Degradation kinetics of C-Phycocyanin under isothermal and dynamic thermal treatments.

C-Phycocyanin (C-PC) represents an alternative to artificial blue/green dyes in food products. This study characterized and gained insights into C-PC thermal stability mechanisms and provided a model to estimate its thermal degradation. Aqueous solutions of C-PC (0.

Temperature-dependence of riboflavin phosphorescence in cryosolvents.

The molecular mobility of amorphous excipients is important for the stability of biomaterials during preservation, facilitating matrix formulation and product design. Phosphorescence spectroscopy is a sensitive optical method to study molecular mobility. However, there is a need to expand the pool of probes available for analysis since molecules differ in sensitivity.

Potential applications of luminescent molecular rotors in food science and engineering.

Fluorescent molecular rotors (MRs) are compounds whose emission is modulated by segmental mobility; photoexcitation generates a locally excited (LE), planar state that can relax either by radiative decay (emission of a photon) or by formation of a twisted intramolecular charge transfer (TICT) state that can relax nonradiatively due to internal rotation. If the local environment around the probe allows for rapid internal rotation in the excited state, fast non-radiative decay can either effectively quench the fluorescence or generate a second, red-shifted emission band. Conversely, any environmental restriction to twisting in the excited state due to free volume, crowding or viscosity, slows rotational relaxation and promotes fluorescence emission from the LE state.

Tryptophan Fluorescence Yields and Lifetimes as a Probe of Conformational Changes in Human Glucokinase.

Five variants of glucokinase (ATP-D-hexose-6-phosphotransferase, EC 2.7.1.

Solvent-Slaved Dynamic Processes Observed by Tryptophan Phosphorescence of Human Serum Albumin.

Despite extensive experimental and computational efforts to understand the nature of the hierarchy of protein fluctuations and the modulating role of the protein hydration shell, a detailed microscopic description of the dynamics of the protein-solvent system has yet to be achieved. By using single tryptophan protein phosphorescence, we follow site-specific internal protein dynamics over a broad temperature range and demonstrate three independent dynamic processes. Process I is seen at temperatures below the bulk solvent T, has low activation energy, and is likely due to fast vibrations that may be enabled by water mobility on the protein surface.

Preparation and characterization of zein thermo-modified starch films.

A new method of preparing films from zein thermo-modified starch was presented. According to data of micro-visco-amylography and rheometer, dry heating with zein significantly decreased the pasting properties of waxy corn starch and distarch phosphate, the values of G' and G″ of starches dry heated with zein decreased, while the loss tangent increased as a function of heating time. Scanning electron microscopy images showed that the surfaces of starch granules became rough after dry heating with zein, suggesting interactions between zein and the granule surface.

Revisiting time-resolved protein phosphorescence.

Analysis of time-resolved phosphorescence data from proteins presents certain problems. Care must be taken in establishing that the analysis is not confounded in the early part of the decay by other emitting species. These species may include tyrosine, impurities found in the solvent, or impurities bound to the protein.

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.

Effects of glycerol on the molecular mobility and hydrogen bond network in starch matrix.

The effects of glycerol on molecular mobility and hydrogen bonding network in an amorphous glassy starch matrix were studied using phosphorescence and IR spectroscopy. Amorphous potato starch films containing varying amounts of glycerol (0, 5, 10, 20 and 30 wt.%) were formulated by rapidly dehydrating aqueous potato starch gel (5%, w/v) with a corresponding content of glycerol; X-ray diffraction data confirm that the films contained negligible content of crystalline starch.

Effect of additives on physicochemical properties in amorphous starch matrices.

The effect of the addition of non-reducing sugars or methylcellulose on the matrix physical properties and rate of non-enzymatic browning (NBR) between exogenous glucose+lysine in a starch-based glassy matrix were studied, using the methods of luminescence and FTIR. Amorphous starch-based matrices were formulated by rapidly dehydrating potato starch gel mixed with additives at weight ratios of 7:93 (additive:starch). Data on the phosphorescence emission energy and lifetime from erythrosin B dispersed in the matrices indicated that sugars decreased starch matrix mobility in a Tg-dependent manner, except for trehalose that interacted with starch in a unique mode, while methylcellulose, the additive with the highest Tg, increased the molecular mobility.

