Abstract
Nuclear magnetic resonance (NMR) is defined as a non-invasive technique for measuring
emulsion droplet size. The diffusion of oil molecules in oil-in-water (O/W) emulsions is
restricted within oil droplet which directly affected by the oil droplet radius. Thus, restricted
diffusion of oil molecules can be used to determine the oil droplet diameter. This research
was aimed to investigate the influence of emulsifier type on emulsion droplet diameter
by NMR comparing with conventional light scattering technique. The 10% wt oil O/W
emulsions were prepared using nanofibrillated cellulose (NFC) or whey protein isolate
(WPI) at concentration of 0.3, 0.5 and 0.7% wt as an emulsifier. Diffusion coefficients (D)
were measured by pulsed-field-gradient stimulated spin-echo (PFG-STE) pulse sequence
using High-field NMR. The results showed that the diffusion coefficients of the O/W
emulsions were dependence on diffusion time (Δ). The increase in diffusion time found
the decay of attenuation of a coherent magnetic signal. Since the diffusion of oil molecules
was limited by adsorbing of NFC at oil-water interfaces, the restricted diffusion was found
in NFC-stabilized emulsions by observing constantly of mean square displacement (Z2)
when the diffusion time was increased. On the other hand, free diffusion was found in
WPI-stabilized emulsions which may occur from the diffusion of oil molecules within
oil droplet and the movement of oil droplet itself. The droplet size determined by NMR
technique showed the results in the same agreement with the light scattering technique.
Hence, the restricted diffusion measurement by PFG-NMR is a novel and an alternative
technique for monitoring emulsion droplet size. However, it is more suitable for emulsions
with slow movement of oil droplets or emulsions with high viscosity of continuous phase.
