Change of lipids in whelks (Neptunea arthritica cumingi Crosse and Neverita didyma) during cold storage

The roles of lipoxygenases and autoxidation during mackerel (Scomberomorus niphonius) dry-cured processing

The roles of enzymatic (Lipoxygenases, LOX) oxidation and autoxidation in the dry-cured processing of mackerel were investigated by adding exogenous substances in this study. Four groups, namely control, chlorogenic acid (inhibiting LOX activity), EDTA-2Na (inhibiting autoxidation), and exogenous LOX (adding eLOX), were assigned. The results showed that lipid oxidation of mackerel was reduced by inhibiting LOX activity and autoxidation, while adding eLOX promoted lipid oxidation. Inhibition of LOX activity and autoxidation suppressed fatty acid accumulation mainly in the air-drying and curing stage, respectively. The total contents of key flavors in the mackerel during dry-cured processing were decreased by inhibiting LOX activity and autoxidation, and the former inhibitory effect was stronger than autoxidation, while it was corresponding increased through adding eLOX, of particular in the later stage of air-drying. Collectively, LOX could promote the flavor formation of the mackerel in the dry-cured processing, which could be applied in the flavor adjustment of aquatic products or some similar fields.

Spectrophotometric- and LC/MS-Based Lipidomics Analyses Revealed Changes in Lipid Profiles of Pike Eel (Muraenesox cinereus) Treated with Stable Chlorine Dioxides and Vacuum-Packed during Chilled Storage

Spectrophotometric- and liquid chromatography/mass spectrometry (LC/MS)-based lipidomics analyses were performed to explore the changes of lipid profiles in pike eel (Muraenesox cinereus) under stable chlorine dioxides (ClO₂) and vacuum-packed treatment during chilled storage. The peroxide value (PV) and malondialdehyde (MDA) content in ClO₂ treated and vacuum-packaged (VP) samples were significantly reduced compared to simple-packaged (SP) samples during whole chilled storage. The LC/MS-based lipidomics analyses identified 2182 lipid species in the pike eel muscle classified into 39 subclasses, including 712 triglycerides (TGs), 310 phosphatidylcholines (PCs), 153 phosphatidylethanolamines (PEs), and 147 diglycerides (DGs), among others. Further, in comparison with fresh pike eel (FE) muscle, 354 and 164 higher and 420 and 193 lower abundant levels of differentially abundant lipids (DALs) were identified in SP samples and VP samples, respectively. Compared with the VP batch, 396 higher and 404 lower abundant levels of DALs were identified in the SP batch. Among these, PCs, PEs, TGs, and DGs were more easily oxidized/hydrolyzed, which could be used as biomarkers to distinguish FE, SP, and VP samples. This research provides a reference for controlling lipid oxidation in fatty fish.

Development of a Multifunctional Edible Coating and Its Preservation Effect on Sturgeon (Acipenser baeri♀× Acipenser schrenckii♂) Fillets during Refrigerated Storage at 4 °C

Although many coatings and films can improve the quality and shelf life of fish fillets during refrigerated storage, a more multifunctional coating material is needed. In this study, an edible alginate/protein-based coating solution was prepared by incorporating antimicrobial agents. The coating properties were characterized and its effects on the quality and shelf life of sturgeon fillets during refrigeration (4 °C) were investigated. Compared with sodium alginate coating (2% sodium alginate + antibacterial agents, H), the composite coatings (2% sodium alginate + antibacterial agents + 1:15 or 1:10 protein solution, HP-15 and HP-10) exhibited a more stable structure and better light, gas, and water barrier properties, and showed better quality-preservation effects on sturgeon fillets. The composite coatings treatments, especially HP-10 composite coating, exhibited significant (p < 0.05) effects in inhibiting microbial growth, maintaining sensory quality, reducing the production of total volatile basic nitrogen (TVB-N), decreasing nucleotide breakdown, and delaying the lipid oxidation and protein degradation in fillets. These findings confirm that the composite coatings can be used as a multifunctional coating material for freshness preservation of sturgeon fillets to improve quality and extend shelf life.

Effect of boiling on texture of abalone muscles and its mechanism based on proteomic techniques

The precise mechanism of texture changes in abalone muscles during boiling was investigated using quantitative proteomic analysis. A total 353 water-soluble proteins were identified in fresh abalone muscle. The number was decreased to 233 (6 min) and 201 (30 min), and then increased to 271 (240 min) during boiling. The undetectable protein in water-soluble fraction caused by boiling mainly belong to hemocyanins, protein kinases, dehydrogenases, phosphorylases, and transferases, while the newly identified proteins in water-soluble fraction during boiling mainly belong to collagen and myofibrillar proteins (MPs).Additionally, results also showed that boiling caused protein oxidation, denaturation, aggregation, crosslinking and degradation. Combined with the texture changes of abalone muscles during boiling, it was speculated that the oxidation, denaturation, aggregation and crosslinking of proteins led to the increase of shear force, however, the degradation of structural proteins such as MPs and collagen caused the decreases in shear force and hardness.

