Metabolomic analysis to study the effect of foliar copper supplementation on sulfur-containing compounds of garlic bulb by LC-MS.

Introduction: Garlic (Allium sativum L.) is renowned for its health-promoting properties, largely due to its sulfur-rich compounds. While copper is essential for plant growth and metabolism, excessive levels can disrupt cellular processes and lead to oxidative stress.

Objectives: This study aims to investigate the impact of copper supplementation on the metabolic profile of garlic, with a particular focus on changes in sulfur metabolism.

Methods: Ito garlic cloves were harvested in 2020 on Red-Yellow Latosol soil. Copper chelate fertilizer was applied foliarly at 300 mL/ha, 30, 20, and 10 days before harvest. After harvesting, cloves were refrigerated and analyzed. Using LC-MS metabolomics, the metabolic profile of garlic was analyzed after copper supplementation to assess changes, specifically in sulfur-containing compounds.

Results: Copper supplementation led to a significant reduction in key sulfur-containing metabolites critical for the health-promoting properties of garlic, including allicin (FC = 0.0947), alliin (FC = 0.0147), and γ-glutamyl-S-allylcysteine (FC = 0.0076). Enrichment analysis identified alterations in pathways related to glutamine, glutamate, alanine, and aspartate metabolism. Additionally, precursors of glutathione (GSH) were depleted, likely as a result of GSH sparing efforts to counteract copper-induced oxidative stress. This redirection may increase susceptibility to ferroptosis, a form of cell death linked to oxidative damage.

Conclusion: The metabolomic analysis of copper-supplemented Ito garlic cloves showed a significant reduction in sulfur compounds allicin, alliin, and γ-glutamyl-S-allylcysteine, important for organoleptic and medicinal properties. This decrease indicates a metabolic shift towards antioxidant defenses, with glutathione being redirected to defense pathways rather than secondary metabolites. Future studies should explore oxidative stress and ferroptosis markers, and lipidomics for a deeper understanding of garlic response to copper exposure.