Morphological changes in adsorbed protein films at the oil-water interface subjected to compression, expansion, and heat processing

Adsorbed films of milk proteins at the oil-water (O-W) interface have been imaged using a Brewster angle microscope (BAM). Special adaptations were made to the BAM to allow imaging of the O-W interface and to enable in situ heating and cooling of the adsorbed films. The proteins beta-lactoglobulin (beta-L) and alphas1-, beta-, and kappa-casein were studied over a range of bulk protein concentrations (Cb) and surface ages at pH 7 and for beta-L at pH 5 also. The adsorbed films were subjected to incremental compression and expansion cycles, such that the film area was typically varied between 125% and 50% of the original film area, and the resulting film structure was recorded via the BAM at 25.0 degrees C. Structuring of beta-L films (the formation of ridges and cracks) was more pronounced at pH 5 (closer to the protein's isoelectric point) than at pH 7 and for longer adsorption times and/or higher Cb. Structuring was also much more apparent at the O-W interface than at the A-W interface on compression/expansion/aging, especially at pH 7. After heating beta-L films adsorbed at low Cb (0.005 wt %) to 80 or 90 degrees C, an even greater degree of film structuring was evident, but beta-L films adsorbed at higher Cb (> or =0.05 wt %) showed fewer but larger fractures. The adsorbed caseins showed little evidence of such features, either before or after heating, apart from slight structuring for the heated films of alphas1- and kappa-casein films after 1 day. Changes in the dilatational elastic modulus of the beta-L films (Cb = 0.005 wt %) were correlated with the variations in the structural integrity of the films as observed via the BAM technique. In particular, there was a marked increase in the elastic modulus on heating, while the cycle of compression and expansion appeared to result in a net film weakening overall. The beta-L films adsorbed at higher Cb (> or =0.05 wt %) behaved as if an even stronger elastic skin completely covered the interface. The overall conclusion is that interfacial protein films subjected to these types of thermal and mechanical perturbations, which are typical of those that occur in food colloid processing, can become highly inhomogeneous, depending on the type of protein and the bulk solution conditions. This undoubtedly has implications for the stability of the corresponding emulsions and foams.     

Dynamics of junction point motions in model network polymers

³¹P solid-state exchange 2D NMR and spin-lattice relaxation times (T₁^P) have been used to investigate the motion of a crosslink unit in model networks. The networks were formed from tris(4-isocyanatophenyl) thiophosphate with telechelic poly(propylene glycol) or poly(tetrahydrofuran). From the variation of the 2D NMR pattern with temperature and mix time, the motion of the crosslink is identified as Brownian reorientational diffusion. Good simulations of the spectra were obtained using the Williams-Watts distribution of correlation times. The temperature dependence of the crosslink motion follows the WLF equation. The parameters derived from the NMR data are sufficient to describe the temperature dependence and breadth of both the dielectric and mechanical loss associated with the glass transition. The T₁^P relaxation data fitted equally well to the Cole-Cole or the Williams-Watts relaxation functions. The motion of the crosslinks can be described quantitatively by the activation energies and the coupling parameters.     

Fracto-emission from neat epoxy resin

Fracto-emission is the emission of particles (e.g. electrons, photons, ions, neutral species) due to crack growth in materials. These emissions can be related to a number of fracture related phenomena including microcracking, crack speed of dynamic crack growth, locus of fracture (in filled materials), and potentially the extent of crack branching. Here, we examine the emission of electrons, positive ions, and photons during and following the fracture of a neat epoxy resin subjected to tensile and tensile impact loading in vacuum. Experiments which detect correlations of crack tip position and emission intensity show that the emissions occur during and following fracture. We also illustrate that observed variations of the fracture surface morphology under different loading conditions correlated with characteristics of the photon and charged particle emission. For example, regions of the surface exhibiting the highest degree of surface roughness resulted in more intense emission.     

Study of extreme cases with respect to the densities of irregular linearly measurable plane sets of points

Mathematische Annalen -     

Influence of ionic calcium on stability of sodium caseinate emulsions

The stability of fine sodium caseinate emulsions (1 wt.% protein, 25 vol.% n-tetradecane, 20 mM imidazole, pH 7) containing various concentrations of calcium chloride has been investigated under perikinetic and orthokinetic conditions by measuring time-dependent changes in droplet-size distribution. Under quiescent storage conditions at 20°C, samples containing at least 10 mM ionic calcium added after emulsification were found to exhibit an increasing average droplet size with time and a developing bimodal droplet-size distribution. Under turbulent conditions of intense shearing, these same emulsions exhibited time-dependent flocculation and coalescence. This interpretation was confirmed by light microscopy. Emulsions prepared with up to 6 mM Ca²⁺ present during emulsification were stable in the presence or absence of flow, but satisfactory emulsions could not be prepared containing more than 6 mM ionic calcium. The results show that the emulsion stability is sensitive to whether the calcium ion content is adjusted before or after homogenization.     

On the photoinactivation of alcohol oxidase from alkane-grown Candida tropicalis

The process of photoinactivation of alcohol oxidase is insensitive to oxygen and to temperature in the range 0–25°C. The process is, however, wavelength dependent. Irradiation and inactivation do not cause any significant change to the visible absorption spectrum. Reaction of the enzyme with sodium sulfite or photoreduction in the presence of EDTA and either 5′-deazaflavin or lumiflavin 3-acetate under anaerobic conditions causes extensive bleaching of the visible spectrum of the enzyme and also protects it from photoinactivation. The presence of substrate under anaerobic conditions also provides very effective protection, but in this case there is no detectable change in the visible spectrum of the enzyme associated with the increase in stability to light.     

Segmental and crosslink point motion in networks

¹³C- and ³¹P-NMR spin lattice relaxation in the rotating frame have been measured on a series of networks prepared from monodisperse and deliberately bimodal poly(propylene glycols) (PPG) crosslinked with tris(4-isocyanatophenyl) thiophosphate. The T_1pC minima correspond to loss maxima in the DMTA (Dynamic Mechanical Testing) measured at 10Hz. The T_1p^P minima fall at higher temperatures than those of T_1p^C for the same network indicating that these crosslinks lag the segments in frequency of motion at a given temperature. The carbon relaxation is biphasic below T_g of the segments indicating two relaxation domains which we assign to bulklike PPG segments and PPG segments proximal to he crosslink. Lineshape analysis by a diffusional model indicates crosslink reorientation is not isotropic until well above T_g. Relaxation and lineshapes for the bimodal networks indicate that junctions are not uniformly plasticized by the segments.     

Emission of neutral molecules during UV laser ablation of a photolabile triazeno polymer

The neutral products of irradiating a photolabile triazeno-polymer with a pulsed laser at 248 nm (KrF excimer) were studied with time-of-flight (TOF) mass spectrometry. At fluences below 1.3 J/cm², N₂ is by far the most intense neutral product. Phenyl radical (mass 76) production was also observed. The leading edge of the N₂ TOF signal shows a shoulder corresponding to kinetic energies of about 1.1 eV, followed by a long tail that lasts hundreds of microseconds. The tail is attributed to delayed emission of reaction products from the polymer. The kinetic energy of the fast peak is attributed to direct ejection of products from surface sites undergoing exothermic decomposition. The fluence dependence of the N₂ signal is highly nonlinear and is shown to fit an Arrhenius equation.