TIME-DOMAIN REFLECTOMETRY IN CARBOHYDRATE SOLUTIONS

With time-domain reflectometry (TDR) the dielectric permittivity of fo odstuffs can be measured with the use of a cheap cable tester which ha s proved its value in soil science. The materials which are examined a re solutions of mono; di- and polysaccharides. The influence of the sp ecies, the composition and the temperature on the dielectric permittiv ity is considered. TDR is a suitable method for determining the water content of a sample, because the dielectric permittivity is mainly inf luenced by this property. Temperature has a complex influence on the m easured dielectric permittivity: at high water contents the relation i s negative, while at low water contents this relation is positive. Thi s results in a cross-over point at water contents of about 55%. The de pendency of the dielectric permittivity on water content is also model ed with a mixing model for non-interactive dispersed media. From this model it can be concluded that, in the frequency range used, the inter active carbohydrate solutions behave more and more as noninteractive m edia at lower temperatures.