Applicability of an MTBE lipid extraction method assisted by microwave in food analysis. Case of study: extraction of pistachio oil

Objective This research aimed to evaluate the effectiveness of a fast and greener lipid extraction method assisted by microwave in fresh pistachios, in which the amount of lipids is up to the 40%. The nutritional and therapeutic significance of Pistachio (Pistacia vera L.) oil is largely attributed to its high levels of unsaturated and essential fatty acids. The extraction method used to isolate natural compounds from the raw material significantly impacts product quality, especially in preserving its nutritional value. Consequently, the study focuses on the impact of the proposed extraction method on the quality and yield of the extracted oil, as well as its fatty acid (FA) composition. Methods Lipid extraction from fresh pistachios was performed using seven different methods, including microwave-assisted extraction (MAE) with methyl-tert-butyl ether (MTBE), used as one-solvent extraction or in mixtures with methanol and water. In the latter, the same solvents composition and ratio of Matyash method were used (10/3/2.5 v/v/v) [1]. MAE methods were compared in terms of extraction yields and FA composition of pistachio oil to Soxhlet and Matyash, considered gold-standard lipid extraction methodologies in food and biological samples. FAs, derivatized into methyl esters (MEs), were analysed through a gas chromatography-flame ionization detector (GC-FID). Results Among the seven methods tested, the MAE-MTBE method showed comparable results to Soxhlet and Matyash methods in terms of extraction yield and FAMEs composition. In all extraction procedures, eight fatty acids were identified in the pistachio samples. The most abundant fatty acid was oleic acid (C18:1n9c), followed by linoleic acid (C18:2n6c) and palmitic acid (C16:0), which together accounted for over 90% of the total FAMEs. Conclusions The results obtained by MAE-MTBE were in line, in terms of extraction yields and FAMEs composition, with the other extraction methodologies. MAE-MTBE also proved to be a greener extraction procedure than the reference methods when evaluated based on the AGREEprep metrics [2], highlighting its environmental benefits over conventional methods.