Can Temperature and UV Exposure Alter the Antimicrobial Properties of the Essential Oils? An Investigation of Origanum vulgare, Cymbopogon citratus, Syzygium aromaticum, and Lippia sidoides.

Essential oils (EOs) are natural compounds widely applied in agriculture, post-harvest preservation, food processing, and human health due to their strong antimicrobial potential. However, the effects of postextraction physical treatments on their chemical and biological properties remain underexplored. This study investigated the effects of 48 h of exposure to heat at 70 °C and UV radiation on EOs from oregano (OV), clove (SA), lemongrass (CC), and the Brazilian native pepper-rosmarin (LS). Chemical profiles were determined by GC-MS, while antimicrobial activities were assessed against Escherichia coli, Staphylococcus aureus, Colletotrichum sp., and Fusarium solani. Both treatments altered EOs chemical compositions, particularly in OV and LS. Interestingly, some antimicrobial activity increased after the treatments, with more consistent improvements observed against fungal than bacterial strains. In addition, micrographs revealed structural damage to the fungal hyphae caused by the treated LS EO, suggesting different effects on hyphal morphology. These findings demonstrate that controlled postextraction physical treatments can modulate the chemical composition and antimicrobial activity of EOs in a specific and controlled manner. This practical approach provides a simple and potentially effective strategy for tailoring EOs bioactivity and supports further investigation of physical processing as a tool for enhancing naturally derived antimicrobial systems.