Weimin Xu

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.

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.

One-step green synthesis of a polypyrrole–Au nanocomposite and its application in myoglobin aptasensor

An electrochemical aptasensor was fabricated based on a polypyrrole–Au nanocomposite (PPy–Au NC) and myoglobin-binding aptamer (MBA). The PPy–Au NC was synthesized using a one-step green synthesis method and was characterized by transmission electron microscopy (TEM), UV-vis spectroscopy and a diffuse reflectance spectrum. The studies revealed that the PPy–Au NC provided a mild micro-environment and large surface area for MBA immobilization and facilitated electron transfer. Glassy carbon electrodes (GCEs) surface modified with PPy–Au NC were grafted with MBA, which had excellent binding affinity and selectivity for myoglobin (Mb). The binding of Mb at the modified GCE surface greatly restrained the access of electrons for a redox probe of [Fe(CN)6]3−/4−. Moreover, the aptasensor could be used for the detection of Mb in biochemical assays, with a wide detection range (0.0001 to 0.15 g L−1) and a low detection limit of 30.9 ng mL−1. The aptasensor had a good anti-interference property towards hemin, glucose oxidase (GOx), cytochrome c and hemoglobin. The idea and method presented herein provide a new approach for the evaluation of the freshness and quality of stored meat.

Effect of ultrasound assisted extraction on the physicochemical and functional properties of collagen from soft-shelled turtle calipash

The aim of the present study was to evaluate the physicochemical and functional properties of acid-soluble collagen by ultrasound assisted extraction (UASC) from calipash of soft-shelled turtle (Pelodiscus sinensis). The results showed the collagen content was increased by 16.3% in UASC over the collagen from the conventional extraction (ASC). Both ASC and UASC contained a moderate amount of imino acid (197 and 216 residues/1000 residues, respectively) and hydrophobic amino acid (353 and 391 residues/1000 residues, respectively) in amino acid composition. Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD) analyses confirmed that the ultrasound treatment did not disrupt the triple-stranded helical structures in UASC. UASC had higher thermal stability compared with ASC by viscosity and differential scanning calorimetry (DSC) measurements, therefore, UASC might have the advantage to be used. In dynamic elastic behavior measurement, UASC showed a larger elasticity than ASC. With a mild modification by ultrasound, UASC had superior functional properties to ASC, including water/oil absorption capacity, water-holding capacity, emulsifying properties and foaming properties. These results suggested that UASC from the soft-shelled turtle calipash had a potential to be used widely in food, medicine, cosmetics and biomedical materials.

Optimization of the Tenderization of Duck Breast Meat by Adenosine 5′-Monophosphate (AMP) using Response Surface Methodology

This study aimed to characterize and optimize the tenderization condition of duck breast meat by adenosine 5′-monophosphate (AMP), with the aid of response surface methodology (RSM). The results showed that the optimal conditions for the tenderization of duck breast meat were at the NaCl concentration of 3.99 g/100 g, AMP concentration of 13.83 mmol/L, temperature of 15.32°C, and marinating time of 8 h. Compared with control duck breast meat, AMP combined with NaCl treatment demonstrated significant effects on improvement of meat tenderness and decrease of cooking loss. Such effects might be ascribed to the combination of a series of biochemical reactions, e.g. increase of muscle pH, dissociation of actomyosin and inhibition of meat shrinkage. Therefore, the mixture of AMP and NaCl could be regarded as an effective tenderization agent for duck breast meat.

Optimization of Flavourzyme Hydrolysis Condition for the Preparation of Antioxidant Peptides from Duck Meat using Response Surface Methodology

The aim of this study was to optimize and characterize Flavourzyme hydrolysis conditions for the preparation of antioxidant peptides from duck meat, using response surface methodology. The results indicated that optimal Flavourzyme hydrolysis conditions for preparation of antioxidant peptides from duck protein were a temperature of 50.19°C, pH 5.45, and a reaction time of 1.03 h. Compared to non-hydrolyzed duck meat, Flavourzyme hydrolysis significantly improved the hydroxyl-radical scavenging, DPPH radical-scavenging, ferrous ion-chelating, reducing, and ABTS radical cation-scavenging activities of duck meat. Therefore, Flavourzyme can be regarded as an effective hydrolytic enzyme for the preparation of antioxidant peptides from duck meat.

Effects of different ultrasound power on physicochemical property and functional performance of chicken actomyosin

The aim of present study was to investigate the effect of different ultrasound power on physicochemical property and functional performance of chicken actomyosin (CAM). The treated CAM had the lowest particle size and the highest absolute zeta potential at 150 W. The conformation changes of treated CAM exhibited the reduction in α-helix as well as the improvement of fluorescence intensity. Ultrasound power at 150 W could significantly increase protein hydrophobicity and reactive SH groups compared to the others (P < 0.05). The disappearance of specific peaks and lower endothermic peaks implied that the treated CAM became thermally instable. The microstructure of CAM revealed small and homogeneous sub-bunches treated by 100-150 W. Furthermore, the solubility and emulsion property of CAM was significantly increased at 150 W (P < 0.05). These results demonstrated that ultrasound treatment at the power of 100-150 W may be an appropriate range to modify CAM for enhancing its functional properties.

Synergistic antibacterial mechanism of the Lactobacillus crispatus surface layer protein and nisin on Staphylococcus saprophyticus

SlpB, a surface layer protein isolated from Lactobacillus crispatus, has the potential to enhance the antimicrobial activity of nisin. Previous research indicated that, when combined with nisin, SlpB acted synergistically to inhibit Staphylococcus saprophyticus growth, thus extending the shelf life of chicken meat. In order to understand how SlpB enhances the antibacterial activity of nisin, electron microscopy, confocal laser scanning microscopy, flow cytometry and transmembrane electrical potential analysis were used to study cell wall organization and cell membrane integrity. No remarkable bacteriolytic effects were observed, indicating that cell death could not be attributed to cell lysis, although SlpB caused dramatic modifications of cell wall, thereby altering cell shape. The combination of SlpB and nisin also induced the release of ATP or UV-absorbing materials, as well as sudden dissipation of the transmembrane electrical potential by compromising membrane integrity. Considering that SlpB led to structural disorganization of the cell wall, and nisin access is enhanced to form a stable pore, cell death is a predictable outcome. SlpB significantly enhanced the effect of nisin at half of the minimum inhibitory concentration, which resulted in cell death by destroying the cell wall and cell membrane, therefore providing a new, feasible approach in food preservation.

Class III bacteriocin Helveticin-M causes sublethal damage on target cells through impairment of cell wall and membrane

Helveticin-M, a novel Class III bacteriocin produced by Lactobacillus crispatus exhibited an antimicrobial activity against Staphylococcus aureus, S. saprophyticus, and Enterobacter cloacae. To understand how Helveticin-M injured target cells, Helveticin-M was cloned and heterologously expressed in Escherichia coli. Subsequently, the cell wall organization and cell membrane integrity of target cells were determined. The mechanism of cellular damage differed according to bacterial species. Based on morphology analysis, Helveticin-M disrupted the cell wall of Gram-positive bacteria and disorganized the outer membrane of Gram-negative bacteria, therefore, altering surface structure. Helveticin-M also disrupted the inner membrane, as confirmed by leakage of intracellular ATP from cells and depolarization of membrane potential of target bacteria. Based on cell population analysis, Helveticin-M treatment caused the increase of cell membrane permeability, but the cytosolic enzymes were not influenced, indicating that it was the sublethal injury. Therefore, the mode of Helveticin-M action is bacteriostatic rather than bactericidal.