Influence of antioxidant structure on local molecular mobility in amorphous sucrose.

The effect of the antioxidants gallic acid and methyl, propyl, and octyl gallate on the molecular mobility and hydrogen bond network in amorphous sucrose was studied. Solid amorphous sucrose films with and without the addition of antioxidants at a mole ratio of 1:5 (antioxidant/sucrose) were cast from solution onto quartz slides. Local molecular mobility from 0 to 70°C was measured using tryptophan amino acid as a luminescent probe dispersed in the films.

Influence of glycerol on molecular mobility and hydrogen bond network in amorphous glucose matrix.

The effect of glycerol on molecular mobility and hydrogen bonding in amorphous glucose matrix was studied. Phosphorescence from erythrosin B (Ery B) was used to characterize the temperature dependence of mobility in glucose/glycerol films over the temperature range from 100 °C down to -10 °C. Analysis of emission energy and excited state decay kinetics from Ery B provided information about thermally activated modes of matrix dipolar relaxation around and collisions with the excited triplet state of the probe.

Antioxidants modulate molecular mobility, oxygen permeability, and microstructure in zein films.

The effect of octyl gallate and propyl gallate on the molecular mobility, oxygen permeability, and microstructure of zein/glycerol films was studied. Films were cast from 70% ethanol/water containing 20% (w/w) glycerol and different amounts of the antioxidants propyl gallate or octyl gallate. The oxygen permeability and local mobility of these films were measured using phosphorescence from the dispersed triplet probe erythrosin B.

Effect of starch on the molecular mobility of amorphous sucrose.

Molecular mobility in amorphous solid biomaterials is modulated by the composition and environment (primarily temperature). Phosphorescence of the triplet probe erythrosin B was used to generate a mobility map within amorphous sucrose films doped with starch ranging from 0.001 to 0.

Vanillin phosphorescence as a probe of molecular mobility in amorphous sucrose.

Changes in molecular mobility are important in defining the stability and quality of amorphous solid foods, pharmaceuticals, and other solid biomaterials. Predictions of stability must consider matrix mobility below and above T(g) (the glass transition temperature); measurement of molecular mobility in amorphous solids over time scales ranging from <10(-9) s to >10(8) s requires specialized methods. This research investigated how the steady-state and time-resolved emission and intensity of phosphorescence from vanillin (4-hydroxy-3-methoxy benzaldehyde), a common flavor compound, can be used to probe molecular mobility when dispersed within amorphous pure sucrose films.

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.

Effect of xanthan on the molecular mobility of amorphous sucrose detected by erythrosin B phosphorescence.

Molecular mobility in amorphous solids is modulated by composition and environmental conditions such as temperature. Phosphorescence of erythrosin B was used to generate a mobility map of amorphous sucrose film doped with xanthan gum at weight ratios of xanthan/sucrose ranging from 0.0001 to 0.

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.

The effect of salts on molecular mobility in amorphous sucrose monitored by erythrosin B phosphorescence.

Salts are present in most amorphous biomaterials such as dried or frozen solid foods, plant seeds, and bacterial spores, and in some pharmaceutical formulations. However, knowledge of how salts modulate the physical properties of amorphous solid sugars, a major component in these systems, is lacking. We have used phosphorescence of the triplet probe erythrosin B (Ery B) to monitor molecular mobility in amorphous sucrose films (dried against P(2)O(5)) containing the salts NaCl, MgCl(2), CaCl(2), NaAcetate, Na(3)Citrate, NaH(2)PO(4), or Na(2)HPO(4) at a mole ratio of 0.

Effect of gelatin on molecular mobility in amorphous sucrose detected by erythrosin B phosphorescence.

