Control of Listeria monocytogenes with combined antimicrobials on beef franks stored at 4 degrees C

Contamination of ready-to-eat meat products such as beef franks with Listeria monocytogenes has become a major concern for the meat processing industry and an important food safety issue. The objective of this study was to determine the effectiveness of combinations of antimicrobials as aqueous dipping solutions to control L. monocytogenes on vacuum-packaged beef franks stored at 4 degrees C for 3 weeks. Commercial beef franks were dipped for 5 min in three antimicrobial solutions: pediocin (6,000 AU), 3% sodium diacetate and 6% sodium lactate combined, and a combination of the three antimicrobials. Samples were then inoculated with 10(7) CFU/g of either four L. monocytogenes strains individually or a cocktail of the four strains, vacuum packaged, and stored at 4 degrees C for 3 weeks. Sampling was carried out at day 0 and after 2 and 3 weeks of storage. Individual strains, as well as the cocktail, exhibited different responses to the antimicrobial treatments. After 2 and 3 weeks of storage at 4 degrees C, pediocin-treated beef franks showed a less than 1-log reduction for all bacterial strains. Samples treated with the sodium diacetate-sodium lactate combination showed about a 1-log reduction after 2 weeks of storage for all strains and between a 1- and 2-log reduction after 3 weeks of storage, depending on the bacterial strain. When the three antimicrobials were combined, reductions ranged between 1 and 1.5 log units and 1.5 to 2.5 log units after 2 and 3 weeks of storage, respectively, at 4 degrees C. These results indicate that the use of combined antimicrobial solutions for dipping treatments is more effective at inhibiting L. monocytogenes than treatments using antimicrobials such as pediocin separately.     

Synthesis and Properties of Polyarylene ether Nitrile Copolymers

Polyether nitrile and its copolymers were synthesized by nucleophilic substitution reaction of 2,6-dichlorobenzonitrile with resorcinol and with varying mole proportions of resorcinol and hydroquinone. The polymers were characterized by different physico-chemical techniques. Thermogravimetric studies showed that all the polymers were stable up to 400°C with a char yield of above 48% at 900°C in N₂ atmosphere. The glass transition temperature was found to increase with increase in concentration of hydroquinone units in the polymer; however no trend was observed in their crystalline melt temperatures. Copolymer composition was determined using FT-IR technique. Crystallinity of the polymers was also studied using wide angle X-ray diffraction.     

Hydrogen evolution by water splitting using novel composite zeolite-based photocatalyst

Novel zeolite-based material showing photocatalytic properties in the visible light have been synthesized by incorporating TiO₂, heteropolyacid (HPA) and transition metal, namely cobalt. This material shows high efficiency for water splitting under visible light irradiation. Hydrogen generation to the tune of 2171 μmol/h/g of TiO₂ has been achieved for the composite photocatalyst synthesized as compared to H₂ evolution rate to the tune of 131.6 μmol/h/g of TiO₂ for Degussa P25. This suggests that the TiO₂ which gets effectively dispersed and stabilized on the surface of zeolite works synergistically with cobalt and heteropolyacid to make the material active in visible light for evolution of hydrogen from water. TiO₂ is the photocatalyst, HPA functions as the dye sensitiser as well as redox system; zeolite functions as support matrix and as electron acceptor in synergy with cobalt. The probable mechanism for improved hydrogen evolution rate using such composite photocatalyst has been discussed.     

Assessing the cross contamination and transfer rates of Salmonella enterica from chicken to lettuce under different food-handling scenarios

Cross contamination of foodborne pathogens from raw meats to ready-to-eat foods has caused a number of foodborne outbreaks. The cross contamination and transfer rates of Salmonella enterica from chicken to lettuce under various food-handling scenarios were determined. The following scenarios were tested: in scenario 1, cutting board and knife used to cut chicken (10⁶ CFU/g) were also used for cutting lettuce, without washing; in scenario 2, cutting board and knife were washed with water separately after cutting chicken, and subsequently used for cutting lettuce; and in scenario 3, cutting board and knife were thoroughly washed with soap and hot water after cutting chicken, and before cutting lettuce. In each scenario, cutting board, knife, chicken and lettuce were sampled for population of S. enterica. For scenario 1, both before and after cutting lettuce, the cutting board and knife each had about 2 logs CFU/cm² of S. enterica, respectively. The cut lettuce had about 3 logs CFU/g of S. enterica. In scenario 2, fewer organisms (0.5–2.4 logs CFU/g or cm²) were transferred. The transfer rates in both scenarios ranged from 0.02 to 75%. However, in scenario 3, <1 log CFU/g or cm² organisms were detected on lettuce, cutting board or knife, after washing and cutting lettuce. This shows that the FDA recommended practice for cleaning cutting boards is effective in removing S. enterica and preventing cross contamination.     

