Microwave-assisted saponification and SPE for the simultaneous or alternative analysis of dialkyl ketones and sterols in fats

Sterols and, in particular, phytosterols play an important role in the human diet and in verifying the authenticity of the oil products (e.g., to discriminate olive oil from seed oil). The traditional determination of sterols usually involved a first saponification step, followed by liquid-liquid extraction of the unsaponifiable fraction, TLC for isolation of the sterol and final instrumental determination, most often in gas chromatography (GC) after derivatization. Interesterification is an industrial process used to redistribute the fatty acids among triglycerides changing the physicochemical characteristics of fat (e.g. changing crystallization behaviour and the melting point, improving plasticity). Different from the enzymatic process, the chemical one leads to the formation of dialkyl ketones (DAKs) as by-products. So far, only two papers have dealt with DAKs determination in food [1,2]. Microwave-assisted saponification followed by a lab-made solid-phase extraction (SPE) was optimized for the characterization of either DAK or sterols or both simultaneously. The final instrumental determination was performed by GC-FID for quantification and GC-MS for confirmation purposes