We have used phosphorescence from the triplet probe erythrosin B (Ery B) to evaluate the effect of gelatin on the molecular mobility of the amorphous sucrose matrix as a function of temperature. Ery B was dispersed in amorphous sucrose and sucrose-gelatin films at ratios of approximately 1:10(4) (probe/sucrose), and delayed emission spectra and emission decay transients were measured over the temperature range from 5 to 100 degrees C. Analysis of spectra using a lognormal function provided the peak energy and bandwidth of the emission.

The effect of sodium chloride on molecular mobility in amorphous sucrose detected by phosphorescence from the triplet probe erythrosin B.

Phosphorescence from the triplet probe erythrosin B provides spectroscopic characteristics such as emission energy and lifetime that are specifically sensitive to molecular mobility of the local environment. This study used phosphorescence of erythrosin B to investigate how variation in NaCl content modulated the mobility of the amorphous sucrose matrix over the temperature range from 5 to 100 degrees C. Addition of NaCl increased the emission energy and the energy difference with excitation at the absorption maximum and the red edge, and increased the lifetime by reducing the non-radiative decay rate in the glass as well as in the undercooled liquid in a concentration dependent manner, indicating that NaCl decreased the matrix molecular mobility.

Phosphorescence of erythrosin B as a robust probe of molecular mobility in amorphous solid sucrose.

Luminescence from the triplet probe erythrosin B (tetra-iodo fluorescein, Ery B) provides spectroscopic characteristics such as lifetime and emission energy that are sensitive to molecular mobility of the local environment in amorphous solids. This study investigated how variations in the local concentration of Ery B free acid as well as the presence of the dispersing solvent affect the spectroscopic measurements of solid matrix properties (the free acid of Ery B is poorly soluble in water and thus must be introduced via an organic solvent). The emission energy of Ery B from 5 to 100 degrees C in thin films of amorphous sucrose at various probe and solvent (N,N-dimethyl formamide, DMF) concentrations was determined using excitation at 500 nm and emission over the range 520-750 nm.

Molecular mobility in amorphous maltose and maltitol from phosphorescence of erythrosin B.

We have used phosphorescence from erythrosin B (tetraiodofluorescein) dispersed in amorphous thin films of maltose and maltitol at mole ratios of 0.8:10(4) dye:sugar to monitor the molecular mobility of these matrixes over the temperature range from -25 to over 110 degrees C. Analysis of the emission peak frequency and bandwidth (full width at half-maximum) and time-resolved intensity decay parameters provided information about thermally activated modes of matrix mobility that enhanced the rate of dipolar relaxation around the triplet state and the rate of intersystem crossing to the ground state (k(TS0)).

Molecular mobility and dynamic site heterogeneity in amorphous lactose and lactitol from erythrosin B phosphorescence.

We have used phosphorescence from erythrosin B to characterize the molecular mobility and dynamic heterogeneity in dry films of amorphous lactose and lactitol from -25 to 120 degrees C. The phosphorescence emission spectra red-shifted and broadened with temperature in both sugars, indicating that both the rate of dipolar relaxation and the extent of inhomogeneous broadening increased dramatically at higher temperature. Phosphorescence intensity decays were well fit using a stretched exponential decay model; the rate constant for non-radiative quenching due to collisions with the matrix was calculated from the lifetimes.

Dynamic site heterogeneity in amorphous maltose and maltitol from spectral heterogeneity in erythrosin B phosphorescence.

We have used phosphorescence from erythrosin B (tetraiodofluorescein) dispersed in thin films of either maltose or maltitol to investigate the physical properties of these amorphous pure sugar matrixes. Intensity decays collected as a function of emission wavelength over the range from 640 to 720 nm were analyzed using a stretched exponential kinetic model in which the lifetime (tau) and the stretching exponent (beta) were the physically relevant parameters. The lifetimes varied systematically with emission wavelength in both matrixes.