Dielectric and conductivity studies of the hydration mechanisms in plant seeds

Abstract

The hydration mechanism of various plant seeds has been investigated by a) sorption-desorption isotherms, b) ac-dielectric spectroscopy in the 10 Hz to 1 GHz frequency range and the -80 to + 40 degrees C temperature range, and c) thermally stimulated depolarization current techniques in the -170 to + 23 degrees C temperature range. Seeds of different chemical composition were studied at water contents varying between 0 and 40% w/w (dry weight basis). Our experimental results permitted us to determine i) the diffusion constant of water in the samples, found to be between 1.4 x 10(-11) and 3.7 x 10(-11) m2/s; ii) a critical water content corresponding to the completion of the primary hydration layer, which is in the range 0.11-0.17 w/w, depending on the seed nature; and iii) the activation energy of the main relaxation mechanism, found to be equal to 0.54 +/- 0.05 eV. Moreover, they make it possible to investigate the dependence of various parameters (conductivity, molecular mobility, plasticizing effect of water) on the water content of the sample, to follow the crystallization of water in the seeds as a function of temperature and confirm that it is not a reversible process, to study the dehydration process as a function of temperature and time, and to propose an alternative technique for the determination of the moisture content in seeds.

Alterations in the chain dynamics of insoluble elastin upon proteolysis by serine elastases

“…For that purpose, we used the thermally stimulated depolarization current (TSDC) technique; TSDC is an established method for studying the physical properties of synthetic and biological polymers in the solid state or at low degrees of hydration. 14,15 It allows us to scan dielectric relaxation processes at a lower equivalent frequency as compared to classical dielectric spectroscopies 16 and, therefore, can separate the different relaxation modes that occur in macromolecules.…”

Characterization of Molecular Mobility in Seed Tissues: An Electron Paramagnetic Resonance Spin Probe Study

“…The physical properties of water have been studied in complex biological systems that are able to survive the removal of their water, such as seeds (Vertucci, 1990;Bruni and Leopold, 1992;Konsta et al, 1996) and Artemia cysts (Seitz et al, 1981). The restricted mobility of water at low hydration levels has been attributed to the formation of intracellular glasses (Williams and Leopold, 1989).…”

Notes and Reflections on Impedance Spectroscopy

“…The dielectric properties are the most widely used in practical agricultural [14]. * In food science: To non-chemical disinfestations of food; for many novel sanitation and preservation purposes; non-food and agricultural commodities and to study the hydration mechanisms in seeds [15,16]. * In human diseases treatments: For the early detection of breast cancer in young women [17].…”