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Clostridium perfringens is an important foodborne pathogen, which has caused serious public health problems worldwide.

To improve the quality of cooked and frozen crayfish after repeated freeze-thaw cycles, the effects of alginate oligosaccharide (1 %, w/v) with ultrasound-assisted (40 W, 3 min) soaking (AUS) on the physicochemical properties were investigated. The AUS samples improved water-holding capacity with 19.47 % higher than the untreated samples. Low-field nuclear magnetic resonance confirmed that mobile water (T

Chlorogenic acid (CA), an ester of caffeic acid, is a major phenolic compound in herbs. The antimicrobial activity of CA against Pseudomonas aeruginosa P1, a foodborne pathogen, was investigated in this study. To understand how CA injured target cells, the influence of CA on cell morphology was assessed. A sunken cell surface and detachment of outer membrane components in P. aeruginosa P1 were observed after being treated by CA. Following this, the intracellular membrane permeability and the content of lipopolysaccharide (LPS), a main component of outer membrane, were determined. The release of intracellular protein and ATP from P. aeruginosa P1 indicated that CA increased intracellular membrane permeability and resulted in the leakage of intracellular materials. The uptake of propidium iodide, a compromised cell membrane nucleic acid stain, further demonstrated that CA acted on the intracellular membrane. CA resulted in the decrease of LPS contents of P. aeruginosa P1, which supported the detachment of outer membrane. CA also downregulated the expression of major genes in LPS biosynthesis, suggesting that CA may inhibit intracellular metabolism of P. aeruginosa P1 cells. Thus, CA increased the intracellular membrane permeability, induced the exfoliation of outer membrane, and disturbed the intracellular metabolism. Damage of intracellular and outer membranes as well as disruption of cell metabolism resulted in cell death eventually. The finding suggested that CA has the potential to be developed as a preservative to control P. aeruginosa-associated foodborne diseases.

The properties, structure and water holding capacity of myosin were analyzed after incubated with myoglobin (Mb) hemin prosthetic group. The results revealed moderate oxidation of hemin prosthetic group could improve the solubility of myosin. Besides, it could stretch the protein structure and cross-link the molecules to form the soluble polymer. Hence, moderate oxidation could improve the gel properties and the gel network structure. However, excessive oxidation would greatly reduce the physical and chemical properties of myosin, which was not conducive to the gel formation and would lead to a decrease in water retention. Moreover, fluorescence spectroscopy and cyclic voltammetry (CV) proved hemin prosthetic group had a high affinity for myosin. The interaction mechanism was further studied by molecular docking and molecular dynamics (MD) simulations. This study provides some fundamental prospects to be applied in the functional regulation of meat protein.

The effects of combined application of ultra-high pressure (300 Mpa, 900 s) and carnosine on the inhibition of fishy off-odor from snakehead meat were investigated. Results showed that the combination effectively inhibited the formation of fishy volatile organic compounds (VOCs) and trimethylamine (TMA-N). Further studies demonstrated that the reduction of VOCs was mainly due to the inhibition of lipids oxidation based on the antioxidant activity of carnosine and the inactivation of lipoxygenase by UHP. Moreover, the reduction of TMA-N was mainly attributed to the ability of UHP processing to reduce bacterial load, which also extended the shelf-life of snakehead fillets by ∼ 6 days and retarded the production of TVB-N. Additionally, the combined application allowed a better retention of pH, color, and textural quality of the fillets compared with the control. Therefore, the current combination is a promising technique in fishy off-odor removing and better preservation of snakehead meat.

An efficient antibacterial nanoemulsion was prepared using zein and NaCas to encapsulate ginger essential oil (GEO). Physical, optical, and mechanical properties as well as the antibacterial activities of GEO nanoemulsion were investigated. At 1:1 mass ratio of zein/NaCas, the GEO nanoemulsion possessed the highest solubility, entrapment efficiency and stability. The GEO/zein/NaCas complex was confirmed by ultraviolet and fluorescence spectroscopy. The addition of GEO led to more amorphous structure formation and the secondary structure changes of zein/NaCas improved the solubility and stability of GEO. GEO nanoemulsion inactivated two common foodborne bacteria, namely, Staphylococcus aureus and Pseudomonas aeruginosa, by destroying the cell membrane. Meanwhile, the GEO nanoemulsion exhibited better preservation effects on chilled chicken breasts than non-emulsified GEO and could effectively prolong the shelf life of chicken breasts for 6 days. This research provides a green and low-cost method for preparing GEO nanoemulsion to control the risk of foodborne pathogens.

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.

The study evaluated the antibacterial activity of chlorogenic acid (CA) against Salmonella Enteritidis S1, a foodborne pathogen in chilled fresh chicken. Its minimum inhibitory concentration for S. Enteritidis S1 was 2 mM. 1 MIC CA treatment reduced the viable count of S. Enteritidis S1 by 3 log cfu/g in chilled fresh chicken. Scanning electron microscopy examination indicated that CA induced the cell envelope damage of S. Enteritidis S1. Following this, 1-N-Phenylnaphthylamine assay and LPS content analysis indicated that CA induced the permeability of outer membrane (OM). Confocal laser scanning microscopy examination further demonstrated that CA acted on the inner membrane (IM). To support this, the release of intracellular protein and ATP after CA treatment was also observed. CA also suppressed the activities of malate dehydrogenase and succinate dehydrogenase, two main metabolic enzymes in TCA cycle and electron transport chain. Thus, damage of intracelluar and outer membranes as well as disruption of cell metabolism resulted in cell death eventually. The finding suggested that CA has the potential to be developed as a preservative to control S. Enteritidis associated foodborne diseases.

This study aimed to evaluate the inhibitory activity of phenyllactic acid (PLA) against the biofilm formation of Enterococcus faecalis and to explore its potential molecular mechanism. The MIC value of PLA that inhibited the growth of E. faecalis R612-Z1 in BHI broth was 5 mg/mL. PLAs at subinhibitory concentrations of 1.25 and 2.50 mg/mL were found to inhibit biofilm formation by a crystal violet staining assay. The cell swimming and swarming motilities of E. faecalis were reduced in the presence of PLA. An apparent decrease in the thickness of PLA-treated biofilms was observed through confocal laser scanning microscopy analysis. The exopolysaccharide production in E. faecalis biofilms was inhibited by EPS quantification assay and scanning electron microscopy (SEM). qRT-PCR analyses showed that PLA down-regulated the transcription of Ebp pili genes (ebpABC) and Epa polysaccharide genes (epaABE). PLA inhibited the biofilm formation by interfering with cell mobility and EPS production of E. faecalis. In addition, PLA at concentrations of 10.0 mg/mL can effectively control the bacterial cells in a three-day-old mature biofilm of E. faecalis grown on 24-well flat-bottom polystyrene plates and stainless-steel surfaces. Thus, PLA is potentially an effective agent to control E. faecalis biofilms.

Objective The aim of this study was to investigate the expression of heat shock protein (HSP) 90, 70, and 60 in chicken muscles and their possible relationship with quality traits of meat. Methods The breast muscles from one hundred broiler chickens were analyzed for drip loss and other quality parameters, and the levels of heat shock protein (HSP) 90, 70, and 60 were determined by immunoblots. Results Based on the data, chicken breast muscles were segregated into low (drip loss≤5%), intermediate (5%0.05). Conclusion Results of this study suggests that higher levels of HSP90 and HSP60 may be advantageous for maintenance of cell function and reduction of water loss, and they could act as potential indicator for better water holding capacity of meat.

The detection of phospholipids oxidation is important for meat control and disease prevention. In this paper, a photoelectrochemical sensor based on printable mesoscopic chip (PMC) for fast and real-time monitoring phospholipids oxidation was designed and fabricated. TiO2, ZrO2 and carbon films of PMC were screen-printed onto the FTO glass layer by layer. The PMC and the feasibility for determination of phospholipids oxidation were investigated by scanning electron microscope (SEM), UV-vis spectroscopy, cyclic voltammograms (CVs) and electrochemical impedance spectroscopy (EIS), etc. The short circuit current (Jsc) was used as a signal current, which would decrease if phospholipids in PMC were undergoing oxidation for the change of electrical properties. Compared with other methods, phospholipids in PMC did not require pretreatment, and the process was nondestructive and real-time. Meanwhile, this method showed high sensitivity and good selectivity. The fabricating process of PMC is simple, and the costs are low, relatively.

Based on single factor experiments, NaCl concentration, adenosine 5'-monophosphate (AMP) concentration and temperature were selected as independent variables for a three-level Box-Behnken experimental design, and the shear force and cooking loss were response values for regression analysis. According to the statistical models, it showed that all independent variables had significant effects on shear force and cooking loss, and optimal values were at the NaCl concentration of 4.15%, AMP concentration of 22.27 mmol/L and temperature of 16.70°C, which was determined with three-dimensional response surface diagrams and contour plots. Under this condition, the observed shear force and cooking loss were 0.625 kg and 8.07%, respectively, exhibiting a good agreement with their predicted values, showing the good applicability and feasibility of response surface methodology (RSM) for improving pork tenderness. Compared with control pig muscles, AMP combined with NaCl treatment demonstrated significant effects on improvement of meat tenderness and reduction of cooking loss. Therefore, AMP could be regarded as an effective tenderization agent for pork.

BACKGROUND Adenosine 5′-monophosphate (AMP) is often used in meat and poultry soups as a flavor enhancer (flavor modifier), or as food additives for specific nutritional purposes. Our previous research as well as evidence from others showed that actomyosin could be dissociated into myosin and actin by AMP in extracted muscle solution. However, there is no report available on the application of AMP to dissociate actomyosin and to improve meat tenderness. The objectives of this study were to evaluate the effect of AMP on duck meat tenderness and other quality traits and to explore the mechanism of the action of AMP on meat tenderness. RESULTS Duck breast muscle was treated with 0, 10, 20, 30, 40 mmol L−1 AMP at 5 °C for 10 h and examined for shear force, microstructure, actomyosin dissociation, myofibril fragmentation index (MFI), pH, water content, cooking loss, CIE* color (L*, a*, b*), inosine monophosphate (IMP) and free amino acid (FAA) contents. Results showed that shear force, cooking loss, L* and b* of the muscles significantly decreased after AMP treatment (P 0.05), and muscle shrinkage in transverse and longitudinal directions were restrained after AMP treatment. CONCLUSION The results suggest that AMP could notably improve meat tenderness, and this effect was probably mainly through increasing muscle pH, promoting actomyosin dissociation and disrupting the Z-line; meanwhile, the conversion of AMP to IMP may contribute to the flavor of meat. © 2015 Society of Chemical Industry

The effect of NaCl stress (0 to 8%, wt/vol) on the growth and tyramine production in two Enterococcus faecalis strains was examined during culture time. The growth of E. faecalis was inhibited by the increase in NaCl concentration, but tyramine production was unaffected. Tyramine accumulated rapidly during the logarithmic phase of the strains, and the final tyramine levels were approximately 800 μg/ml. Relative gene expression of four genes in the tyrosine decarboxylase locus, namely, tyrRS, tyrDC, tyrP, and nhaC, was evaluated at different incubation times. The results showed that NaCl stress could upregulate the expression of tyrDC and tyrP to improve the tyramine production of a single E. faecalis strain under certain conditions, and TyrS could act as a negative regulator on the genetic regulation of the tyramine cluster.

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.