Effects of antioxidants of bamboo leaves on protein digestion and transport of cooked abalone muscles

The effects of oxidation on protein digestion and transport in cooked abalone muscles were investigated using a combination of simulated digestion and everted-rat-gut-sac models for the first time. Boiling heat treatments caused protein oxidation in the abalone muscles, reflected by increases in the carbonyl group and disulfide bond contents, protein hydrophobicity and aggregation degree, as well as decreases in the free sulfhydryl group and amino acid contents. Protein oxidation significantly inhibited the degree of hydrolysis, digestion rate, and digestibility of the abalone muscles in the simulated digestion model. The results from the everted-rat-gut-sac model showed that amino acid and peptide transport levels from the digestion products of the cooked abalone muscles were lower than those of the uncooked samples. In contrast, the addition of antioxidants of bamboo leaves mitigated heat-treatment-induced protein oxidation, aggregation and increased hydrophobicity, and consequently improved abalone muscle protein digestibility and transport levels.

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

Shewanella putrefaciens is a microorganism with strong spoilage potential for aquatic products. This study aimed to investigate the potential spoilage factors of S. putrefaciens by comparative proteomic analysis. The spoilage potential of two strains of S. putrefaciens (00A and 00B) isolated from chilled spoiled bigeye tuna was investigated. The results of total volatile basic nitrogen (TVB-N), trimethylamine (TMA) in fish inoculated with S. putrefaciens, extracellular protease activity of S. putrefaciens, and degradation of fish proteins indicated that the spoilage potential of S. putrefaciens 00A was much higher than that of 00B. Fish proteins are usually degraded by spoilage microorganism proteases into small molecular peptides and amino acids, which are subsequently degraded into spoilage metabolites in bacterial cells, leading to deterioration of fish quality. Thus, proteomic analysis of the extracellular and intracellular proteins of 00A vs. 00B was performed. The results indicated that the intracellular differentially expressed protein (IDEP) contained 243 upregulated proteins and 308 downregulated proteins, while 78 upregulated proteins and 4 downregulated proteins were found in the extracellular differentially expressed protein (EDEP). GO annotation revealed that IDEP and EDEP were mainly involved in cellular and metabolic processes. KEGG annotation results showed that the upregulated proteins in IDEP were mainly involved in sulfur metabolism, amino acid metabolism, and aminoacyl-tRNA biosynthesis, while downregulated proteins were related to propanoate metabolism. In contrast, EDEP of KEGG annotation was mainly involved in ribosomes, quorum sensing, and carbohydrate metabolism. Proteins associated with spoilage containing sulfur metabolism (sulfite reductase, sulfate adenylyltransferase, adenylyl-sulfate kinase), amino acid metabolism (biosynthetic arginine decarboxylase, histidine ammonia-lyase), trimethylamine metabolism (trimethylamine-N-oxide reductase), and extracellular proteins (ATP-dependent Clp protease proteolytic subunit) were identified as upregulated. These proteins may play a key role in the spoilage potential of S. putrefaciens. These findings would contribute to the identification of key spoilage factors and understanding of the spoilage mechanism of microorganisms.

Differences in lipid composition of Bigeye tuna (Thunnus obesus) during storage at 0 °C and 4 °C

This study aimed to investigate the lipid oxidation and distribution in Bigeye tuna stored at 0 °C and 4 °C for 6 days. Tuna were evaluated by determining the peroxide value (POV), acid value (AV), anisidine value (AnV), polyene index, fluorescence ratio (FR), phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylinositol (PI) content, and major glycerophospholipid molecular species. The value of lipid oxidation indexes (POV, AV, AnV, FR, PC, PE and PI) increased as the storage time increased. High-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) results indicated that the major types of lipids included diacylglycerol (DAG), monoacylglycerol (MAG), phospholipid (PL), and triacylglycerol (TAG). At least 136 PC and 64 PE molecular species were identified in Bigeye tuna. The results of the confocal laser scanning microscope analysis indicated the distribution of TAG and PL particles. In addition, principal component analysis showed that the contents of PI and TAG were positively correlated with PC, polyene index and lipid content but negatively correlated with PI, POV, FR, AOV, AnV, MAG, and DAG, which might be explained by distinguishing the lipid parameters affecting lipid oxidation. Therefore, this study may provide a novel method to evaluate lipid changes and contribute to the balanced nutritional value of aquatic foods during cold storage.