Microbiological aspects and shelf life of processed seafood products

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.

Potassium Chloride, Sodium Lactate and Sodium Citrate Impaired the Antimicrobial Resistance and Virulence of Pseudomonas aeruginosa NT06 Isolated from Fish

Sodium chloride (NaCl) is a commonly used additive in minimally processed fish-based products. The addition of NaCl to fish products and packaging in a modified atmosphere is usually efficient with regard to limiting the occurrence of the aquatic environmental pathogen Pseudomonas aeruginosa. Given the negative effects of excess NaCl in the diet, there is a growing demand to reduce NaCl in food products with safer substituents, but the knowledge of their impact on antibiotic resistant P. aeruginosa is limited. This study aimed to evaluate the physiological and transcriptome characteristics of P. aeruginosa NT06 isolated from fish and to determine the effect of selected concentrations of alternative NaCl compounds (KCl/NaL/NaC) on the P. aeruginosa NT06 virulence phenotype and genotype. In the study, among the isolated microorganisms, P. aeruginosa NT06 showed the highest antibiotic resistance (to ampicillin, ceftriaxone, nalidixic acid, and norfloxacin) and the ability to grow at 4 °C. The Comprehensive Antibiotic Resistance Database (CARD) and the Virulence Factor Database (VFDB) revealed the presence of 24 and 134 gene products assigned to AMR and VF in the P. aeruginosa NT06 transcriptome, respectively. KCl, KCl/NaL and KCl/NaL/NaC inhibited pyocyanin biosynthesis, elastase activity, and protease activity from 40 to 77%. The above virulence phenotypic observations were confirmed via RT-qPCR analyses, which showed that all tested AMR and VF genes were the most downregulated due to KCl/NaL/NaC treatment. In conclusion, this study provides insight into the potential AMR and VF among foodborne P. aeruginosa and the possible impairment of those features by KCl, NaL, and NaC, which exert synergistic effects and can be used in minimally processed fish-based products.

A Systematic Review of Butterfly Pea Flower (Clitoria ternatea L.): Extraction and Application as a Food Freshness pH-Indicator for Polymer-Based Intelligent Packaging

The butterfly pea flower (Clitoria ternatea L.) (BPF) has a high anthocyanin content, which can be incorporated into polymer-based films to produce intelligent packaging for real-time food freshness indicators. The objective of this work was to systematically review the polymer characteristics used as BPF extract carriers and their application on various food products as intelligent packaging systems. This systematic review was developed based on scientific reports accessible on the databases provided by PSAS, UPM, and Google Scholar between 2010 and 2023. It covers the morphology, anthocyanin extraction, and applications of anthocyanin-rich colourants from butterfly pea flower (BPF) and as pH indicators in intelligent packaging systems. Probe ultrasonication extraction was successfully employed to extract a higher yield, which showed a 246.48% better extraction of anthocyanins from BPFs for food applications. In comparison to anthocyanins from other natural sources, BPFs have a major benefit in food packaging due to their unique colour spectrum throughout a wide range of pH values. Several studies reported that the immobilisation of BPF in different polymeric film matrixes could affect their physicochemical properties, but they could still effectively monitor the quality of perishable food in real-time. In conclusion, the development of intelligent films employing BPF's anthocyanins is a potential strategy for the future of food packaging systems.

Effect of Physicochemical Characteristics and Storage Atmosphere on Microbiological Stability and Shelf-Life of Minimally Processed European Sea Bass (Dicentrarchus labrax) Fillets

The aim of the present work was to evaluate the effect of various hurdles such as aw and pH as well as the storage atmosphere on the microbiological and sensory changes of minimally processed (lightly brined or marinated with acetic or citric acid) European sea bass (Dicentrarchus labrax) fillets. The results indicated that the shelf-life of brined fillets stored aerobically was 6 d while that of vacuum and MAP-stored was 12 d, since a reduced growth rate of spoilage bacteria was recorded. The physicochemical characteristics such as aw and water phase salt (WPS) were not considerably changed, while the oxygen levels into the packages ensure the microbiological safety of the product. The fillets marinated with acetic acid exhibited a longer shelf-life at 30 and 40 d under aerobic and reduced oxygen conditions, respectively, while the products marinated with citric acid were at 25 and 35 d respectively. A low pH resulted in reduced or even limited microbial levels, especially for the fillets marinated with acetic acid; something that ensures microbiological safety as well. The low or limited microbial levels in conjugation with the sensory attributes indicated that spoilage may be due to other mechanisms such as autolysis rather than microbial activity. Overall, the present work highlights the potential for further research and development of minimally processed, microbiologically safe and stable with extended shelf-life value added seafood to satisfy the corresponding consumer demands.

