Daoying Wang

Changes of intramuscular phospholipids and free fatty acids during the processing of Nanjing dry-cured duck

In this study, changes of intramuscular phospholipids and free fatty acids were tracked during the processing of Nanjing dry-cured duck. Phospholipids were identified and quantified by high performance liquid chromatography combined with UV and evaporative light scattering detectors. The types and quantities of free fatty acids and fatty acids derived from phospholipids were analyzed by capillary gas chromatography. The results showed that raw duck meat had high quantities of phosphatidylethanolamine, and phosphatidylcholine (37.95% and 54.07% of total phospholipids, respectively), which contained high percentages of polysaturated fatty acids. The percentages of total phospholipids, phosphatidylethanolamine, and phosphatidylcholine decreased during processing, with a concomitant increase in quantities of free fatty acids. The lipolysis of phospholipids, especially phosphatidylethanolamine is the main contributor to the increase of free fatty acids.

The level of heat shock protein 90 in pig Longissimus dorsi muscle and its relationship with meat pH and quality.

The 90 kDa heat shock protein (HSP90) is a molecular chaperone that participates in various cellular processes, the role and significance of HSP90 in postmortem muscle though remains unclear. In the present study, pig Longissimus dorsi muscles, categorized into three pH groups, were tested for HSP90 levels and meat quality parameters (i.e. water holding capacity, colour, tenderness and lipid oxidation). The muscles with a high initial pH (pHi) group (pH>6.4) possessing the greatest water holding capacity and lightness, contained the highest HSP90 level, followed by intermediate (6.0-6.4) and low pHi groups (pH<6.0). Statistical analysis indicated HSP90 level was significantly and negatively correlated with cooking loss, drip loss, and lightness (r=-0.797, -0.785, -0.604, respectively, P<0.01). The results suggest that HSP90 may play a crucial role in water retention of meat and may be involved in postmortem meat quality development.

Changes in actomyosin dissociation and endogenous enzyme activities during heating and their relationship with duck meat tenderness.

The objectives of this study, were to examine the relationship between duck meat tenderness, actomyosin dissociation and endogenous enzyme activities when heating the duck breast muscle, to the internal temperature of 30, 40, 50, 60, 70, 80, 90°C. The shear force increased in the temperature range of 30-50°C and 70-90°C and decreased from 50 to 70°C, which was negatively related with liberated actin (P<0.05). The activity of cathepsin B and L was stable while heating the meat to a temperature below 50°C, then it decreased rapidly with temperature increase. The calpain activity kept decreasing with the temperature increase. There was no significant change in the cathepsin D activity below 70°C but it declined rapidly thereafter, and its activity was strongly correlated with actomyosin dissociation (P<0.05). The results suggest that actomyosin dissociation and cathepsin D, could contribute to the tenderness of duck meat during the cooking process.

Composition of intramuscular phospholipids and free fatty acids in three kinds of traditional Chinese duck meat products

Composition of intramuscular phospholipids and free fatty acids in 3 kinds of traditional Chinese duck meat products (dry-cured duck, roasted duck, and water-boiled salted duck) was investigated. Phospholipids were identified and quantified by HPLC combined with ultraviolet and evaporative light scattering detectors. The types and quantities of free fatty acids and fatty acids derived from phospholipids were analyzed by capillary gas chromatography. The results showed that raw duck meat had high quantities of phosphatidyl-ethanolamine and phosphatidylcholine (28.1 and 64.7% of total phospholipids, respectively), which contained high percentages of polyunsaturated fatty acids. The percentages of total phospholipids, phosphatidylethanolamine, and phosphatidylcholine decreased during processing, with a concomitant increase in quantities of free fatty acids. A selective degradation of fatty acids distributions of phospholipids was found through the dry-cured duck processing, but was not found during the roasted and water-boiled duck processing.

Apoptosis during postmortem conditioning and its relationship to duck meat quality

The aim of this work was to examine the relationship of skeletal muscle apoptosis and postmortem development of meat quality. Colour, cooking loss, myofibril fragmentation index (MFI) and shear force of duck breast and thigh meat postmortem were measured, and changes of positive nuclei were assessed with Terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphophate nick end-labelling method (TUNEL). Correlation analysis revealed that apoptosis were positively correlated with colour (L(*), a(*) and b(*)), cooking loss and MFI (P<0.05), while it is negatively correlated with shear force (P<0.05). Our results indicate the growing level of duck skeletal muscle cell apoptosis was associated with the postmortem development of meat quality traits such as meat colour, water holding capacity and tenderness.

