Changes of microflora in high pressure treated Indian white prawn (Fenneropenaeus indicus)

ABSTRACT

This study was to investigate the piezotolerance and diversity indices of microflora of Indian white prawn (Fenneropenaeus indicus) after high pressure (HP)-treatment. Indian white prawns subjected to HP-treatments and its effect was studied up to species level and compared with unpressurized samples. The bacterium was identified by using bacterial identification schemes, biochemical tests and API kits (bioMérieux, Marcyl’Etoile, France). Diversity analysis was performed using PRIMER (Plymouth Routines in Multivariate Research) software v 5.2.2. The significant elimination of microflora was found to be proportional with the pressure level. In the case of spore formers, mere destruction was noticed after HP-treatment. Arthrobacter spp., Listeria grayi and Corynebacterium spp. were the most piezotolerant bacteria in HP-treated samples. Diversity indices revealed a significant reduction of microflora of Indian white prawn. The apparent reduction of microflora with pressure level was clearly evident from the diversity indices; moreover a diminished piezotolerance of Gram negative spoilage bacteria was also observed.     

Clarification of the recovery mechanism of Escherichia coli after hydrostatic pressure treatment

High hydrostatic pressure (HP) technology has gained more attention as a non-thermal food pasteurization technology. Recently, a limitation of the HP technology was reported by Koseki and Yamamoto [Recovery of Escherichia coli ATCC 25922 in phosphate buffered saline after treatment with high hydrostatic pressure. Int. J. Food Microbiol. 2006;110:108–111], who completely recovered Escherichia coli species after HP treatment. We investigated the recovery mechanism of E. coli after HP treatment. The cells were treated with 200–300 MPa at 0–25°C for 24 h. The HP-treated E. coli was recovered in phosphate-buffered saline (PBS) during 120 h of incubation at 25°C, confirming the results reported by them. However, E. coli did not grow in PBS but grew with inactivated cells in PBS. In addition, the results of our “population size experiments” demonstrated that the recovery of E. coli cells depended on both the degree of pressure and the population size. These results suggest that some portion of cells recovered from the damage and then grew by using inactivated cells.     

Effect of high pressure processing on textural and microbiological quality of pink perch (Nemipterus japonicus) sausage during chilled storage

The non-thermal high pressure (HP) processing was studied on fish sausage to enhance the quality during chilled storage. Pink perch (Nemipterus japonicus) sausages, packed in poly amide casing under vacuum were subjected to 400, 500 and 600?MPa pressures (dwell time: 10?min and ramp rate: 300?MPa/min) and compared with heat-set samples for physico-chemical and microbial quality parameters. Pressurized samples formed softer and glossier gels with a slight reduction in water-holding capacity. HP made the texture of sausage softer, cohesive and less chewy and gummier than heat-treated ones. Folding test seen higher acceptance values in samples treated at 500 and 600?MPa, during storage. Maximum log reduction in microbial count was observed in 600?MPa immediately, and significant difference in cooked and pressurized sausages was seen only up to 7th day. This revealed the potential application of HP in replacing conventional heat treatment for sausages preparation with enhanced shelf-life.     

Refrigerated shelf-life evaluation of high pressure processed,raw and sous vide cooked lobster

ABSTRACT

High pressure processing (HPP) and sous vide may increase the shelf-life of high value seafood products without the use of additives. This study investigated the effects of 150MPa or 350MPa for 10min on microbial, sensory, and physicochemical qualities of raw and subsequently sous vide cooked (65°C) lobster tails during 28 days of refrigerated storage. Raw lobster pressurized at 350MPa or sous vide cooked maintained significantly lower microbial counts, total volatile base nitrogen, and biogenic amine levels. Due to off-odors, 90% and 60% of sensory respondents rejected the control and 150MPa raw samples, respectively, by day 7, while 70% rated the 350MPa samples as still acceptable on day 28. For cooked lobster, only 20% of the respondents rejected any samples by day 28. Moderate HPP conditions were effective in extending refrigerated shelf-life of vacuum-packaged raw lobster tails. However, HPP pretreatment did not contribute to additional shelf-life extension for sous vide cooked products.     

