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

Abstract

Diffusing wave spectroscopy (DWS) is one of the few techniques enabling the investigation of 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 or emulsion. In this article, DWS in both back-and forward-multiple scattering was used to monitor the in vitro digestion of turbid undiluted emulsions. Eight formulations were tested using 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 those from other techniques. We first extended the cumulants/moments fit method used for single scattering to obtain a particle size distribution (PSD) by DWS for multiple scattering. In the case of unimodal distributions, this compares well to PSD obtained from single scattering by dynamic light scattering (DLS). A second interpretation based on the multiple forward-scattering allowed the timeresolved diffusion coefficient to be measured. This was compared to the diffusion monitored by nuclear magnetic resonance (NMR) of turbid undiluted emulsions. Both techniques report similar diffusion coefficients, although NMR measures a true molecular diffusion in different environments whereas DWS measures the diffusion of supramolecular objects in the aqueous phase. These techniques are thus complementary, NMR resolving the kinetics of lipolysis, and DWS resolving the structural transitions, found to be first from a droplet to a vesicle and then from a vesicle to a micelle. In this study, the main formulation parameter influencing the digestion was found to be the type of triglyceride.

Formulation of sub‐micron emulsions containing docosahexaenoic acid esterified in triacylglycerols or phospholipids

“…This indicates an increase of the viscosity of the aqueous medium, in agreement with the decreased diffusion coefficient of PC/T80 droplets. A decrease of water diffusion coefficient upon incubation in simulated digestive conditions has previously been observed , but digestion is accompanied of very large change of the molecular and supramolecular structures. Desorption of Tween‐80 molecules due to the decrease of total surface area of the droplets with coalescence could participate to this phenomenon.…”

“…The mobility of the TAG molecules inside the oil droplets is hindered because of the viscosity of the lipid phase, whereas the diffusion of PL is restricted to their lateral diffusion within the interfacial monolayer, as determined by its microfluidity. The coefficients were lower than diffusion coefficients at 37°C of triolein in emulsions (mean droplet size varying between 350 and 400 nm) stabilized by sodium oleate or β‐lactoglobulin (around 1 × 10 −11 m 2 s −1 ) . This difference could result from a higher viscosity of our lipid blends as compared to triolein, including a temperature effect.…”

The tribological properties of lubricating greases produced on vegetable base and modified of polytetrafluoroethylene

“…In the transmission mode, scattered light is detected after passing through the sample, and intensity fluctuations are correlated using the correlation intensity function (ICF). In contrast, in the backscattering mode, the light that disperses back towards the incident beam is collected and its fluctuations are measured [43][44][45].…”

Spectral Properties of Foams and Emulsions

“…Forward-scattering DWS measurements, complementary to nuclear magnetic resonance diffusion measurements, permitted to determine the diffusion coefficients. It was observed that during digestion, the transitions were from a droplet to a vesicle and afterwards to a micelle [174].…”