Foliar application of biostimulants improves nutritional and bioactive quality of walnuts

Owing to their health benefits, walnuts are attracting interest as a good option for nutritious meals, thereby promoting their production. Furthermore, the adoption of ecologically and environmentally friendly agriculture strengthens biostimulant use as a sustainable complement to traditional fertilizers. This study evaluated the effects of different foliarapplied biostimulants in walnut tree orchards, in northeastern Portugal, on walnuts' chemical composition and bioactivity. RESULTS: Walnut samples were rich in fat (particularly the polyunsaturated linoleic acid), dietary fiber and protein. Sucrose was the most prevalent soluble sugar, followed by glucose and fructose. Studied samples also showed an antioxidant activity comparable (or superior) to that of Trolox. Some plant biostimulants (e.g. Sprint Plus®) had a positive impact on the nutritional composition of walnuts, more specifically by boosting tocopherol levels, besides improving the bioactivity of walnut extracts against specific bacteria. CONCLUSION: Overall, this research demonstrated that important quality traits of walnuts can be improved using sustainable agricultural bioproducts and practices. This work was supported by national funds through FCT/MCTES (PIDDAC): CIMO, UIDB/00690/2020 (DOI: 10.54499/UIDB/00690/2020) and UIDP/00690/2020 (DOI: 10.54499/UIDP/00690/2020); and SusTEC, L.A. Pascoalino/0007/2020 (DOI:10.54499/LA/P/0007/2020). The authors also thank the National funding by FCT – Foundation for Science and Technology, through the institutional scientific employment program, contract with L.Barros, and the individual scientific employment program, contract with JP (DOI: 10.54499/CEECIND/01011/2018/CP1578/CT0002), F.S. Reis (2021.03728.CEECIND) and J.C.M. Barreira (CEECIND/04479/2017). LAP thanks FCT for her individual research grant (UI/BD/153745/2022).