Citation: Pedro, S.I.; Rosado, T.; Barroca, C.; Neiva, D.; Alonso-Herranz, V.; Gradillas, A.; García, A.; Gominho, J.; Gallardo, E.; Anjos, O. Characterisation of the Phenolic Profile of Acacia retinodes and Acacia mearnsii Flowers’ Extracts. Plants 2022, 11, 1442. https:// doi.org/10.3390/plants11111442 Academic Editors: Jana Šic Žlabur, Sanja Radman and Martina Skendrovi´ c Babojeli´ c Received: 3 May 2022 Accepted: 24 May 2022 Published: 28 May 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 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/). plants Article Characterisation of the Phenolic Profile of Acacia retinodes and Acacia mearnsii Flowers’ Extracts Soraia I. Pedro 1,2 , Tiago Rosado 3,4 , Celina Barroca 1,2,5 , Duarte Neiva 2,6 , Vanesa Alonso-Herranz 7 , Ana Gradillas 5 , Antonia García 5 , Jorge Gominho 2 , Eugenia Gallardo 3,4 and Ofélia Anjos 1,2,5, * 1 Centro de Biotecnologia de Plantas da Beira Interior, 6001-909 Castelo Branco, Portugal; soraia_p1@hotmail.com (S.I.P.); celinasbarroca@gmail.com (C.B.) 2 Centro de Estudos Florestais (CEF), Instituto Superior de Agronomia, Universidade de Lisboa, 1349-017 Lisboa, Portugal; duarteneiva@isa.ulisboa.pt (D.N.); jgominho@isa.ulisboa.pt (J.G.) 3 Centro de Investigação em Ciências da Saúde (CICS-UBI), Universidade da Beira Interior, 6200-506 Covilhã, Portugal; tiago.rosado@ubi.pt (T.R.); egallardo@fcsaude.ubi.pt (E.G.) 4 Laboratório de Fármaco-Toxicologia—UBIMedical, Universidade da Beira Interior, 6200-506 Covilhã, Portugal 5 Instituto Politécnico de Castelo Branco, 6001-909 Castelo Branco, Portugal; gradini@ceu.es (A.G.); antogar@ceu.es (A.G.) 6 Centro Ecologia Aplicada “Prof. Baeta Neves” (CEABN), Instituto Superior de Agronomia, Universidade de Lisboa, 1349-017 Lisboa, Portugal 7 (CEMBIO) Centro de Metabolómica y Bioanálisis, Facultad de Farmacia, Universidad San Pablo CEU, CEU Universities, Campus Monteprincipe, Boadilla del Monte, 28660 Madrid, Spain; valonso@ceu.es * Correspondence: ofelia@ipcb.pt; Tel.: +351-272-339-900 Abstract: Acacia spp. is an invasive species that is widespread throughout the Portuguese territory. Thus, it is pertinent to better understand this species in order to find different applications that will value its use. To evaluate the phenolic profile in Acacia flowers, ethanolic extracts obtained through an energized guided dispersive extraction were analysed, focusing on two species, Acacia retinodes and Acacia mearnsii, at two flowering stages. The phytochemical profile of each extract was determined by ultra-high performance liquid chromatography coupled with quadrupole time-of- flight mass spectrometry and high-performance liquid chromatography coupled with diode array detector. The FTIR-ATR technique was used to distinguish the different samples’ compositions. The results showed the presence of high concentrations of phenolic compounds (>300 mg GAE/g extract), among which are flavonoids (>136 mg QE/g extract), for all combinations of species/flowering stages. The phytochemical profile showed a complex composition with 21 compounds identified and quantified (the predominant ones being epicatechin, rutin, vanillin, and catechol). Both species and flowering stages presented significant variations regarding the presence and quantity of phenols and flavonoids, so much so that a principal component analysis performed with FTIR-ATR spectra data of the extracts was able to discriminate between species and flowering stages. Keywords: Acacia species; flowers; phenolic compounds; flavonoid content; UHPLC/ESI-QTOF-MS; HPLC-DAD; FTIR-ATR 1. Introduction Natural compounds obtained from plants offer research opportunities due to their significant pharmacological and toxicological properties [1]. They are often considered as potential new drugs against drug-resistant pathogens [2] and for treating diseases. A variety of medicinal species belonging to the genus Acacia suggest the potential presence of bioactive metabolites. The most characteristic in this genus are flavonoids and tannins compounds [3]. The literature that is focused on plant extracts indicates that these species are rich in phytochemical compounds such as polyphenols, flavonoids, saponins, alkaloids, among others. The accumulations are made in different tissues/organs Plants 2022, 11, 1442. https://doi.org/10.3390/plants11111442 https://www.mdpi.com/journal/plants