Solid Fat Content Determination of Dispersed Lipids by Time‐Domain NMR

Abstract

Time domain nuclear magnetic resonance (TD‐NMR) is used to determine the solid fat content (SFC) of dispersions stabilized by a high molecular weight hydrocolloid (gum arabic, GA) containing a high melting lipid (tristearin, SSS). Since the lipid is molten prior to homogenization for the preparation of the dispersion it recrystallizes during cooling and storage. It is known that the recrystallization in a disperse system differs from bulk lipids and TD‐NMR can be a helpful tool to investigate the phenomenon. SFC measurement by TD‐NMR is well established and widely used in food science for oils, spreads, and seeds. In the case of dispersions, however, the situation is more demanding due to the quasi‐continuous phase. A suitable TD‐NMR method has to account for that and can be realized when combining longitudinal and transverse relaxation properties to separate the signal contribution of the quasi‐continuous phase and the solid lipid and liquid lipid dispersed phase. Signal from water and emulsifier is eliminated by magnetization inversion with an initial 180° pulse and a subsequent dedicated inversion delay. The emulsifier shows a longitudinal relaxation similar to the aqueous phase. With a carefully chosen inversion delay, both signal contributions of water and emulsifier can be suppressed, and a quantitative determination of the SFC is possible via dedicated data processing.Practical Applications: The method can be applied in characterization, stability tests and quality control of complex food emulsions and solid lipid particles, which are recently under development as drug carrier systems.TD‐NMR is used to determine the solid fat content (SFC) of dispersions with high water content, a hydrocolloid as emulsifier and fat. Since the fat is molten prior to homogenization it recrystallizes during cooling. It is known that recrystallization in a dispersed system differs from bulk and TD‐NMR is a helpful tool to investigate the phenomenon. The situation is demanding due to the quasi‐continuous phase. With magnetization inversion, a preset 180° pulse, and a carefully chosen inversion delay, signal contributions of water, and emulsifier can be suppressed, and a quantitative determination of the SFC is possible.