Investigation of spectral properties of Eu<Superscript>3+</Superscript> and Tb<Superscript>3+</Superscript> doped strontium zirconium trioxide orthorhombic perovskite for optical and sensing applications

In this paper, the structural, morphological and spectral properties of Eu³⁺ and Tb³⁺ doped strontium zirconium trioxide perovskite phosphors are reported. The samples were synthesized by solid state reaction route with different doping concentrations of Eu³⁺ and Tb³⁺ ions. These synthesized phosphors were characterized by PXRD for structural analysis. The phosphors report orthorhombic structure with average crystallite size of 48 nm. FESEM and HRTEM analysis were done here for topographical and morphological studies. Also, the FTIR spectra of synthesized samples were investigated for functional group analysis. Photoluminescence and thermoluminescence spectra of synthesized samples were studied. On subjecting to 230 nm excitation, the phosphors give three distinct emissions of 596, 610 and 690 nm in the visible region corresponding to ⁵D₀ → ⁷F₁, ⁵D₀ → ⁷F₂ and ⁵D₀ → ⁷F₄ of Eu³⁺ ions. The synthesized samples were also subjected to CIE and Afterglow decay analysis. The average decay lifetime is recorded as 56.24 ns confirming the luminescence decay characteristics of short duration. In TL analysis of these phosphors, second-order kinetics with low activation energy varying from 0.50002 to 0.65668 eV is reported. The enhanced optical characteristics of prepared perovskite phosphor substantiate it as a proficient alternative for photovoltaic, optical and sensing applications.     

Survival of Listeria monocytogenes in vanilla-flavored soy and dairy products stored at 8 degrees C

The survival of Listeria monocytogenes V37 in vanilla-flavored yogurt (low-fat and nonfat) and soy milk (low-fat and Plus) stored at 8 degrees C for 31 days was investigated. Commercial samples of yogurt and soy milk were used. These samples were inoculated with either 10(4) or 10(7) CFU of L. monocytogenes per ml. Sampling was carried out every 3 to 4 days initially and was then carried out weekly, for a total storage time of 31 days. Each time a sample was collected, the pH of the sample was measured. After 31 days, low-fat plain, low-fat vanilla, and nonfat plain yogurt samples inoculated with 10(4) CFU/ml showed 2.5-log reductions in viable cell populations, and nonfat vanilla yogurt showed a 3.5-log reduction. For yogurt inoculated with 10(7) CFU/ml, reductions of 2.5 log CFU/ml were observed for plain low-fat and nonfat yogurts, and reductions of 5 log CFU/ml were observed for vanilla-flavored low-fat and nonfat yogurts. In vanilla-flavored and plain low-fat and Plus soy milk samples, cell counts increased from 10(4) and 10(7) CFU/ml to 10(9) CFU/ml at 7 and 3 days of storage, respectively, at 8 degrees C. Coagulation in soy milk samples was observed when the cell population reached 10(9) CFU/ml. In soy milk, the L. monocytogenes population did not change for up to 31 days. Vanillin had an inhibitory effect on L. monocytogenes in yogurt but not in soy milk.     

Nano-ferrites for water splitting: unprecedented high photocatalytic hydrogen production under visible light

In the present investigation, hydrogen production via water splitting by nano-ferrites was studied using ethanol as the sacrificial donor and Pt as co-catalyst. Nano-ferrite is emerging as a promising photocatalyst with a hydrogen evolution rate of 8.275 μmol h(-1) and a hydrogen yield of 8275 μmol h(-1) g(-1) under visible light compared to 0.0046 μmol h(-1) for commercial iron oxide (tested under similar experimental conditions). Nano-ferrites were tested in three different photoreactor configurations. The rate of hydrogen evolution by nano-ferrite was significantly influenced by the photoreactor configuration. Altering the reactor configuration led to sevenfold (59.55 μmol h(-1)) increase in the hydrogen evolution rate. Nano-ferrites have shown remarkable stability in hydrogen production up to 30 h and the cumulative hydrogen evolution rate was observed to be 98.79 μmol h(-1). The hydrogen yield was seen to be influenced by several factors like photocatalyst dose, illumination intensity, irradiation time, sacrificial donor and presence of co-catalyst. These were then investigated in detail. It was evident from the experimental data that nano-ferrites under optimized reaction conditions and photoreactor configuration could lead to remarkable hydrogen evolution activity under visible light. Temperature had a significant role in enhancing the hydrogen yield.     

Influence of zeolitic structure on photoreduction property and hydrogen evolution reaction

A new photocatalytic material developed by supporting TiO₂ in combination with transition metal ion like cobalt and heteropolyacid (HPA) on the surface is facilitating enhanced photoreduction of water and methyl orange. Zeolites being a solid acid play an important role in the electron transfer reaction, facilitated by the Lewis acid sites in the form of aluminium ions. In the present work, four different zeolite matrices namely, NaY zeolite, ultrastable zeolite Y, beta zeolite and titanium silicate-1 have been used for the synthesis of new photocatalytic materials. These materials have been evaluated for water splitting by an initial screening procedure using methyl orange photoreduction. The photocatalyst containing Na Y has emerged as a potential photocatalyst with hydrogen evolution rate of 2730 μmol/h/g of TiO₂. Hydrogen evolution was not observed for the composite photocatalysts synthesized using the other zeolite matrices. It has been observed that physico-chemical properties like Si/Al ratio, acidity and basicity of the zeolite support have a tremendous influence on the photoreduction property of these zeolite matrices.