Listeria monocytogenes and Pseudomonas spp. Distribution in a Processing Facility of Spotted Sorubim (Pseudoplatystoma corruscans) in Brazil

ABSTRACT

The ecology of Listeria monocytogenes and Pseudomonas spp. during the slaughtering of spotted sorubim (Pseudoplatystoma corruscans) in a fish processing facility was assessed. Fish samples (n = 28) were obtained in different points of slaughtering (A, arrival; B, washing; C, gutting; and D, cooling) and subjected to detection of L. monocytogenes and enumeration of Pseudomonas spp. High frequencies of Listeria spp. (17 of 28 to 22 of 28) and L. monocytogenes (6 of 28 to 9 of 28) were identified in all slaughtering points but were not significantly different (P ≥ 0.05). All L. monocytogenes isolates (n = 33) were identified as belonging to serogroup IVb (serotype 4b) and subjected to macrorestriction with ApaI and AscI. The results indicated a continuous entry of L. monocytogenes in the facility, as well as a temporary persistence of a specific pulsotype. Pseudomonas spp. counts significantly decreased between points A and D (P < 0.05), but the mean counts in the end products (D) remained higher than 3 log CFU/g, suggesting the potential for fast spoilage. The obtained results show that L. monocytogenes and Pseudomonas spp. are widely distributed during spotted sorubim slaughtering, indicating the need for proper hygienic procedures to control these bacteria in the processing facility.

HIGHLIGHTS

An Active Peptide-Based Packaging System to Improve the Freshness and Safety of Fish Products: A Case Study

Fresh fish are highly perishable, owing mainly to their moisture content, high amount of free amino acids and polyunsaturated fatty acids. Microorganisms and chemical reactions cause the spoilage, leading to loss in quality, human health risks and a market value reduction. Therefore, the fishing industry has always been willing to explore new technologies to increase quality and safety of fish products through a decrease of the microbiological and biochemical damage. In this context, antimicrobial active packaging is one such promising solution to meet consumer demands. The main objective of this study was to evaluate the effects of an active polypropylene-based packaging functionalized with the antimicrobial peptide 1018K6 on microbial growth, physicochemical properties and the sensory attributes of raw salmon fillets. The results showed that application of 1018K6-polypropylene strongly inhibited the microbial growth of both pathogenic and specific spoilage organisms (SSOs) on fish fillets after 7 days. Moreover, salmon also kept its freshness as per volatile chemical spoilage indices (CSIs) during storage. Similar results were obtained on hamburgers of Sarda sarda performing the same analyses. This work provides further evidence that 1018K6-polymers have good potential as antimicrobial packaging for application in the food market to enhance quality and preserve the sensorial properties of fish products.

Effect of the Combination of Vanillin and Chitosan Coating on the Microbial Diversity and Shelf-Life of Refrigerated Turbot (Scophthalmus maximus) Filets

The effect of the combination of vanillin and chitosan (VC) coating on the microbiota composition and shelf-life of turbot (Scophthalmus maximus) filets during a 15-day storage period at 4 ± 1°day was investigated in this study. The control and coated fish samples were analyzed periodically for sensory and chemical attributes [total volatile basic nitrogen (TVB-N), thiobarbituric acid reactive substances (TBARS), and pH] and the presence of dominant spoilage microbiota. The results suggested that the sensory and the chemical quality of turbot filets effectively improved after treatment with vanillin (final concentration 2 mg/ml) combined with 1% chitosan, and the shelf-life was prolonged for 6 to 7 days compared with the control group. Furthermore, high-throughput sequencing showed that Proteobacteria (52.2%) and Firmicutes (29.8%) were the dominant bacteria at the phylum level in fresh turbot filets, while Pseudomonadaceae (40.2%) and Lactobacillaceae (39.4%) were the dominant bacteria at the family level in deteriorated turbot filets. However, after VC treatment, the relative abundance of Pseudomonadaceae and Lactobacillaceae decreased significantly due to the growth inhibition of potential bacteria, specifically spoilage bacteria, along with the rich bacterial diversity at the end of storage. Therefore, our data indicated that VC treatment might be effective in decreasing bacteria-induced quality deterioration and in extending the shelf-life of refrigerated turbot filets.

