Temperature-dependent decoupling of postmortem metabolism and mitochondrial structural damage in Nile tilapia (Oreochromis niloticus)

This study investigated the temperature-dependent postmortem metabolism and structural dynamics of Nile tilapia ( Oreochromis niloticus ) stored at 4 °C and 20 °C. By evaluating macroscopic rigor kinetics, ATP depletion, pH, mitochondrial structural activity (MSA), tissue microstructure, and electrical impedance, we identified two fundamentally divergent pathways of postharvest quality loss. At 20 °C, the onset of rigor mortis was delayed; however, this physical stiffening was coupled with a coordinated, catastrophic collapse of organelle integrity. This was evidenced by a rapid surge in MSA to 100%, severe microstructural gaping, and advanced nucleotide autolysis during extended storage. In contrast, immediate storage at 4 °C triggered rapid cold-shock-induced rigor, drastically accelerating the onset of an irreversible rigor state accompanied by rapid ATP depletion and a steep decline in pH. Crucially, however, the 4 °C environment induced a mechanistic decoupling between macroscopic rigor and cellular damage, where physical contraction occurred independently of organelle rupture. Despite the intense physical contraction, normalized electrical impedance ( Q -value) and MSA confirmed that substantial mitochondrial and global membrane integrity was preserved well through the extended storage phase. These findings demonstrate that while immediate low-temperature chilling is suboptimal during early postmortem processing due to cold-shock-induced rigor, it remains superior for preserving muscle structural architecture over prolonged storage. Consequently, these biophysical insights provide a valuable theoretical foundation for exploring potential temperature-conditioning strategies to optimize raw-material handling and postharvest quality in tropical aquaculture species.