A way to valorize pomace from olive oil production: Lignin nanoparticles to biostimulate maize plants

Agriculture will increasingly face in coming years numerous challenges, such as climate change, the growing global demand for food, its environmental impact due to green-house gas emissions, the release of pollutants into the environment, and the production of significant amounts of waste.This study focused on pomace, a waste of olive pressing, as it contains substances that can be valorized. Specifically, this study aimed to obtain lignin nanoparticles (LNPs) by treating the biomass with an ionic liquid (IL) composed of triethylamine and sulfuric acid [Et3NH][HSO4], having different concentrations of water (IL_95, IL_90 and IL_80). The LNPs obtained were characterized by Fourier Infrared Spectroscopy (FT-IR), Field Emission Scanning Electron Microscopy (FE-SEM), and Thermogravimetric (TGA) analysis. The 95/5 IL/water ratio allowed for obtaining the best LNPs regarding purity, yields and morphology, which were further characterized by investigating Zeta Potential (& xi;) and Energy Dispersive x-ray Spectroscopy (EDX). The LNPs from IL_95 were applied to maize plants at 25, 50 and 200 mg L-1. Improvements in growth, physiological and biochemical traits were ascertained in the treated samples. LNPs generally induced photosynthetic activity, stomatal conductance and reduced cellular CO2 concentration. In addition, improvements in biomass production, root morphology and pigment content were ascertained. Finally, the study of the cellular redox state showed that the lower dosages did not cause oxidative perturbations; instead, they had ameliorative effects. In conclusion, this study opens a new way to valorize olive oil pomace by obtaining nano-scaled lignin, a sustainable and biobased material with interesting biostimulant action.