Effects of freshness-locked performance during the quality determination period on the iced Takifugu rubripes freshness quality

Market demand for farmed fish products is growing rapidly, However, not all aquaculture sectors produce the premium quality at end of the market. To produce farmed seafood with consistent optimum quality, solutions of stress minimizing and deterioration delaying are worth studying. To explore mechanism and feasibility of “lock in freshness” of farmed fish chilled products, farmed Takifugu rubripes was taken as raw material. The experiment was performed in two post mortem stages, including a quality determination period (QDP) corresponding to on-site handling and post quality determination period (P-QDP) corresponding to the ice storage. The delayed effect of the QDP chilling treatment on the P-QDP was investigated. On-site handling was carried out using humane slaughter followed by instant bleeding in –1 °C sea water with 20 minutes, gutted and rinsed fish were individually wrapped and stored with flake ice surrounded. Meanwhile, the Control group as chilling-free was compared to the Treatment group with chilling at the QDP. The chilled T. rubripes postmortem biochemical metabolism was measured by rigor index, pH, lactic acid content, ATP and ATP-related compounds and K-Value. Meanwhile, the quality was analyzed by muscle ultrastructural changes in two treatments. Treatment temperature after chilling in quality determination period dropped rapidly from 10.9 to 2.7 °C in 20 minutes, which has a significant effect of chilling. Treatment temperature was increased dramatically from 2.7 to 8.5 °C in 1 hour because of the special strengthening body washing process of T. rubripes after being processed. And the fish temperature was reduced to 0.5 °C after 12 h iced storage. The delayed effect of the QDP chilling treatment on the P-QDP can be clearly observed by the muscle ultrastructure. Regardless of the Treatment or the Control, in subsequent chilling storage, muscle tissue degraded gradually. Notable, distinct difference can be observed between the Treatment and the Control. The phenomenon of cell structure degraded of the Control occurred compared with the Treatment on day 0. And intermyofibrillar spaces increased. Sarcomeres were non-parallel and swollen sarcoplasmic reticulum was obvious. Especially on day 4, sarcomeres were altered significantly, mainly at the Z-line and I-band level disruptions. Structure was obscured and destroyed more significantly than the Treatment. But the results showed that traditional biochemical indicators could not be detected for sensitive difference of the two treatments. The Treatment biochemical metabolism rate kept pace with the Control, which the rigor mortis progression was similar and rigor state was maintained 4-5 days. Lactate acid, pH, nucleotide metabolism rate and K-value had no significant difference, and K-value was 15% in 8^th day chilling storage. There was a quality determination period after fish was captured, which had the delayed effect of chilled fish quality in the post quality determination period. The degradation of muscle cell could be prolonged by QDP-chilling, which had significant effect of “lock in freshness” on quality of chilled fish. In this way, the image of seafood quality of domestic fisheries could be improved fundamentally, providing significant practical value in China.