This study was conducted in order to investigate the specific spoilage organisms (SSOs) in cold stored channel catfish and their spoilage ability. Eight strains of spoilage bacteria were isolated and identified from channel catfish at the end of refrigerated storage by traditional selective culture combined with 16S rDNA sequence analysis. Based on the sensory score of channel catfish inoculated with each of the spoilage strains after 0–8 days of storage, four strains of SSOs were selected for identification by their colony and morphology characteristics, physiological and biochemical properties and 16S rDNA sequence. The strains were inoculated into sterile fish fillets and stored at 4 ℃ for up to eight days. The total number of colonies and total volatile basic nitrogen (TVB-N) content were determined during the storage period. The yield factor of spoilage bacteria metabolites (Y_TVB-N) was used as an indicator to measure the spoilage ability of spoilage bacteria. The results showed that the SSOs in channel catfish were two strains of Shewanella putrefaciens, Pseudomonas aeruginosa and Pseudomonas aeruginosa. All the four strains could cause spoilage of sterile fish fillets, with Shewanella having the strongest spoilage ability.

To investigate the effects of different cooking degrees on the quality and digestibility of crayfish (Procambarus clarkii), crayfish was cooked until the internal temperature reached 70, 80, 90, or 100 ℃. The changes in the moisture content, microstructure, and texture properties of crayfish meat were measured, along with the carbonyl and sulfhydryl content, surface hydrophobicity, secondary structure, and digestibility of proteins to identify the optimal cooking temperature for maintaining the quality and digestibility of crayfish meat. The results indicated that as the internal temperature of crayfish meat increased, the gaps between muscle fiber bundles widened, and surface hydrophobicity and water loss rose, resulting in increased hardness and reduced elasticity, ultimately causing quality deterioration. Additionally, increased internal temperature significantly exacerbated protein oxidation, as evidenced by a significant rise in the carbonyl content (P < 0.05), reaching 3.569 nmol/mg at 100 ℃. In contrast, the sulfhydryl content showed a significant decrease (P < 0.05). Protein oxidation induced protein cross-linking and aggregation, and moderate protein oxidation was found to enhance protein digestibility. The highest protein digestibility, 61.73%, was observed at an internal temperature of 90 ℃, which declined with increasing internal temperature beyond 90 ℃. In conclusion, different cooking degrees significantly affect the oxidation and digestibility characteristics of crayfish meat. An internal temperature of 90 ℃ results in moderate protein oxidation and optimal in vitro digestibility while maintaining appropriate hardness and elasticity, thereby preserving the overall quality of crayfish meat to the greatest extent.

The effects of vacuum-assisted high pressure curing on the histological structure and sensory and physicochemical quality of grass carp pieces were studied. Fish pieces cured at normal pressure (control) or at high pressures (0, 2.3, 4.6 and 6.9 kPa) in vacuum were evaluated for salt content, histological structure and total volatile basic nitrogen (TVB-N) content, water content and water distribution. Results indicated that during curing, salt gradually penetrated into fish tissue, and vacuum curing resulted in a decreased yield of the fish product, an increase in shear force, hardness, resilience and viscosity, a decrease in thiobarbituric acid reactive substance (TBARs) value, water content and centrifugal loss, and an increase in the intercellular spaces. After vacuum-assisted high pressure curing treatment, the salt content was increased, the product yield was decreased, and the whiteness was increased. The fish cured at 6.9 kPa had the lowest shear force, hardness, cohesiveness, elasticity, and viscosity, but the TVB-N content was not significantly changed, and the juice loss rate was increased. In conclusion, vacuum-assisted high pressure curing can improve the quality of cured fish, and slow down the spoilage rate.

Konjac glucomannan (KGM) was degraded by β-glucanase. The structural characteristics of KGM and its hydrolysate were identified by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM), and their molecular masses were determined by gel permeation chromatography with multiple angle laser light scattering. The chemical characteristics of the hydrolysate were evaluated by measuring their intrinsic viscosity, deacetylation degree, soluble polysaccharide content and electrical characteristics. The results showed that the major chain structure of the hydrolysate did not change compared with KGM. After 120 min of treatment with a five-fold excess of the enzyme, a weak crystalline region may appear. SEM results showed that the surface of the hydrolysate gradually became lamellated, and its molecular weight decreased to (36.48 ± 1.23) kDa. The characteristic viscosity decreased by 98%, the degree of deacetylation increased significantly (P < 0.05), and the content of total soluble sugar decreased significantly (P < 0.05). This study can provide a reference for the enzymatic modification of KGM to promote the high-value utilization of KGM hydrolysate resources.