Comparison of activity, expression and S-nitrosylation of glycolytic enzymes between pale, soft and exudative and red, firm and non-exudative pork during post-mortem aging.

The activity, expression and S-nitrosylation of glycogen phosphorylase (GP), phosphofructokinase (PFK) and pyruvate kinase (PK) was compared between pale, soft and exudative (PSE) and red, firm and non-exudative (RFN) pork. The nitric oxide synthase (NOS) activity of RFN pork was higher than PSE pork (P < 0.05). Glycogen and lactic acid content were significantly different between PSE and RFN samples at 1 h postmortem (P < 0.05). Compared to PSE pork, RFN pork had lower activities and higher S-nitrosylation levels of GP, PFK and PK (P < 0.05). Moreover, GP expression in RFN pork was lower (P < 0.05) while no significant differences of PFK and PK expression were observed between these two groups. These data suggest that protein S-nitrosylation can presumably regulate glycolysis by modulating glycolytic enzymes activities and then regulate the development of PSE pork.

Electrochemical sensor using gold nanoparticles and plasma pretreated graphene based on the complexes of calcium and Troponin C to detect Ca2+ in meat.

A simple electrochemical sensor was developed to determine the concentration of Ca2+ in meat. Graphene was treated with oxygen plasma for 10 s and 30 s comparing with the pristine graphene. Through analyzing morphology and chemical composition, the graphene with the lowest defect density was chosen to mix with bovine serum albumin molecule-functionalized gold nanoparticles. It was interesting that only a few gold nanoparticles were trapped in the graphene with 10 s plasma treatment. Then, under the optimal condition measured, the limit of detection was detected as 3.9 × 10-8 M with a linear relationship from 5 × 10-8 to 3 × 10-4 M. Finally, the proposed electrochemical method was applied to detect Ca2+ in the pork sample with stability and reproducibility verified by parallel detections. Thus, the proposed method demonstrates its potential for effectively detecting Ca2+ in meat and prominently reduces time consumption on operations and pretreatments.

Expression of Pork Plectin during Postmortem Aging.

The current study investigated the distribution and degradation of pork plectin during postmortem aging. Longissimus thoracis (LT) muscles from 12 pig carcasses were vacuum-packaged and aged at 4 °C for 0 h, 6 h, 12 h, 1 day, 3 days, 7 days, and 13 days. Immunofluorescence analysis showed that pork plectin was distributed in a honeycomb-like pattern in the cross section and a regularly striated pattern in the longitudinal section. However, plectin was found preferentially expressed in fibers that were stained with high anti-fast-MyHC. Double immunostaining revealed the colocalization of plectin and desmin in the cytoplasm and beneath the sarcolemma. Western blot analysis showed that the amount of intact plectin was rapidly reduced during the early postmortem aging (P < 0.05) and almost disappeared at day 3. The degraded 240 kDa plectin accumulated fast and was further cleaved after 3 days of aging (P < 0.05). The plectin degradation could be significantly blocked by calpain inhibitor MDL-28170 rather than caspase-3 inhibitor Ac-DEVD-CHO (P < 0.05). Double immunostaining of µ-calpain and plectin showed a large amount of overlap at 0 h and 3 days of postmortem. Accordingly, these findings showed that plectin was preferentially expressed in fast muscle fiber and regularly distributed along with desmin at the strategic cellular sites. Plectin suffered a prominent and prompt degradation during postmortem aging, which might be attributed to µ-calpain.

Comparison of Activity, Expression, and S-Nitrosylation of Calcium Transfer Proteins between Pale, Soft, and Exudative and Red, Firm, and Non-exudative Pork during Post-Mortem Aging.

The research was performed to investigate the difference of activity, expression, and S-nitrosylation of calcium transfer proteins between pale, soft, and exudative (PSE) and red, firm, and non-exudative (RFN) pork. Seven PSE and seven RFN pork longissimus thoracis (LT) muscles were chosen according to pH and L* at 1 h post-mortem and identified by drip loss at 24 h. The nitric oxide synthase (NOS) activity and neuronal nitric oxide synthase (nNOS) expression showed a significant difference between two groups ( p < 0.05). PSE meat had a considerably higher sarcoplasmic calcium concentration compared to RFN meat at 1 h post-mortem aging ( p < 0.05). In PSE meat, the expression of ryanodine receptor 1 (RyR1) and sarcoplasmic reticulum calcium ATPase 1 (SERCA1) was lower than that in RFN meat, while the relative S-nitrosylation level of RyR1 and SERCA1 was higher ( p < 0.05). In addition, a lower activity of SERCA was detected in PSE meat compared to RFN meat ( p < 0.05). Those results indicate that S-nitrosylation of RyR1 and SERCA1 can putatively play a crucial part in regulating calcium homeostasis. A high level of RyR1 and SERCA1 S-nitrosylation can induce the imbalance of calcium in cytoplasm, leading to accelerated pH decline and the development of PSE meat.