Xiaochang Liu

Effects of Chilling and Partial Freezing on Rigor Mortis Changes of Bighead Carp (Aristichthys nobilis) Fillets: Cathepsin Activity, Protein Degradation and Microstructure of Myofibrils.

To investigate the effects of chilling and partial freezing on rigor mortis changes in bighead carp (Aristichthys nobilis), pH, cathepsin B, cathepsin B+L activities, SDS-PAGE of sarcoplasmic and myofibrillar proteins, texture, and changes in microstructure of fillets at 4 °C and -3 °C were determined at 0, 2, 4, 8, 12, 24, 48, and 72 h after slaughter. The results indicated that pH of fillets (6.50 to 6.80) was appropriate for cathepsin function during the rigor mortis. For fillets that were chilled and partially frozen, the cathepsin activity in lysosome increased consistently during the first 12 h, followed by a decrease from the 12 to 24 h, which paralleled an increase in activity in heavy mitochondria, myofibrils and sarcoplasm. There was no significant difference in cathepsin activity in lysosomes between fillets at 4 °C and -3 °C (P > 0.05). Partially frozen fillets had greater cathepsin activity in heavy mitochondria than chilled samples from the 48 to 72 h. In addition, partially frozen fillets showed higher cathepsin activity in sarcoplasm and lower cathepsin activity in myofibrils compared with chilled fillets. Correspondingly, we observed degradation of α-actinin (105 kDa) by cathepsin L in chilled fillets and degradation of creatine kinase (41 kDa) by cathepsin B in partially frozen fillets during the rigor mortis. The decline of hardness for both fillets might be attributed to the accumulation of cathepsin in myofibrils from the 8 to 24 h. The lower cathepsin activity in myofibrils for fillets that were partially frozen might induce a more intact cytoskeletal structure than fillets that were chilled.

The effect of essential oils on microbial composition and quality of grass carp (Ctenopharyngodon idellus) fillets during chilled storage

Antimicrobial and antioxidant effects of essential oils (oregano, thyme, and star anise) on microbial composition and quality of grass carp fillets were investigated. Essential oils treatment was found to be effective in inhibiting microbial growth, delaying lipid oxidation, and retarding the increase of TVB-N, putrescine, hypoxanthine, and K-value. Based on sensory analysis, shelf-life of grass carp fillets was 6days for control and 8days for treatment groups. Among the essential oils, oregano essential oil exhibited the highest antimicrobial and antioxidant activities. GC-MS analysis of essential oils components revealed that carvacrol (88.64%) was the major component of oregano essential oil. According to the results of high-throughput sequencing, Aeromonas, Glutamicibacter, and Aequorivita were the predominant microbiota in fresh control samples. However, oregano essential oil decreased the relative abundance of Aeromonas, while thyme and star anise essential oils decreased the relative abundance of Glutamicibacter and Aequorivita in fresh treated samples. The microbial composition of both control and treatment groups became less diverse as storage time increased. Aeromonas and Pseudomonas were dominant in spoiled samples and contributed to fish spoilage. Compared to the control, essential oils effectively inhibited the growth of Aeromonas and Shewanella in grass carp fillets during chilled storage.

Quality Changes and Biogenic Amines Accumulation of Black Carp (Mylopharyngodon piceus) Fillets Stored at Different Temperatures

Postmortem quality changes of black carp (Mylopharyngodon piceus) fillets stored at 20, 4, and 0°C (in ice) were determined in terms of pH value, K value, total volatile basic nitrogen, free amino acids, biogenic amines, drip loss, electrical conductivity (EC), sensory score, and microbial growth. The results showed that black carp fillets could maintain a good quality for 2, 9, and 12 days when stored at 20, 4, and 0°C, respectively. Pseudomonads, Aeromonas, and Enterobacteriaceae were the main spoilage bacteria in black carp. Tryptamine, 2-phenylethylamine, putrescine, cadaverine, and tyramine increased significantly (P < 0.05) during storage at the three temperatures, but not spermidine and spermine, among which tyramine and putrescine were the main biogenic amines in black carp fillets. A significantly higher concentration of histamine (132.05 mg/kg on the third day) was detected in the samples stored at 20°C (P < 0.01) than at 4 and 0°C (0.62 to 3.28 mg/kg) throughout storage, indicating storage of samples at 20°C favored the formation of histamine. The accumulations of tyramine, cadaverine, and histamine were highly correlated with the productions of tyrosine, lysine, and histidine, respectively. Correlations between EC and sensory, physical, chemical, and microbial parameters at the three storage temperatures showed that EC could be used as a better quality indicator to assess the overall quality of fish stored at 4 and 0°C (low temperature) than at 20°C.

