•2-D PAGE/MS is suited for studies on degradation patterns of protein.•TP is effective in preservation of large yellow croaker fillets during storage.•TP has an effective impact on muscle proteins integrity post-mortem.Tea polyphenols (TP) are known to be important for the post-mortem deterioration of fish muscle and can enhance food quality. To shed light on the influence of TP on the status of large yellow croaker muscle proteins, control and treated fillets (0.1% TP, 0.2% TP and 0.3% TP, w/v) were analysed periodically for myofibrillar protein functional properties (Ca2+-ATPase activity, surface hydrophobicity, total sulfhydryl content, emulsion stability index and rheological behaviour). Degradation of the myofibrillar protein myosin could be clearly observed; several proteins were also observed to vary in abundance following post-mortem storage for 25 days. The present study offers new evidence that TP have an effective impact on muscle protein integrity post-mortem.

Green tea polyphenols (GTP) are widely believed to function as antioxidants and antimicrobial agents. Here we observed that GTP and epigallocatechin gallate, the most abundant catechin in GTP, could also function as prooxidants and produce hydrogen peroxide (H2O2) to inhibit the growth of Pseudomonas aeruginosa. pH value of the medium was the key factor that affected prooxidant versus antioxidant property of GTP. Under weakly acidic conditions (pH 5.5–6.5), GTP showed antioxidant activity by eliminating H2O2; whereas, under neutral and weakly alkaline conditions (pH 7.0–8.0), GTP showed prooxidant activity and inhibited the growth of P. aeruginosa. Furthermore, we studied the effects of GTP on gene expression profiles of a few oxidative stress-related genes by quantitative real-time PCR analysis. After 10 min to 1 h of exposure under weakly alkaline condition, GTP significantly up-regulated expression levels of katB, sodM, ohr, lexA, and recN gene. These findings highlight that the pH-dependent H2O2 production by GTP contributes to the antibacterial activity and can induce oxidative stress-related responses in P. aeruginosa.

The effect of the natural preservatives, tea polyphenols and rosemary extract, on microbiological [total viable count (TVC)], chemical [pH, total volatile base nitrogen (TVB-N), K-value and thiobarbituric acid (TBA) values], texture and sensory changes of air-packaged whole crucian carp (Carassius auratus) stored at 4 ± 1 °C was investigated for 20 days. The shelf-life of crucian carp was found to be 7–8 days for untreated group (control), 13–14 days for tea polyphenols group and 15–16 days for rosemary extract treated group according to sensory assessment results, for which the corresponding microbiological assessment also showed an increased shelf-life. Meanwhile, the increases of pH, TVB-N, K-value and TBA values were significantly delayed in both treated groups of samples compared to the control group. Thus, either tea polyphenols or rosemary extract could be used as potential preservatives to extend the shelf-life of crucian carp during chilled storage.Highlights► Effects of natural preservatives on quality of crucian carp were investigated. ► Microbiological, physicochemical, and sensory attributes were assessed. ► The dipping treatments could effectively extend the shelf-life of the fish. ► The shelf-life of the fish could be extended by 6–8 days.

The freshness of large yellow croaker (Pseudosciaena crocea) fillets was evaluated over 20 days of chilled storage under vacuum packaging. The physicochemical properties [pH, K value, thiobarbituric acid (TBA), texture profile analyses (TPA), color], microbiological properties [total viable count (TVC)], sensory attributes, transcriptomics (levels of transcripts coding for cathepsin L), and functional properties of proteins [emulsion activity (EA) and emulsion stability (ES)] were assessed at 0, 5, 10, 15, and 20 days of storage. This study also investigated the effect of the storage time on fish muscle proteome in large yellow croaker using two-dimensional gel electrophoresis (2-DE) and matrix-assisted laser desorption ionization time-of-flight tandem mass spectrometry (MALDI-TOF-MS/MS). The parameters that were the most sensitive to storage duration were color (C*ab), TPA (springiness, chewiness, and resilience), pH, K value, TVC, levels of transcripts coding for cathepsin L, EA, ES, and sensory attributes. The three altered proteins were successfully identified. Therefore, these parameters might be considered suitable indicators for evaluating the freshness of large yellow croaker fillets during chilled storage under vacuum packaging.

