A multi-analytical approach for the chemical characterization of copal Mbaka from Guibourtia demeusei (Harms) J.Leonard

Résumé

Abstract :
Copal from the Mbembe forest in the north of the Republic of Congo, known locally as “Mbaka”, is traditionally used fresh as an adhesive and to light repellent fires. This copal, produced by Guibourtia demeusei (Harms) J.Leonard, has physical characteristics similar to those of other copals exported and studied in Europe, but has never been studied chemically. The main aim of this work is therefore to chemically characterize this copal using a multi-analytical approach. Infrared analyses confirmed that this copal is a terpenoid resinous exudate. Analysis of the volatile fraction, obtained either by hydrodistillation (HD) or headspace solid-phase microextraction (HS-SPME), revealed the presence of monoterpenes, sesquiterpenes and diterpenes. The essential oil of this copal consists mainly of sesquiterpenes with a majority of β-caryophyllene (40%). Using two-dimensional gas chromatography (GCxGC), 19 additional minor compounds were identified compared to the 1D GC results. Non-volatile organic compounds were extracted using Soxhlet, then processed before analysis by high-temperature gas chromatography with mass spectrometric detection (HT-GC-MS). They are labdane-type diterpenic acids. The presence of cativic acid distinguishes this copal from other Congolese copals, and its non-volatile fraction shows similarities to copal samples from Latin America, particularly those from the genus Hymenaea.

Keywords : Copal, Guibourtia demeusei, Terpenoid resin, HS-SPME, GCxGC-MS, HT-GC-MS.