Effects of static magnetic field-assisted freezing on physicochemical indices and bacterial communities of shrimp (Penaeus vannamei)

To inhibit the melanization of shrimp (Penaeus vannamei) and improve its freezing quality, different intensities of static magnetic field (MF) were used to assist freezing, with MF intensities of 0, 2, 4, 6, and 8 mT. The effects of different freezing treatments on the freezing parameters, microstructure, enzyme activities, quality indicators, and bacterial communities were investigated. The results indicated that the phase transition and total freezing time significantly decreased under the action of 2 mT MF (8.4% and 15.4%, p < 0.05). Meanwhile, 2 mT treatment significantly reduced polyphenol oxidase and Ca2+-ATPase activities (45.2% and 99.1%), drip loss (46.0%), color change (24.4% and 20.9%), myofibril fragmentation index (20.4%), thiobarbituric acid reactive substances (30.6%) and total viable count (24.2%) (p < 0.05); improved hardness and chewiness (32.2% and 33.3%) (p < 0.05); and protected muscle microstructure compared to common freezing. Isolation and examination of pathogenic bacteria revealed that the 2 mT MF significantly reduced the number of Vibrio parahaemolyticus (50.3%) (p < 0.05). High-throughput sequencing analysis also demonstrated that a 2 mT magnetic field is preferable for assisting in the freezing process of Penaeus vannamei. It effectively decreases the microbial richness and diversity of shrimp, along with the abundance of spoilage bacteria such as Vibrio and Pseudoalteromonas.