04 % to 107.37 %. The correlation coefficient between our developed colorimetric method and the HPLC method was 0.98. Importantly, our proposed method holds several advantages over alternative techniques, particularly in terms of cost-effectiveness, precision, and speed. Consequently, this methodology shows great promise for the early detection of freshness changes in aquatic samples.

Microbiological quality assessment of Clarias gariepinus, Bagrus bajad, and Pangasianodon hypophthalmus fillets

In this study, 80 catfish fillets were randomly collected from Egyptian local markets and retailers. The samples included 20 African catfish (Clarias gariepinus), 20 bayad (Bagrus bajad), and 40 pangasius catfish (Pangasianodon hypophthalmus) fillets. Pangasianodon hypophthalmus fillet samples were divided into 20 white basa and 20 red basa fillets. We conducted a microbiological analysis of catfish fillet samples, evaluating mesophilic aerobic bacteria, psychrophilic aerobic bacteria, H2S-producing bacteria, Staphylococcus spp., Enterobacteriaceae, Coliforms, and fecal Coliform counts. Additionally, we identified the existence of Salmonella spp., Vibrio spp., Yersinia spp., Escherichia spp., Aeromonas spp., and Pseudomonas spp. in the catfish fillet samples. In our study, the psychrophilic bacterial counts in Bagrus bajad (5.21 log CFU/g) were found to be higher compared to the counts in Clarias gariepinus (4.31 log CFU/g) and Pangasianodon hypophthalmus (3.89-4.7 log CFU/g). The fecal Coliform in Clarias gariepinus fillets was significantly higher than in other catfish fillets. We isolated Escherichia coli, Escherichia fergusonii, Aeromonas hydrophila, and Pseudomonas luteola from the catfish fillets, while no Salmonella spp., Vibrio spp., or Yersinia spp. were detected. These isolates were identified using 16S rRNA sequencing and phylogenetic analysis. Furthermore, ten Escherichia spp. were serologically identified, revealing that O26 and O78 were the most commonly occurring serotypes. This study highlights the microbiological analysis conducted on catfish fillets and concludes that the fillet samples from these catfish were of superior quality and deemed acceptable for human consumption.

The inhibitory action of lactocin 63 on deterioration of seabass (Lateolabrax japonicus) during chilled storage

BACKGROUND

The bacteriocins, particularly derived from lactic acid bacteria, currently exhibit potential as a promising food preservative owing to their low toxicity and potent antimicrobial activity. This study aimed to evaluate the efficacy of lactocin 63, produced by Lactobacillus coryniformis, in inhibiting the deterioration of Lateolabrax japonicas during chilled storage, while also investigating its underlying inhibitory mechanism. The measurement of total viable count, biogenic amines, and volatile organic compounds were conducted, along with high-throughput sequencing and sensory evaluation.

RESULTS

The findings demonstrated that treatment with lactocin 63 resulted in a notable retardation of bacterial growth in L. japonicas fish fillet during refrigerated storage compared with the water-treated and nisin-treated groups. Moreover, lactocin 63 effectively maintained the microbial flora balance in the fish fillet and inhibited the proliferation and metabolic activity of specific spoilage microorganisms, particularly Shewanella, Pseudomonas, and Acinetobacter. Furthermore, the production of unacceptable volatile organic compounds (e.g. 1-octen-3-ol, hexanal, nonanal), as well as the biogenic amines derived from the bacterial metabolism, could be hindered, thus preventing the degradation in the quality of fish fillets and sustaining relatively high sensory quality.

CONCLUSION

The results of this study provide valuable theoretical support for the development and application of lactocin 63, or other bacteriocins derived from lactic acid bacteria, as potential bio-preservatives in aquatic food. © 2024 Society of Chemical Industry.

CRISPR/Cas tools for enhancing the biopreservation ability of lactic acid bacteria in aquatic products

Lactic acid bacteria (LAB) plays a crucial role in aquatic products biopreservation as it can inhibit many bacteria, in particular the specific spoilage organisms (SSOs) of aquatic products, by competing for nutrients or producing one or more metabolites which have antimicrobial activity, such as bacteriocins. Lactobacillus spp. and Lactococcus spp. are the most commonly used Lactic acid bacterias in aquatic products preservation. The improvement of gene editing tools is particularly important for developing new lactic acid bacteria strains with superior properties for aquatic products biopreservation. This review summarized the research progress of the most widely used CRISPR/Cas-based genome editing tools in Lactobacillus spp. and Lactococcus spp. The genome editing tools based on homologous recombination and base editor were described. Then, the research status of CRISPRi in transcriptional regulation was reviewed briefly. This review may provide a reference for the application of CRISPR/Cas-based genome editing tools to other lactic acid bacteria species.

The Adhesion and Spoilage of Shewanella putrefaciens in Tilapia

Shewanella putrefaciens is a typical spoilage bacteria organism in seafood. The adhesion ability of three S. putrefaciens strains (HR-15, JR-18, HC-71) isolated from putrefied tilapia were evaluated by mucus adhesion in vitro and intestinal adhesion in vivo. The results of the spoilage of the inoculated fish fillets and spoilage of the refrigerated fish both showed that the adhesion ability of S. putrefaciens was positively correlated with the spoilage ability. High-throughput sequencing and GC-MS results showed that S. putrefaciens with high adhesion ability also significantly changed the intestinal flora of fish, causing an increase in the intestinal bacteria such as Plesionomas, Macellibacteroides, Acinetobacter, and Legionella, which then led to the increase in volatile substances such as low-grade aldehydes, alcohols, and ketones in the fish, serious fatty acid oxidation, and excitement of the fishy smell.