Microwave-Assisted Saponification Method Followed by Solid-Phase Extraction for the Characterization of Sterols and Dialkyl Ketones in Fats.

Steven Mascrez,Sabine Danthine,Giorgia Purcaro

doi:10.3390/foods10020445

Steven Mascrez, Sabine Danthine + Show 1 more

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https://doi.org/10.3390/foods10020445

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Abstract

Unlike other fields, the methods routinely applied for fats and oils are still tied to traditional, time- and solvent-consuming procedures, such as saponification, column chromatography and thin-layer chromatography. In this paper, microwave-assisted saponification followed by a lab-made solid-phase extraction was optimized for the characterization of either dialkyl ketones (DAK) or sterols or both simultaneously. The instrumental determination was performed by gas chromatography- flame ionization detector (GC-FID) for quantification and gas chromatography-mass spectrometry (GC-MS) for confirmation purposes. The proposed method showed good recoveries (>80%) and limit of quantification (0.04–0.07 μg/g for the 4 DAK and of 0.07 μg/g for α-cholestanol). Repeatabilities (n = 3) were below 15% for DAKs and generally lower than 6% for sterols. Accuracy on the entire sterol profile was confirmed in comparison to the International Olive Council reference method. The method was finally applied to real-world samples before and after chemical interesterification.

Highlights

From other fields, such as pharmaceutical, food analysis is highly dependent on a preliminary sample preparation step, mainly the extraction and isolation of the target analytes
After each test for the MAS optimization, a purification step is required before the final determination, which was performed by solid-phase extraction (SPE) after proving the equivalence with the official thin-layer chromatography (TLC) procedure
For the optimization of both MAS and SPE, an olive oil sample was spiked with a mix of dialkyl ketones (DAK) (C10:0-C9:0, C11:0-C11:0, C14:0-C14:0, C18:0-C18:0) and the Internal standards (ISs) for sterols (α-cholestanol and betulin)

Summary

Introduction

From other fields, such as pharmaceutical, food analysis is highly dependent on a preliminary sample preparation step, mainly the extraction and isolation of the target analytes. Despite the advancement in the field, with the introduction of highly efficient instrumentation, automated sample-preparation workstations and miniaturized techniques, most of the methods routinely applied to food analysis remain tedious, timeconsuming and highly manipulative [1,2]. This is true in the field of fats and oil, where still Soxhlet extraction, saponification involving a large amount of solvents, followed by thin-layer chromatography (TLC) or column chromatography, are widely used. MAE is a rapid, solvent saving and efficient extraction technique It exploits the energy produced by non-ionizing radiations to intimately heat the sample-extractant system in few seconds by inducing dipole rotation and ionic conduction [3]. A limited number of applications have exploited the use of MAE to accelerate the saponification step (microwave-assisted saponification, MAS) [4–11]

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