A new microwave-assisted extraction technology for the profiling of free and esterified fatty acid in food matrices

Microwave-assisted extraction (MAE) is a fast and efficient extraction technique based on the use of microwaves to heat the sample/solvent mixture to facilitate and improve the extraction of the analyte both in terms of efficiency and throughput. Several comparative studies have demonstrated the excellent performance, in terms of recovery and precision, obtainable with MAE compared to other traditional extraction techniques [Food Res. Int. 33 (2000) 733–741]. The main advantage is linked to the homogeneity and the rapidity of the heating process, which occurs inversely compared to a traditional heating process when polar compounds are present. The use of microwave technology can bring also other benefit, such as the possibility to merge different sample preparation steps in a unique process. Examples have been reported performing saponification and extraction simultaneously. In a previous work, we demonstrated the excellent performance in terms of accuracy and throughput of performing extraction and derivatization simultaneously in a procedure called microwave-assisted derivatization/extraction (MADE) [Adv. Sample Prep. 4 (2022) 100039]. The method was developed for characterizing the fatty acid profile of a large variety of food commodities. In this work the potential of a new microwave technology was explored. This novel instrument in principle coupled the benefit of microwave technology with the use of high-pressure, which should, beyond increasing the boiling temperature of the extraction solvent, facilitate solvent penetration into the solid matrix, thus improving the overall performance of extraction. Moreover, the specific design of the novel system, consisting in a single chamber accommodating multiple vessels, allows for sample miniaturization. The potentiality of this synergic coupling of microwave and pressure have been investigated in the extraction and derivatization of fatty acids, comparing with the previous developed method. Moreover, a different procedure was developed by using dedicated experimental design to characterize free and esterified fatty acids present in hazelnuts, as marker of sample stability over time. The obtained fatty acid methyl esters (FAMEs) have been characterized using multidimensional comprehensive gas chromatography (GC×GC) coupled to FID. Such a fully integrated platform represents a key platform for detailed large-scale screening in any lipid applications.