Very fast chilling is associated with altered RyR1-DHPR interaction and Ca²⁺ release during postmortem pork...

Very fast chilling (VFC) is a critical technology for improving meat tenderness, likely by increasing sarcoplasmic Ca²⁺. However, its molecular mechanisms remain unclear. Porcine longissimus lumborum muscles were incubated with modulators (caffeine/tetracaine/vehicle) to manipulate the gating state of the key calcium channel ryanodine receptor 1 (RyR1), followed by VFC treatment (35 °C to 1 °C, 13 °C/h). Results showed that myofibrillar fragmentation was higher in the vehicle and activation groups, with increased super-contracted sarcomeres and μ-calpain activity. Ca²⁺ release from the sarcoplasmic reticulum to the sarcoplasm and RyR1-dihydropyridine receptor (DHPR) co-localization were also greater in these groups compared to the inhibition group. Molecular dynamics simulation for the chilling process demonstrated that the RyR1-DHPR interaction was more stable at 15 °C and 1 °C than at 35 °C, mainly driven by electrostatic interactions and hydrogen bonds. The related residues primarily included RyR1_Arg 1073/Arg 1076 and DHPR_Asp 665/Asn 800. Overall, VFC could preserve the interaction between RyR1 and its regulatory protein DHPR, which was associated with activating the channel to massively release Ca²⁺ at early postmortem time, thus causing myofiber ruptures and meat tenderization.