Effect of high hydrostatic pressure and reducing sodium chloride and phosphate on physicochemical properties of beef gels

ABSTRACT

The effect of high hydrostatic pressure (HHP) treatment (100–200?MPa, 10?min, 20°C) combined with sodium chloride and sodium phosphate on the physicochemical properties of beef gels was investigated. The water content, cooking losses, color, protein composition by SDS-PAGE analysis and texture parameters of beef gels were determined. The beef gels treated with high pressure at 150?MPa showed a synergistic effect in the increased water content and the decreased cooking losses compared with the unpressurized gels. The L*, a* and b* color values of beef gels were slightly decreased under HHP treatment at 100–200?MPa. In the SDS-PAGE analysis, the staining intensity of the α-actinin protein band was decreased in pressurized samples. The cohesiveness, adhesiveness, gel strength and modulus of elasticity were improved after HHP treatment. Application of high pressure treatment (150–200?MPa) before heat treatment would be beneficial for the manufacturing of low salt and/or low phosphate meat products for a healthy diet.     

Studies upon Qualification of Meat from Animals Irradiated and Contaminated with Radiocaesium

Abstract

The problem concerning qualification of food originated from animals irradiated and contaminated with ¹³⁷caesium appeared especially after the Chernobyl accident. So, it was a reason to undertake respective studies on 108 rabbits divided into three groups: group I – non-irradiated rabbits, group II – irradiated with a dose of 103 mCkg^?1 (400 R), group III – irradiated with a dose of 206 mCkg^?1 (800 R). All animals were contaminated intragastrically with an aqueous solution of ¹³⁷CsCl. After slaughter samples of the muscles were cured in 1, 3, 5, 10, and 15% brine or were cooked for 2 hrs. In the case of curing the radioactivities of meat and brine, and the concentrations of salt in cured meat were estimated after 7, 14, and 21 days. The radioactivities of cooked meat, broth, and condensed water vapour were estimated after 1 and 2 hrs. Taking into account the decrease of the radioactivities, duration of curing, and concentrations of salt in cured meat the optimum results were achieved when the meat from non-irradiated rabbits was cured for 7 days in 3% brine, and that of irradiated rabbits in 5% brine with regard to a lower stability of this meat. The decontamination effectiveness of cooking was similar in all examined rabbits. Radiocaesium penetrates into the brine or broth and escapes with water vapour thereafter.     

Deactivation of Escherichia coli with different volumes in drinking water using cold atmospheric plasma

This experimental study aimed to evaluate the potential of cold atmospheric plasma jet to deactivate Escherichia coli from drinking water. We studied the effect of the volume of water samples on the performance of plasma jet on deactivation of E. coli of 1, 500, 1,000, 1,500, and 2,000 cubic centimetres. The results of deactivation of E. coli in 500 and 1,000 cc water samples were the same as one cc of a water sample and we observed 8-log reduction of E. coli using 50 W. In 1,500 and 2,000 cc water samples at 8 min using a power of 50 W, 4.5 and 2.9 log reduction of E. coli was achieved and while we used 20 W, 2.5 and 1.8 log reduction of E. coli bacteria was performed. This indicated that the increasing volume of water above 1,500 cc caused the reduction of the efficiency of E. coli removal. Also, increasing power caused to increase E. coli removal efficiency. In addition, we monitored changes in pH values and temperature during experiments. Using 20 W, the temperature was increased (natural temperature of the water was 22 °C) 2 °C after 8 min while applying 50 W, the temperatures were raised 5 °C. pH of the water after 8 min in the 1,000 cc water sample, with an input power of 20 W, decreased from 7.1 to 5.5; while the input power was 50 W, pH changed from 7.1 to 4.3. With an increase in plasma irradiation time, the number of E. coli had a significant decrease per min while using in samples of 1 cc. After 8 min, we observed 4-log reductions of E. coli with the input power of 20 W and 8-log reduction of bacteria with the input power of 50 W. In 1,500 and 2,000 cc of water samples using plasma radiation for 8 min, 2.5 log and 1.8 log reduction of E. coli was achieved, respectively. This means that an increasing volume of water above 1,500 cc needs more power and time to deactivate E. coli from the water.     

