In vitro digestion of emulsions: diffusion and particle size distribution using diffusing wave spectroscopy and diffusion using nuclear magnetic resonance

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English. Diffusing wave spectroscopy (DWS) is one of the few techniques enabling the investigationof structures and dynamics in turbid systems, that is in the multiple light scattering domain.This makes it an important technique to study colloidal dispersions such as foam, gel oremulsion. In this article, DWS in both back- and forward- multiple scattering was used tomonitor the in vitro digestion of turbid undiluted emulsions. Eight formulations were testedusing two triglycerides, two emulsifiers and two emulsifier concentrations.The main goal of the study was to interpret the DWS data and compare the results to thosefrom other techniques. We first extended the cumulants/moments fit method used for singlescattering to obtain a particle size distribution (PSD) by DWS for multiple scattering. In thecase of unimodal distributions, this compares well to PSD obtained from single scattering bydynamic light scattering (DLS). A second interpretation based on the multiple forward-scattering allowed the time-resolved diffusion coefficient to be measured. This was comparedto diffusion monitored by nuclear magnetic resonance (NMR) of turbid undiluted emulsions.Both techniques report similar diffusion coefficients, although NMR measures a truemolecular diffusion in different environments whereas DWS measures the diffusion ofsupramolecular objects in the aqueous phase. These techniques are thus complementary,NMR resolving the kinetics of lipolysis, and DWS resolving the structural transitions, foundto be first a droplet to vesicle one, then a vesicle to micelle one. In this study, the mainformulation parameter influencing the digestion was found to be the type of triglycerides.