Chemical and microbiological analyses of 25-year-old lemon essential oils

Essential oils (EOs) are volatile natural compounds widely used in perfumery, food, pharmaceuticals, and as solvents. Although their nominal shelf-life after opening is 12 months, their antibacterial and antiviral properties may enable longer preservation if properly stored. This study investigates the long-term stability of samples of lemon EOs accidentally stored in hermetically sealed glass bottles for 25 years. Comprehensive analyses were conducted to evaluate their chemical and biological properties. Gas chromatography with flame ionization detection (GC-FID) was used to compare the aged samples to a genuine and organic certified reference essential oil (CREO) produced in Catania, Sicily in 2024 and bottled in functional units of 10 mL by LaborBio, Collegno (Turin, Italy). Additionally, microbiological tests and nuclear magnetic resonance (NMR) spectroscopy were performed to identify and characterize a white-grey precipitate found in the samples. The findings reveal that EOs can maintain their composition and functionality well beyond the expected shelf-life, suggesting significant opportunities for reducing industrial waste and optimizing storage practices.