Postmorten biochemistry and rigor development of pufferfish (Takifugu rubripes)

Takifugu rubripes were instant killed, bled and gutted, two treatments for 6 days storage were designed including storage in ice and at ambient temperature, respectively. During storage, the progression of rigor mortis and body temperature were recorded. Sampling and assay were carried out at both different rigor stages and every storage day, and rigor index, ATP and related compounds, glycogen, pH and phosphoprotein were selected as indicators as postmortem biochemical changes. The results showed that the onset of rigor mortis for iced treatment started at around 7^th hour after being slaughtered, and its maximum rigor index was up to 89% with 20-24 hours duration in stiff, the fish body maintained at rigor with rigor index at 9%-16% after 4 days icing storage. However, the maximum rigor index of 71% was observed fleetingly in the control treatment with higher temperature ambient, and the whole rigor progression or stages were undefined. Glycogen degraded sharply at the initial post-mortem period for all treatments. Comparing with the trace amounts was still detected in 5 days storage for the iced treatment, glycogen was almost depleted after 3 days storage in the control treatment. The pH decreasing patterns of two treatments reflected the different glycogen consumption rates between the two storage treatments. ATP was rapidly depleted in all treatments with accumulation of IMP exclusively. Maximum of IMP reached to 9.5 μmol/g on the 3rd day and remained at about 7.5 μmol/g on the 6^th day of the iced treatment. As to the control treatment, IMP was degraded rapidly after the maximum of 9.2 μmol/g on the 1st storage day with higher temperature. Compared to the iced treatment with a trace Hx amounts, the control treatment presented a significant accumulation of Hx. Muscle protein phosphorylation indicated that the rigor mortis progression of T. rubripes was also related to the properties of muscle protein components. Notably, the protein components related to glycolytic enzymes had a significant difference in phosphorylation between the iced and ambient treatment. The ambient treatment presented higher phosphorylation level, which is consistent with the glycolysis properties observed in ambient treatment. In conclusion, T. rubripes advanced in icing stability and high accumulation of IMP after being slaughtered, and the association between protein phosphorylation level and the process of rigor mortis is worth exploring further.