Synergistic effects of ε-polylysine hydrochloride and gallic acid on Shewanella putrefaciens and quality of refrigerated sea bass fillets

Structural characterization of an acidic polysaccharide from scagassum and its effect on shelf life of golden pompano fillets during cold storage

This study investigated the structural characteristics of an acidic polysaccharide (SCP-B) isolated from scagassum and the use of SCP-B coatings to enhance the quality and shelf life of golden pompano fillets. The results indicated that the main glucoside bond structure of SCP-B was →3)-α-Fucp-(1 → 4)-β-ManA-(1 → 3)-α-GulA-(1→, whereas the terminal residues of β-ManA-(1 → and α-Fucp-(1 → linked to O-2 of →2,3)-β-Fucp-(1→, and α-GulA-(1 → linked to O-2 of →2,3)-α-GulA-(1→. When the SCP-B concentration reached 3.13 μg/mL, it exerted a significant antimicrobial effect against Shewanella putrefaciens. This study demonstrated that SCP-B prolonged the shelf life of golden pompano fillets (≥2 d) by inhibiting the proliferation of microorganisms. Furthermore, SCP-B substantially inhibited discoloration, texture deterioration, and water loss, which displayed a concentration dependence. The SCP-B with antimicrobial activity could effectively extend the shelf life of cold stored fillets, which broadens the application of scagassum polysaccharide in the field of aquatic products.

Effects of Irradiation Combined with Partial Freezing Treatment on Texture, Flavor Compounds, and Storage Quality of Fermented Stinky Sea Bass

The preservation of fermented stinky sea bass (FSSB) has always been a major challenge. In this study, four preservation methods, including partial freezing (PF), freezing (F), irradiation + partial freezing (IPF), and irradiation + freezing (IF), were employed, and their effects on the storage quality of vacuum-packed fermented stinky sea bass were investigated. The results revealed that histamines and coliforms were not detected in any of the four preservation methods. Meanwhile, the TVB-N, peroxide value, pH, and cooking loss showed an increasing trend, while the hardness, springiness, and chewiness showed a decreasing trend, following FSSB vacuum packaging during the 30-day preservation period. Compared with PF or F only, irradiation significantly reduced the total plate number, TVB-N, pH, L*, and whiteness of the FSSB samples but increased the peroxide value content while maintaining the cohesiveness, gumminess, and chewiness. Furthermore, the of 1-butanol, propanal, and (E)-2-pentenal contents increased. In contrast, IPF preservation showed a better ability to maintain the texture quality of the FSSB. The safety index of the FSSB samples complied with the Chinese Standard GB10136-2015 National Food Safety Standards Animal Aquatic Products, following the 30-day preservation period under the four preservation methods. Overall, the experimental results suggest that the IPF preservation method is the most preferable approach to preserving FSSB, which can significantly maintain the product quality and save energy.

Preparation, characterization, and antibacterial and antioxidant activities of caffeic acid grafted ε-polylysine

The antioxidant activity of ε-polylysine (EPL) can be enhanced by grafting phenolic compound caffeic acid (CA) onto its amino groups. To enhance the antioxidant activity of EPL, this study synthesized caffeic acid-ε-polylysine conjugate (CA-EPL) by grafting CA onto EPL using carbodiimide coupling reaction. Fourier transform infrared spectroscopy, 1H nuclear magnetic resonance (NMR) spectroscopy confirmed the successful conjugation of caffeic acid and ε-polylysine. The ultraviolet-visible absorption spectra, grafting ratio, and Zeta potential data indicate that the molar ratio of CA to EPL has a significant impact on the grafting degree and Zeta potential of the conjugates. In particular, the highest grafting degree and the lowest Zeta potential were obtained when the molar ratio of carboxyl groups in CA to amino groups in EPL was 3:1. Furthermore, the antimicrobial and antioxidant activities of the conjugates were evaluated. The results of antimicrobial activity indicate that the conjugate CA-EPL still exhibits excellent antimicrobial properties. The results of antioxidant activity show a significant increase in the antioxidant activity of the conjugate CA-EPL, which was significantly higher than that of free EPL. In addition, the research results on the antimicrobial mechanism show that CA-EPL has a similar antimicrobial mechanism to EPL: by interacting with the bacterial cell membrane, it disrupts the cell membrane, causing leakage of cell contents, ultimately leading to bacterial death. These results indicate that CA-EPL, as a novel dual-functional active substance, has broad prospects in the food and pharmaceutical industries.

