Association between paramyosin and the heat‐induced toughening of adductor muscle in Pacific oysters (Crassostrea gigas)

BACKGROUND The phenomenon of increased toughness of adductor muscle of Pacific oysters ( Crassostrea gigas ) during heat treatment considerably impacts their palatability. Thus, the present study was conducted aiming to investigate the relationship between the adductor muscle proteins and observed toughness. RESULTS During heat treatment with boiling, the smooth muscle exhibited greater difficulty in detaching from the shell compared to the striated muscle, indicating more pronounced toughness. The hardness and shear force values of both muscle types were significantly enhanced with an increase in heat treatment duration, with smooth muscle exhibiting markedly higher hardness and shear force than striated muscle. Differential scanning calorimetry analysis showed three thermal absorption peaks in both striated and smooth muscles. However, after heat treatment at 100 °C for 10–20 min, only one endothermic peak was detected, which is presumably attributed to paramyosin. At this time, the enthalpy of paramyosin in smooth muscle (61.90 ± 1.96 J kg −1 ) was higher than that observed in striated muscle (40.16 ± 5.28 J kg −1 ). In addition, the salt solubility of fresh striated muscle was approximately 89%, whereas it was 48% in the case of smooth muscle. Liquid chromatography‐tandem mass spectrometry revealed a 4.54‐fold higher concentration of paramyosin in smooth muscle (9.29 × 10 9 ) compared to striated muscle (2.04 × 10 9 ). CONCLUSION Based on textural properties and protein denaturation characteristics, oysters that have undergone 5 min of heat treatment are deemed optimal quality for consumption. The high content of paramyosin and its thermal stability are likely key determinants contributing to the toughening of the adductor muscles.