Free and/or bound water by dielectric measurements

In the past few years, the research on new methods (FTIR, NMR, microwaves) to measure the quantity and quality of water has been largely improved, particularly in the agricultural industry. Numerous studies have been made in order to establish a relationship (BET, GAB, …) between parameters such as temperature, the water content in the matrix and the partial pressure of water vapour. The dielectric spectroscopy in the microwave domain shows a strong discrimination between bound and free water. The measurements in a resonant cavity allow calculation of the complex permittivity. This methodology has been used to quantify the grade of a seedʹs viability, and by extension, to discriminate between living seeds, containing mostly bound water, and dead seeds, containing particularly free water. This was explored with the society CLAUSE, in tomato, pimento and melon seeds. In a resonant cavity, the dielectric response of each seed is dependent on the weight, the heterogeneity of the shape (depolarisation factor of the electric field), and the anisotropy of density distribution of water in the matrix. Consequently, in order to take into account these parameters, the rotation of the seed in the electric field gives the total dielectric response or the dielectric signature of each seed. In this first approach, using only four perpendicular positions of the seed in the cavity, the mathematical envelope of the dielectric response is usually greater when the seed is dead.