The role of phloretin in the thermal degradation of myofibrillar protein induced by myofibril-bound serine protease: Insights into structural and molecular mechanisms.

During thermal processing, myofibril-bound serine protease (MBSP) can degrade myofibrillar protein (MP), thereby affecting the aquatic product quality. Phloretin, a natural polyphenol, has been shown to delay the thermal degradation of MP. However, its specific mechanism of action remains unclear. To address this, MP (M group) was used as the control to investigate the effects of phloretin on the degradation degree, conformational changes, microstructure, and molecular interactions of MBSP-supplemented MP (M-M group) at 55 °C. SDS-PAGE analysis showed that phloretin could inhibit the degradation of myosin heavy chain induced by MBSP. With increasing phloretin concentration, the myofibrillar fragmentation index of the M-M group decreased more significantly than that of the M group. At 50 μM phloretin, the growth rate of active sulfhydryl in the M-M group (70.17%) was higher than that in the M group (54.91%), while total sulfhydryl in the M-M group (49.06%) was much lower than that in the M group (92.85%). Furthermore, the addition of phloretin caused fluorescence quenching and an initial increase followed by a decrease in α-helix content in the samples. And, the surface height and roughness values of M-M group decreased more significantly. Additionally, phloretin bound to MBSP mainly via hydrogen bonds and van der Waals forces, while binding to myosin primarily through hydrophobic interactions at 55 °C. Notably, phloretin exhibited a stronger binding affinity for MBSP. Overall, phloretin bound to the active site of MBSP, inhibiting its activity and thereby effectively delaying the thermal degradation of MP.