Determination of Solid Fat Content in Plain Fats and Suspensions with Lab-scale SAXS Device

Abstract

Fat suspensions, i.e. heterogenous mixtures of solid particles in a fat, are omnipresent in food products. Depending on the temperature, the lipid phase consists of a liquid and a solid fraction, often expressed as solid fat content (SFC). In suspensions, the solid particles also tend to affect the SFC, which makes it an important parameter to study. Conventionally, for plain fats, the SFC is acquired via an NMR measurement (AOCS Cd16b-93). Complex mixtures, like suspensions, are more difficult to study by NMR, as the solid particles produce an interferent signal. This can be overcome by using a specific standard and an adapted method (AOCS Cd16-81). As an alternative, the use of small-angle X-ray scattering (SAXS) for determining the SFC was studied. The aim of this study was to develop a methodology for determining the SFC in plain fats, but also in complex mixtures, without the need for extra standards or calibration. Moreover, SAXS has proven to be a suitable technique as there is no (or a constant) contribution of solid particles to the signal obtained from the fat. The SAXS equipment used is a Xenocs Xeuss 3.0 equipped with a Cu-source and moveable detector. Plain palm oil and palm oil-sucrose mixtures were studied at several isothermal crystallization temperatures. The SAXS technique allows to follow the SFC continuously over time during isothermal crystallization, which is not possible with NMR. From a SAXS profile, the liquid and solid fat contribution can be clearly separated. The separation of the solid and liquid contribution and their respective quantification was optimized. Special interest was put into the contribution of different triacylglycerol polymorphs. For plain fats, the results were compared to conventional results obtained with NMR and were found to be very similar. For suspensions, the results were verified with other techniques, such as DSC.