The influence of superchilling storage methods on the location/distribution of ice crystals during storage of Atlantic salmon ( Salmo salar )

Effect of low voltage electrostatic field combined with partial freezing on the quality and microbial community of large yellow croaker

The effect of low voltage electrostatic field combined with partial freezing (LVEF- PF) treatment on storage quality and microbial community of large yellow croaker was studied. Three different methods including chilled (C), partial freezing (PF) and 6 kV/m electrostatic field combined partial freezing storage were used to preserve large yellow croaker for 18 days. Total viable counts (TVC), sensory evaluation, and physiochemical index including pH, total volatile basic nitrogen (TVB-N), K value and centrifugal loss were examined. During storage, the large yellow croaker was susceptible to microbial growth and spoilage. However, LVEF-PF treatment was found to be effective in enhancing sensory quality, inhibiting microbial growth, and maintaining myofibril microstructure. Low field nuclear magnetic resonance showed that LVEF-PF treatment reduced the migration of immobilized water to free water. At 18th day, the TVC value of LVEF-PF, PF and chilled group were 3.56 log CFU/g, 5.11 log CFU/g, 7.73 log CFU/g, respectively. Therefore, from the results of TVB-N and TVC value, the shelf life of LVEF-PF group was at least 3 days longer than PF group, and 6 days longer than the chilled group. High-throughput sequencing showed that the microbial community diversity significantly decreased during storage. The predominant bacteria in chilled, PF, LVEF-PF group at 18th day were Pseudomonas, Psychrobacter and Shewanella, respectively, and the relative abundance of spoilage bacteria such as Pseudomonas and Psychrobacter were reduced by LVEF-PF treatment, that corresponding with lower values of TVB-N and TVC value. LVEF-PF treatment could be used as a new processing and storage method to delay deterioration and prolong shelf life of large yellow croaker.

A Mixture of Full-Fat and Defatted Hermetia illucens Larvae and Poultry By-Products as Sustainable Protein Sources Improved Fillet Quality Traits in Farmed Barramundi, Lates calcarifer

The physicochemical quality and shelf-life of fillets from barramundi, which were fed for 56 days on a mixture of poultry by-product meal (PBM), full-fat Hermetia illucens (FHI), and defatted HI (DHI), were investigated and compared to a fishmeal (FM) control diet. The proximate and total amino acids compositions of the fillets were unaffected by the test diets, while the mixture of PBM and HI larvae improved the sensory quality. An eight-day shelf-life study showed that PBM-HI-based diets improved the texture profile based upon the chewiness, cohesiveness, gumminess, and hardness, regardless of the storage time. The improved texture was aligned with comparatively less degradation of the microstructure of the muscle tissue in the same diets. An improvement in the quality index (QI) value, an increase in pH, and a decrease in lipid oxidation were also found in the fillets of barramundi fed test diets compared with the control diet during the storage time. The test diets positively influenced flesh lightness and redness, while the color profiles were negatively influenced by the storage time. Overall, the maintenance of compositional attributes; the enhancement of fillet sensory attributes, texture, and brightness; and the improved raw fillet shelf-life support the inclusion of PBM-HI-based diets in aquafeed.

The Effect of Pressure-Shift Freezing versus Air Freezing and Liquid Immersion on the Quality of Frozen Fish during Storage

In this study, a self-cooling laboratory system was used for pressure−shift freezing (PSF), and the effects of pressure−shift freezing (PSF) at 150 MPa on the quality of largemouth bass (Micropterus salmoides) during frozen storage at −30 °C were evaluated and compared with those of conventional air freezing (CAF) and liquid immersion freezing (LIF). The evaluated thawing loss and cooking loss of PSF were significantly lower than those of CAF and LIF during the whole frozen storage period. The thawing loss, L* value, b* value and TBARS of the frozen fish increased during the storage. After 28 days storage, the TBARS values of LIF and CAF were 0.54 and 0.65, respectively, significantly higher (p < 0.05) than the 0.25 observed for PSF. The pH of the samples showed a decreasing trend at first but then increased during the storage, and the CAF had the fastest increasing trend. Based on Raman spectra, the secondary structure of the protein in the PSF-treated samples was considered more stable. The α-helix content of the protein in the unfrozen sample was 59.3 ± 7.22, which decreased after 28 days of frozen storage for PSF, LIF and CAF to 48.5 ± 3.43, 39.1 ± 2.35 and 33.4 ± 4.21, respectively. The results showed that the quality of largemouth bass treated with PSF was better than LIT and CAF during the frozen storage.

