Richard D. Ludescher

Temperature- and Surfactant-Induced Membrane Modifications That Alter Listeria monocytogenes Nisin Sensitivity by Different Mechanisms

ABSTRACT Nisin interacts with target membranes in four sequential steps: binding, insertion, aggregation, and pore formation. Alterations in membrane composition might influence any of these steps. We hypothesized that cold temperatures (10°C) and surfactant (0.1% Tween 20) in the growth medium would influence Listeria monocytogenes membrane lipid composition, membrane fluidity, and, as a result, sensitivity to nisin. Compared to the membranes of cells grown at 30°C, those of L. monocytogenes grown at 10°C had increased amounts of shorter, branched-chain fatty acids, increased fluidity (as measured by fluorescence anisotropy), and increased nisin sensitivity. When 0.1% Tween 20 was included in the medium and the cells were cultured at 30°C, there were complex changes in lipid composition. They did not influence membrane fluidity but nonetheless increased nisin sensitivity. Further investigation found that these cells had an increased ability to bind radioactively labeled nisin. This suggests that the modification of the surfactant-adapted cell membrane increased nisin sensitivity at the binding step and demonstrates that each of the four steps can contribute to nisin sensitivity.

Trends in development of porous carbohydrate food ingredients for use in flavor encapsulation

The objectives of this paper are to: (1) present a brief overview of established flavor encapsulation techniques; (2) describe an alternative based on physical adsorption of flavors onto the surface of highly porous carbohydrates; (3) provide a literature review of the porosity of carbohydrate food ingredients; (4) describe methods to produce microporous carbohydrates; and (5) propose potential applications for the use of these novel flavor carriers.

Theory and applications of fluorescence spectroscopy in food research

Abstract Fluorescence spectroscopy is a rapid, sensitive method for characterizing molecular environments and events. In spite of its utility, food researchers have been slow to adopt fluorescence methodology, partly because its value has gone unrecognized. This article presents a brief overview of the theory of fluorescence spectroscopy, together with some examples of applications of this technique to illustrate its potential for addressing key problems in food science.

Fluorescence quenching study of resveratrol binding to zein and gliadin: towards a more rational approach to resveratrol encapsulation using water-insoluble proteins

Several health benefits have been ascribed to consumption of resveratrol, a polyphenol that can be extracted from grape skins. However, its use as a nutraceutical ingredient is compromised by its low water solubility, chemical stability, and bioavailability. Encapsulation of resveratrol in protein nanoparticles can be used to overcome these issues. Fluorescence quenching experiments were used to study the interaction of resveratrol with gliadin and zein. Resveratrol interacted with both proteins, but the binding constant was higher for zein than for gliadin at 35 °C. Furthermore, binding between resveratrol and gliadin increased at higher temperatures, which was not observed for zein. Analysis of the thermodynamic parameters suggested that resveratrol-gliadin binding mainly occurs through hydrophobic interactions while the binding with zein is predominantly mediated through hydrogen bonds. These results help rationalise ingredient selection and production of protein nanoparticles and microparticles for encapsulation, protection and release of resveratrol and potentially other bioactive compounds.

Beyond Tg: Optical luminescence measurements of molecular mobility in amorphous solid foods

Abstract Current research recognizes the importance of the glassy state for stabilizing amorphous solid foods and the importance of the glass transition (Tg) as an index temperature for food stability. This reflects a realization that molecular mobility modulates both physical properties such as texture and physical and chemical processes such as reaction rate, crystallization rate, solute diffusion, and collapse; the Tg is the onset temperature for cooperative translational motion in amorphous solids. The existence of complex structural features in foods with lengths ranging from nanometers to centimeters and the recognition that complex vibrational motions are activated in the glassy state, brings about the need to go beyond macroscopic measurements of product Tgs. It is now important to determine how molecular structure and mobility as well as microscopic organization modulate the macroscopic physical properties of foods. Luminescence spectroscopy provides a powerful arsenal of biophysical tools to investigate the structure and molecular mobility of amorphous solids; measurements of emission intensity, energy (wavelength), and polarization can provide direct information about molecular structure and mobility. Luminescence measurements of the effect of hydration and temperature on amorphous solid proteins and sugars reviewed here indicate that the molecular mobility due to local vibrational and rotational motions (as opposed to global translational mobility) in glassy foods is actually quite extensive with motions occurring on time scales ranging from nanoseconds to seconds. There is thus a need to identify how the rates of specific chemical and physical processes involved in food degradation are influenced by specific modes of molecular mobility in amorphous solid foods.

Lactocin 160, a Bacteriocin Produced by Vaginal Lactobacillus rhamnosus, Targets Cytoplasmic Membranes of the Vaginal Pathogen, Gardnerella vaginalis

Bacterial vaginosis (BV) is a commonly occurring vaginal infection that is associated with a variety of serious risks related to the reproductive health of women. Conventional antibiotic treatment for this condition is frequently ineffective because the antibiotics tend to inhibit healthy vaginal microflora along with the pathogens. Lactocin 160, a bacteriocin produced by healthy vaginal lactobacilli, is a promising alternative to antibiotics; this compound specifically inhibits the BV-associated vaginal pathogens such as Gardnerella vaginalis and Prevotella bivia without affecting the healthy microflora. This study investigates the molecular mechanism of action for lactocin 160 and reveals that this compound targets the cytoplasmic membrane of G. vaginalis, causing the efflux of ATP molecules and dissipation of the proton motive force.

