Update on the microwave-assisted saponification conditions for mineral oil hydrocarbons determination in fats and oils

Abstract

The analysis of mineral oil saturated hydrocarbons (MOSH) and mineral oil aromatic hydrocarbons (MOAH) in edible fats and oils typically includes saponification followed by liquid–liquid extraction. The official ISO 20122:2024 method has shown limitations, particularly due to inconsistency in recoveries of MOAH internal standards (ISs), which compromises quantitative accuracy. A previously developed microwave-assisted saponification/extraction (MASE) method improved IS recovery consistency through optimized solvent composition but proved insufficient to fully saponify certain oils (e.g., hydrogenated fats) under its original conditions (60 °C, 30 min). In this study, saponification parameters were reoptimized and validated by gravimetric control of residual fat and evaluation of IS ratios, which are ideally 1.00. The final conditions (120 °C, 20 min) ensured complete saponification across a wide range of fats and oils with varying compositions and melting points. IS ratios were consistently closer to 1.00 than with the ISO method, although matrix-dependent deviations persisted. These effects correlated with the fatty acid profiles of the oils, which affect the properties of the soaps formed during saponification and, in turn, the partition of MOAH ISs during extraction.