Conductance and relaxations of gelatin films in glassy and rubbery states

Analysis of water sorption isotherms of amorphous food materials by solution thermodynamics with relevance to glass transition: evaluation of plasticizing effect of water by the thermodynamic parameters

Relation between the thermodynamic parameters obtained from water sorption isotherms and the degree of reduction in the glass transition temperature (T_g), accompanied by water sorption, was quantitatively studied. Two well-known glassy food materials namely, wheat gluten and maltodextrin were used as samples. The difference between the chemical potential of water in a solution and that of pure water ([Formula: see text]), the difference between the chemical potential of solid in a solution and that of a pure solid ([Formula: see text]), and the change in the integral Gibbs free energy ([Formula: see text]) were obtained by analyzing the water sorption isotherms using solution thermodynamics. The parameter [Formula: see text] correlated well with ΔT_g (≡T_g - T_g0; where T_g0 is the glass transition temperature of dry material), which had been taken to be an index of plasticizing effect. This indicates that plasticizing effect of water on foods can be evaluated through the parameter [Formula: see text].

A Review: Origins of the Dielectric Properties of Proteins and Potential Development as Bio-Sensors

Polymers can be classified as synthetic polymers and natural polymers, and are often characterized by their most typical functions namely their high mechanical resistivity, electrical conductivity and dielectric properties. This bibliography report consists in: (i) Defining the origins of the dielectric properties of natural polymers by reviewing proteins. Despite their complex molecular chains, proteins present several points of interest, particularly, their charge content conferring their electrical and dielectric properties; (ii) Identifying factors influencing the dielectric properties of protein films. The effects of vapors and gases such as water vapor, oxygen, carbon dioxide, ammonia and ethanol on the dielectric properties are put forward; (iii) Finally, potential development of protein films as bio-sensors coated on electronic devices for detection of environmental changes particularly humidity or carbon dioxide content in relation with dielectric properties variations are discussed. As the study of the dielectric properties implies imposing an electric field to the material, it was necessary to evaluate the impact of frequency on the polymers and subsequently on their structure. Characterization techniques, on the one hand dielectric spectroscopy devoted for the determination of the glass transition temperature among others, and on the other hand other techniques such as infra-red spectroscopy for structure characterization as a function of moisture content for instance are also introduced.

Effect of microbial transglutaminase on gel properties and film characteristics of gelatin from lizardfish (Saurida spp.) scales

The addition of microbial transglutaminase (MTGase) generally increased the gel strength of lizardfish (Saurida spp.) scale gelatin gels (P≤0.05) with an increase in gel strength with the addition of MTGase up to 0.5% (w/v). The texture profile analysis compression tests of lizardfish scale gelatin gel with and without MTGase were studied to determine their effects on gel characteristics. MTGase added to the gels decreased the band intensity of the β- and α-components with increasing concentrations of enzyme. Gel microstructures with various concentration of MTGase showed denser strands in the gels with enzyme compared with the looser stands in non-enzyme-treated gel samples. Films cast from lizardfish scale gelatin with and without 0.5% MTGase and bovine gelatin films were transparent and flexible. The lizardfish gelatin films were all slightly yellowish while the bovine gelatin films were clearer. The L value of bovine gelatin films had the highest value (P≤0.05) whereas lizardfish scale gelatin films with and without enzyme were not significantly different (P>0.05) for L, a, and b values and ΔE. The film's mechanical properties included tensile strength (TS) and elongation at break (E) were not significantly different (P > 0.05) for E and the films of lizardfish scale gelatin showed higher TS than the films without enzyme added (P ≤ 0.05). The water vapor permeability of films from lizardfish scale gelatin with and without 0.5% MTGase and bovine gelatin films were 21.0 ± 0.17, 26.3 ± 0.79, and 25.8 ± 0.09 g·mm/m(2)·d·kPa, respectively, while the oxygen transmission rate of all 3 types of films were less than 50 cc O(2)/m(2)·d.

Molecular weight effects on the glass transition of gelatin/cosolute mixtures

The structural properties of four gelatin fractions in mixture with sucrose and glucose syrup have been investigated extensively using small deformation dynamic oscillation. The total level of solids was 80%, the number average molecular weight of the protein ranged from 29.2 to 68 kD, and the temperatures were between 60 and -60 degrees C. Remarkably, the nature of the time and temperature dependence on the viscoelastic functions of all samples could be reduced to master curves using horizontal shift factors. The construction of master curves indicates a common mechanism of structure formation, which, in accordance with the synthetic polymer literature, comprises the rubbery zone, glass transition region, and glassy state. Application of Ferry's free-volume formalism and Rouse theory suggests that there is no change in the thermodynamic state of materials during vitrification, with changes in molecular weight simply introducing shifts in the time scale and temperature range of contributions to viscoelasticity. The thermorheological simplicity allowed development of the concept of "rheological" Tg. This was defined as the point between free-volume phenomena of the polymeric backbone occurring in the glass transition region and an energetic barrier to rotation required for local chain rearrangements in the glassy state. Mechanical relaxation and retardation distribution functions were calculated, thus obtaining values for the effective friction coefficient per monomer unit of the protein. It appears that the local friction coefficient is governed by a linear relationship between fractional free volume and the decreasing molecular weight of the protein, which introduces additional voids due to molecular ends.