This study aimed to investigate the effects of different aquaculture modes on the thermal processing and digestive characteristics of tilapia meat (Oreochromis niloticus). Tilapia meat from a recirculating aquaculture system (RAS) and a traditional aquaculture pond (TAP) was cooked by boiling or roasting and subjected to in vitro simulated digestion. Protein digestibility was determined and the crude peptide content, particle size, microstructure, and antioxidant activity of the digestion products were systematically analyzed. The results showed that in the gastric digestion stage, the digestibility of raw, boiled and roasted fish was significantly 3.1%, 3.5% and 2.2% higher in the RAS group than in the TAP group, respectively (P < 0.05), the highest value being observed in the boiled fish. The crude peptide content of gastric digestion products in the RAS group was significantly increased by 26.7%, 12.5%, and 23.3%, respectively (P < 0.05). In the intestinal digestion stage, the boiled RAS fish had the highest crude peptide content (5.4 mg/mL), the smallest average particle size (810 nm), and the lowest protein residue, indicating the most complete digestion. Antioxidant analysis showed that the intestinal digestion products of the boiled fish had the strongest free radical scavenging capacity, while no significant difference was found between the roasted and control groups. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis revealed weaker protein bands at 16−37 kDa in the gastric digestion products of the boiled RAS fish, indicating higher digestion degree. Two-way analysis of variance (ANOVA) showed that the interaction between culture system and thermal processing had a significant effect (P < 0.05) on the crude peptide content and 2,2’-biazobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) cation radical scavenging capacity of the gastric and intestinal digestion products as well as the 1,1-diphenyl-2-trinitrophenylhydrazine (DPPH) radical scavenging capacity of the intestinal digestion products. In conclusion, RAS combined with boiling significantly enhances the digestive characteristics of tilapia meat and the antioxidant activity of the digestion products, providing a theoretical basis for tilapia culture and processing.

In order to investigate the effect of arginine (Arg) on the microwave-induced pre-gelation of myofibrillar protein (MP) from sturgeon under low salt condition, MP added with different concentrations of Arg was microwaved and evaluated for physicochemical, structural and morphological properties and intermolecular interactions after 1, 3 and 5 min (< 40 ℃). It was found that the solubility of MP decreased with increasing microwaving time and was improved by appropriate concentrations of Arg (P < 0.05). The turbidity of MP microwaved for 5 min significantly decreased with increasing addition of Arg (P < 0.05). The particle size decreased with increasing levels of Arg addition. In addition, Arg inhibited the formation of large protein clusters during microwave heating as shown by atomic force microscopy. In the control group, the contents of ionic and hydrogen bonds decreased significantly after microwave treatment for 3 min, while the contents of hydrophobic interaction and disulfide bond increased significantly (P < 0.05). The addition of 40 mmol/L Arg inhibited the ionic bond and hydrophobic interaction and increased the hydrogen and disulfide bonds. The molecular dynamics simulation results showed that at 300 K, the root mean square deviation (RMSD) for myosin increased from about 0.52 to 5.85 nm after Arg binding to it, and the radius of gyration (R_g) also increased, indicating that Arg promoted the dissociation of MP aggregates under low salt condition, and the aggregate characteristics changed from larger protein clusters to smaller particles. Furthermore, binding of Arg to myosin decreased its structural tightness, resulting in more loose protein conformation. The findings of this study provide sufficient conditions for enhancing protein cross-linking in the gel strengthening stage.

In order to establish the correlation between physicochemical indexes and muscle metabolites in giant salamander meat during cold storage, differential metabolites between giant salamander muscle stored for different periods (0, 2, 4 and 8 days) at 4 ℃ were analyzed by gas chromatography-mass spectrometry (GC-MS) non-targeted metabolomics combined with multivariate statistical model. The results showed that the composition of metabolites in giant salamander muscle refrigerated for 8 days was significantly different from those stored for 0, 2 and 4 days. According to partial least squares-discriminant analysis (PLS-DA) and variable importance in projection (VIP) (VIP ≥ 1, P < 0.05 in t-test), 69 differential metabolites were identified including organic acids and their derivatives (21), amino acids and their derivatives (14), sugars and their derivatives (7), nucleotides and their derivatives (10), amines and their derivatives (6), and other compounds (11). According to the hierarchical cluster heatmap, the giant salamander meat samples could be divided into three groups: early (days 0–2), middle (day 4) and late stages (day 8). Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis showed that the important metabolic pathways during the cold storage of giant salamander meat were purine metabolism, aminoacyl-tRNA biosynthesis, glyoxylic acid and dicarboxylic acid metabolism, pyruvate metabolism and the tricarboxylic acid cycle. Metabolic pathway mapping and Pearson’s correlation analysis showed that L-lysine, L-serine, L-isoleucine, L-methionine, pyruvic acid, succinic acid, glycine could be used as potential markers for the change in meat quality of giant salamander.

