Oil Diffusion in Fat Crystal Matrices: Characterization by NMR Relaxometry and Diffusometry

A novel technique based on high resolution (HR)-NMR diffusometry is presented to investigate oil diffusion on the (sub)-micron scale level in fat crystal networks in situ and in a non-destructive way. The use of a high-gradient probe enables the observation of the time (Δ)-dependent diffusion behavior in fat blends (FBs) of different solid fat content (SFC), as obtained by mixing soft palm mid fraction and high-oleic sunflower oil. Hereby, the NMR-diffusion data are analyzed using CONTIN to obtain a continuous distribution of diffusion coefficients. As such, the hindrance of the oil diffusion by the fat crystal network is examined. The characterization of the lipid matrices is completed with 1H-LR-NMR relaxometry, X-ray diffraction, and microstructural visualization. For the investigated FBs, the average diffusion coefficient D(Δ) decreased with increasing SFC, indicating an increased tortuosity of the diffusive path due to an increasing density of the fat crystal networks as observed by polarized light microscopy. This is also supported by an increase in crystal surface area which is indicated by T2-relaxation analysis. This study shows that NMR diffusometry is a promising technique for investigation of structure-function relationships in fat systems. Practical Applications: The study shows that NMR diffusometry is a promising technique for investigation of structure-function relationships in fat systems. For the first time, oil diffusion in fat crystal networks has been studied by HR-NMR diffusometry with high gradients to collect the diffusional echo signals, while CONTIN-analysis has been used for the first time to process the data. © 2021 Wiley-VCH GmbH