Green enrichment of α-terpineol from niaouli oil residue via molecular distillation

Abstract

The bottom fraction, obtained as a residual by-product after commercial 1,8-cineole recovery from the fractional distillation of Melaleuca quinquenervia essential oil, is often underutilized despite its potential as a source of valuable bioactive compounds. In this study, the residue was recovered and further purified using molecular distillation to enhance the concentration of α-terpineol. Key processing parameters, including pressure (Pa), evaporator surface temperature (°C), and feed flow rate (mL min⁻¹), were systematically investigated and optimized using response surface methodology (RSM) to maximize α-terpineol content. The optimal conditions were determined to be 209.7 Pa, 35.4 °C, and 1.39 mL min⁻¹, resulting in an α-terpineol content of 70.97% with a recovery rate of 89.2%. GC–MS analysis confirmed that molecular distillation effectively concentrated α-terpineol in the light fraction, while valuable oxygenated sesquiterpenes were enriched in the heavy fraction. Antibacterial activity, evaluated by the agar disk diffusion method, demonstrated that the α-terpineol-enriched light fraction was active against both Gram-positive and Gram-negative bacteria, with efficacy comparable to ampicillin. Anti-inflammatory activity was further confirmed by dose-dependent inhibition of nitric oxide production in LPS-stimulated RAW 264.7 macrophages, while high cell viability indicated low cytotoxicity. These findings demonstrate that molecular distillation provides an effective and solvent-free approach for sustainably valorizing the bottom fraction of M. quinquenervia essential oil into bioactive fractions.