Applications of High-Hydrostatic Pressure on Milk and Dairy Products

Interest in high-pressure (HP) applications on milk and dairy products has recently increased. Pressures between 300 and 600 MPa has been shown to be an effective method to inactivate microorganisms including most infectious food-borne pathogens. In addition to microbial destruction, it has been reported that HP improves rennet or acid coagulation of milk without detrimental effects on important quality characteristics, such as taste, flavour, vitamins, and nutrients. These characteristics offer to dairy industry numerous practical applications to produce microbial safety, minimally processed dairy products with improved performances, and to develop novel dairy products of high nutritional and sensory quality, novel texture and increased shelf life.     

Effects of High Pressure Treatment on the Microbiological Quality,Texture and Colour of Vacuum Packed Pork Meat Products

The aim of the study was to define usefulness of high pressure treatment for inactivation of microorganisms and prolongation of shelf life of two types of cooked pork ham and raw smoked pork loin. The samples of ham and loin in the presentation of standard 200 g pieces were vacuum packed in polylayer polyethylene bags and exposed to high pressure treatment in the range of 300-600 MPa and time of exposure of 10-30 minutes. Results indicate that 300 MPa and 400 MPa pressure applied for 10 minutes was insufficient for prolongation of storage period of ham. Pressure of 500 MPa, applied for 10 minutes caused significant decrease of microbiological parameters studied such as: total bacterial count, psychrophylic bacteria, acidophylic bacteria and enterococci in investigated samples, stored in refrigarator conditions for 4 weeks. Pressure of 600 MPa applied for 10 minutes reduced the number of all investigated microorganisms by 10 5 -10 6 fold. Application of this pressure prolonged storage period of traditionally produced ham to 6-8 weeks. Physico-chemical characteristics of ham, measured 24 h after high pressure treatment and after 4, 6 and 8 weeks of storage, did not change when compared to the initial samples. High pressure treatment caused increase in the colour lightness parameters only in pork smoked loin.     

Effect of initial texture on texture evolution in cold-rolled AA 5182 aluminium alloy

AA 5182 aluminium alloy with a strong cube texture was cold rolled to different reductions along the following directions: firstly, the original rolling direction; secondly, at angles of 22.5 and 45° to the original rolling direction. The evolution of texture in the cold-rolled samples with different initial textures was then investigated by X-ray diffraction. The texture evolution was quantified by mathematical formulae of texture volume fractions and rolling true strain. The results show that initial texture has a strong influence on the evolution of rolling texture. AA 5182 aluminium alloy with an initial rotated-cube (r-cube) (45° normal direction r-cube) texture exhibits the fastest rate of formation of the β fibre. The rate of formation of the β fibre decreases as the initial texture changes from the r-cube texture to the cube texture. The relationship between the rate of formation of the β fibre (k _β value in the mathematical formula for the volume fraction of the β fibre) and the initial texture (M _cube and M _r-cube: the volume fractions of the cube and r-cube components respectively) can be expressed as k _β ?=?0.37???0.03(M _cube /5.41???M _r???cube /5.64).     

Size effects and magnetoelastic couplings: a link between Hall–Petch behaviour and coercive field in soft ferromagnetic metals

Size effects regarding Hall–Petch (HP) relation are studied in this work for cobalt, nickel and Fe–3wt.%Si (FeSi), from polycrystalline to multicrystalline states. The materials show a breakdown in HP plot for thickness (t) to grain size (d) ratio less than a critical value. This appears in the beginning of plasticity for cobalt and FeSi whereas a plastic strain threshold must be overcome for nickel. Measurements of the coercive field on strained samples are able to depict such modification for low t/d ratio. Values of the coercive field in the polycrystalline domain allow an estimation of the magnetocrystalline anisotropy energy, related to the grain volume fraction concerned by reversal mechanisms for magnetic domains. Multicrystalline samples of cobalt and FeSi becomes magnetically softer at the yield stress. This is linked to a delay of the maximum intergranular stress towards higher strains for FeSi. For cobalt, non-linear elasticity and strong basal texture modify the magnetoelastic effects in coarse grain samples. For nickel, size effect on the coercive field appears after a few per cent of plastic strain as for HP relationship. A mean internal stress can be captured by magnetic measurements on polycrystals, related to the intragranular part of the kinematic stress. The softening of the magnetic properties for strained nickel multicrystals is due to a competition between the apparition of dislocation cells, which increases the coercive field by mechanisms of magnetic domain wall pinning, and surface softening of multicrystals, which tends to decrease the value of H_c.     

