Humic substances from green compost increase bioactivity and antibacterial properties of essential oils in Basil leaves

The Essential oils (EOs) are important bioactive secondary metabolites of aromatic plants, such as Basil, and find extensive utilization in pharmaceutical sector as therapeutic agents. A more eco-friendly industrial production of EOs requires new sustainable methods to improve yield and quality of these bioactive compounds in aromatic plants. Here, we evaluated the biostimulation effects of natural organic materials, such as humic substances (HS) extracted from a humified green compost made with artichoke biomasses. The molecular characteristics of HS from green compost were determined by 13C-CPMAS NMR spectroscopy and offline pyrolysis–gas chromatography/mass spectrometry and combined to the bioactivity of the EOs extracts to investigate the structural–activity relationship. Basil plants were grown under HS treatments at different concentrations and the yield, the chemical composition and the antioxidant and antimicrobial properties were determined for EOs extracted by steam distillation method from Basil leaves. HS showed a positive effect on total extraction yield of the most bioactive EO components, with a progressive enhancement of abundance for eugenol, eucalyptol and geranyl acetate with increasing HS concentrations. Humic biostimulation influenced the EOs antioxidant proprieties, as well as their antimicrobial activity against some common Gram-negative bacterial strains such as Klebsiella pneumoniae. The HS biostimulation of Basil plants was associated to their structural hydrophobic characteristics that may have favoured the interactions with the Basil rhizome and to specific bioactive molecular components, such as a lignin-derived phenols and polar saccharidic and aminoacidic compounds. Our results support the potential use of humic substances from green compost as promising effective biostimulants to improve the production and bioactive properties of EOs in aromatic plants.