The Antibacterial Activity and Mechanisms of a Mixed Bio-Preservative on the Bacillus Stains in Crab Roe Sauce

Crab roe sauce (CRS) is prone to spoilage due to microbial contamination. Therefore, this study aimed to investigate the inhibitory effects and mechanisms of a mixed bio-preservative (0.025% ε-polylysine hydrochloride (ε-PL) + 0.01% nisin (NS) + 0.01% tea polyphenols (TPs)) on the specific spoilage bacteria (SSB) in CRS. First, the SSB in CRS were isolated and identified by 16S rRNA sequencing. Two isolates were selected as representative strains based on their enzymatic spoilage potential and spoilage capability in CRS. By comparing the inhibition zones, ε-PL, NS, and TPs were selected from five conventional bio-preservatives (ε-PL, NS, TPs, grape seed extract (GSE), and rosemary extract (RE)) to prepare the mixed bio-preservative. The results showed that the minimum inhibitory concentration (MIC) of the mixed bio-preservative against Bacillus pumilus and Bacillus subtilis was 56.3 µg/mL. The growth curves and cell viability tests revealed that the mixed bio-preservative reduced the viability of both strains. The conductivity, alkaline phosphatase activity, and nucleic acid and soluble protein leakage indicated that the mixed bio-preservative disrupted the integrity of the cell walls and membranes of the two isolates in a concentration-dependent manner. Scanning electron microscopy further confirmed the damage to the cell membranes of the two isolates by the mixed bio-preservative. Overall, the mixed bio-preservative exhibited excellently inhibitory effects on the SSB and could be a promising method for the preservation of CRS.

Antibacterial activity of zinc oxide nanoparticles against Shewanella putrefaciens and its application in preservation of large yellow croaker (Pseudosciaena crocea)

Specific spoilage organisms (SSOs) are the key factors affecting the deterioration of large yellow croaker. This study investigated the antibacterial activity and mechanism of Zinc oxide nanoparticles (ZnO-NPs) against Shewanella putrefaciens. The effects of different concentrations of ZnO-NPs (0.5, 1, 2 mg/mL) combined with seawater slurry ice preservation on storage quality and microbial community of large yellow croaker were further investigated. The results showed that ZnO-NPs had a strong antibacterial effect on Shewanella putrefaciens, which destroyed the integrity of the cell membrane, resulting in nucleic acid leakage and increased electrical conductivity. In addition, ZnO-NPs could effectively inhibit the proliferation of microorganisms, slow down the rate of lipid oxidation, delay the rise of pH value and total volatile basic nitrogen, and maintain the color of fish. Among them, 2 mg/mL ZnO-NPs treatment showed the best preservation effect on large yellow croaker. High-throughput sequencing results showed that Pseudoalteromonas and Shewanella became the dominant spoilage bacteria with the extension of storage time. ZnO-NPs significantly reduced the relative abundance of dominant spoilage bacteria and changed the microbial composition of fish. Inhibition of the growth of SSOs was important for delaying spoilage and prolonging the shelf-life of large yellow croaker. Therefore, ZnO-NPs combined with seawater slurry ice preservation could be used as a new storage method, which provides a new idea for food quality and safety control.

Investigating the synergistic antibacterial effects of chlorogenic and p-coumaric acids on Shigella dysenteriae

Chlorogenic acid (CGA) is a well-known plant secondary metabolite exhibiting multiple physiological functions. The present study focused on screening for synergistic antibacterial combinations containing CGA. The combination of CGA and p-coumaric acid (pCA) exhibited remarkably enhanced antibacterial activity compared to that when administering the treatment only. Scanning electron microscopy revealed that a low-dose combination treatment could disrupt the Shigella dysenteriae cell membrane. A comprehensive analysis using nucleic acid and protein leakage assay, conductivity measurements, and biofilm formation inhibition experiments revealed that co-treatment increased the cell permeability and inhibited the biofilm formation substantially. Further, the polyacrylamide protein- and agarose gel-electrophoresis indicated that the proteins and DNA genome of Shigella dysenteriae severely degraded. Finally, the synergistic bactericidal effect was established for fresh-cut tomato preservation. This study demonstrates the remarkable potential of strategically selecting antibacterial agents with maximum synergistic effect and minimum dosage exhibiting excellent antibacterial activity in food preservation.

