**4. Conclusions**

Phenolic compounds such as quercetin 3-β-D-glucoside (4.92 mg/g), neochlorogenic acid (2.91 mg/g), and chlorogenic acid (1.83 mg/g) have been recovered from walnut (*Juglans major 209 x Juglans regia*) leaves by maceration in aqueous ethanol solutions under optimized conditions, 75 ◦C, 120 min, and 50% aqueous ethanol, selected based on extraction yield and extract antioxidant properties. The experimental values for the optimal extract properties were: Extraction yield, 30.17%; FRAP, 1468 nmol AAE/mg extract d.b.; DPPH, 1.318 mmol TRE/g extract d.b.; DPPH EC50, 0.11 mg/mL; ABTS, 1.256 mmol TRE/g extract d.b. and ABTS EC50, 0.985 mg/mL. Therefore, the present work proposes a valorization way of walnut leaves as a source of valuable compounds for various industrial applications based on their antioxidant properties.

**Author Contributions:** Conceptualization, M.S.F. and J.G.-Á.; formal analysis, M.S.F. and J.G.-Á.; investigation, A.F.-A., A.C.-I., M.S.F., and J.G.-Á.; methodology, A.F.-A. and A.C.-I.; resources, J.G.-Á.; software, A.F.-A. and A.C.-I.; supervision, M.S.F. and J.G.-Á.; validation, M.S.F. and J.G.-Á.; writing—original draft, J.G.-Á.; writing—review and editing, A.F.-A., A.C.-I., M.S.F. and J.G.-Á. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Acknowledgments:** The authors want to thank the use of RIAIDT-USC analytical facilities and Bosques Naturales S.A. for supplying walnut leaves.

**Conflicts of Interest:** The authors declare no conflict of interest.