The freshness of yellow grouper (Epinephelus awoara) stored under vacuum-packing at 0 °C was assessed by physicochemical, sensory and microbiological methods. No significant differences were found in pH and thiobarbituric acid (TBA) values during the storage, while TVB-N, TMA-N, HxR, Hx and K values increased significantly with time. The content of IMP was decreased significantly with the storage time. The texture profile, hardness and chewiness were significantly decreased with the time. L∗ values, the values of chroma and hue were all decreased. However, the increased b∗ values were observed. Furthermore, the significant variations and correlations of sensory attributes were shown with the storage time. A regression analysis for total viable counts yielded a shelf life of 26 days. This suggested that the TMA-N, IMP, HxR, Hx, K value, hardness, chewiness, colour, sensory attributes and microbiological counts may be considered suitable indicators for evaluating yellow grouper fillets spoilage during refrigerated storage.Research highlights► Postmortem quality changes of yellow grouper muscle were assessed. ► The shelf life was 26 days under vacuum packaging at 0 °C. ► TMA-N, IMP, HxR, Hx, K value, hardness, chewiness, colour, sensory attributes and microbiological counts were possible spoilage indicators.

The synthesis of complex oligosaccharides has been a challenge due to their multifarious protections, deprotection processes and time-consuming chromatography. Herein, an effective strategy for the establishment of a library of oligosaccharides using imidazolium-type cation as a soluble functional support with ester and ether as linkage was demonstrated and developed. Noteworthy, IL-linkages have defined structures and molecular weights in contrast to polymer linkages, which are functionalized materials with variable loading capabilities allowing the efficient homogenous reaction conditions. All IL-tagged intermediates can be clipped off and purified by a simple phase-separation technique without further column chromatography after each glycosylation step.

Ultrasound-assisted extraction (UAE) of polysaccharides from mulberry leaves was studied. The effects of four factors on the yield of polysaccharides were investigated. The results showed that optimum conditions were extraction power of 60 W, extraction temperature of 60 °C, extraction time of 20 min and ratio of water to raw material of 15:1 (ml/g). The three different methods (UAE, MAE and CSE) were compared for extracting polysaccharides from the mulberry leaves by SEM images. Totally, UAE had the largest yield of polysaccharides. The crude polysaccharides obtained from UAE were purified and two components (MPS-1 and MPS-2) were obtained. Their structure was analysed with chemical methods. From FT-IR, they were polysaccharides. MPS-1 had more functional groups than MPS-2. From HP GPC analysis, molecular weights of MPS-1 and MPS-2 were 24898D and 61131D, respectively. From GC analysis, MPS-1 was composed of Sor, Ara, Xyl and Glc, and MPS-2 was composed of Rha, Ara, Xyl, Glc, Gal and Man.Research highlights► Extraction conditions of UAE of polysaccharides from mulberry leaves were optimised. ► Compared with MAE and CSE, UAE had a larger yield of polysaccharides. ► Polysaccharides extracted from the three methods showed similar physicochemical characteristics. ► Polysaccharides extracted by the three methods showed similar FT-IR spectra. ► Structure of MPS-1 and MPS-2 was preliminary researched by FT-IR, GPC and GC analysis.

The rep-PCR DNA fingerprinting performed with REP, BOX A1R, and (GTG)5 primers was investigated as a way to differentiate between human, livestock, and poultry sources of fecal pollution on the area of Xiangshan Bay, East China Sea. Of the three methods, the BOX-PCR DNA fingerprints analyzed by jack-knife algorithm were revealed high rate of correct classification (RCC) with 91.30, 80.39, 89.39, 86.14, 93.24, 87.72, and 89.28% of human, cattle, swine, chicken, duck, sheep, and goose E. coli isolates classified into the correct host source, respectively. The average rate of correct classification (ARCC) of REP-, BOX-, and (GTG)5-PCR patterns was 79.88, 88.21, and 86.39%, respectively. Although the highest amount of bands in (GTG)5-PCR fingerprints could be observed, the discriminatory efficacy of BOX-PCR was superior to both REP- and (GTG)5-PCR. Moreover, the similarity of 459 isolates originated from shellfish and growing water was compared with fecal-obtained strains. The results showed that 92.4 and 96.2% E. coli strains isolated from midstream and downstream shellfish samples, respectively, had a ≥80% similarity with corresponding strains isolated from fecal samples. It was indicated that E. coli in feces could spread from human sewage or domestic farms to the surrounding shellfish culture water, and potentially affect the quality of shellfish. This work suggests that rep-PCR fingerprinting can be a promising genotypic tool applied in the shellfish growing water management on East China Sea for source identification of fecal pollution.