Aquatic products are easily affected by microorganisms and endogenous enzymes during distribution, resulting in their quality deterioration. Non-thermal sanitization technology can maintain the nutritional value, delay the process of spoilage, prolong the shelf-life and enhance the commodity value of aquatic products. This review paper compares the principles and main characteristics of the common non-thermal sterilization technologies, describes the sterilization mechanism of cold plasma technology, and summarizes recent progress in its application in the quality improvement, bacterial decontamination, blackening inhibition, and safety control of aquatic products. Moreover, possible solutions to the problems of applying cold plasma technology alone are proposed, and future trends in the development of cold plasma technology are discussed. Through this review, we hope to provide a theoretical rationale for the application of this technology in the preservation of aquatic products.

The mechanism of action of ultrasound (US) combined with slightly acidic electrolyzed water (SAEW) treatment against Shewanella putrefaciens was studied. The spoilage causing bacterium Shewanella putrefaciens was treated with US, SAEW or US + SAEW for 10 min, and untreated cells suspended in sterile normal saline was used as a control. The changes in the cell membrane and internal environment of this bacterium were evaluated by measuring the reduction in bacterial count, bacterial growth curve, electrical conductivity, propidium iodide (PI) intake, alkaline phosphatase (AKP) and lactate dehydrogenase (LDH) activity, the leakage of ultraviolet-absorbing materials. The microstructure was also observed by scanning electron microscopy (SEM) before and after treatment. The results showed that US + SAEW treatment reduced the bacterial count by 2.48 (lg (CFU/mL)). Compared with the control and single treatment groups, US + SAEW greatly damaged the cell membrane integrity, causing the leakage of intracellular components and a significant increase in electrical conductivity, AKP and LDH activity (P < 0.05). After US + SAEW treatment, the bacterial cells collapsed obviously, the outer membrane was broken, the cell wall was damaged, and a large amount of cellular contents leaked out of the cells.Therefore, ultrasonic treatment can seriously damage the cell wall and cell membrane of Shewanella putrefaciens, promoting SAEW to enter into cells, enhancing the bactericidal efficacy, and leading to cell death eventually.

This work was undertaken in order to study the combined treatment effects of ultrasound and caffeic acid on the quality of sea bass (Lateolabrax japonicas) during refrigerated storage. Fresh sea bass fillets were arbitrarily allocated into five groups: ultrasonic treatment at 20 kHz and 600 W for 10 min (US), dipping in 2.0 g/L caffeic acid for 10 min (CA), ultrasonic treatment at 20 kHz and 600 W for 5 min followed by dipping in 2.0 g/L caffeic acid for 5 min (US + CA), dipping in sterile water for 10 min (blank control, CK), and dipping in 1% acetic acid for 10 min (AA). After draining off the soaking solution, the samples were packed separately with polyethylene (PE) pouches, and then stored in a refrigerator at 4 ℃. Total viable count (TVC), physicochemical properties such as pH, total volatile basic nitrogen (TVB-N) content, thiobarbituric acid (TBA) value, texture profile analysis (TPA) parameters, and water-holding capacity (WHC), intrinsic fluorescence intensity (IFI) and sensory quality were measured every two days. The results showed that the US and CA treatments retarded the growth of TVC. On the fifth day, the TVC values in the CA and US groups were 18.49% and 15.53% lower than that in the control group, respectively. The increase of pH and TVB-N values in the treatment groups was obviously slower than that in the control group. On the 10th day of storage, the TVB-N content of the control group exceeded the spoilage limit, reaching (33.88 ± 0.56) mg/100 g compared to (16.71 ± 0.41) mg/100 g for the US + CA group. Both the US and CA treatments improved the WHC of fish greatly, while the CA treatment also had a stronger inhibitory effect on lipid oxidation in fish. Among the five groups, the US + CA group had the best overall quality. Compared with the CK group, the US + CA treatment maintained the quality better and extended the shelf-life of sea bass by four days at least.

In order to explore the combined effects of dual-frequency ultrasound (DUS) and citric acid (CA) on the quality changes of large yellow croaker (Pseudosciaena crocea) during refrigerated storage, fresh fillet samples were treated with sterile distilled water (as a control), DUS at 20/28 kHz and 175 W, 8.0 g/L CA or DUS combined with CA (DUS + CA) for 10 min, packaged in sterile bags and stored at 4 ℃. Microbial parameters (total viable count (TVC), and psychrophilic bacterial count (PBC)), physicochemical properties (texture characteristics, color difference, pH, total volatile base nitrogen (TVB-N) content, thiobarbituric acid reaction substance (TBARS) value), water migration (water-holding capacity (WHC), low-field nuclear magnetic resonance (LF-NMR), magnetic resonance imaging (MRI)) and sensory evaluation weremeasured every two days during storage. The results showed that CA treatment could inhibit lipid oxidation and microbial growth in large yellow croaker during refrigerated storage. On the 8th day of storage, the logarithm of TVC in the control group was (8.26 ± 0.02) (lg(CFU/g)), which exceeded the spoilage limit and was significantly higher than that of the CA group (6.60 ± 0.06) (lg(CFU/g)). The TBARS value of the CA group was (0.51 ± 0.05) mg/kg on the 8th day of storage, which was significantly lower than that of the control group (P < 0.05). DUS treatment delayed the transformation of immobile water (T₂₂) into free water (T₂₃), indicating improved WHC. Overall, the quality of large yellow croaker treated with DUS + CA was better than that of all other groups during refrigerated storage. At the end of storage, the TVB-N content of the DUS + CA group was (13.79 ± 0.57) mg/100 g and its quality was the best. Collectively, we concluded that 20/28 kHz, 175 W dual-frequency ultrasound combined with 8.0 g/L citric acid treatment can significantly delay the quality deterioration of large yellow croaker, and prolong the shelf-life for at least six days during refrigerated storage compared with the control group.

Being rich in high-quality proteins and polyunsaturated fatty acids, aquatic products are susceptible to microorganisms and endogenous enzymes during storage and processing, resulting in quality deterioration such as fat oxidation. Therefore, it is necessary to carry out research to develop preservation methods for aquatic products. This paper presents the latest progress on preservation methods for aquatic products, illustrates the current status of the application of physical, chemical and biological preservation methods to aquatic products, summarizes the shortcomings of these reservation methods, and proposes possible solutions. It is concluded that the optimum combination of different preservation methods to extend the shelf life of aquatic products can be discovered based on the principle of hurdle technology. Finally, an outlook on future trends in the preservation of aquatic products is given. We expect that this review will provide theoretical reference for efficient freshness preservation and quality improvement of aquatic products.