Investigation of the effect of pork compositions on freezing points in different pork cuts by measuring thermal properties and water mobility and distribution

This work was to compare the difference of freezing point in the four pork cuts (chuck roll, picnic shoulder, loin, and topside) and evaluate the effect of pork compositions on the freezing points. Loin exhibited lower freezing points and accompanied by higher content of unfreezable water, lower relaxation times, and higher proportions of bound water, compared with other pork cuts. Low freezing points of pork may be attributed to high sarcoplasmic protein solubility, due to high sarcoplasmic protein solubility related to increase of bound water proportion and decrease of NMR T₂ relaxometry. In addition, correlation analysis revealed that sarcoplasmic protein solubility and ash content were negatively related to the freezing point, which was verified by a quadratic polynomial correlation between the sarcoplasmic protein solubility and the freezing point in vitro. These results could help to better understand the freezing point of pork and provide more theories for improving superchilled storage.

Differential roles of ice crystal, endogenous proteolytic activities and oxidation in softening of obscure pufferfish (Takifugu obscurus) fillets during frozen storage

Obscure pufferfish (Takifugu obscurus) softening during frozen storage remains to be solved. This study was therefore aimed to provide explanations by differentiate the roles of three potential factors in fish softening. The influences of ice crystal, endogenous proteolytic activities, and oxidization were distinguished by treatment of fish fillets with liquid nitrogen, iodoacetic acid, and tea polyphenol with ascorbic acid, respectively. This distinguishing method was verified to be effective by investigation in ice crystal microstructure, endogenous proteolytic activities and lipid and protein oxidation. In comparison of three factors, it showed that the shear force of fish fillets with smaller ice crystals was about 15.5% and 13.7% higher than those with the inhibition of endogenous proteolytic activities and oxidation respectively, indicating the dominant role of ice crystal in frozen fish softening. Besides, quality decline of frozen fish was initially fast and then slowed down during the storage.

A study of fractal dimension as a quality indicator of hairtail (Trichiurus haumela) samples during frozen storage

Hairtail fish samples were stored at different freezing temperatures of -5 °C, -20 °C, -40 °C and -80 °C. To establish an effective quality evaluation approach for hairtail samples during frozen storage, fractal dimension was used to observe the porous microstructure that resulted from the ice crystal formation in frozen hairtail meat. The results showed that the initial value of fractal dimension of all the samples was 1.968. After frozen storage, the fractal dimension of samples at -5 °C, -20 °C, -40 °C and -80 °C decreased to 1.539, 1.682, 1.856 and 1.896, respectively. Traditional quality indicators such as water activity, color and textural properties (i.e., hardness, springiness and chewiness) also exhibited a similar decreasing trend, and the rate of change decreased with a decrease in storage temperature. The relationships were analyzed, and these traditional quality indicators were correlated with the fractal dimension with determined correlation coefficients within ±0.900. Moreover, based on the fractal dimension model, the first-order kinetic equation of fractal dimension variation during storage was [Formula: see text], which can be used to predict the shelf life of preserved hairtails at different storage temperatures. The results demonstrated fractal dimension was a novel and feasible method to evaluate the quality of hairtails in frozen storage.

Modified Atmosphere Systems and Shelf Life Extension of Fish and Fishery Products

This review aims at summarizing the findings of studies published over the past 15 years on the application of modified atmosphere (MA) systems for shelf life extension of fish and fishery products. This review highlights the importance of CO₂ in the preservation of seafood products, and underscores the benefits of combining MA technology with product storage in the superchilled temperature range. It is generally accepted that MA technology cannot improve product quality and should not be utilized as a substitute for good sanitation and strict temperature control. Benefits derived from application of MA, however, can significantly impact preservation of product quality and it subsequent shelf-life. For this reason, this review is the first of its kind to propose detailed handling and quality guidelines for fresh fish to realize the maximum benefit of MA technology.