From agro-industrial by-products to immunomodulators for sustainable crop protection

Olive mill waste (OMW) poses environmental concerns due to its high organic and phenolic content. While anaerobic digestion offers a sustainable route for biogas production, the environmental impact of the digestate remains unclear. In this study, two-phase olive pomace and its digestate were upcycled into bioactive immunomodulators for sustainable crop protection. Three extracts were obtained: a glycan-rich fraction containing immunostimulant oligosaccharides; a phenolic extract enriched in hydroxytyrosol, oleuropein, and related compounds; and a microbial protein extract from the digestate, containing MAMPs and DAMPs such as flagellin, EF-Tu, and Golven peptides. These extracts triggered immune responses in Arabidopsis and tomato, including MAPK phosphorylation, reactive oxygen species production, and defense gene upregulation. Pretreatment with these formulations enhanced Arabidopsis and tomato resistance to Botrytis cinerea and Pseudomonas syringae. The phenolic extract also showed broad-spectrum antimicrobial activity against key phytopathogens, including Xylella fastidiosa. These results represent the proof of concept for the Horizon Europe OLinWASTE project, which aims to develop a zero-emission system for converting olive mill waste into bio-based products such as immunostimulants, biopesticides, biofertilizers, bioplastics, and bioenergy.