Edible Coatings for Fish Preservation: Literature Data on Storage Temperature, Product Requirements, Antioxidant Activity, and Coating Performance-A Review

Fresh fish is among the most nutritive foodstuffs, but it is also the most perishable one. Therefore, huge efforts have been made to find the most suitable tools to deliver fish of the highest quality to exigent consumers. Scientific studies help the industry to exploit the newest findings to scale up emerging industrial technologies. In this review article, the focus is on the latest scientific findings on edible films used for fish coatings and storage. Since today's packaging processing and economy are governed by sustainability, naturality underpins packaging science. The synthesis of edible coatings, their components, processing advantages, and disadvantages are outlined with respect to the preservation requirements for sensitive fish. The requirements of coating properties are underlined for specific scenarios distinguishing cold and freezing conditions. This review raises the importance of antioxidants and their role in fish storage and preservation. A summary of their impact on physical, chemical, microbiological, and sensory alterations upon application in real fish is given. Studies on their influence on product stability, including pro-oxidant activity and the prevention of the autolysis of fish muscle, are given. Examples of lipid oxidation and its inhibition by the antioxidants embedded in edible coatings are given together with the relationship to the development of off-odors and other unwanted impacts. This review selects the most significant and valuable work performed in the past decade in the field of edible coatings whose development is on the global rise and adheres to food waste and sustainable development goals 2 (zero hunger), 3 (good health and well-being), and 12 (responsible consumption and production).

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

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

Food-grade silica-loaded gallic acid nanocomposites: Synthesis and mechanism for enhancing water-based biological activity

As the low water solubility of gallic acid (GA), its biological activities such as water-based antioxidant effect may be greatly reduced. Therefore, GA-loaded nanocomposites (F-SiO2@GA) with high water solubility were synthesized via solvent evaporation using food-grade silica (F-SiO2) as carriers in this work. The assessment of antioxidant capacity revealed that F-SiO2@GA exhibited considerably greater free-radical scavenging ability than free GA and the physical mixture of F-SiO2 and GA. In the photooxidation experiment of food-grade gardenia yellow pigment (GYP), F-SiO2@GA showed a notable antioxidant effect on GYP solution. Additionally, in the storage experiment on chilled whiteleg shrimp (Litopenaeus vannamei) treated with F-SiO2@GA, pH, total volatile basic nitrogen (TVBN), and thiobarbituric acid reactive substance (TBARS) values were effectively inhibited. In conclusion, the internal encapsulation of GA effectively prevented the self-aggregation phenomenon, thereby facilitating the exposure of its active phenolic hydroxyl group and significantly enhancing its water-based biological activity.

Preparation and characterization of zein/gelatin electrospun film loaded with ε-polylysine and gallic acid as tuna packaging system

BACKGROUND

Composite nanofiber films loaded with ε-polylysine (PL) and gallic acid (GA) were prepared using a zein/gelatin (ZG) electrospinning method to develop effective active packaging films for tuna preservation. The morphology, structure, thermal stability, hydrophobicity, antibacterial, and antioxidant properties of the films, and their application for tuna during a period of storage of 4 °C were investigated.

RESULTS

PL reduced the average diameter of ZG fibers, whereas GA increased it. The PL/GA/ZG film possessed a well distributed fiber morphology with an average diameter of 810 ± 150 nm. Fourier-transform infrared spectroscopy and X-ray diffraction results showed the physical loading of PL and GA in ZG film with the main chemical bonds and crystal structure unchanged. The addition of both PL and GA reduced hydrophobicity of the ZG film while the PL/GA/ZG film was still hydrophobic. GA enhanced its thermal stability and contributed to its antioxidant activity. PL and GA synergetically enhanced the antibacterial activity of ZG film against Shewanella putrefaciens. PL combined with GA is more suitable for modifying ZG film than GA alone. The PL/GA/ZG film effectively inhibited total viable counts, total volatile base nitrogen, fat oxidation, and texture deterioration of tuna fillets at 4 °C storage, and could extend the shelf life by 3 days.

CONCLUSIONS

The PL/GA/ZG nanofiber film demonstrated promising potential for application in the preservation of aquatic products as a new antibacterial and antioxidant food packaging. © 2023 Society of Chemical Industry.

Superabsorbent whey protein isolates/chitosan-based antibacterial aerogels: Preparation, characterization and application in chicken meat preservation

Traditional absorbent pads are composed of hard-to-degrade polyethylene film and non-woven bottom layer, which have the characteristic of low absorption rate, without antibacterial effect. The objective of this study is to fabricate a novel superabsorbent and antibacterial aerogel, which consists of whey protein isolate (WPI) and chitosan (CS). The citric acid (CA) and ε-polylysine hydrochloride (ε-PLH) are incorporated into WPI/CS-based aerogel as cross-linking and antibacterial agent, respectively. The application in meat preservation as an absorbent pad is investigated. Results of water absorption, water vapor absorption and stress-strain show that aerogel comprised of 6 % WPI, 1.2 % CS, 2.0 % CA, and 2.0 % ε-PLH have the best water absorption capacity and stress. The density of WPI/CS/CA/ε-PLH aerogel is 82.7 ± 6.4 mg/cm3, and has a uniform and polyporous microstructure, resulting in superabsorbent capacity. Antibacterial rate of WPI/CS/CA/ε-PLH aerogel against Staphylococcus aureus, Escherichia coli, Salmonella and Listeria monocytogenes reach around 80 %. The WPI/CS/CA/ε-PLH aerogel significantly reduces increased velocity of b⁎, pH, total volatile base nitrogen, and total viable counts and decreased velocity of L⁎ and b⁎ of chicken meat (P < 0.05). Results indicate WPI/CS/CA/ε-PLH aerogel effectively extends shelf-life of chicken meat to 7 days, and could be used as an absorbent pad in meat preservation.