The sensitivity of freshness indicator labels/films has become an important research direction of intelligent food packaging. In this study, a high-sensitivity indicator film containing gelatin and Fe²⁺ was prepared by electrospinning using blueberry anthocyanins as the indicator and zein as the matrix for monitoring fish freshness. The validity and sensitivity of the indicator film for detecting the freshness of silver carp were tested and the potential mechanism was elucidated. The results of pH sensitivity, ammonia sensitivity and anthocyanin release showed that the addition of gelatin and Fe²⁺ improved the sensitivity of the indicator film to pH and ammonia, and contributed to better binding of the anthocyanins in the film. There was a strong correlation between the color response (P = (L* + a* + b* + R + G + B)/a*) of the film and the content of total volatile basic nitrogen (TVB-N) content in fish meat as a freshness indicator (R² > 0.98). In conclusion, the prepared indicator film can effectively monitor fish freshness, and the hydrogen bond interactions between anthocyanins and gelatin/Fe²⁺ may affect the color response characteristics and sensitivity of the indicator film.

The purpose of this study was to explore the effect of freeze treatment on the binding characteristics of fillets to flavor substances in fish soup with pickled mustard greens. The study focused on the effects of freeze-thaw treatment and freeze storage on the physicochemical properties of snakehead myofibrillar protein and its binding characteristics to hexanal, octanal, linalool and myrcene. The results showed that after 7 days of storage, the solubility of myofibrillar protein decreased by about 26% in the freeze-thaw group. Compared with the freeze storage group, the oxidation degree and tertiary structural changes of myofibrillar protein were higher and more soluble aggregates were formed in the freeze-thaw group. The solubility of myofibrillar protein decreased by about 33% in the freeze storage group, which showed a more significant decrease compared to the freeze-thaw treatment (P < 0.05), resulting in more insoluble aggregates. The major force for the aggregation of myofibrillar proteins after freezing was non-covalent bonding. Molecular docking results indicated that linalool, hexanal and octanal could bind to myofibrillar proteins through hydrophobic interactions and hydrogen bonds, while the major driving force for the binding of myrcene to myofibrillar proteins was hydrophobic interaction. Freeze treatment reduced the binding capacity of hexanal and octanal to sulfhydryl groups in myofibrillar proteins through hydrogen bonds, improved the surface hydrophobicity of myofibrillar proteins, but increased the binding ability of myrcene and linalool to myofibrillar proteins. Freeze-thaw treatment increased the binding capacity of myofibrillar proteins to myrcene compared with freeze storage treatment. The results of this research provide a theoretical basis and reference for flavor control of frozen prepared fish soup with pickled mustard greens.

The addition of oil played a significant role in the gelling properties and flavor qualities of the ready-to-eat surimi gels. In order to investigate the effects of sturgeon oil and reheating methods on the qualities of sturgeon surimi gels, the prepared sturgeon surimi gels containing sturgeon oil (with the direct addition named SO and with the Pickering emulsion named PPE) were reheated by boiling, steaming, microwave, and frying, respectively. The gel properties, non-volatile and volatile flavor substances and digestibility were determined. Boiling and steaming made gels higher brightness value (L*) (82.07–84.16), with lower cooking loss (7.11%–8.83%), relatively intact protein network structures and strong protein digestibility. The greatest lipid oxidation of the sturgeon surimi gels was induced by frying, followed by microwave. Furthermore, the gels reheated by microwave showed the highest total flavor-presenting nucleotides, while the steamed ones had the highest total percentage of fresh and sweet amino acids. The addition of sturgeon oil (direct addition and Pickering emulsion) decreased the textural properties of the reheated gels, but significantly improved the L* and protein digestibility of boiled and steamed gels (P < 0.05). The gastric digestibility and gastrointestinal digestibility of the SO and PPE groups were 68.60%–76.33% and 80.69%–85.05%. Moreover, the addition of sturgeon oil also changed the ratio of non-volatile and volatile flavor compounds. Compared with the direct addition of sturgeon oil, the preparative Pickering emulsion was more conducive to the retention of better textural properties as well as the more flavor-presenting nucleotides and volatile flavor substances. The above results enrich the theory of quality difference of sturgeon surimi products caused by different reheating methods, and provide reference for the development of high-quality products.

