Mario Horvat

Influence of medium-chain triglycerides on expansion and rheological properties of extruded corn starch.

Enhancement of product properties of extruded starch based products can be achieved by incorporating health promoting oil into the matrix. In order to achieve a preferably high expansion with a homogeneous pore structure, the expansion mechanisms have to be understood. In our study, we applied a customized twin-screw extruder set up to feed medium-chain triglycerides after complete gelatinization of corn starch, minimizing its effect on the starch gelatinization. Despite the fact, that the addition of up to 3.5% oil showed no influence on the extrusion parameters, we observed a three-fold increase in sectional expansion. Longitudinal expansion was less affected by the oil content. Rheological properties of the gelatinized starch were measured using an inline slit die rheometer. In addition to shear viscosity, we presented a method to determine the Bagley pressure, which reflects the elongational properties of a fluid. We were able to observe an increase in the Bagley pressure from about 25 bar up to 35-37 bar due to the addition of oil.

Structures in Food: Possibilities of Imaging and Diffusometry

Apart from chemical composition, structure is an important parameter which influences not only food processing schemes, but also product characteristics as taste/mouth feeling and finally shelf life. Structure analytics should be non-destructive and non-invasive, but also capable to determine structure of fluids as well as solids over several orders of magnitude of length and time scales. NMR imaging has been applied for almost all foods, and structural parameters as size distributions have been determined in wet and dry foods. As relaxation properties of foods vary, a variety of imaging techniques were explored. They range from single point imaging for short T2-materials over conventional spin and gradient echo methods to spectroscopic imaging. The limiting factors are voxel size (minimally 15 µm×15 µm×15 µm), with respect to the accessible length scale, and the measurement time with respect to the time resolution of temporally changing products. Below the length scale of imaging, down to about 1 µm, diffusion properties can be exploited in liquid foods. The most prominent example is the measurement of size distribution functions of emulsions. Whereas this approach is already rather old, it is still further developed and applied on various emulsion types. An overview over imaging and diffusion methods is given with respect to their advantages and limitations.