Antimicrobial activity of reuterin in combination with nisin against food-borne pathogens

Antimicrobial activity of reuterin individually or in combination with nisin against different food-borne Gram-positive and Gram-negative pathogens in milk was investigated. Reuterin (8 AU/ml) exhibited bacteriostatic activity against Listeria monocytogenes, whereas its activity was slightly bactericidal against Staphylococcus aureus at 37 degrees C. Higher bactericidal activity was detected against Escherichia coli O157:H7, Salmonella choleraesuis subsp. choleraesuis, Yersinia enterocolitica, Aeromonas hydrophila subsp. hydrophila and Campylobacter jejuni. A significant synergistic effect on L. monocytogenes and a slight additive effect on S. aureus after 24 h at 37 degrees C were observed when reuterin was combined with nisin (100 IU/ml). The combination of reuterin with nisin did not enhance the antimicrobial effect of reuterin against Gram-negative pathogens.     

Different enrichment procedures for recovery of Listeria monocytogenes from raw chicken samples can affect the results of detection (by chromogenic plating or real-time PCR) and lineage or strain identification

This study aimed to evaluate the effect of different enrichment procedures on the detection of Listeria monocytogenes in food, by a comparison of subculture onto chromogenic agar with real-time PCR. Two different culture media, the primary and secondary enrichment broths of the U.S. Food Safety and Inspection Service (FSIS) method used for PCR detection of L. monocytogenes, were compared for the primary enrichment of retail ground chicken samples. L. monocytogenes was detected after the completion of each enrichment procedure in 63% (complete FSIS procedure) and 60% (plain FSIS secondary enrichment broth incubated for 48 h) of the samples by both culture and PCR, whereas a combination of the results for the two enrichment procedures revealed 86% of the samples to be positive. Most of the samples analyzed contained a mixture of lineage I and II strains, and their ratio varied for each enrichment procedure. This mixture could have a significant effect on the result of detection of L. monocytogenes for each individual sample, explaining the increase in positive samples when the results of the two enrichment procedures were combined. The use of different isolation procedures can affect the specific samples identified as positive and the specific strains isolated.     

RCS1, a gene involved in controlling cell size in Saccharomyces cerevisiae

Cloning and sequencing of RCS1, Saccharomyces cerevisiae gene whose product seems to be involved in timing the budding event of the cell cycle, is described. A haploid strain in which the 3'-terminal region of the chromosomal copy of the gene has been disrupted produces cells that are, on average, twice the size of cells of the parental strain. The critical size for budding in the mutant is similarly increased, and the disruption mutation is dominant in a diploid heterozygous for the RCS1 gene. Spores from this diploid have a reduced ability to germinate, the effect being more pronounced in the spores carrying the disrupted copy of RCS1. However, disrupted cells recover from alpha-factor treatment equally as well as wild-type cells.     

Detection of bovine DNA in raw and heat-processed foodstuffs, commercial foods and specific risk materials by a novel specific polymerase chain reaction method

The identification of beef in animal foods is a major concern not only for the prevention of commercial fraud, but also to avoid safety risks deriving from the presence of prohibited bovine material that might be harmful to both human and animal health. Here we report a novel set of bovine-specific primers, CYTbos1 (forward) and CYTbos2 (reverse), which allow the specific amplification of a 115 base pair fragment of the bovine cytochrome b gene (cytb) between nt 844 (mitochondrial site 15,590) and nt 958 (mitochondrial site 15,704), no cross-reaction being observed with DNA from another 12 frequent commercial meat species. The polymerase chain reaction product obtained is cleaved specifically by endonucleases ScaI and TspE1 to achieve further confirmation evidence. The sensitivity of the proposed method was 0.025%. The CYTbos primers successfully detected bovine DNA in meat samples processed for 20 min at 133 °C/300 kPa or for 2 h at 121 °C. CYTbos primers also detected bovine DNA in heat-processed commercial meat products exhibiting a complex nature, as well as in bovine specific risk materials. The proposed polymerase chain reaction method, aimed at detecting a small and specific fragment of the bovine mitochondrial DNA, may be especially useful for the direct identification of bovine DNA in foodstuffs subjected to severe heating under overpressure conditions.     

Effect of phytic acid degradation by soaking and exogenous phytase on the bioavailability of magnesium and zinc from Pisum sativum, L.

