Certification of primary standards for solid fat content (SFC) determination

Spreadability of fat containing food products can be easily assessed by the solid fat content (SFC). Usually, SFC is determined by direct methods based on low-resolution nuclear magnetic resonance spectrometry. A system of primary and secondary reference materials is required to calculate so-called “F-factors” accounting for instrument dead times. Secondary standards (“plastic-in-oil” standards; PIO) are intended for daily use. They are usually provided by instrument manufacturers and prepared in a “proprietary” manner, i.e. linked to manufacturers' PIO master batches. For better comparability of SFC results worldwide, a harmonized and sustainable approach was demanded by AOCS to establish a reference system based on primary standards, being independent from instruments used. IRMM as independent and experienced institute was contacted to produce blends of tristearin (solid) and triolein (liquid) of high purity from independent sources. Three sets of reference materials (“IRMM-805”) each comprising of four triglyceride standards (TGS) were produced as primary standards for calibration of secondary standards. Stability of the samples was thoroughly tested and confirmed. A “sequential” interlaboratory comparison involving eleven laboratories demonstrated that the calculated F-factors were independent from the SFC of the respective triglyceride blend and from the instruments used. In addition, participants measured six PIO samples following two different measurement protocols. No significant differences of the obtained F-factors were found.