**4. Conclusions**

The response surface methodology was successfully employed to optimize total phenolic extraction yield from dried *M. communis* pericarp by non-conventional solvent extraction process, namely using UAE. As compared to MAE and CSE extractions, the proposed UAE method allowed a higher phenolic recovery yield and antioxidant activity with a short working time and a lower solvent consumption. The quantification of the amounts of phenolic compounds in the three types of extract complemented with PCA analysis also allowed concluding that the *M. communis* pericarp extract obtained under optimal UAE experimental conditions contained higher levels of flavonoids, tannins and anthocyanin than the remaining extracts and, particularly, the latter phenolic components could be correlated to its antioxidant activity. According to UHPLC-DAD-ESI-MSn analysis, flavonols, particularly myricetin-*O*-hexoside and myricetin-*O*-deoxyhexoside, were the prevalent phenolic components of UAE-OPT.

**Author Contributions:** N.B.-M. performed the experiments (extraction, optimization and quantification of phenolics and antioxidant activity), analyzed the data and wrote the original draft; L.B.-M. contributed to conceptualization, supervision, data curation, and writing—review and editing; K.M. conceptualized and supervised the research; A.M.S.S. contributed resources and performed writing—review and editing; S.D. contributed to the methodology; S.O.-B. contributed to the investigation; S.M.C. contributed to the supervision, data curation and writing—review and editing.

**Funding:** Foundation for Science and Technology (FCT), the European Union, the National Strategic Reference Framework (QREN), the European Regional Development Fund (FEDER), and Operational Programme Competitiveness Factors (COMPETE), for funding the Organic Chemistry Research Unit (QOPNA) (FCT UID/QUI/00062/2019), through national funds and where applicable co-financed by the FEDER, within the PT2020 Partnership Agreement. Project AgroForWealth (CENTRO-01-0145-FEDER-000001), funded by Centro2020, through FEDER and PT2020, financed the research contract of Susana M. Cardoso.

**Conflicts of Interest:** The authors have declared no conflict of interest.
