Evaluation of Sustainable Recycled Products to Increase the Production of Nutraceutical and Antibacterial Molecules in Basil Plants by a Combined Metabolomic Approach

Abstract

Background: An important goal of modern medicine is the development of products deriving from natural sources to improve environmental sustainability. In this study, humic substances (HS) and compost teas (CTs) extracted from artichoke (ART) and coffee grounds (COF) as recycled biomasses were employed on Ocimum basilicum plants to optimize the yield of specific metabolites with nutraceutical and antibacterial features by applying sustainable strategies.

Methods: The molecular characteristics of compost derivates were elucidated by Nuclear Magnetic Resonance spectroscopy to investigate the structure-activity relationship between organic extracts and their bioactive potential. Additionally, combined untargeted and targeted metabolomics workflows were applied to plants treated with different concentrations of compost extracts.

Results: The substances HS-ART and CT-COF improved both antioxidant activity (TEAC values between 39 and 55 μmol g^-1) and the antimicrobial efficacy (MIC value between 3.7 and 1.3 μg mL^-1) of basil metabolites. The metabolomic approach identified about 149 metabolites related to the applied treatments. Targeted metabolite quantification further highlighted the eliciting effect of HS-ART and CT-COF on the synthesis of aromatic amino acids and phenolic compounds for nutraceutical application.

Conclusions: The combination of molecular characterization, biological assays, and an advanced metabolomic approach, provided innovative insight into the valorization of recycled biomass to increase the availability of natural compounds employed in the medical field.

Keywords: antibacterial properties; antioxidant capacity; metabolomics; phenolic compounds; recycling biomasses.

Figure 1

¹³C-CPMAS-NMR spectrum of humic substances and relative compost tea from artichoke and coffee composted biomasses (HS-ART, HS-COF, CT-ART, CT-COF).

Figure 2

Effect of HS and CTs on weight fresh biomass of Ocimum basilicum plants. The different colors are associated to organic treatments applied (CTRL-red; HS-ART-green; HS-COF light green; CT-ART-brown; CT-COF orange). Vertical bars represent the standard deviation of the mean. Columns (mean ± S.D.) followed by different letters indicate significant difference according to LSD test (p ≤ 0.05).

Figure 3

Antioxidant capacity (a) and Total Phenolic Content (b) of basil leaves from plants treated with humic substances (HS) and compost teas (CTs) extracted from artichoke and coffee composted vegetable wastes at different concentration (10–50–100 g L⁻¹). The different colors are associated to organic treatments applied (CTRL-red; HS-ART-green; HS-COF yellow; CT-ART-brown; CT-COF orange). Vertical bars represent the standard deviation of the mean. Columns (mean ± S.D.) followed by different letters indicate significant difference according to LSD test (p ≤ 0.05).

Figure 4

PCA score-plot based on untargeted metabolomics data obtained using Liquid Chromatography High Resolution Mass Spectrometry (LC-HRMS) of basil leaf extracts treated with humic substances (a) and compost teas (b) from artichoke and coffee grounds composted vegetable wastes (HS-ART, HS-COF, CT-ART, CT-COF) at different doses (10, 50, 100 g L⁻¹). Names and directions of most significant PCA loading vectors involved in the differentiation of treatments are reported along the score-plot borders. The PCA scores represent the single value of four different biological replicates.

Figure 5

PCA biplot based on metabolites identified by targeted LC-HRMS in the apolar fraction of leaves extracts from basil plants treated with different organic extracts (a). Heatmap prepared from targeted metabolomics data. Each row represents a metabolite feature, and each column represents a treatment. The row Z-score or scaled expression value of each feature is plotted in yellow-green-blue-red color scale. The yellow color of the tile indicates high abundance and blue indicates low abundance. The metabolites abbreviation used are: 13PHGLY: 3-Phosphoglycerate; 3AMP: 3-AMP; ASP: Asparagine; CIT: Citrate; ERY4P: Erythrose-4-phosphate; FRU6P: Fructose-6-phosphate; FUM: Fumarate; GAL: Galactose; GLU: Glucose; GLU1P: Glucose-1-phosphate; GLU6P: Glucose-6-phosphate; GLUTOX: Glutathione, oxidized; ISOCIT: Isocitrate; PHE: Phenylalanine; R5P: Ribose-5-phosphate; RIBUL5P: Ribulose-5-phosphate; SEDEP7P: Sedoheptulose-7-phosphate; TRP: Tryptophan; TYR: Tyrosine; ROSACID: Rosmarinic Acid; CAFACID: Caffeic acid; 4HYDRBENZACID:4-Hydroxy benzoic acid. The PCA and Heatmap scores represent the average value of nine replicates (b).

Figure 6

Biochemical pathways of different primary and secondary metabolites identified by nontarget and targeted LC-HRMS approaches in the apolar fraction of leaves extracts from basil plants treated with different organic extracts.