Applying transcriptomics to better understand the molecular mechanisms underlying fish filet quality

Microfluidic capillary electrophoresis and real-time PCR were successfully applied to investigate the postmortem alterations in RNA extracted from fish muscular tissue in relation to three parameters: slaughtering method, time, and storage temperature. Postmortem proteolytic degradation of fish filets, which leads to textural changes such as muscle softening and gaping, is a major problem for fish freshness. Endogenous proteases such as calpains and cathepsins are assumed to play the major role in this process, although the exact mechanisms underlying fish meat tenderization have yet to be determined. In the course of the present study we first identified the cDNA sequences coding for µ- calpain and cathepsin L in sea bass (Dicentrarchus labrax). Then we determined the total RNA and µ-calpain- and cathepsin L-specific mRNA integrity over 5 days of storage at two different temperatures (1°C and 18°C) in sea bass slaughtered by three different methods (asphyxia in air, hypothermia, and immediately severing the spinal cord). The results of this study show that, RNA degradation is a slow process under the conditions investigated and, although postmortem storage temperature negatively affects the integrity of total RNA (higher degradation at 18°C), the transcripts of μ-calpain and cathepsin L are present for up to 5 days postmortem in the muscle of sea bass stored at either 1°C or 18°C.