Characterization of active films based on chitosan/polyvinyl alcohol integrated with ginger essential oil-loaded bacterial cellulose and application in sea bass (Lateolabrax japonicas) packaging

The poor mechanical properties, low water-resistance, and limited antimicrobial activity of chitosan (CS)/polyvinyl alcohol (PVA) based film limited its application in aquatic product preservation. Herein, bacterial cellulose (BC) was used to load ginger essential oil (GEO). The effects of the addition of BC and different concentrations of GEO on the physicochemical and antimicrobial activities of films were systematically evaluated. Finally, the application of sea bass fillets was investigated. Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction analysis (XRD) analysis indicated dense networks were formed, which was verified by enhanced physical properties. The mechanical properties, barrier properties, and antimicrobial activities enhanced as GEO concentration increased. CPB0.8 (0.8 % GEO) film had better tensile strength (TS) and barrier performance, improved the quality, and extended the shelf-life of sea bass for another 6 days at least. Overall, active films are potential packaging materials for aquatic products.

Identification and characterization of interferon regulatory factor 1 from Lateolabrax japonicus involved in antiviral immune response against grouper nervous necrosis virus infection

Interferon regulatory factors (IRFs) play a key role in mediating the host response against pathogen infection and other important biological processes. In the present study, an interferon regulation factor 1 gene was identified from Lateolabrax japonicus (designated LjIRF-1), the cDNA sequence of LjIRF-1 was 1394 bp long, and with an open reading frame (ORF) of 945 bp that encodes a peptide of 314 amino acids. Bioinformatics data showed that LjIRF-1 possesses a DNA-binding domain (DBD) and two low complexity regions, which shared 56-81% identity to other fish IRF-1s. The LjIRF-1 transcripts were detectable in all examined tissues of healthy L. japonicus, with higher levels in the blood, head-kidney, intestine, gill and spleen. When challenged with grouper nervous necrosis virus (GNNV) and poly (I:C) infection, both the mRNA expression levels of LjIRF-1 and L. japonicus interferon-1 gene (designated LjIFN-1) were significantly up-regulated. Furthermore, like with poly (I:C), the active purified recombinant protein (rLjIRF-1) was also capable of increasing the expression level of LjIFN-1; controlling the copy number of GNNV under lethiferous titer (10¹¹-10¹² copies/μL) and promoting the survival rate of GNNV infected L. japonicas. Combine all the results, we deduced that LjIRF-1 is involved in defending GNNV infection by simulating LjIFN-1 signal pathway in L. japonicas.

Metabolic disorder induces fatty liver in Japanese seabass, Lateolabrax japonicas fed a full plant protein diet and regulated by cAMP-JNK/NF-kB-caspase signal pathway

A 10-week growth trial was conducted to investigate the effects of replacing dietary fishmeal with plant proteins on nutrition metabolism, immunity, inflammation and apoptosis responses in liver tissues of Japanese seabass, Lateolabrax japonicas (initial body weight = 10.42 ± 0.01 g). Two isonitrogenous and isoenergetic diets were formulated. A basal diet containing 54% fishmeal (FM), whereas another diet was prepared by totally replacing FM with a plant protein blend (PP) composed with soybean protein concentrate and cottonseed protein concentrate. Although essential amino acids, fatty acids, and available phosphorus had been balanced according to the FM diet profile, the significantly lower growth performance, metabolic disorder, and fatty liver symptom were observed in the PP group. Compared with the FM group, fish in the PP group showed significantly lower plasma free EAA level and PPV. Glucose metabolism disorder was expressed as the uncontrollable fasting glycolysis and pyruvate aerobic oxidation at postprandial 24 h with significantly up-regulated GK, PK and PDH genes expression, which potentially over-produced acetyl-CoA as the substrate for protein and lipid synthesis. Significantly reduced plasma GLU, but increased GC level, along with very significantly reduced liver GLY storage could be observed in the PP group. Plasma TG and hepatic NEFA contents were significantly decreased, but the hepatic TC content was very significantly increased in the PP group, in addition, hepatocyte vacuolation appeared. The significantly up-regulated cholesterol synthesis gene (HMGCR) expression but down-regulated bile acid synthesis gene (CYP7A1) expression could be the main reason for the fatty liver induced by cholesterol accumulation. The reduced plasma IgM content accompanied by the up-regulated mRNA levels of pro-inflammatory cytokines (TNFα and IL1β) and activated apoptosis signals of liver tissues were found in the PP group. The hyperthyroidism (higher plasma T3 and T4) and the accelerated energy metabolism rate decreased the growth performance in the PP group. The activated p65NF-kB may promote the hepatocytes apoptosis via the extrinsic pathway (caspase8/caspase3). Simultaneously, a "self-saving" response could be observed that activated cAMP promoted the lipolysis/β-oxidation process and up-regulated gene expression of anti-inflammatory cytokine IL10 via promoting CREB expression, further inhibited the over-phosphorylation of JNK protein, which might impede the intrinsic apoptosis pathway (caspase9/caspase3). In conclusion, the nutrient and energy metabolic disorder induced fatty liver related to the cholesterol accumulation in Japanese seabass fed full PP diet, which was under the regulation by cAMP-JNK/NF-kB-caspase signaling pathway. The hemostasis phosphorylation of JNK protein protected the liver tissues from more serious damage.

