Matthias Rother

How to Meet the Freeze Drying Standard in Combined Drying Processes: Pre and Finish Drying of Carrot Dice

Freeze-drying (FD) processes are well known to produce high-quality consumer products. Major problems are long drying times, high investment costs, and resulting maintenance and operating costs that make FD a very costly process. In this study, the potential of air drying (AD) and microwave vacuum drying (MVD) is tested to reduce freeze-drying times and make better utilization of the investment by combining FD with alternative lower cost drying processes using a pre or finish drying step while preserving the qualwity of the final product. Using carrot dice as a sample product, predrying did not lead to the desired qualities and reduction in drying time, whereas finish drying produced promising results. FD/MVD was 40% faster than pure FD and achieved freeze-drying standards regarding volume retention, shape, color, and rehydration. The good performance of microwave vacuum finish drying can directly be traced back to a time effect that is possibly linked to a characteristic collapse time of the cellular matrix. In order to use this effect, a stable skeleton must have developed at the point of process changeover, changeover has to be immediate, and finish drying has to be quick.

Waveguide Microwave Imaging: Spherical Inclusion in a Dielectric Sample

A new 3-D microwave imaging technique is proposed for the detection of a position and size of a spherical object in a dielectric sample located in a waveguide system. The reconstruction is based on a radial basis function neural network inversion, backed by finite difference time domain analysis and requires only elementary measurements of complex reflection and transmission coefficients. Functionality of the technique is illustrated by computational experiments in reconstructing the parameters of a glass sphere and an air bubble in a rectangular Teflon block. It is shown that, at 915 MHz, the spheres of not less than 15 mm diameter are reconstructed with the average errors of 0.9%-2.2%.

Dielectric and Thermal Properties of Rice Cake Formulations Containing Different Gums Types

In this study, dielectric properties of rice cake formulations containing different gum types (xanthan, guar, locust bean, HPMC, and kappa-carrageenan) were determined at temperatures between 25 and 90°C at 2450 MHz. Moreover, thermal properties of these formulations were determined by using differential scanning calorimeter (DSC). Dielectric properties of cake batters were found to be dependent on cake formulation. Xanthan and guar gum containing cake batters had the highest dielectric constant and loss factor values at 25°C. Temperature dependence of dielectric properties was not significant until temperature of 85°C. Gelatinization enthalpy of batter increased with the addition of gums.