Processing Stability of Squalene in Amaranth and Antioxidant Potential of Amaranth Extract

The processing stability of squalene in amaranth and the antioxidant capacity of the oil-rich fraction of amaranth were studied. The processes investigated were continuous puffing and roasting. Puffing was carried out using a single screw extruder, while roasting was carried out in a convection oven. High-performance liquid chromatography was used to quantify squalene content before and after processing. The L-ORAC method was used to study the antioxidant activity of pure squalene and lipophilic amaranth extract containing squalene. It was found that squalene was stable during all of the processing operations with a maximum loss of 12% during roasting (150 degrees C, 20 min) and no loss during puffing. The L-ORAC test showed pure squalene to be a weak antioxidant, whereas the lipophilic extract of amaranth showed higher antioxidant activity as compared to pure squalene at the same concentration, suggesting that tocotrienols and other minor ingredients also played a role as antioxidants.

INFLUENCE OF HYDRATION ON THE INTERNAL DYNAMICS OF HEN EGG WHITE LYSOZYME IN THE DRY STATE

Abstract— Proteins exist in a predominately aqueous solvent environment. Hydration of the protein surface significantly affects many aspects of the proteins structure and function; these effects may be related to the molecular dynamics of the protein. We have examined the influence of hydration on the internal dynamics of hen egg white lysozyme using room‐temperature phosphorescence from the intrinsic tryptophan residues. Powders of lyophilized lysozyme were hydrated in a phosphorimeter using a flow system that allowed for continuous manipulation of relative humidity over the range 0–92%; this system allowed us to directly compare intensity differences that result from changes in hydration. Lysozyme phosphorescence intensity decreased as a function of hydration over the entire relative humidity range; the decrease was not linear but appeared to occur in distinct phases. The phosphorescence intensity decays were multiexponential over the hydration range studied, and hydration had the largest influence on the long lifetime component. These data suggest that the protein exists in multiple, static conformations in the dry state and that water binding to polar (as opposed to charged) sites on the protein surface induces local and/or global softening of the protein structure.

ROOM TEMPERATURE PHOSPHORESCENCE FROM TRYPTOPHAN AND HALOGENATED TRYPTOPHAN ANALOGS IN AMORPHOUS SUCROSE

Abstract. Tryptophan phosphorescence lifetime and quantum yield are sensitive to the local environment. The phosphorescence from tryptophan analogs, however, has not been studied. We report here data on the room temperature phosphorescence of tryptophan, 4‐, 5‐ and 6‐fluoro‐DL‐tryptophan (4‐F‐trp, 5‐F‐trp and 6‐F‐trp) and 5‐bromo‐DL‐tryptophan (5‐Br‐trp) embedded in glassy powders of freeze‐dried sucrose. In aqueous solution, the absorption of the analogs was either blue‐shifted (4‐F‐trp), red‐shifted (5‐F‐trp and 5‐Br‐trp) or not shifted (6‐F‐trp) with respect to tryptophan. The phosphorescence emission spectra of all analogs were red‐shifted compared to trp (442 nm) with maxima at 446 nm (5‐F‐trp), 451 mn (6‐F‐trp), 452 nm (5‐Br‐trp) and 469 nm (4‐F‐trp). The 5‐F‐trp and 6‐F‐trp analogs had emission intensities similar to tryptophan (relative quantum yields of 0.68 and 0.91, respectively, compared to tryptophan), while the intensities of the 4‐F and 5‐Br analogs were lower (relative quantum yields of 0.039 and 0.022, respectively). All analogs exhibited complex decay behavior requiring several exponentials for an adequate fit; the average lifetimes were all lower than that of trp (1039 ms). The average lifetimes of the fluorinated analogs (5‐F, 721 ms; 6‐F, 482 ms and 4‐F, 35 ms) scaled approximately with the relative quantum yields while that of 5‐Br (0.53 ms) was significantly lower. Analysis of the individual lifetimes suggested that the fluorinated analogs differ in their sensitivity to environmental interactions, with 5‐F‐ and 6‐F‐trp quenched 1.5‐2‐fold and 4‐F‐trp about 23‐fold more efficiently than tryptophan. The red‐shifted 5‐F‐trypto‐phan analog, which has been incorporated into proteins, may provide an alternative phosphorescence probe for selective phosphorescence detection of a specific protein in a complex mixture.

The Trans-Atlantic Slocum Glider Expeditions: A Catalyst for Undergraduate Participation in Ocean Science and Technology

This paper provides an overview of the education programs developed for underwater gliders, how these programs were applied to the trans-Atlantic missions, and the educational lessons learned. It concludes with a perspective on how this educational effort provides the foundation for an international partnership to explore the world ocean on a second NOAA challenge, a repeat of the 1870 Challenger Mission, the first scientific circumnavigation of the globe.