Pulley-free directly-connected hydraulic pumping unit lift technology, developed based on the characteristics of Jilin Oilfield, can be applied to produce cost-effectively the difficult-to-produce reserves, and to improve the low fluid production and reduce the high energy consumption of developed oilfields. Featuring low cost, low energy consumption and high efficiency with one unit serving several wells, this technology can meet the lift demand of different flow rate at different well depth. The hydraulic pumping system consists of three discrete units, namely main frame, hydraulic station and electric cabinet. The piston and sucker rod of the main frame are connected directly. When the system works, the pump of the hydraulic station provides power for the hydraulic cylinder of the main frame, which drives directly the reciprocating movements of the sucker rod to lift fluid via the reciprocating movements of the piston. The centerline of the main frame coincides with that of the casing, and so there is no unbalance loading. Substituting for the polish rod, the piston rod of the pumping unit connects directly with the sucker rod. The elimination of pulley, wire rope, rope hanger and packing box minimizes the wear parts of the system. Besides, when the system is in service, the main frame can be disassembled like tubing, having no impact on workover. The electric cabinet acquires signals via the displacement sensor and pressure sensor on the main frame and processes them, with such information as indicator diagram, stroke and stroke times displayed on the touch screen. The ground equipment in this technology has light weight, which is about 15% of a beam pumping unit of the same model. With this technology, long stroke, low stroke times, big pump size lift, reduced rod-casing wear, prolonged maintenance free period and improved operation efficiency can be realized. Compared with existing pumping units, its investment in equipment is less. The cost of a twin well system can be reduced by more than 30%, and the energy conservation at the same fluid production rate is above 25%. By December 2016, 24 wells of different depth in Jilin Oilfield had been subjected to pilot test successively. The "one driving one" hydraulic pumping units applied to two wells had operated stably for more than 700 days free of trouble, and the pumping efficiency had been improved by 35% compared with other types. The successful application of this system has verified its overall stability and its adaptability to the extremely cold environment in the northeast China. The "one driving two" hydraulic pumping units had been applied to 22 wells, and the test results show that both the process flow and the system are stable.

Rosin was once widely used for removal of duck feathers in China and is still being used secretly in some poultry processing enterprises. Abietic acid (AA) and dehydroabietic acid (DHAA) are the major compounds of rosin. In the present study, 90 duck samples were collected for investigation of AA and DHAA residues. Abietic acid and DHAA were simultaneously detected in 13 out 40 raw ducks, 8 out of 26 water-boiled salted ducks, and 7 out of 24 roasted ducks, respectively. In positive samples, averages of AA were significantly higher than those of DHAA in positive samples of the 3 types of ducks (P0.05). Averages of AA and DHAA in positive raw ducks were significantly higher than those in positive roasted ducks (P0.05). The results indicated that almost one-third of raw ducks were defeathered by means of rosin-containing defeathering agent, and cooking processes could reduce the AA and DHAA residues to some extent, but could not eliminate them completely.

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.

Phospholipid hydrolysis, as the main stage and cause of phopholipid degradation, is generally attributed to phospholipases. In this study, the changes of phospholipase A 2 (PLA 2 ) 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 2 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 PLA 2 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 2 and PLC contribute to the degradation of intramuscular phospholipids during the processing of dry-cured duck.

Abietic acid (AA) and dehydroabietic acid (DHAA) are major components of rosin, and both of them are well-recognized causes of skin allergy. Rosin was once widely used for removal of duck feathers in China. In the present study, an analytical method was developed for simultaneous determination of AA and DHAA in duck meats. AA and DHAA were extracted with acetonitrile and cleaned by solid-phase extraction, followed by chromatographic separation on C18 column with methanol/2 mM phosphoric acid (86/14, v/v) as mobile phase. AA was detected by photodiode array detection (PAD) at 240 nm, while DHAA was detected by fluorescence detection (FLD) with excitation and emission at 225 and 287 nm, respectively. Limits of quantification for AA and DHAA were 50 and 15 μg/kg, respectively. The method was applied to analysis of AA and DHAA residues in meats of rosin-defeathered ducks and commercial ducks. The results indicated that removal of duck feathers by means of rosin could lead to residues of AA and DHAA in duck skins, and 5 out of 32 commercial ducks were found to be contaminated by AA and DHAA, ranging from 1,556.1 to 9,638.7 μg/kg and 476.4 to 2,623.8 μg/kg, respectively. The proposed method could be used to identify those rosin-defeathered ducks and to monitor the illegal use of rosin in duck processing.