Multi-Analyte MS Based Investigation in Relation to the Illicit Treatment of Fish Products with Hydrogen Peroxide

Fishery products are perishable due to the action of many enzymes, both endogenous and exogenous. The latter are produced by bacteria that may contaminate the products. When fishes age, there is a massive bacteria growth that causes the appearance of off-flavor. In order to obtain “false” freshness of fishery products, an illicit treatment with hydrogen peroxide is reported to be used. Residues of hydrogen peroxide in food may be of toxicology concern. We developed two mass spectrometry based methodologies to identify and quantify molecules related to the treatment of fishes with hydrogen peroxide. With ultra-high-performance liquid chromatography–mass spectrometry (UHPLC-MS) we evaluated the concentration of trimethylamine-N-oxide (TMAO), trimethylamine (TMA), dimethylamine (DMA), and cadaverine (CAD) in fish products. After evaluating LOQ, we measured and validated the lower limits of quantification (LLOQs as first levels of calibration curves) values of 50 (TMAO), 70 (TMA), 45 (DMA), and 40 (CAD) ng/mL. A high ratio between TMAO and TMA species indicated the freshness of the food. With a GC-MS method we confirmed the illicit treatment measuring the levels of H₂O₂ after an analytical reaction with anisole to give 2-hydroxyanisole as a marker. This latter product was detected in the headspace of the homogenized sample with simplification of the work-up. A LLOQ of 50 ng/mL was checked and validated. When fish products were whitened and refreshed with hydrogen peroxide, the detected amount of the product 2-hydroxyanisole could be very important, (larger than 100 mg/kg). The developed analytical methods were suitable to detect the illicit management of fishery products with hydrogen peroxide; they resulted as sensitive, selective, and robust.

Virtual screening for quorum-sensing inhibitors of Pseudomonas fluorescens P07 from a food-derived compound database

AIMS

Pseudomonas fluorescens are important psychrotrophic food spoilage bacteria that are frequently detected in dairy, meat and aquatic products. Quorum sensing (QS) is an intercellular communication and gene regulation mechanism that enables bacteria to monitor their cell densities and regulate a variety of physiological processes. Hence, targeting the bacterial QS system might be a feasible approach to improve food quality and safety by regulating the spoilage caused by P. fluorescens.

METHODS AND RESULTS

In this study, we screened a food-derived three-dimensional (3D) compound database to search for potential QS inhibitors (QSIs) with higher security. The 3D structures of LuxI- and LuxR-type proteins of P. fluorescens P07 were used as targets to screen for QSIs. A total of 25 compounds with high docking scores were tested for their anti-QS activities by indicator strains. The results show that 19 compounds possessed anti-QS activities. Among them, (+)-catechin had the strongest anti-QS activity. The results show that (+)-catechin significantly inhibited the production of extracellular enzymes, swimming motility, biofilm formation, acyl-homoserine lactones and extracellular polymeric substances (EPSs) of P. fluorescens P07. The inhibitory mechanism of (+)-catechin on the QS system of P. fluorescens P07 was discussed in the context of molecular docking analysis and real-time quantitative PCR (RT-qPCR).

CONCLUSIONS

Virtual screening was useful in finding novel QSIs with high security of P. fluorescens P07 from a food-derived 3D compound database. The high hit rate suggested that foods are rich sources of QSIs, and have great potential for exploration.

SIGNIFICANCE AND IMPACT OF THE STUDY

The modelled LuxI- and LuxR-type proteins could be used as targets to discover P. fluorescens P07 QSIs. (+)-catechin, (-)-epicatechin, propyl gallate, hesperidin and lycopene which were identified as potent QSIs, and may be applied in food preservation and biofilm elimination.

