LAUSR

This study investigated changes in the physicochemical indexes, water dynamics, and microbial communities of bigeye tuna (Thunnus obesus) during simulated cold chain logistics. With increasing storage time, the color and water activity decreased gradually, while drip loss gradually increased, and pH increased with a fluctuating pattern. The trend of bound water content was not obvious, trapped water declined, and free water increased with fluctuations over time, according to low‐field nuclear magnetic resonance (LF‐¹H NMR). High‐throughput sequencing results indicated that fluctuating temperatures inhibited Acinetobacter and Pseudomonas and promoted Pelomonas, Psychrobacter, and Shewanella. Principal component analysis and redundancy analysis revealed significantly different microbial community interactions among the four groups, and environmental factors had distinct effects on bacterial community assemblages. LF‐NMR and high‐throughput sequencing can be used to monitor dynamic quality changes in bigeye tuna during simulated cold chain logistics with fluctuating temperatures.