Dry-cured duck is a high quality meat product processed by the traditional dry-curing procedure. The objective of this paper was to study the physical-chemical parameters and microstructure of the duck muscle during the manufacturing process. Thirty six ducks were used in this study and samples were taken after dry salting, marinating, piling, and drying for 6 days and 12 days. The increase in NaCl, TBA, protein, fat, and shear force were observed whereas water, cooking loss, L*, a*, b* and myofiber diameter decreased during the whole process. It showed the quality parameters such as NaCl, TBA, shear force and water were strongly correlated and associated with the microstructural changes of the muscles.

A new hydrophilic interaction liquid chromatography (HILIC) method was developed for the determination of deoxynivalenol-3-glucoside (D3G) in cereals. D3G was extracted with water and cleaned with an immunoaffinity (IA) column, followed by chromatographic separation on a Syncronis HILIC column with acetonitrile-water (90:10, v/v) as the mobile phase, and detected at 220 nm by UV detection. The calibration curve was found to be linear in the range of 0.1–2.0 μg/ml. Limit of detection and limit of quantification were 8 and 25 μg/kg, respectively. The method was applied to the determination of D3G in 14 cereal samples, which were analyzed as well as by LC-MS/MS. The results indicate that the method can be considered as an alternative to LC-MS/MS and could be adopted by nonprofessional analytical labs.

The potential to produce biogenic amines was investigated with 15 Lactococcus lactis and 15 Enterococcus faecalis strains isolated from water-boiled salted duck. The production of biogenic amines from the isolated strains grown in de Man Rogosa Sharpe broth containing precursor amino acids was determined by thin-layer chromatography and high-performance liquid chromatography. None of the L. lactis strains produced any biogenic amines, whereas 12 strains of E. faecalis produced tyramine and b -phenylethylamine. PCR assays were used to detect the presence of tyrosine decarboxylase genes in all of the isolated strains. Only the 12 biogenic amine-producing Enterococcus strains had a 924-bp fragment characteristic for the tyrosine decarboxylase gene. The comparison of the amplified partial tyrDC gene sequences of the 12 positive Enterococcus strains revealed 99% similarity within the same species. The tyramine production of the sterilized water-boiled salted duck inoculated with E. faecalis R612Z1 increased significantly during storage. This study reveals that the isolated E. faecalis strains can produce tyramine and β-phenylethylamine in the medium; however, they can only produce tyramine in water-boiled salted duck.

The low control reserve of a single well and the difficult on energy supplement in the reservoir are two key problems in tight oil reservoir development. It is testified that non-liquid CO2 fracturing not only efficiently increases the reservoir energy but also intensifies the reservoir transformation through the field test in Jinlin oil field. The transformation volume of non-liquid CO2 fracturing is confirmed, through micro-seismic data monitor in the borehole during fracturing, that it is 2.5 times of that of normal hydraulic fracturing with the same liquid volume usage, which can remarkably increase the complexity of the fracture. Through the laboratory experiments and the oil sampling analysis after fracturing, CO2 is verified that it can reduce the oil viscosity efficiently, therefore, it can make oil miscible and enhance the flooding efficiency by non-liquid fracturing implementation. The results of reservoir static pressure test after fracturing prove that reservoir pressure remarkably increases compared with that before fracturing and has the effects of advanced energy storage. Five tight oil wells fracturing have been successful in Jilin oil field until now. Oil production after fracturing increases obviously compared with that before fracturing. The average oil production increase per well is 2.31 ton. According to the research, the stimulation effects of non-liquid CO2 fracturing are seriously underestimated and there is wide prospect in the application of the technique during the tight oil reservoir development.

