Potential of solid wastes from the walnut industry: Extraction conditions to evaluate the antioxidant and bioherbicidal activities

Background: Walnut production (Juglans regia) generates a large amount of waste, mainly comprised of husk and shell. The two by-products have several bioactive compounds, mainly phenolic compounds with antioxidant activity. Given the above, this work seeks to establish productive and adequate conditions for the recovery of compounds with antioxidant activity (juglone among them) from such discards to use the extract as a bioherbicide. Results: Temperature and extraction solvent (type of solvent and use of hydroalcoholic mixtures) are relevant factors on phenolic compounds’ (TPC, Folin-Ciocalteu method) recovery and antioxidant activity (AA, DPPH method), observing values from 2 to 17 mg GAE/g shell and 0.5 and 23 mg GAE/g husk, and 3 to 28 mg TE/g shell and 0.2–36 mg TE/g husk for TPC and AA, respectively. Using 50°C and ethanol as extraction solvent, 14,000 µmol TE/100 g of ORAC activity was obtained for both shell and husk. This value increased when a hydroalcoholic mixture was used. Juglone was recovered only from the husk at 166 mg/100 g. The bioherbicidal potential of the extract was evaluated; a phytotoxic effect and a lower plantar density when applying the product to broad-leaf weeds were observed. Conclusions: In conclusion, the walnut process's residues have a high potential to be used under the circular economy concept in the agri-food sector by obtaining products with high added value. How to cite: Soto-Maldonado C, Caballero-Valdés E, Santis-Bernal J, et al. Potential of solid wastes from the walnut industry: Extraction conditions to evaluate the antioxidant and bioherbicidal activities. Electron J Biotechnol 2022;58. https://doi.org/10.1016/j.ejbt.2022.04.005 © 2022