NMR Imaging in the Study of Diffusion of Water in Foods

Abstract Most studies of moisture transport in foods and related polymeric materials have of necessity been integral experiments, for instance, the characterization of the drying of a food from the drying rate data only. Integral data are often insufficient to allow the investigation of the underlying physics of moisture transport, particularly in heterogeneous systems such as foods. Magnetic resonance imaging makes it possible to resolve spatially and temporally both moisture saturation and water self-diffusion coefficients. This information can then be used to determine effective transport coefficients, material structure, and material properties, and additionally to assist in the study of physicochemical processes. Classical characterizations of moisture transport in food systems have employed integral techniques such as sorption-desorption or gravimetric analysis. These studies have proven useful for control of industrial processes, although they have failed to provide detailed insight or information on the role of material structure and properties in moisture transport. Magnetic resonance imaging is a new technology capable of providing measurements of component saturations and material properties on a spatially resolved basis. Through analysis and interpretation of magnetic resonance imaging measurements it is possible to map internal structure, internal variations in transport rates, and internal variations in material properties such as membrane permeabilities. Nuclear magnetic resonance and magnetic resonance imaging can be utilized to measure the transport of mass by measuring molecular diffusion coefficients and/or by measuring internal gradients in component saturations. These two different data sets can then be applied to estimating the structure and properties of the material under study. This paper presents an introduction to magnetic resonance and outlines the strategy for characterizing moisture transport in food materials using magnetic resonance saturation profiles and self-diffusion measurements.

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