Olive mill waste water valorization: bioactive molecules-enriched fractions recovered by tangential-flow membrane filtration (TFMF) to elicit plant defence responses

In modern olive oil extraction process (Multi-phase Leopard Decanter), in addition to oil and a kernel dehydrated fraction, a hydrated pulp named "Patè" is produced. After centrifugation, the vegetative water (VW) can be recovered from Patè as supernatant. VW is rich of bioactive molecules such as oligosaccharides and phenols effective in plant protection against pathogens. VW have been fractionated by TFMF. NMR spectroscopy analysis indicated the presence of bioactive phenols such as tyrosol, hydroxytyrosol and oleuropein with a known antimicrobial activity. The profile of TFMF fractions obtained by HPAEC-PAD indicated the presence of pectin-derived oligogalacturonides (OGs) well known elicitors of plant defence responses as the early intracellular increase of Ca2+ levels. A dose dependent elicitation of Ca2+ was induced by OG enriched TFMF fractions. Remarkably, pre-treatment with specific OG-enriched TFMF fractions reduces plant disease symptoms against microbial pathogens. The possibility that phenols cooperate with OGs in inducing plant immunity is not excluded. This finding highlights the potential of this waste as bio-stimulant of plant defense responses.