Cartilage is a nonedible byproduct with little saleable value. However, previous studies have proposed the possibility of producing peptides from cartilage with immune function modulation potential. The current study aimed to investigate the potential anti-inflammatory activity of peptides derived from sturgeon (Acipenser schrenckii) cartilage in lipopolysaccharide (LPS)-stimulated RAW264.7 macrophages. Five peptide sequences, including four novel peptides, were identified from ethanol-soluble cartilage hydrolysates. Among these five peptides, LTGP, LLLE, LLEL and VGPAGPAGP reduced the production of nitric oxide (NO) and interleukin-6 (IL-6) while increasing interleukin-10 (IL-10) excretion. Transcriptome analysis suggested the inhibition of activated mitogen-activated protein kinase (MAPK) and interleukin-17 (IL-17) signaling pathways after LLEL intervention. MAPK, which is involved in the IL-17 signaling pathway, was further proved to be blocked by downregulating the phosphorylation of p38, extracellular-signal regulated protein kinase (ERK), and c-jun N-terminal kinase (JNK). This novel peptide offers an attractive approach to develop functional foods.

In this study, a gene encoding serine protease (PmSpr288) from cold-adapted bacterium, namely Planococcus maritimus XJ11, was cloned and overexpressed in Escherichia coli BL21 (DE3). Bioinformatics analysis revealed that PmSpr288 belongs to serine protease S8 superfamily with a classical catalytic triad comprised by the Asp49, His86 and Ser251. Moreover, PmSpr288 was found to be active over broad alkaline pH and low-moderate temperature, and exhibited wide range of protein substrate specificity. In addition, PmSpr288 was able to hydrolyze the meat proteins actin and myosin, and molecular docking results suggested that the crucial interaction between PmSpr288 and actin/myosin complexes was mainly occupied by hydrogen bonds. The muscle protein hydrolysates of silver carp prepared by PmSpr288 was shown to have antioxidant activity via DPPH radical scavenging assay, which presented an IC₅₀ valve of 1.309 mg/mL. In conclusion, these characteristics imply that PmSpr288 has potential biotechnological application prospect for the production of bioactive peptides.

Shrimp sauce, one of the traditional salt-fermented food in China, has a unique flavor that is influenced by the resident microflora. The quality of salt-fermented shrimp sauce was evaluated in this work by determining the total volatile basic nitrogen (TVB-N), the amino acid nitrogen (AAN), organic acid, 5’-nucleotide and free amino acids (FAA). Moreover, the dynamics of microbial diversity during processing was investigated by using high-throughput sequencing technology. The results showed that the AAN, TVB-N, organic acid, 5’-nucleotide and FAA content were in range of 0.93–1.42 g/100mL, 49.91–236.27 mg/100mL, 6.65–20.68 mg/mL, 3.51–6.56 mg/mL and 81.27–102.90 mg/mL. Among the microbial diversity found in the shrimp sauce, Tetragenococcus, Flavobacterium, Polaribacter, Haematospirillum and Staphylococcus were the predominant genera. Correlation analysis indicated that the bacteria Tetragenococcus and Staphylococcus were important in the formation of non-volatile compounds. Tetragenococcus positively correlated with a variety of FAAs; Staphylococcus positively correlated with 5’-nucleotides. The analysis indicated that Tetragenococcus and Staphylococcus were the core genera affecting non-volatile components. These findings indicate the dynamics of the bacterial community and non-volatile components inter-relationships during shrimp sauce fermentation and provide a theoretical basis for improving the fermentation process of shrimp sauce.

Traditionally fermented shrimp paste has a long fermentation period and is susceptible of external factors, which leads to unstable quality and limits its development and application. Therefore, the purpose of this study is to analyze the flavor changes in the shrimp paste fermentation process and screen out the key volatile aroma components in the shrimp paste to control the flavor quality of the shrimp paste products. The overall odor profile was detected by the electronic nose. A total of 106 volatile flavor compounds in the shrimp paste samples at different fermentation stages were identified by solid-phase microextraction-gas chromatography-mass spectrometry (SPME-GC-MS) and headspace-gas chromatography-ion mobility spectrometry (HS-GC-IMS). The main aroma components alcohols, aldehydes, pyrazines and other substances in the fermentation process showed an overall upward trend. A total of 17 key volatile aroma components in shrimp paste at different fermentation stages were identified by the relative aroma activity value (ROAV) method. The combination of electronic nose, SPME-GC-MS and HS-GC-IMS could comprehensively reflect the changes of volatile components in shrimp paste at different fermentation stages, which helps to further understand the mechanism of shrimp paste flavor formation and provides a basis for the regulation of the flavor quality of shrimp paste products.