The spoilage microbiota in water-boiled salted duck during storage at 4 degrees C was determined using culture-dependent and independent methods. Analysis of the denaturing gradient gel electrophoresis (DGGE) patterns of PCR amplicons targeting the V3 region of the 16S rDNA and sequencing of the bands allowed profiling of the microbiota present in the duck. Community DNA extracts were prepared directly from water-boiled salted duck and from culturable bacterial fractions harvested from both MRS and PCA media. The spoilage bacteria mainly consisted of Staphylococcus saprophyticus, Macrococcus caseolyticus, Weissella, Halomonas sp. or Cobetia sp., and Exiguobacterium sp. based on sequencing and homology search of the DGGE bands. It appeared that both the bacterial counts and diversity increased during storage time. By plating method, bacterial counts in MRS agar increased from 10(4) to 10(8) CFU/g from day 1 to 10, while total bacterial counts in PCA agar reached 10(9) CFU/g after 10 d. Total of 14 strains isolated from PCA and MRS agar were identified as M. caseolyticus (2), S. saprophyticus (7), S. sciuri (1), W. paramesenteroides (2), and W. confusa (2) by 16S rDNA sequencing. The identification of the spoilage-related microbiota is helpful to better understand the bacteria ecology in water-boiled salted duck and may lead to the discovery of appropriate preservation strategies.

Water-cooked salted ducks were tray-packaged and stored under refrigeration (4±1°C) in order to evaluate the quality changes during storage. pH, total volatile basic nitrogen (TVB-N), sensory and microbiological analysis were determined at 0, 2, 4, 6, 8, 9 and 10 days of storage. pH value and TVB-N (mg N/100 g) varied from 6.47±0.16 to 6.69±0.10 and from 5.90±0.93 to 13.42±2.46, respectively. Sensory results indicated that ducks were unacceptable at the 10th day of storage. The predominant spoilage bacteria at the end of the shelf-life were Brochothrix thermosphacta, lactic acid bacteria (LAB) and minor components were Enterobacteriaceae, members of Micrococci, yeasts and moulds. Pseudomonads were also detected. Both total bacteria and the various spoilage ones, overall, increased from the initial sampling to the final day.

Composition of intramuscular lipids, phospholipid classes and phospholipid molecular species in traditional Chinese duck meat products was investigated. Free fatty acids and phospholipids were identified and quantified by gas and high performance liquid chromatography, and phospholipid molecular species were determined by mass spectrometry. The results showed that raw duck meat had high quantities of phosphatidylethanolamine and phosphatidylcholine. The percentages of phospholipid classes decreased during three kinds of processing of duck meat products. A selective degradation of phospholipid molecular species with polyunsaturated fatty acids was found in dry-cured duck, but was not found in roasted and water-boiled duck 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.

In this study, intramuscular phospholipid classes and molecular species in Gaoyou duck meat were determined. Classes of phospholipids were identified and quantified by normal phase HPLC combined with UV and evaporative light scattering detectors (ELSD). The main phospholipid classes (phosphatidylcholine and phosphatidylethanolamine) were prepared on a semi-preparative silica gel column by HPLC. Reverse phase HPLC was coupled in parallel with both an ELSD and a mass spectrometry in order to characterise molecular species of phosphatidylcholine (PC) and phosphatidylethanolamine (PE). The results showed that Gaoyou duck meat had high quantities of PC and PE (64.66% and 28.10% of total phospholipids, respectively). Arachidonic acid was mainly present in PE and formed molecular species containing a saturated fatty acid, such as stearic or myristic acid; however, oleic acid together with palmitic or stearic acid formed the main molecular species in PC. The content of the molecular species with polyunsaturated fatty acids in PE accounted for 98.33%, while that in PC only 46.20%.