Effect of heat shock protein 90 against ROS-induced phospholipid oxidation

The antioxidative role of Hsp90 purified from duck muscle on phospholipid was investigated in this study. Lipid oxidation was assessed by ferric thiocyanate method, and particle size, zeta potential measurements and transmission electron microscopy were employed to detect physical and chemical changes during oxidation of liposomes. Increase of the peroxidation products, decrease of the particle size and disruption of the spherical unity of the liposomes were detected when liposome was exposed to hydrogen peroxide (H2O2) oxidation, and Hsp90 was shown to protect liposome against oxidation. To further test the protection of Hsp90 on cell membrane, the Hsp90 transformed E. coli cell model was built. The Hsp90-containing E. coli showed higher survival and better membrane integrity as compared to the control upon H2O2 exposure. It is expected that Hsp90 plays an important role in the prevention of phospholipids oxidation in meat and has potential use as a food antioxidant.

Proteolysis and cathepsin activities in the processing of dry-cured duck

Changes in sarcoplasmic and myofibrillar proteins, free amino acids, and cathepsin activities were measured to evaluate the contribution of cathepsins to the proteolysis of muscle proteins in dry-cured duck processing. Thirty-six dry-cured ducks were processed with the traditional method, and samples were collected at different stages. Sarcoplasmic and myofibrillar proteins were found to be degraded to some degree at different stages, whereas content of free amino acids increased from 43.9 to 133.97 mg/100 g during the whole process. Cathepsin B, D, and L activities decreased significantly, and the activities in the end product were 22.4, 26.2, and 40.5% of those in the raw material, respectively. Statistical analysis showed there were significant correlations among changes in proteins, free amino acids, and cathepsin activities. The results indicated that cathepsins are involved in the proteolysis of muscle proteins in dry-cured duck processing.

A label-free and high sensitive aptamer biosensor based on hyperbranched polyester microspheres for thrombin detection

In this paper, we have synthesized hyperbranched polyester microspheres with carboxylic acid functional groups (HBPE-CA) and developed a label-free electrochemical aptamer biosensor using thrombin-binding aptamer (TBA) as receptor for the measurement of thrombin in whole blood. The indium tin oxide (ITO) electrode surface modified with HBPE-CA microspheres was grafted with TBA, which has excellent binding affinity and selectivity for thrombin. Binding of the thrombin at the modified ITO electrode surface greatly restrained access of electrons for a redox probe of [Fe(CN)6](3-/4-). Moreover, the aptamer biosensor could be used for detection of thrombin in whole blood, a wide detection range (10fM-100nM) and a detection limit on the order of 0.90fM were demonstrated. Control experiments were also carried out by using bull serum albumin (BSA) and lysozyme in the absence of thrombin. The good stability and repeatability of this aptamer biosensor were also proved. We expect that this demonstration will lead to the development of highly sensitive label-free sensors based on aptamer with lower cost than current technology. The integration of the technologies, which include anticoagulant, sensor and nanoscience, will bring significant input to high-performance biosensors relevant to diagnostics and therapy of interest for human health.

Postmortem changes in actomyosin dissociation, myofibril fragmentation and endogenous enzyme activities of grass carp (Ctenopharyngodon idellus) muscle

The changes of actomyosin, proteolytic activities and myofibril fragmentation during the postmortem aging of grass carp were studied. The study revealed dramatically increased actomyosin dissociation within 6 h of storage postmortem in grass carp, and it was associated with the drop of pH from 6.9 to 6.7, while liberated actin remained almost unchanged after 6 h postmortem. The myofibril fragmentation also increased significantly with the storage time in 6 h, and a highly positive correlation (P<0.01) existed between MFI and cathepsin B, D, H activities. The study indicated both actomyosin dissociation and cathepsin B, D, H played a role in postmortem tenderization and textural changes in grass carp.

Changes of phospholipase A2 and C activities during dry-cured duck processing and their relationship with intramuscular phospholipid degradation

Phospholipid hydrolysis, as the main stage and cause of phopholipid degradation, is generally attributed to phospholipases. In this study, the changes of phospholipase A₂ (PLA₂) and C (PLC) activities, neutral lipid, free fatty acids and phospholipids in dry-cured duck leg muscles during processing, were examined. The composition of free fatty acids and neutral lipids increased significantly (P<0.05) with extension of processing time while the phospholipids composition decreased. The PLA₂ and PLC activity decreased in the final product, but retained 83.70% and 86.78% of their initial activities, respectively. The relative activities of both PLA₂ and PLC highly correlated with the decline of phospholipids and the increase of free fatty acids. High correlations were also obtained between the relative activities of PLC and the increase of neutral lipid (P<0.01). All these results suggest that PLA₂ and PLC contribute to the degradation of intramuscular phospholipids during the processing of dry-cured duck.