Using fluorescence measurement of zinc ions liberated from ZnS nanoparticle labels in bioassay for <Emphasis Type="Italic">Escherichia coli</Emphasis> O157:H7

In this study, an alternative approach using ZnS nanoparticle biolabels as fluorescence signal transducers is reported for the immunoassay of E. coli O157:H7 in tap water samples. Instead of measuring the fluorescence of ZnS nanoparticles in the assay, the fluorescence signal is generated through the binding of zinc ions released from nanoparticle labels with zinc-ion sensitive fluorescence indicator Fluozin-3. In the assay, ZnS nanoparticles around 50 nm in diameter were synthesized, bioconjugated, and applied for the detection of E. coli O157:H7. The assay shows a detection range over two orders of magnitude and a detection limit around 1000 colony-forming units (cfu) of E. coli O157:H7.     

Effect of pH and high pressure at sub-zero temperature on the viability of some bacteria

The objective of this study was to investigate the viability of Escherichia coli and Staphylococcus aureus in apple juice after treatment with high pressure at sub-zero temperature and during subsequent storage at 5 and 20 °C. The viability of E. coli and S. aureus cells suspended in the apple juice with a pH of 3.8 did not decrease considerably after pressure treatment at 193 MPa and?20 °C. However, viability losses occurred during storage of samples after pressure treatment. Living cells of both strains were not detected in pressurized samples of apple juice stored for 10 days at 20°C. The lethal effect was lower when the samples after pressure treatment were incubated at refrigerated temperature; the number of E. coli and S. aureus decreased by 6 log cycles when the juice was stored for 10 days at 5 °C.     

Proton resonance imaging and relaxation in raw and cooked hen eggs

In-vivo proton magnetic resonance imaging and relaxation time measurements were carried out on raw and cooked eggs. The relaxation time measurements revealed several interesting results. While there was very little change in the T₁ values between the raw and cooked egg white, the T₂ values followed the decreasing trend expected of water becoming bound. However, both the CH₂ and CH₃ moieties of the yolk lipids registered a statistically significant increase in their relaxation times. The T₂ of the CH₂ group, in particular, increased by 113% in the cooked egg. No striking changes, however, were observed between the proton images of the raw and cooked eggs.     

Effect of high pressure treatment on the characteristics of a model emulsion

The aim of this study was to investigate the use of HP (high pressure) technology as a possible alternative method for decontamination of non-food medium. HP (500?MPa) did not modify significantly the physicochemical characteristics of a model non-food emulsion. A 10?min HP treatment inactivated totally Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Aspergillus niger and Candida albicans even if all the five microorganisms were inoculated together, regardless of the initial load. No recovery was observed until six months of storage at 25°C.     

Chitosan Nanoparticles: Preparation and Application in Antibacterial Paper

Chitosan nanoparticles (CSNP) were obtained by H₂O₂ degradation of chitosan. Their morphology and size were determined by atomic force microscope (AFM), and the particles were found smooth and approximately 36 nm in size. CSNP-0.5% HAc solutions (1, 2, 5, and 10 mg/mL) were used in antibacterial paper by addition in pulp, impregnation, dispersion coating on the handsheets, and insufflation. The antibacterial activity of CSNP against Escherichia coli and Staphylococcus aureus was measured by the inhibition zone and bacterial reduction methods. Results showed that the antibacterial activity of CSNP was improved with the increase in concentration. For E. coli, at a CSNP concentration of 5 mg/mL, the antibacterial rate reached approximately 95%. However, for S. aureus, the antibacterial rate only reached 81%. In addition, the antibacterial activity of the antibacterial paper was determined by inhibition zone method. The paper prepared by insufflation had the greatest activity. For E. coli, at a CSNP concentration of 10 mg/mL, the inhibition zone reached 8.0 mm. For S. aureus, the inhibition zone was 6.8 mm.     

On the nature and the practical relevance of the molecular modifications induced in wheat proteins by high pressure treatment

Abstract

Modifications induced by the combined application of pressure (up to 800 MPa) and temperature (up to 80° C) were studied on wet and dry semolina, and on fresh pasta as such and after cooking. Rheological and immunochemical properties of the treated products were investigated, along with parameters indicating the extent of protein denaturation. No modification occurs in semolina treated at less than 45% water, below 60°C/800MPa for 10min. Egg noodles prepared from pressure/heat treated semolina had increased protein digestibility and low recognition by anti-gliadin antibodies either before or after cooking. The same effects were observed in heat/pressure treated pasta, but were lost upon subsequent cooking, although we found decreased immunochemical reactivity after heat/pressure treatment of cooked pasta. No sensory difference was found between cooked and pressure-treated semolina products.     

