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.