Microbiological Quality of Seafood Marketed in Taiwan

Seafood is often associated with foodborne illnesses, and Vibrio parahaemolyticus is the most common pathogen implicated in outbreaks in Taiwan. In this study, the microbiological quality of 300 raw or mixed ready-to-eat (RTE) and other cooking-needed seafood samples was examined. The total aerobic and coliform counts of the RTE samples were significantly higher than those of other cooking-needed samples. On average, 55.8 and 29.7% of the RTE samples failed to meet the local microbiological standards for total aerobic (5 log CFU/g) and coliform (3 log most probable number [MPN] per g), counts respectively; the corresponding percentages for the RTE samples from Taipei City were 9.1 and 18.2%, respectively. The total aerobic and coliform counts in the RTE samples from supermarkets and chain restaurants were significantly lower than those from traditional restaurants. The Vibrio species were more frequently identified in the cooking-needed samples than in RTE samples. Low incidences of V. parahaemolyticus (1.4%), V. vulnificus (1.9%), and V. cholerae (0%) were detected in most RTE samples. High densities of V. parahaemolyticus and V. vulnificus (1,200 MPN/g) were detected in a few RTE samples, only one of which contained toxigenic (tdh(+)) V. parahaemolyticus. The results of this investigation reveal that better hygiene of seafood providers such as chain restaurants, supermarkets, and traditional restaurants in Taipei City would effectively improve the microbiological quality of the seafood. The results will facilitate the establishment of measures for controlling the risks associated with seafood in Taiwan.

Origin and ecological selection of core and food-specific bacterial communities associated with meat and seafood spoilage

The microbial spoilage of meat and seafood products with short shelf lives is responsible for a significant amount of food waste. Food spoilage is a very heterogeneous process, involving the growth of various, poorly characterized bacterial communities. In this study, we conducted 16S ribosomal RNA gene pyrosequencing on 160 samples of fresh and spoiled foods to comparatively explore the bacterial communities associated with four meat products and four seafood products that are among the most consumed food items in Europe. We show that fresh products are contaminated in part by a microbiota similar to that found on the skin and in the gut of animals. However, this animal-derived microbiota was less prevalent and less abundant than a core microbiota, psychrotrophic in nature, mainly originated from the environment (water reservoirs). We clearly show that this core community found on meat and seafood products is the main reservoir of spoilage bacteria. We also show that storage conditions exert strong selective pressure on the initial microbiota: alpha diversity in fresh samples was 189±58 operational taxonomic units (OTUs) but dropped to 27±12 OTUs in spoiled samples. The OTU assemblage associated with spoilage was shaped by low storage temperatures, packaging and the nutritional value of the food matrix itself. These factors presumably act in tandem without any hierarchical pattern. Most notably, we were also able to identify putative new clades of dominant, previously undescribed bacteria occurring on spoiled seafood, a finding that emphasizes the importance of using culture-independent methods when studying food microbiota.

Antimicrobial effect of bayberry leaf extract for the preservation of large yellow croaker (Pseudosciaena crocea)

BACKGROUND

Chemical preservatives have been widely used to keep large yellow croaker fresh. However, the potential harm to human health cannot be ignored. This study was undertaken to investigate the antimicrobial effect of bayberry leaf extract and to evaluate the efficacy of this natural product on the preservation of large yellow croaker.

RESULTS

The minimum inhibitory concentration (MIC) values of bayberry leaf extract against bacteria were 1.0 mg mL⁻¹ for Micrococcus luteus, 0.5 mg mL⁻¹ for Staphylococcus aureus, 0.25 mg mL⁻¹ for Escherichia coli, 0.5 mg mL⁻¹ for Pseudomonas aeruginosa, 0.0625 mg mL⁻¹ for Vibrio parahaemolyticus, and 0.03125 mg mL⁻¹ for Listeria monocytogenes, respectively. This result was confirmed by the diameters of inhibition zone (DIZ) assay. Further studies showed that the bacterial growth was significantly retarded when large yellow croaker was pretreated with bayberry leaf extract (2 g L⁻¹) compared to that in the control group. Moreover, the generation of total volatile basic nitrogenous compounds (TVB-N), ATP degradation products (K-value) and thiobarbituric acid-reactive substances (TBARS) were significantly reduced compared to that in the control group.

CONCLUSION

Our results demonstrated that the shelf life of large yellow croaker can be extended when supplemented with bayberry leaf extract, which might have implications for natural preservatives.