Characterization and Antibacterial Properties of Egg White Protein Films Loaded with ε-Polylysine: Evaluation of Their Degradability and Application

There is an ongoing trend to design new kinds of food packaging materials with excellent properties which are environmentally friendly enough. The aim of this study was to prepare and characterize egg white protein (EWP)-based composite films with and without ε-polylysine (Lys), as well as to compare their physical-chemical properties, structural properties, degradation and antibacterial properties. The results showed that with the addition of Lys, the composite films showed a decreasing tendency of the water permeability due to the enhanced interaction between proteins and water molecules. As indicated by the structural properties, stronger cross-linking and intermolecular interactions happened with increasing concentration of Lys. In addition, the composite films presented excellent antibacterial activities against Escherichia coli and Staphylococcus aureus on chilled pork in the presence of Lys. Therefore, our prepared films might be used as a freshness-keeping material with an application in meat preservation. The biodegradation evaluation demonstrated that the composite films were environmental-friendly and have potential applications in the field of food packaging.

Effects of conjugates of ε-polylysine-dextran created through Maillard reaction on quality and storage stability of the chicken gel

The present study mainly focused on the effects of the conjugates of PL-dextran produced through the Maillard reaction on the quality and storage stability of chicken gel for 5 days at 4 ℃. According to the results of the texture profile, water retention capacity (WRC), low-field nuclear magnetic resonance (LF NMR), aerobic plate count (APC), and total volatile basic nitrogen (TVBN), ε-polylysine (PL) could improve chicken gel storage stability while decreasing the quality of protein gels (p < 0.05). Additionally, adding dextran with high or low molecular weight could significantly increase the quality of gel during storage (p < 0.05), whereas decreased storage stability could be obtained (p < 0.05). In general, conjugates formed by PL and dextran with high molecular weight were beneficial for quality maintenance. In comparison, the polymers produced from the low molecular weight of dextran could modify the storage stability of gels. Adding conjugates of dextran and PL benefited the structure formation of protein gel, while PL would retain part of antibacterial activity when crosslinked with dextran. Therefore, it could be concluded that the quality improvement effect of PL-dextran addition on gel quality was greater than its antibacterial effect, which would impact the formulation design of novel emulsion-type meat products.

Development of novel fermented stinky sea bass and analysis of its taste active compounds, flavor compounds, and quality

This paper developed novel fermented stinky sea bass (FSSB) products and reports the first analysis of its taste active compounds, flavor compounds, and quality. The FSSB with Xian Hen stinky tofu (F-XH) had the best sensory quality. After fermentation, the texture of FSSB improved, and the umami amino and sweet amino acid contents significantly increased, whereas that of the bitter amino acids decreased. Moreover, the IMP content and EUC in FSSB increased significantly. Of the six key volatile flavor compounds distinguished, the key volatile flavor compounds of F-XH are Ethyl Acetate, Propan-2-ol, alpha-pinene, 2-methylbutanal, acetol, 4-Methylpentan-2-one. Ethyl Acetate and 2-propanol were thought to give F-XH its unique wine flavor after cooking. The quality evaluation results demonstrated that the six FSSB complied with the Chinese Standard (GB10136-2015) (2015) animal aquatic products. Six types of FSSB products with unique flavors were developed, and a reference was provided for their industrial application.

Unraveling the effect of the combination of modified atmosphere packaging and ε-polylysine on the physicochemical properties and bacterial community of greater amberjack (Seriola dumerili)

The combined effect of ε-polylysine (PL) and modified atmosphere packaging (MAP; 60% CO2/40% N2) on the bacterial community of greater amberjack filets and their physicochemical properties was evaluated at 4°C. The total viable counts (TVC), psychrotrophic bacterial count, sensory index, texture analysis, and total volatile basic nitrogen (TVB-N) revealed that PL, MAP, and MAP + PL treatment delayed the deterioration of greater amberjack filets. These treatment groups also showed decreased accumulation of biogenic amines. High-throughput 16S rRNA gene sequencing results indicated that these treatments suppressed the growth of Pseudomonas in greater amberjack filets. Furthermore, the MAP + PL treatment group was observed to be more effective than the PL and MAP groups, extending the shelf life of greater amberjack filets by 6 days. This investigation showed that the combination of PL and MAP has the potential to retain the quality and extend the shelf life of greater amberjack.