processes Article Extraction of Added-Value Triterpenoids from Acacia dealbata Leaves Using Supercritical Fluid Extraction Vítor H. Rodrigues , Marcelo M. R. de Melo, Inês Portugal and Carlos M. Silva *   Citation: Rodrigues, V.H.; de Melo, M.M.R.; Portugal, I.; Silva, C.M. Extraction of Added-Value Triterpenoids from Acacia dealbata Leaves Using Supercritical Fluid Extraction. Processes 2021, 9, 1159. https://doi.org/10.3390/pr9071159 Academic Editor: Juan Francisco García Martín Received: 21 June 2021 Accepted: 2 July 2021 Published: 3 July 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). CICECO—Aveiro Institute of Materials, Department of Chemistry, University of Aveiro, Campus Universitário de Santiago, 3810-193 Aveiro, Portugal; vitorhrodrigues@ua.pt (V.H.R.); marcelo.melo@ua.pt (M.M.R.d.M.); inesport@ua.pt (I.P.) * Correspondence: carlos.manuel@ua.pt Abstract: Forestry biomass is a by-product which commonly ends up being burnt for energy gen- eration, despite comprising valuable bioactive compounds with valorisation potential. Leaves of Acacia dealbata were extracted for the first time by supercritical fluid extraction (SFE) using different conditions of pressure, temperature and cosolvents. Total extraction yield, individual triterpenoids extraction yields and concentrations were assessed and contrasted with Soxhlet extractions using solvents of distinct polarity. The extracts were characterized by gas chromatography coupled to mass spectrometry (GC-MS) and target triterpenoids were quantified. The total extraction yields ranged from 1.76 to 11.58 wt.% and the major compounds identified were fatty acids, polyols, and, from the triterpenoids family, lupenone, α-amyrin and β-amyrin. SFE was selective to lupenone, with higher individual yields (2139–3512 mg kg −1 leaves ) and concentrations (10.1–12.4 wt.%) in comparison to Soxhlet extractions, which in turn obtained higher yields and concentrations of the remaining triterpenoids. Keywords: Acacia dealbata; GC-MS; leaves; lupenone; supercritical fluid extraction; Soxhlet extrac- tion; triterpenoids 1. Introduction The genus Acacia is widespread through the Portuguese landscape, consisting of three main species: Acacia dealbata, Acacia longifolia and Acacia melanoxylon [1]. A. dealbata was introduced for dune erosion protection as well as ornamental and wood supply purposes during the 19th and 20th century [2]. Currently, it is considered a plague due to its fast growth and dominance over the natural flora [1,3]. From 2005 to 2015, the occupied area of Acacia species increased 4000 ha in Portugal, corresponding to an estimated total arboreal biomass growth of 2 Mt [4]. The removal of these trees generates forest biomass that, under the Renewable Energy Directive II of the European Union Commission [5], can be utilized for the production of liquid and gaseous biofuels. However, it is a common practice to leave these residues in the forest for soil remediation. The research towards A. dealbata biomass extraction has focused on several morphological parts, namely wood [6–10], bark [6–8,10–14], flowers [11,15–20] and leaves [6,8,11,17,21,22]. The explored extraction methods so far consist of solid-liquid extraction with organic solvents, such as dichloromethane, ethanol, methanol, hexane, acetone and some hydroal- coholic mixtures. Extraction of essential oils by steam distillation has been applied only to flowers [16]. Besides these conventional methods, there are few works on greener and more innovative extraction procedures, such as the work of Borges et al. [22], who applied microwave and ultrasound-assisted extraction to the leaves, and Lopez-Hortas et al. [16], using microwave hydrodiffusion to obtain the flower essential oil. One alternative tech- nique for the extraction of vegetable biomass is supercritical fluid extraction (SFE) [23]. It is mainly employed with carbon dioxide (CO 2 ) as solvent due to its low cost, safety, Processes 2021, 9, 1159. https://doi.org/10.3390/pr9071159 https://www.mdpi.com/journal/processes