Pressure induced graft-co-polymerization of acrylonitrile onto <Emphasis Type="Italic">Saccharum cilliare</Emphasis> fibre and evaluation of some properties of grafted fibre

In the present work, graft co-polymerization of acrylonitrile (AN) onto Saccharum cilliare fibre has been carried out in the presence of potassium persulphate and ferrous ammonium sulphate (FAS-KPS) as redox initiator. The reactions were carried out under pressure in an autoclave. Various reaction parameters such as pressure, time, pH, concentrations of initiator and monomer were optimized to get maximum graft yield (35·59%). Grafted and ungrafted Saccharum cilliare fibres were then subjected to evaluation of some of their properties like swelling behaviour in different solvents, moisture absorbance under different humidity levels, water uptake and resistance towards chemicals such as hydrochloric acid and sodium hydroxide. The characterization of the graft copolymers were carried out by FTIR spectrophotometer, X-ray diffraction (XRD) and scanning electron microscopic (SEM) studies.     

Marked intra-strain variation in response of Listeria monocytogenes dairy isolates to acid or salt stress and the effect of acid or salt adaptation on adherence to abiotic surfaces

During food processing, and particularly in cheese manufacturing processes, Listeria monocytogenes may be exposed routinely to environments of low pH or high salt concentration. It has been suggested that these environmental conditions may contribute to bacterial adherence to abiotic surfaces and increased resistance to disinfection. In this study strains isolated from the environment of artisanal cheese-making dairies were used to investigate the behaviour of L. monocytogenes in response to acid and salt stress and clear differences between strains was observed. In planktonic culture, strains varied in resistance to low pH or high NaCl concentration and in the occurrence of an adaptive response to moderate acid or NaCl. There was dislocation in responses to salt and acid. Strains resistant, or adaptive, to acid were not resistant or adaptive to NaCl. The reverse also was observed. Exposure to moderate acid did not promote adherence to polystyrene but survival, at low pH or high NaCl concentration, of cells adherent to stainless steel was increased, even for strains that had no adaptive response planktonically, but the detail of these observations varied between strains. In contrast to acid adaptation, with some strains salt adaptation enhanced adherence of L. monocytogenes to polystyrene but this was not true for all strains. For some strains salt- or acid adaptation may enhance the survival of sessile cells exposed to hypochlorite disinfection.     

Kinetics and equilibria of tea infusion. Analysis and partition constants of theaflavins,thearubigins, and caffeine in koonsong broken pekoe

Koonsong Broken Pekoe tea leaf was equilibrated with water at 79.5 and 94.0°C using water: leaf ratios from 25:1 to 100:1. The concentrations of theaflavins, thearubigins, and caffeine were measured in the aqueous extracts. Analysis of the results by a simple two-phase model gave the concentrations of the three constituents in the original leaf without the necessity for the usual assumption of complete extraction. The theory also yielded the partition constants (distribution coefficients) of the three constituents between swollen leaf and aqueous solution, and the enthalpy changes for their extraction.     

Kinetics and equilibria of tea infusion: Kinetics of extraction of theaflavins,thearubigins and caffeine from Koonsong broken pekoe

The rates of infusion of theaflavins, thearubigins, and caffeine from Koonsong Broken Pekoe into water were measured at 79.5 and 94.0°C. The kinetic data have been interpreted in terms of a simple two-phase model, and the rate constants of infusion and of re-absorption were calculated. At low infusion times thearubigins were extracted faster than theaflavins, with the caffeine rate intermediate. However, the rate constants for the overall infusion process were quite similar for the three constituents. The corresponding activation energies are small as are those calculated from Long's data on the rate of extraction of all soluble material.     

Cold atmospheric gas plasma disinfection of chicken meat and chicken skin contaminated with Listeria innocua

Gas plasmas generated at atmospheric pressure and ambient temperatures offer a possible decontamination method for poultry products. The efficacy of cold atmospheric gas plasmas for decontaminating chicken skin and muscle inoculated with Listeria innocua was examined. Optimization of operating conditions for maximal bacterial inactivation was first achieved using membrane filters on which L. innocua had been deposited. Higher values of AC voltage, excitation frequency and the presence of oxygen in the carrier gas resulted in the greatest inactivation efficiency, and this was confirmed with further studies on chicken muscle and skin. Under optimal conditions, a 10 s treatment gave > 3 log reductions of L. innocua on membrane filters, an 8 min treatment gave 1 log reduction on skin, and a 4 min treatment gave > 3 log reductions on muscle. These results show that the efficacy of gas plasma treatment is greatly affected by surface topography. Scanning electron microscopy (SEM) images of chicken muscle and skin revealed surface features wherein bacteria could effectively be protected from the chemical species generated within the gas plasma. The developments in gas plasma technology necessary for its commercial application to foods are discussed.     

Modeling UV-induced inactivation of microorganisms on surfaces

A model is presented to account for inactivation by UV light of microorganisms on the surfaces of solid materials. In the model, the surface is divided into a discrete number of zones, each having a characteristic exposure factor (alpha). This is the ratio of UV intensity actually "seen" by the microorganism to that incident on the surface. Application of the model requires inactivation data obtained under conditions where the surface microorganisms are fully exposed to incident UV (alpha = 1) as well as kinetic inactivation data for the same microorganisms actually present on the surface of interest during UV irradiation. The kinetics in question may apply either to a single species or to the characteristic microflora associated with a particular material. Standard nonlinear programming techniques were used to determine the number of zones among which the microorganisms are distributed, the alpha for each zone, and the fraction of the microbial population present in each zone. The model was applied to data previously published by Gardner and Shama for UV inactivation of Bacillus subtilis spores on the surfaces of filter papers and also to the data of Stermer et al. for UV irradiation of beef. Good representation of the kinetics was obtained, and a maximum of three zones was required to adequately represent the experimental data. One direct application of the model is that it yields quantitative information about the UV fluences necessary to achieve specified reductions in microbial viability.     

The use of biodosimetry to measure the UV-C dose delivered to a sphere, and implications for the commercial treatment of fruit

Commercialization of UV-C treatment of horticultural produce in order to induce beneficial responses in the produce following treatment requires both accurate dose delivery and a method of treating large quantities of produce efficiently. Furthermore, it has long been assumed that such effects require the entire surface of the horticultural commodities - typically fruit - to be exposed to UV-C. This has invariably been achieved by manually rotating the fruit in a UV-C field whilst reducing the dose delivered at each rotation in direct proportion to the number of rotations. However, the resulting UV-C dose distributions achieved under these circumstances are generally not reported in the literature. In the work described here a polystyrene sphere (dia. 70 mm) was used to simulate fruits such as tomatoes, apples, peaches, etc., that have an approximately spherical form in order to provide a means of measuring the total doses of UV-C accumulated during treatment and comparing such estimates to theoretically-derived ones. This was achieved using dosimetry based on spores of Bacillus subtilis in which spore-impregnated membranes were attached to the surface of the sphere. The fraction of spores surviving exposure was used to estimate dose from a dose-response curve for the spores. Under irradiation conditions leading to a theoretically calculated dose of 10.6 J, spore dosimetry yielded estimates of 9.1, 10.7 and 6.1 J for UV-C delivered in, respectively, one, two or four exposures. In the case of exposure of the sphere during continuous mechanical rotation for the same length of time (80 s) a value of only 3.5 J was obtained. Irradiation conditions resulting in the spores being subject to intermittent exposure to UV-C led to dose estimates below the theoretically derived ones. The circumstances under which spore dosimetry can be used to obtain surface dose distributions are discussed.