This study evaluated the antibacterial effect of the combination of e-polylysine (e-PL) and nisin against Enterococcus faecalis strains. The combination of e-PL and nisin showed synergistic antibacterial activity against three Enterococcus strains. Scanning electron microscopy and a membrane permeability assay revealed that the combined treatment with e-PL and nisin synergistically damaged the cell morphology of E. faecalis strain R612Z1 cells. Both e-PL and nisin can dissipate the transmembrane electric potential of E. faecalis R612Z1 cells, but these peptides did not affect the transmembrane pH gradient. The combination of e-PL and nisin can produce a high reactive oxygen species level in E. faecalis R612Z1 cells. The results indicated that the uptake of e-PL into cells was promoted through nisin and that the combination of e-PL and nisin could produce a high reactive oxygen species level in E. faecalis R612Z1 cells, leading to cell growth inhibition.

Adenosine 5'-monophosphate (AMP) is often used in meat and poultry soups as a flavor enhancer (flavor modifier), or as food additives for specific nutritional purposes. Our previous research as well as evidence from others showed that actomyosin could be dissociated into myosin and actin by AMP in extracted muscle solution. However, there is no report available on the application of AMP to dissociate actomyosin and to improve meat tenderness. The objectives of this study were to evaluate the effect of AMP on duck meat tenderness and other quality traits and to explore the mechanism of the action of AMP on meat tenderness.Duck breast muscle was treated with 0, 10, 20, 30, 40 mmol L(-1) AMP at 5 °C for 10 h and examined for shear force, microstructure, actomyosin dissociation, myofibril fragmentation index (MFI), pH, water content, cooking loss, CIE* color (L*, a*, b*), inosine monophosphate (IMP) and free amino acid (FAA) contents. Results showed that shear force, cooking loss, L* and b* of the muscles significantly decreased after AMP treatment (P0.05); actomyosin dissociation, MFI, pH, water content, fiber diameter, sarcomere length, IMP and ammonia significantly increased (P0.05); no significant change in a* or other FAA content was observed (P0.05), and muscle shrinkage in transverse and longitudinal directions were restrained after AMP treatment.The results suggest that AMP could notably improve meat tenderness, and this effect was probably mainly through increasing muscle pH, promoting actomyosin dissociation and disrupting the Z-line; meanwhile, the conversion of AMP to IMP may contribute to the flavor of meat.

Based on single factor experiments, NaCl concentration, adenosine 5'-monophosphate (AMP) concentration and temperature were selected as independent variables for a three-level Box-Behnken experimental design, and the shear force and cooking loss were response values for regression analysis. According to the statistical models, it showed that all independent variables had significant effects on shear force and cooking loss, and optimal values were at the NaCl concentration of 4.15%, AMP concentration of 22.27 mmol/L and temperature of 16.70°C, which was determined with three-dimensional response surface diagrams and contour plots. Under this condition, the observed shear force and cooking loss were 0.625 kg and 8.07%, respectively, exhibiting a good agreement with their predicted values, showing the good applicability and feasibility of response surface methodology (RSM) for improving pork tenderness. Compared with control pig muscles, AMP combined with NaCl treatment demonstrated significant effects on improvement of meat tenderness and reduction of cooking loss. Therefore, AMP could be regarded as an effective tenderization agent for pork.

Tyramine production by Enterococcus faecalis R612Z1 in water-boiled salted ducks was evaluated during storage at different temperatures. The results showed that E. faecalis R612Z1 could produce tyramine in meat samples when the storage temperature was no less than 4°C. The E. faecalis R612Z1 counts of the meat samples reached 10(8) CFU/g on day 7 at 4°C and on day 4 at 10°C. However, the tyramine content of the meat samples stored at 10°C increased to 23.73 μg/g (on day 10), which was greater than the level in the samples stored at 4°C (7.56 μg/g). Reverse transcription quantitative PCR detection of the expression level of the tyrDC gene in E. faecalis R612Z1 in the meat samples revealed no significant changes at different storage temperatures. Thus, the changes in tyramine production of E. faecalis R612Z1 may be due to the different enzymatic activities at different storage temperatures.