Effects of slaughter stress on freshness-locked products of Sebastes schlegelii

China’s coastal commercial species of marine fish are both rich and varied. However, most of the catch is produced by the small-scale fisheries, and the small-scale landings are destined for local human consumption and sold as primary products. Economic benefit is constrained because lack of quality control concern. A construction of value chain based on freshness-locked products with upper limit quality instead of primary products is worth to explore. One of species, S. schlegelii was taken as case study. In order to change the existing sales mode of primary agricultural products of S. schlegelii through product design, the exploration was carried out from two aspects: the upper limit of quality and the effect of freshness-lock. Firstly, from the slaughter stress intensity, the limit quality of S. schlegelii was explored, including the upper limit of quality under the minimum stress and the lower limit of quality under fatigue death, compared with the quality status of commercial products. Then, through the management of quality determination period, the effect of freshness-locking on high end S. schlegelii was discussed. According to the degree of slaughter stress, healthy living animals were divided into three treatment groups: minimum stress-spinal cord destruction (SCD), low stress - spinal cord cutting (SCC) and high stress - suffocation in air (SA). The commercially available products were from supermarket (SM) and local fish market (FM), respectively. The measures of freshness-locking were to cool the fish to about 0 °C immediately after quick killing, and to refrigerate the fresh products at 2 °C. The characteristics of postmortem rigor of S. schlegelii were analyzed from rigor index, muscular contraction and breaking strength. The quality of muscle and its stability in cold storage were analyzed by whiteness value, pH value, ATP-related compounds and microstructure. The results showed that: ① Under the lowest stress, the maximum rigor of S. schlegelii reached 24 h after death and lasted for 24 h. In the high stress group, the rigor index reached 90% after 6 h and was free from rigor after 48 h. Muscular contraction is correlated with rigor index. Muscles under high stress showed no signs of contraction during storage, while those under low stress contracted rapidly before the occurrence of maximum rigor. During cold storage, muscle breaking strength showed a decreasing trend, but it was significantly delayed in the lowest stress group. ② Under the minimum stress, the initial ATP value was 2.83 μmol/g, and the minimum pH value was 6.58. Under low stress, ATP value was 0.94 μmol/g at 6 h after death, and the lowest pH was 6.56. Under high stress, ATP value was 0.50 μmol/g and the lowest pH was 6.54 at 6 h after death. ③ delayed effect, the whiteness of muscle fibers was gradually degraded and the space between muscle cells was expanded during cold storage, but the lowest stress group could effectively slow down the above trend. ④ quality status at the sales, the results of fresh product quality analysis of the supermarket group and the fish market group showed that the quality of the supermarket group was similar to that of the low stress group at 6 h after death, and the quality of the fish market group was similar to that of the high stress group at 120 h after death. To sum up, the commercially available primary agricultural products intermingle different levels of quality for S. schlegelii. The product design is applied through the treatment of freshness-locking, which not only effectively prolongs the shelf life of chilled fish, but also meets the needs of consumers for high quality.