电刺激对宰后牦牛肉成熟过程中肌钙蛋白-T和肌间线蛋白及嫩度的影响

为研究电刺激对宰后牦牛肉成熟过程中Troponin-T和Desmin降解及嫩度的影响,本实验利用聚丙烯酰胺凝胶电泳（SDS-PAGE）、剪切力法及肌原纤维小片化指数法分别对比测定并动态监测宰后不同处理（电刺激、未电刺激）对牦牛的冈上肌、背阔肌和半腱肌3个部位肉在成熟0,1,2,3,5,7,14 d时Troponin-T、Desmin、剪切力及MFI影响的变化特点。结果表明:电刺激组牦牛三个部位肉Troponin-T和Desmin的降解速度和降解程度均较高,且两个处理组背阔肌Troponin-T 28 k Da、Desmin 38 k Da和36 k Da特征降解产物出现的时间较其他两个部位均早,降解程度也较高;成熟14 d后,电刺激组牦牛冈上肌、背阔肌和半腱肌的剪切力值下降百分率较未电刺激组分别显著高2.93%、9.47%、5.08%（p<0.05）,但电刺激对MFI值无显著影响。由此可见,电刺激处理能显著加快宰后牦牛肉肌原纤维骨架蛋白Troponin-T和Desmin的降解程度及剪切力的下降速度,且背阔肌的宰后嫩化较其他两个部位快。      

Rate and extent of pH decline affect proteolysis of cytoskeletal proteins and water-holding capacity in pork

The objective of this study was to determine the extent to which early postmortem (PM) pH decline influences proteolysis of the intermediate filament protein desmin, the costameric proteins vinculin and talin and autolysis of μ-calpain in the longissimus muscle (LM) of pigs from two genetic lines. Based on the LM 3 h pH (H = 3 h pH of LM > 6.0; L = 3 h pH of LM pH < 5.7) PM, 10 carcasses per line and pH group were selected. The average 3 h pH within pH group was 6.23 (H) and 5.44 (L). The LM samples were collected 24, 48, 72, and 120 h PM and percent drip loss was measured after 1, 2, and 4 d of storage. Samples collected at 24, 48, 72, and 120 h PM were used to monitor desmin, vinculin, and talin degradation and samples collected at 24 h PM were used to determine the extent of μ-calpain autolysis by immunoblotting. Higher (P < 0.01) pH values at 45 min, 6 h, and 24 h PM and lower (P < 0.01) drip losses after 1, 2, and 4 d of storage were recorded in the H-compared to the L-group. Abundance of the 76 kDa μ-calpain autolysis product was greater (P < 0.01), proteolysis of talin at all measured time points and proteolysis of desmin after 24 and 48 h PM was greater (P ? 0.03) in the H-group than in the L-group. The current findings indicate activation rate of μ-calpain may be associated with proteolysis of desmin and talin and could play a role in the development of drip loss. The rate of early PM pH decline can partly explain the variation of desmin and talin degradation by affecting the activation of μ-calpain.     

The impact of desmin on texture and water‐holding capacity of ice‐stored grass carp (Ctenopharyngodon idella) fillet

The objective of this work was to analyse the role of desmin in texture softening and water‐holding capacity (WHC) of ice‐stored grass carp fillet. Results indicated that shear force of the fillet decreased sharply within 3 days, while drip loss increased during the whole ice storage. Water mobility and distribution were measured by low‐field ¹H NMR T₂ relaxation that revealed a positive correlation (P < 0.01) between WHC and the mobility of the immobilised water (T₂₁ relaxation time). Meanwhile, negative correlation could be established between intact desmin and drip loss (P < 0.01). Intact desmin was extremely correlated with shear force (P < 0.01) and positively correlated with calpains activity (P < 0.05). This study demonstrated that the degradation of desmin was involved in the mobility of the myofibrillar water and softening of grass carp fillet during ice storage. Furthermore, calpains autolysis seemed to result in desmin degradation.     

Stress relaxation behaviour and structural changes of muscle tissues from Gilthead Sea Bream (Sparus aurata L.) following high pressure treatment

Sea Bream muscle tissue was subjected to different high pressure treatments, and rheological changes were monitored during storage by means of the stress relaxation test. The best fit was obtained by application of the three term Maxwell exponential model, followed by the Nussinovich model. The application of 300 and 400 MPa pressures appeared to enable preservation of elasticity and stiffness of fish muscle during storage, compared to untreated samples. On the contrary, samples treated at 200 MPa underwent a decrease in elasticity during storage. The water holding capacity of dorsal muscle was also assessed, and it was found to decrease with increasing pressures. Immunoblot studies performed on the main structural proteins revealed that a pronounced time-dependent degradation of desmin, observed in untreated samples, could be prevented by treatment at 400 MPa. Taken together, our results strongly suggest that high pressure treatments inactivate degrading enzymes acting on proteins that are related to tissue integrity preservation, texture quality, and water holding capacity.     

Contribution of postmortem changes of integrin, desmin and μ-calpain to variation in water holding capacity of pork

The purpose of this study was to examine the relationship between integrin, desmin, μ-calpain and water holding capacity in fresh pork. High levels of intact integrin at one day postmortem were negatively correlated with day 1 (P<0.05) and days 1-5 (cumulative) drip loss (P<0.05). High levels of intact integrin at five days postmortem were negatively correlated with days 1-7 (cumulative) purge loss (P<0.05). Intensity of intact desmin at one day postmortem was positively correlated with days 1-7 purge loss (P<0.01). There were positive correlations between intensity of intact desmin at day 7 and day 1 (P<0.01), days 1-5 drip loss (P<0.01) and days 1-7 purge loss (P<0.05). Autolysis of μ-calpain was associated with the degradation of desmin and drip or purge loss postmortem. Our results indicate that low levels of degradation of integrin and high levels of desmin degradation were associated with low drip loss values in fresh pork.     

Variation in bull beef quality due to ultimate muscle pH is correlated to endopeptidase and small heat shock protein levels

This study set out to determine if ultimate pH (pH_u) affected the performance of intracellular small heat shock protein and endopeptidase dynamics in muscle during beef ageing. Longissimus dorsi muscles from 39 Angus or Limousin × Angus bulls were examined to see if pH_u achieved at 22 h post mortem (rigor) affected tenderness and water holding capacity of beef. Samples were segregated into three pH_u groups termed high (pH > 6.3), intermediate (5.7 < pH < 6.3) and low (pH < 5.7) pH_u beef. More than 30% of bull beef did not achieve acceptable tenderness at 8 days post mortem with this ageing regime. No significant differences in calpain or cathepsin enzyme levels due to meat pH were observed until after 22 h post mortem, but low pH_u beef had elevated caspase 3/7 activity soon after slaughter. At 22 h post mortem, greater levels of μ-calpain enzyme were found in the high and intermediate pH_u beef and cathepsin B levels were superior in the low pH_u beef after 2 days post mortem. Different rates of desmin and troponin T protein degradation were also observed in aged bull beef. Both proteins were degraded within 6 h post mortem for high pH_u beef, but took >3 days post mortem for intermediate pH_u beef. High levels of alpha β-crystallin (aβC) at 22 h post mortem coincided with delayed muscle protein degradation for low pH_u beef. Our results support the hypothesis that aβC shields myofibrils and buffers against endopeptidase degradation of beef structure during ageing.