Validation of a gas-chromatographic method for the determination of milk fat contents in mixed fats by butyric acid analysis

Gas-chromatographic analysis of butyric acid (C4) in mixed spreadable fats can be used to calculate the milk fat proportion, either by additional analysis of the underlying pure milk fat (component sample) or by using a mean C4 content instead. After comparison of several analytical variants and subsequent development of an improved draft standard for quantitation of milk fat in mixed fats, this draft was checked for accuracy in three EU-wide ring tests performed with 26 participating laboratories. Due to the natural variation of the butyric acid content in European milk fats, deviations from the actual milk fat content may amount up to +/-10% in addition to analytical errors when calculating with a mean C4 content instead of the C4 content of a component sample. Though the reproducibility could be improved by application of correction factors derived from a reference fat, only the calculation based on the additional analysis of a component sample of the pure milk fat led to an acceptable accuracy concerning the trueness of the results in combination with good repeatability (r) and reproducibility (R). Finally, several further improvements of the draft standard led to a precision of r = 4.3% and R = 6.0% relative to the mean of two milk fat contents determined. Thus, the tested procedure proved its suitability for a control method of the declared milk fat content in mixed fat spreads.