The objective of this study was to investigate the differences in protein modifications between pale, soft, and exudative (PSE) and red, firm, and nonexudative (RFN) pork during postmortem (PM) aging. Longissimus dorsi (LD) including 8 PSE and 8 RFN muscles were individually removed from 16 carcasses. These 16 LD muscles were vacuum packaged at 24 h after slaughter and stored at 4°C for 1, 3, and 5 d. The centrifugation loss, drip loss, color, protein solubility, protein oxidation, protein degradation including desmin, troponin T, and integrin, and μ-calpain activation were determined. The pH of PSE samples was significantly lower than that of RFN samples at both 1 and 24 h PM (P < 0.05). The L* values of PSE pork were significantly greater than that of RFN pork at different time point during PM storage (P < 0.01). The centrifugation loss of PSE samples at d 1 was extremely greater than samples from RFN pork (P < 0.01). The cumulative drip loss for d 0 to 1, d 0 to 3, and d 0 to 5 in PSE pork were significantly greater than that from RFN pork (P < 0.05). The carbonyl content of myofibrillar proteins was not significantly different between PSE and RFN pork samples (P > 0.05). In addition, PSE pork presented a lower solubility of sarcoplasmic protein, myofibrillar protein, and total protein than RFN pork except the solubility of myofibrillar protein at d 1 (P < 0.05). The intensity of intact desmin and troponin T 2 in PSE pork at d 3 and 5 were significantly greater than that in RFN pork (P < 0.05), whereas no significant difference was detected at d 1. The intensity of intact troponin T 1 in PSE pork at d 5 was greater than that in RFN pork (P < 0.05). However, more degradation products of integrin were detected in PSE pork compared to that of RFN pork at d 1 (P < 0.05). Red, firm, and nonexudative pork presented lower intensity of intact 80 kDa calpain and greater intensity of autolyzed 76 kDa product compared to PSE pork (P < 0.01). The results indicate that the degree of μ-calpain activation, the extent of protein degradation including desmin and integrin, and the level of protein solubility in PSE pork could contribute to its low water holding capacity during PM storage.
Xingshuang Lv,Zhi Li,Haojia Wei,Shuaishuai Yuan,Xiaohui Fu,Zhibo Li
The synthesis and optimization of antibacterial agents for thermoplastic polyurethane (TPU) matrices is highly imperative for the development of antibacterial TPUs, especially for applications in biomedical devices. Macromolecular or polymer-based antimicrobials are extremely appealing for their environmental compatibility, low toxicity toward host cells, and low-leachable characteristic, making them ideal additives for antibacterial materials. Herein, quaternary ammonium salt (QAS)-containing copolyesters of P(MBL-N+-CL) were designed and synthesized as polymeric antimicrobials via ring-opening copolymerization (ROCP) of α-methylene-γ-butyrolactone (MBL) and ε-caprolactone (ε-CL) followed by selective post-functionalization via the thiol–ene “click” reaction to introduce cationic moieties. Owing to the flexibility of the synthetic routes, the density and distribution of QAS groups can be conveniently tuned by adjusting the content and functionality of pendent vinyl groups, giving an efficient immobilization strategy for the preparation of antibacterial modifiers. Commercial TPU Estane 58277 was then physically blended with the cationic P(MBL-N+-CL)s (∼9 wt %) to prepare a series of P(MBL-N+-CL)/TPU composite films via the solvent casting method. It was found that the addition of cationic P(MBL-N+-CL) did not alter the basic physical properties of TPU but showed much lower leachability and hemolysis ratio than that of TPU blends with a small molecular QAS additive. Particularly, P(MBL-N+-CL)-3/TPU with 1.5 wt % QAS units showed almost 100% contact-bactericidal rate against Staphylococcus aureus (S. aureus), and such effects were still maintained after 10 cycles of surface washing. The influence of different P(MBL-N+-CL) additives on surface, thermal, and mechanical properties and cytotoxicity was systematically investigated. The results revealed that the hydrophilicity of the TPU films improved after blending with P(MBL-N+-CL) due to the hydration of QAS units. The thermal stability of the composite films was almost maintained with a degradation temperature of 5% mass loss (Td,5%) above 310 °C and the elasticity was improved, but the tensile strength slightly decreased. The high antibacterial activity, low leachability, negligible hemolytic activities, and low cytotoxicity endow these optimized antibacterial TPU composite films with great potential applications in various medical devices.
危险品化学品经营许可证（带存储）