Comparing diverse extraction methodologies to infer the performance of 1,8-cineole extraction from Eucalyptus cinerea: process optimization, kinetics, and interaction mechanisms

Abstract

Eucalyptus oil is highly valued for its anti-inflammatory, antiviral, and antibacterial qualities. Research has shown that it is a powerful combatant against cancer cells, making it an extremely interesting area of research. For the first time, the present study proposes to extract 1,8-cineole from Eucalyptus cinerea leaves using different extraction methodologies, namely, hydro-distillation (HD), Soxhlet (SE), ultrasonication (UE), and microwave (ME) extraction techniques. In conventional extraction, HD yielded a maximum of 72.85% 1,8-cineole using a minimum solid–solvent ratio of 1 : 10 g mL⁻¹ within 3 h compared to SE. The first-order kinetic equation was applied in the HD experimental dataset to understand the extraction mechanism. In modern extraction technology, ME achieved the highest yield of 1,8-cineole (95.62%) at the optimal solid–solvent ratio of 2 g mL⁻¹, extraction time of 4.5 min, and irradiation power of 640 W using the response surface methodology (RSM). Furthermore, the kinetic analysis of UE was investigated using three different empirical models. The chemical components of the essential oil extracted using each extraction method were identified as oxygenated monoterpenes, sesquiterpenes, and oxygenated sesquiterpenes using gas chromatography. Following extraction using various techniques, the morphology of spent leaves lost its distinct texture, their oil glands were entirely distorted, and their vascular bundles could still be identified. It was observed that the hydrogen bond interaction between the solvent molecule and 1,8-cineole-like value-added components played a role in the extraction. Among the investigated techniques, the solvent-free ME method is the most environmentally acceptable method and could effectively extract essential oil from E. cinerea leaves.