Theory and computer simulation of tweed texture

Abstract

An analytical theory of the ordering interaction J(R _ij ) in structural phase transitions mediated by elastic relaxation in the material is outlined. The ordering process in cell i sets up a local stress field due to the sizes, shapes or displacements of atoms or atomic groups, which is propagated elastically to a distant cell j. The atomistic theory for ferro- and antiferro-elastic transitions takes into account two types of singularity, one due to elastic anisotropy and the other to the Zener interaction J _z of infinite range in ferroelastic transitions. The form of J _k in Fourier space is highly anisotropic with a few “soft” directions coinciding with the orientation of twin boundaries. The asymptoptic J(R) at large R is shown to be very anisotropic as well and decays as R ^?3 in ferroelastic and R ^?5 in antiferroelastic systems.

Computer simulations for a three-dimensional model of about 29,000 particles show a strong tendency to form tweed texture, as observed experimentally. Well above the structural phase transition temperature, the strain fluctuations show well-developed embryos of the tweed texture. On quenching to below the transition temperature, a pronounced micro-twinning appears which follows almost exactly the shape of the embryos and then develops towards a stripe texture. After a certain time needle-shaped domains are formed and a peculiar step-wise process of generating new stripes is observed.     

Novel ocotillol-derived lactone derivatives: design,synthesis, bioactive evaluation,SARs and preliminary antibacterial mechanism

A new series of ocotillol-derived lactone derivatives were designed and synthesized to consider their antibacterial activity, structure–activity relationships (SARs), antibacterial mechanism and in vivo antibacterial efficacy. Compound 6d, which exhibited broad antibacterial spectrum, was found to be the most active with minimum inhibitory concentrations (MICs) of 1–2 μg/mL against Gram-positive bacteria and 8–16 μg/mL against Gram-negative bacteria. The subsequent synergistic antibacterial tests displayed that 6d had the ability to improve the susceptibility of MRSA USA300, B. subtilis 168, and E. coli DH5α to kanamycin and chloramphenicol. This active molecule 6d also induced bacterial resistance more slowly than norfloxacin and kanamycin. Furthermore, compound 6d was membrane active and low toxic against mammalian cells, and it could rapidly inhibit the growth of MRSA and E. coli and did not obviously trigger bacterial resistance. Compound 6d also displayed strong in vivo antibacterial activity against S. aureus RN4220 in murine corneal infection models. Additionally, absorption, distribution, metabolism, and excretion properties of this type of compounds have shown drug-likeness with good oral absorption and moderate blood–brain barrier permeability. The obtained results demonstrated that ocotillol-derived compounds are a promising class of antibacterial agents worthy of further study.

Graphic abstract

     

The Use of DRAQ5 to Monitor Intracellular DNA in <Emphasis Type="Italic">Escherichia coli</Emphasis> by Flow Cytometry

Flow cytometry provides a rapid and high-content multiparameter analysis of individual microorganisms within a population. In the past years, several fluorescent stains were developed in order to monitor DNA content distribution and cell-cycle phases, mainly in eukaryotic cells. Recently, due to its low detection limits, several of these fluorescent stains were also applied to prokaryotic cells. In this study, the ability of a novel far-red fluorescent stain DRAQ5 in assessing intracellular DNA content distribution in Escherichia coli DH5α was evaluated. The results showed that a DRAQ5-labelled live E. coli suspension can be obtained by incubation of 1 × 10⁶ cells/mL with 5 μM DRAQ5 in PBS buffer supplemented with EDTA (pH = 7.4) during 30 min at 37 °C. Flow cytometric analysis of fixed E. coli cells revealed that ethanol should be used in detriment of glutaraldehyde for DRAQ5 labelling. After the analysis of RNase and DNase digested samples, DRAQ5 was proven to be a specific DNA labelling stain. The present study demonstrates that the use of DRAQ5 as a DNA-labelling stain provides an easy assessment of intracellular DNA content and cell-cycle phases in Gram-negative bacteria such as E. coli.