A Novel Method To Measure Emulsification

Introduction The rate of lipolysis of dietary fat depends critically on emulsion particle size, which influences fat absorption and metabolism. In order to study the factors affecting fat emulsification within the gastric lumen it is necessary to measure the degree of emulsification in vivo. The measurement of emulsification is also important in the food industry and in other areas. NMR has been widely used to measure droplet size distributions using PGSE methods1, which are sensitive to motion and require high gradient amplitudes. A technique based on relaxation would be inherently more robust, particularly in vivo. We are not aware of any literature on using NMR relaxometry in this way, although it has been used to characterise emulsion fat fraction2. We have previously observed3 that T2 depends on droplet size, and have hypothesised that this may be due to diffusion in local field gradients between the droplets and water3,4. This paper presents a technique for measuring emulsification based on EPI relaxometry, and a theoretical model5 to explain the data. Changes in 1/T2 of 5 oil-in-water emulsions in the range 0.4-20.9 μm were measured and modeled in vitro at 37°C. Theory The signal changes due to microscopic susceptibility variations can be quite complex and have been modeled using Monte Carlo techniques5. As validation we can use also outer-sphere relaxation theory to obtain analytical solutions in the motionally narrowed regime, valid for δω· τR<<1 (δω = equatorial frequency shift and τR = R2/D with R = oil droplet radius and D = water diffusion coefficient at 37°C). For the particle sizes we are investigating, the secular component is dominant and the change in transverse relaxation rate ΔR2 can be expressed as6: