1 Acta Chim. Slov. 2021, 68, – Ruiz-Domínguez et al.: Variability of Omega-3/6 Fatty Acid Obtained ... DOI: 10.17344/acsi.2020.6621 Scientifc paper Variability of Omega-3/6 Fatty Acid Obtained Trough Extraction-Transesterifcation Processes from Phaeodactylum tricornutum Mari Carmen Ruiz-Domínguez, 1, * Constanza Toledo, 1 Daniel Órdenes, 1, 2 Carlos Vílchez, 3 Paula Ardiles, 1 Jenifer Palma 1 and Pedro Cerezal 1 1 Laboratorio de Microencapsulación de Compuestos Bioactivos, (LAMICBA), Departamento de Ciencias de los Alimentos y Nutrición, Facultad de Ciencias de la Salud, Universidad de Antofagasta, 1240000 Antofagasta, Chile 2 Departamento de Tecnología Médica, Facultad de Ciencias de la Salud, Universidad de Antofagasta, 1240000 Antofagasta, Chile 3 Algal Biotechnology Group, CIDERTA and Faculty of Sciences, University of Huelva, 21007 Huelva, Spain * Corresponding author: E-mail: maria.ruiz@uantof.cl Received: 12-22-2020 Abstract Te efect of direct transesterifcation methods on the omega-3/6 composition of extracts from Phaeodactylum tricornu- tum was studied. Te aim of this work was to identify an extraction method which allowed to obtain the most suitable profle of fatty acids in terms of its potential benefts to health, particularly if further used in the food industry. Seven methods using acids, alkalis, and heterogeneous-catalysts, (namely methods from 1 to 7, abbreviated as M1-M7) were performed to determine α-linolenic (ALA), linoleic (LA), docosahexaenoic (DHA) and eicosapentaenoic (EPA) acids. Te composition of fatty acids was in all cases characterized by the major abundance of palmitic (23.95–34.08%), palmit- oleic (30.94–35.56%), oleic acids (3.00–7.41%), and EPA (0.5–6.45%). Unsaturated fatty acids extraction yield was higher with a two-step transesterifcation process (M6, 63.65%). Te total fatty acid methyl ester content (FAME) obtained with acid-transesterifcation (M1) reached about 21% wt, and 60% w/w total lipids. ALA higher relative content (ALA/LA ratio) was obtained when a lipid pre-extraction step was performed prior to acid-catalysis (M4). Te transesterifcation method based on alkali-catalyst (M3, KOH catalyst) led to obtain higher DHA relative contents (DHA/EPA ratio up to 0.11), although its FAME content was 3.75-fold lower than that obtained with acid-transesterifcation (M1). Overall, this study shows that direct transesterifcation with alkali-catalyst (M3) improves the determination of PUFA content from the diatom through a more efcient transesterifcation-based extraction process, and thus allow to assess the value of the biomass more accurately for application in the food industry. Keywords: diatom; lipids; fatty acids; DHA/EPA; ALA/LA; PUFA 1. Introduction Microalgae cultivation has gained much interest these days because of the need for renewable resources with the ability to synthesize valuable products such as pigments, carbohydrates, and fatty acids, among other compounds. 1,2 Phaeodactylum tricornutum, in particu- lar, is a model pennate diatom used for physiological studies and biotechnological food and nutritional appli- cations. 3,4 Tis diatom is known for its rapid growth and antioxidant capacity owing to fucoxanthin (carotenoid) and/or long-chain polyunsaturated fatty acids (PU- FAs). 5–7 P. tricornutum is one of the few microalgae spe- cies that can produce high levels of eicosapentaenoic acid (EPA; C20:5n-3), along with low levels of docosa- hexaenoic acid (DHA; C22:6n-3) and arachidonic acid (ARA; 20:4n-6). 8 Tis ability is relevant to the biotech- nological industry since PUFAs have benefcial human health efects. DHA and EPA are essential nutrients that play an important role in infant growth and development, along with adult cardiovascular health. 9, 10 Accordingly, several reports demonstrate that consuming a diet rich in ome-