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Bound and free water determination by dielectric spectroscopy

Svetlana von GratowskiInstitute of Radio Engineering and Electronics, Russian Academy of Sciencesfrank.vongratowski@nexgo.de

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Food consist of chemical components:

n water , n protein, n lipid, n carbohydraten vitamin, n mineral, n flavor,n color, n etc…

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Type of water in food

n Bound water : n Free water - bulk water

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Bound water is heterogeneous, consist of

Monolayer Water is bound in food - restricted in its movement due to charges, hydrogen bond, physical entrapment. Hard to remove from food. Never be able to remove water completely.

Multilayer Water - additional layer of water around food particle. Not as hard to remove as the monolayer.

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Water Activity – measure of Bound Water

Free (pure) Watern free flowing, n great solvent for

chemical/biochemical (food)

Bound Watern held tightly to other

molecules, n Exhibit no flow

properties, n not a solvent, n high density, n Lack of VP, n inability to freeze, n cannot be

expressed from tissues

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Standart measurement of bound water

n Nuclear Magnetic Resonnance(NMR)

n Differential Scanning Calorimeter (DSC) (freezing and melting calorimetry)

n Dielectrical spectroscopy

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Two peaks of dielectrical relaxation

n Dielectric relaxation time measurements (Mashimo et al., 1987) on living tissue and a number of biological materials provide direct understanding of the motions of water molecules in such systems at ordinary temperatures (20 oC). The living materials in this study include carp muscle; the non-living materials include tuna, beef, pork, and chicken muscle. In all of the materials, two dielectric absorption peaks are observed, one peak around 100MHz and the other around 20 GHz.

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Two peaks of dielectrical relaxation

n Peak nearby 100 MHz is connected with bound water.

n Hence, the bound water correlation times are 125 times larger than those of the free water.

n Peak at 20 GHz is connected with free water

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Method of calculation

n For theoretical investigation of dielectric properties and free and bound water content we calculate the Debye relaxation of dielectric permittivity for a admixture of free water, bound water in the nonpolar matrix. matrix.

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Appropriate experimantal methodn Suppose, that all bound water have the

same relaxation frequency. For such free-bound water model measurement of real and image parts ε can be out carried on 2 frequencies.

n One frequency in millimeter wave range, near 1/τ rel of free water. In this frequency range there is better sensitivity to free water.

n The other frequency in MHz range near 1/τ rel of bound water . In this frequency range there is better sensitivity to bound water.

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Theoretical calculation

n For theoretical investigation of dielectric properties and free and bound water content we calculate the Debyerelaxation of dielectric for a admixture of free water and bound water in food matrix. Let us consider, that food matrix consist of nonpolar substances. In frequency ranges, mentioned above other food substances like proteins, fats and carbohydrates have no Debye relaxation and they can be considered as a nonpolar. r matrix is negligible. matrix.

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Theoretical calculationn Let us consider that Debye relaxation in

nonpolar matrix is negligible. n Then for determination of dielectric

permittivity of nonpolar matrix with two different polar admixtures dielectric permitivity of each part was calculated and volume average value was obtained.

n The obtained coplex dielectric permittivity ε depends on full moisture content, dielectric properties of bound water and percent of bound water in full water content.

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Theoretical results

freebound εααεε )1( −+=

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Theretical results

boundfreerel

boundfreeboundfreeboundfree

i ,

,,0

,1 ωτ

εεε ω

+−+=

∞

( ) =ωε boundfree,

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Theretical results

n α- percent of free, 1-α percent of bound water. The measurement of real and image parts ε on some frequencies of microwave and millimeter wave range give possibility to find out α, or percent of free and bound water. For measurement of free water better to use investigation in millimeter wave range, on frequencies near 1/τ rel of free water [4]. In this range there are reliable date for free water [5]. The investigation of bound water must be carried out in microwave range, near 1/τrel of bound water.

n

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Literature

n [1] S. Clerjon,J.-D. Daudin, J.-L.Damez. Water activity and dielectric properties of gels in the frequency range 200 MHz –6 GHz. Food Chemistry. 2003.

n [2]F. Henry, S. Houitte, L. C. Costa, M. Serpelloni. Dielectric method for the determination of aw. 2nd International Workshop on Water in Food. Reims, France

n [3] F. Henry, M. Gaudillat, L. Cadillon Costa, F. Lakkis. Free and/or bound water by dielectric measurements 2nd International Workshop on Water in Food. Reims, France.

n [4] H.J Liebe, G.A. Hufford, T. Manabe, F model for the complex permittivity of water at frequencies below 1 THz, International Journ. Of Infrared and Millimeter Waves, vol.12, no7, pp. 659-675, 1991

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Literature

n [5] V.V. Meriakri, E.E. Chigrai, M.P. Parkhomenko, Millimeter waves for water content monitoring in materials and media, 11. Feuchtetag 2002, 18/19. Vortrage, September in Weimar, s. 13-22.

n [6] A. CADUFF, C.KAPITZA, R.DEWARRAT, E.HIRT, L.HEINEMANN. Non-invasive,Continuous Glucose Monitoring System based on Impedance Spectroscopy:A Proof of Concept Study

n [6] D. A. Boyarskii, V. V. Tikhonov, and N. Yu. Komarova MODEL OF DIELECTRIC CONSTANT OF BOUND WATER IN SOIL FOR APPLICATIONS OF MICROWAVE REMOTE SENSING. Progress In Electromagnetics Research, PIER 35, 251–269, 2002