Improved microwave-assisted saponification for reliable MOSH and MOAH determination in edible fats and oils

Mineral oil saturated hydrocarbons (MOSH) and mineral oil aromatic hydrocarbons (MOAH) are frequently detected contaminants in foods, particularly in lipid-rich matrices such as edible fats and oils. The official method for their determination in these matrices is ISO 20122:2024, which includes a saponification/extraction step, purification from interferences, and on-line HPLC-GC-FID analysis. However, the ISO 20122:2024 protocol presents limitations related to inconsistent recoveries of MOAH internal standards during sample preparation, affecting quantitative reliability.
A microwave-assisted saponification/extraction (MASE) method has previously been proposed to improve the consistency of internal standard recovery through optimized solvent composition. Nevertheless, the original conditions (60 °C, 30 min) were insufficient to ensure complete saponification of some matrices, particularly hydrogenated or high-melting fats.
In this study, the saponification conditions of the MASE approach were re-optimized to ensure efficient fat removal across a range of edible oils and fats differing in melting point and fatty acid composition. The process was evaluated by gravimetric determination of residual fat and by monitoring the ratio of MOAH internal standards, which ideally equals 1.00. The optimized conditions (120 °C, 20 min) ensured complete saponification while producing internal standard ratios consistently closer to unity than those obtained with the ISO method.
Although matrix-dependent deviations were still observed and were found to correlate with the fatty acid composition of the oils, the ratios remained systematically closer to 1.00 compared with the ISO procedure.