Effect of a Sodium Alginate Coating Infused with Tea Polyphenols on the Quality of Fresh Japanese Sea Bass (Lateolabrax japonicas) Fillets

Sodium alginate (SA) and tea polyphenols (TP) are natural preservatives commonly used in the food industry, including the production of fish products. The effect of SA coating infused with TP on the quality of fresh Japanese sea bass (Lateolabrax japonicas) fillets was evaluated over a 20-day period at 4 °C. SA (1.5%, w/v) or TP (0.5%, w/v) treatment alone, and the SA coating infused with TP (SA-TP) all reduced microbial counts, with the SA-TP providing the greatest effect. Fish fillet samples treated with SA-TP had significantly lower levels of total volatile basic nitrogen, lipid oxidation, and protein decomposition during the storage period, relative to the remaining treatments. The samples treated with SA-TP had the highest sensory quality rating as well. Collectively, sodium alginate coating infused with tea polyphenols may represent a promising treatment for preservation of Japanese sea bass fillets during cold storage.

PRACTICAL APPLICATION

The sodium alginate-tea polyphenols composite coating has strong potential to be used as a new biopreservative for maintaining fish fillet quality.

Molecular cloning, characterization and expression analysis of Toll-like receptor 5M gene in Japanese sea perch (Lateolabrax japonicas) after bacterial infection

Toll-like receptor 5M belongs to Toll-like receptors (TLRs) family, which plays a crucial role in innate immunity due to its important role in the recognition of bacteria invasion and in the activation of immune related pathways downstream. In the present study, we firstly cloned the full-length cDNAs of TLR 5M (LjTLR 5M) from Japanese sea perch (Lateolabrax japonicas). The full-length cDNAs of LjTLR 5M include an open reading frame (ORF) of 2676 bp encoding a polypeptide of 891 amino acid residues. The deduced amino acid sequence analysis showed that LiTLR 5M contains LRRs (extracellular leucine rich repeats), transmembrane and TIR (Toll/interleukin-1 receptor) domain. Transcriptional expression analysis indicated that LiTLR 5M mRNAs were ubiquitously expressed in wide array of tissues and the peak level was observed in the head-kidney. The expression patterns of LjTLR 5M after Vibro harveyi and Streptococus agalactiae infection were detected by qRT-PCR, and the results showed that LjTLR 5M was significant up-regulated in spleen, liver and head-kidney. Additionally, the expression patterns of LjTLR 5M in infected spleen and head-kidney were further validated by in situ hybridization (ISH). In summary, these findings indicate that LjTLR 5M is significant induced after different bacterial infection and is involved in immune response. Furthermore, this study will provide foundational information for other TLRs research of L. japonicas against different bacterial pathogens invasion.