The effect of dephytinization of Pisum sativum, L. flour on the bioavailability of Mg and Zn was evaluated in growing rats. Processing of legume flours under optimal conditions for phytase activity (pH 5.5, 37 °C, 60 min) and subsequent removal of the soaking solution led to a 42 and 61% reduction in the content of Mg and Zn, respectively. Treatment with phytase led to an additional reduction in the concentration of the above-mentioned seed flour components, compared to the raw pea flour (69% and 74% for Mg and Zn, respectively). The considerable reduction in the content of inositol phosphates with high degree of phosphorylation attained under both processing conditions did not affect the digestive utilization of Mg, whereas the metabolic utilization of this mineral increased significantly. The digestive and metabolic utilization of Zn increased significantly in response to both processes assayed, reaching the highest values in the experimental group that was fed the phytase-treated pea flour diet. The amount of Mg retained by the experimental animals was reflected in the content of this mineral in the different tissues studied (femur, sternum, kidney, and heart), whereas no correlation was found in the case of Zn.     

Indigestible fraction and starch availability in peas measured in vitro

 Profiles of flavonoid compounds of Apis mellifera and Melipona spp. honeys from Venezuela were analysed to evaluate entomological-dependent differences. The presence of ellagic acid was a characteristic of A. mellifera honeys from Venezuela, but its presence was variable in Melipona spp. samples. The number of flavonoid types present in individual samples did not exceed six and occasionally only one phenolic type was present. The diversity of flavonoid compounds in tropical honeys from Venezuela was lower than that previously measured in temperate honeys. Flavonoids such as myricetin, an unidentified chalcone and a flavonol glycoside were only found in Melipona honeys but not in all the samples; therefore, they cannot be foreseen as entomological markers to differentiate between the Apis and Melipona honeys under study. A preliminary discussion is made regarding flavonoids present in Melipona honeys and their probable link with the putative anticataract action of stingless bee-honeys. Received: 22 February 1996     

Anisotropic thermal conductivity of silicon nitride ceramics containing carbon nanostructures

Silicon nitride (Si₃N₄) composites containing carbon nanotubes (CNTs) or graphene nanoplateles (GNPs) are of great relevance in the electronic and aerospace industries where the search for new materials with enhanced and anisotropic thermal conductivity to work in harsh environments is a strategic guideline. Here we study thermal conduction in Si₃N₄ composites with different amounts of carbon nanostructures. The effects of the nanostructure orientation respect the heat flux, the testing temperature and the α/β Si₃N₄ phase ratio are analyzed. The addition of CNTs and GNPs leads to an anisotropic thermal response, decreasing the through-thickness thermal conductivity of the Si₃N₄ composites and raising the in-plane thermal conductivity, especially for GNPs that enhance it up to twice that of the monolithic Si₃N₄. This effect is related to the preferred orientation of the nanostructures that gives a less resistive network in the in-plane direction and the intrinsic anisotropy of their thermal conductivity.     

The NSAID dexketoprofen trometamol is as potent as mu-opioids in the depression of wind-up and spinal cord nociceptive reflexes in normal rats

The aim of this study was to examine the potency of the antinociceptive effects of the non-steroidal antiinflammatory drug (NSAID), Dexketoprofen Trometamol (the active enantiomer of ketoprofen) on spinal cord nociceptive reflexes. These effects were compared with those of the mu-opioid receptor agonist fentanyl in normal animals. The experiments were performed in male Wistar rats anaesthetised with alpha-chloralose. The nociceptive reflexes were recorded as single motor units in peripheral muscles, activated by mechanical and electrical stimulation. Both dexketoprofen and fentanyl inhibited responses evoked by mechanical and electrical stimulation with doses in the same nanomolar range (dexketoprofen ID50s: 100 and 762 nmol kg-1 and fentanyl: 40 and 51 nmol kg-1, respectively). Dexketoprofen and fentanyl also significantly inhibited wind-up. Since fentanyl has been shown to be some 1000 times more potent than morphine in this type of experiments, we conclude that dexketoprofen has central analgesic actions in normal animals and depresses nociceptive responses with a potency similar to that of mu-opioid agonists.     

High temperature oxidation characteristics of Nb–10W–XCr alloys

The effect of Cr content on the microstructure and cyclic oxidation behavior of Nb–10W–XCr alloys with four different compositions has been investigated. Experiments were conducted in air at 900 °C and 1300 °C; the oxidation kinetics have been evaluated in terms of weight change per unit area with respect to exposure time. Alloy's microstructure consists of Nb solid solution phase regions surrounded by a network of NbCr₂ Laves phase. A trend of improvement in oxidation resistance with increase of the intermetallic phase is observed at 1300 °C and oxidation kinetics follow a parabolic behavior. At 900 °C, alloys with higher Cr content exhibit higher oxidation rates than alloys with lower Cr content. The oxidation products are a mixture of CrNbO₄, and Nb₂O₅ and the amount of each oxide present in the mixture is related to the intermetallic phase content. Results delineate the influence of microstructure and composition on the oxidation mechanisms of these alloys that represent a promising base for high-temperature intermetallic alloy development.