Antimicrobial activity of cyclodextrin entrapped allyl isothiocyanate in a model system and packaged fresh-cut onions.

The aim of this work was to determine the antimicrobial effect of allyl isothiocyanate (AIT) entrapped in alpha and beta cyclodextrin inclusion complexes (ICs). In model experiments, AIT formulations were applied to filter paper discs fixed inside the lid of Petri dishes, where the agar surface was inoculated with the target organism (Penicillium expansum, Escherichia coli or Listeria monocytogenes). Solid phase microextraction coupled with gas chromatography was used to determine static headspace concentrations of AIT formulations. The antimicrobial effect of beta IC was determined during aerobic storage of packaged fresh-cut onions at 5 °C for 20 days. AIT entrapped in beta IC exhibited a significantly (p < 0.05) better antimicrobial effect compared to unentrapped AIT. AIT vapour concentrations in the static system were highest for unentrapped AIT followed by beta IC and alpha IC. Application of beta IC (200 µl/l) to packaged fresh-cut onions effectively decreased numbers of L. monocytogenes, which were also decreased at slower rates to undetectable levels on untreated cut onion. After 10 days, total aerobic counts were ca. 4 log CFU/g lower on onions treated with beta IC (100 and 200 µl/l) compared to untreated controls. This work demonstrates the utility of beta IC as an antimicrobial treatment with potential applications in packaged fresh-cut vegetable products.

Time-temperature studies of gellan polysaccharide-high sugar mixtures: effect of sodium ions on structure formation.

Changes to the viscoelastic storage and loss moduli were measured as a function of temperature and oscillatory frequency for 0.5% (w/w) gellan:80% (w/w) cosolute dispersions with added Na(+) (40 to 160 mM). Isothermal frequency (0.15 to 15 Hz) and thermal scans (at 0.15 Hz) were performed over a decreasing then increasing temperature range of 85 to 5 degrees C and 5 to 85 degrees C, respectively. Moduli were found to increase in magnitude with decreasing temperature and increasing levels of Na(+) during cooling, then remained relatively thermally irreversible upon heating. Isothermal frequency (ITF) data were described using the time-temperature superposition (TTS) principle and the modified Cole-Cole (MCC) analysis. Both TTS and the MCC analyses successfully described the behavior of samples containing 40 mM added Na(+) during cooling and heating, and at the 100-mM Na(+) level during cooling. TTS superposed ITF data over the entire temperature range, whereas successful superposition was restricted to lower temperatures in the MCC analysis, where the viscoelastic response was dominated by the long-range relaxation of gellan chains between junction zones. Failure of both analyses was attributed to the formation of junction zones composed of polymer-polymer associations. It is proposed that the addition of Na(+) promotes the formation of a weakly cross-linked gellan network.

Kinetic and mechanistic considerations in the gelation of genipin-crosslinked gelatin.

The gelling properties (gel time (t(gel)) and gel strength) of a 10% (w/w) gelatin sol were investigated as a function of genipin (GP) concentration (0-15 mM) and temperature (25-55 degrees C) to discern mechanisms and optimal conditions for fixation. Gel time increased with increasing temperature, reached a maximum, and then declined as temperature was raised further. By contrast, network strength data followed the opposite trend. From the thermal behavior of t(gel) and network strength, it was inferred that gelation in the low-temperature regime was dominated by hydrogen bonding, while in the high-temperature regime it was dominated by covalent crosslinking. At higher temperatures, crosslinking was described by an Arrhenius rate law expression, with activation energies between 63.2 and 67.8 kJ/mol, depending on GP concentration. In the low temperature regime, an Arrhenius plot resulted in negative activation energies of -75.8 and -64.4 kJ/mol in the presence of 10 and 15 mM GP, respectively. With an increase in both GP concentration and temperature, the gelatin network gradually shifted from being dominated by hydrogen bonds (physical crosslinks) to covalent crosslinking (chemical crosslinks).

Some physical and microstructural properties of genipin-crosslinked gelatin-maltodextrin hydrogels.

The physical properties and microstructure of gelatin-maltodextrin hydrogels fixed with genipin (GP) were investigated as a function of pH (3-7), maltodextrin (MD) (0-9%, w/w) and GP (0-10 mM levels), at a constant gelatin (G) concentration (10%, w/w). Network strength (elastic modulus, E) and swelling behavior were characterized by large deformation testing and by swelling index (SI). In general, network strength increased and swelling decreased at higher pH, MD and GP levels, except at pH 3, where E was independent of the GP concentration until approximately 7.5 mM, above which it declined. Confocal scanning laser microscopy (CLSM) images showed phase separation to be suppressed at pH 3, whereas at pH 7, separation into a self-similar dispersed phase was apparent. Overall, the judicious use of GP to crosslink G was an appropriate means of kinetically trapping MD within the gelatin network.

Impedance spectroscopy: an accurate method of differentiating between viable and ischaemic or infarcted muscle tissue.

The object of the paper is to present results that show that impedance spectroscopy is an accurate method of assessing the condition of muscle tissue. Specimens of muscle tissue were excised from 36 Atlantic salmon and subjected to impedance spectroscopy measurements made at intervals during an 8h period of ischaemia and necrosis. These measurements were conducted for three different temperatures and for both the longitudinal and the transverse orientations of the muscle fibres. The specimens were also subjected to ATP, pH and visco-elastic measurement and analysis to establish the degree of correlation between changes in these quantities and impedance spectroscopy parameters due to ischaemia. It was concluded that the mean relaxation time, tau(c) was the impedance spectroscopy parameter that best described the changes taking place in the muscle tissue during the post-mortem period, decreasing by 60-76% during the 8h. This was the case for all three temperatures and for both orientations. Furthermore, the muscle tissue changes due to ischaemia, as reflected in the decrease in the mean relaxation time tau(c), were highly correlated with changes in the tissue ATP, pH and dynamic shear storage modulus G'.

Modeling of orthokinetic flocculation of Saccharomyces cerevisiae.

This study examined the flocculation behavior of two Saccharomyces cerevisiae strains expressing either Flo1 (LCC1209) genotype or NewFlo (LCC125) phenotype in a laminar flow field by measurement of the fundamental flocculation parameter, the orthokinetic capture coefficient. This orthokinetic capture coefficient was measured as a function of shear rate (5.95-223 s(-1)) and temperature (5-45 degrees C). The capture coefficients of these suspensions were directly proportional to the inverse of shear rate, and exhibited an increase as the temperature was increased to 45 degrees C. The capture coefficient of pronase-treated cells was also measured over similar shear rate and temperature range. A theory, which predicts capture coefficient values due to zymolectin interactions, was simplified from that developed by Long et al. [Biophys. J. 76: (1999) 1112]. This new modified theory uses estimates of: (1) cell wall densities of zymolectins and carbohydrate ligands; (2) cell wall collision contact area; and (3) the forward rate coefficient of binding to predict theoretical capture coefficients. A second model that involves both zymolectin interactions and DLVO forces was used to describe the phenomenon of yeast flocculation at intermediate shear ranges, to explain yeast flocculation in laminar flow.

Localization, characterization and partial purification of TMAO-ase.

1. Formaldehyde (FA) and dimethylamine (DMA) are generated in several species of fish of commercial importance. 2. The present study describes the localization, partial purification and characterization of an enzyme recovered from cod kidney tissue which is responsible for the reduction of trimethylamine oxide (TMAO) to FA and DMA. 3. The enzyme, TMAO-ase was found to be bound to purified cod kidney lysosomes and was separated into at least four distinct isozymes by isoelectric focussing.