| Antarctic krill ( Euphausia superba ) is a vital species in the Antarctic ecosystem, boasting substantial reserves and high nutritional value. It has emerged as a significant commercial fishery resource in the Southern Ocean. However, due to its exceptionally high autolytic enzyme activity, it is susceptible to autolysis and blackening during processing, storage, and transportation, resulting in a decline in sensory quality and nutritional value of raw materials. Shrimp melanosis is the result of a series of enzymatic reactions mediated by phenoloxidase (PO) with in the body. PO facilitates the oxidation of phenolic substances, leading to the formation of highly unstable quinone compounds, which further react to produce melanin. The accumulation of melanin significantly impacts the appearance of Antarctic krill, thereby reduing its commercial value. Sulfites, due to their cost-effectiveness and potent anti-blackening effects, are commonly used as shrimp anti-black agents. Sodium metabisulfite is one of the compounds allowed to be used for shrimp preservation under GB 2760-2014 regulations. It can not only inhibits PO activity but also reduces quinone compounds, to achieve the effect of preventing blackening. However, excessive use of sulfite can lead to discomfort and health issues such as gastrointestinal problems, liver disturbances, dyspnea, vomiting, diarrhea, and headaches. Therefore, GB2760-2014 stipulates that the residual SO2 content should not exceed 0.1 g/kg. At present, the utilization of sodium metabisulfite in production is widespread but lacks standardized requirements, with limited guidance available on how to regulate its usage. Therefore, to assess the impact of sodium metabisulfite on the control of blackening in Antarctic krill and refine the treatment process, experiments were conducted to measure the changes of SO2 residue and PO activity in Antarctic krill subjected to various concentrations of sodium metabisulfite solutions and soaking times. Furthermore, observations and analyses were conducted to monitor the blackening of Antarctic krill during cold storage and frozen storage. The results demonstrated a positive correlation between the SO2 residue in Antarctic krill and the concentration of sodium metabisulfite solution. A concentration of 1 g/L sodium metabisulfite solution resulted in a SO2 residue of 0.065 g/kg in Antarctic krill, below the national standard limit of 0.1 g/kg. However, treatment with a 2 g/L solution led to the SO2 residue of 0.166 g/kg in shrimp, exceeding the national standard limit. Treatment with a 3 g/L solution resulted in the SO2 residue of 0.254 g/kg in shrimp, significantly surpassing the national standard limit. Consequently, it was recommended to use 1 g/L or 2 g/L sodium metabisulfite solutions to prevent blackening in Antarctic krill while maintaining the SO2 residue below 0.1 g/kg. Under these conditions, treatment time for a 1 g/L sodium pyrosulfite solution could be extended to 300 s, with a relative PO activity of 21.2 %. For a 2.0 g/L sodium pyrosulfite solution, a treatment time of 30 s was suitable, yielding a relative PO activity of 34.5 %. During storage, it was observed that the control group exhibited noticeable blackening after storage at 4°C for 24 h and frozen storage for 6 months, predominantly in the head, chest, abdomen, and tail sections. and there were slight variations in the blackening process among individuals. Compared to the control group, the sodium metabisulfite treatment group displayed significantly lower blackening scores during storage (P < 0.05). Specifically, the 1 g/L sodium metabisulfite solution with a 300 s treatment group and the 2 g/L sodium metabisulfite solution with a 30 s treatment group showed obvious blackening at 48 h and 72 h of cold storage and after 12 months of frozen storage, indicating that higher concentrations of sodium metabisulfite solution during treatment yielded better control effect on the blackening of Antarctic krill during storage. It is worth noting that PO activity is jsut one of the factors influencing the melanosis process. Although the 1 g/L sodium metabisulfite solution treatment for 300 s could better inhibit PO activity, the anti-black effect of this group was not as pronounced as that of the 2 g/L sodium metabisulfite solution treatment for 30 s during storage. In summary, soaking in 1 g/L sodium metabisulfite solution for 300 s and 2 g/L sodium metabisulfite solution for 30 s resluted in relative enzyme activities of PO at 21.2 % and 34.5 %, respectively. Simultaneously, the SO2 residues in shrimp were measured at 0.094 g/kg and 0.096 g/kg, respectively, meeting the GB 2760-2014 limit of SO2 residue not exceeding 0.1 g/kg. Compared to the control group, sodium metabisulfite treatment effectively delayed the blackening process of Antarctic krill during cold storage and frozen storage, with the 2 g/L sodium metabisulfite solution soaking for 30 s exhibiting superior anti-blackening effects. This suggests that a high concentration of sodium metabisulfite solution, and a short period of time of treatment had a better effect on the blackening inhibition.These findings offer a theoretical foundation and technical guidance for maintaining the quality of Antarctic krill during storage and transportation. |
