Diffusion of fat and water in cheese as studied by pulsed field gradient nuclear magnetic resonance

Abstract

Pulsed field gradient nuclear magnetic resonance was used to measure water and fat self-diffusion coefficients in Cheddar and Swiss cheeses. The water diffusion coefficients are about one-sixth that of bulk water at the same temperature and there is strong evidence to suggest that water diffusion is confined to surfaces within the protein matrix. The echo attenuation for the fat indicates restricted diffusion consistent with the fat being present in the form of small droplets within the cheese. The theory of restricted diffusion has been extended to allow for a spread of droplet size. The data conform to a gaussian distribution of molecular numbers (sphere volume) over droplet radius. A small attenuation approximation is used in the theory but consistent values of droplet radii and standard deviations in droplet size are obtained over a large echo attenuation range.