The roles of bacteria in the biochemical changes of chill-stored bighead carp (Aristichthys nobilis): Proteins degradation, biogenic amines accumulation, volatiles production, and nucleotides catabolism

This study investigated the biochemical changes (proteins degradation, total volatile basic nitrogen, biogenic amines, volatile organic compounds, nucleotides catabolism and related enzymes) of bighead carp samples inoculated with four different bacteria (Shewanella putrefaciens, Aeromonas sobria, Acinetobacter bohemicus, and Pseudomonas helmanticensis) during storage at 4 ± 1 °C. A. sobria exhibited the strongest proteolytic activity. A. sobria, P. helmanticensis, and S. putrefaciens were responsible for putrescine production, whereas S. putrefaciens was the sole producer of cadaverine. Alcohols and S-compounds were mainly released by A. sobria and S. putrefaciens, respectively. The fastest degradation rates of hypoxanthine riboside and hypoxanthine were found in samples inoculated with P. helmanticensis and S. putrefaciens. Inosine nucleosidase was mainly resulted by A. sobria, P. helmanticensis and S. putrefaciens, whereas xanthine oxidase was derived from both fish muscle and secretions of P. helmanticensis and S. putrefaciens.

Comparison between the Arrhenius model and the radial basis function neural network (RBFNN) model for predicting quality changes of frozen shrimp (Solenocera melantho)

ABSTRACT Changes in quality indices [total volatile base nitrogen (TVB-N), salt extractable protein (SEP), hypoxanthine (Hx), K-value, sensory assessment (SA), and electrical conductivity (EC)] for shrimp (Solenocera melantho) stored at −28, −20, and −12°C for 112 days were investigated in this study. The Arrhenius model and the radial basis function neural network (RBFNN) model were established to predict changes in the quality of shrimp during storage. Quality of shrimp stored at −12°C changed more quickly during 56–112 days, but those stored at −28°C deteriorated slowly during the entire storage period. Additionally, the indicators SEP, EC, and SA all fitted to the Arrhenius model well (relative errors within ±10%), but this model did not perform well in the prediction of K-value, Hx, and TVB-N on some days. However, the RBFNN model showed excellent accuracy for all indicators (relative errors within ±0.5%). The RBFNN model performed better than the Arrhenius model in predicting the quality of shrimp stored at −28°C to −12°C.

Application of Artificial Neural Network to Predict K-Value, Inosine Mono-Phosphate, and Hypoxanthine Concentrations of Grass Carp (Ctenopharyngodon idellus) Fillets During Storage

K-value, inosine mono-phosphate, and hypoxanthine concentrations of grass carp (Ctenopharyngodon idellus) fillets were determined during storage at 273, 277, 281, 288, and 293 K. Simultaneously, a feed-forward artificial neural network was developed to predict these changes in grass carp fillets during storage, and a comparative study on K-value prediction between the artificial neural network and Arrhenius model was also performed. The results showed that the K-value and hypoxanthine concentrations increased with storage time, while inosine mono-phosphate reached a peak and then decreased with time. The artificial neural network was successful in predicting changes in the K-value, inosine mono-phosphate, and hypoxanthine concentrations throughout storage, and it was even more effective in predicting K-value with lower relative errors than the Arrhenius model. The high regression coefficient (R2) and low mean squared error indicated that the artificial neural network could be a potential tool in modeling changes in K-value, inosine mono-phosphate, and hypoxanthine concentrations of grass carp fillets within 273–293 K.

Relationship between Lipid Oxidation, Protein Function Properties, and Freshness Changes of Salt-Treated Blunt-Snout Bream (Megalobrama amblycephala) Fillets Stored at 4°C

ABSTRACT The aim of this study was to investigate the relationship between lipid oxidation, protein function properties, and freshness changes of blunt-snout bream (Megalobrama amblycephala) fillets treated with 2% and 4% salt during storage at 4°C. Salting with 2% and 4% salt could delay quality deterioration and protein denaturation, thus improving sensory attributes to some extent. But, 4% salt promoted lipid oxidation of blunt-snout bream fillets. There is a significant correlation (p < 0.05) between freshness indexes and lipid oxidation or protein function properties (total SH content, Ca2+-ATPase activity). Salting with 2% salt is an ideal treatment to control the quality of blunt-snout bream fillets stored at 4°C.