Headspace analysis and characterisation of South African propolis volatile compounds using GCxGC-ToF-MS

Propolis also known as bee glue or bee resin is a resinous mixture of bee saliva or bee wax and exudate from tree trunks and flowers, produced by honeybees. The composition of propolis varies depending on the vegetation the bees can access. It is therefore expected that propolis obtained from various localities may have different chemical profiles. In this study, the headspace volatiles of propolis (n = 39) collected from various locations in South Africa (Gauteng, Northern Cape and Western Cape Provinces) were explored for the first time using GCxGC-ToF-MS. Several GCxGC parameters were optimised including; incubation time, temperature and modulation period. Multivariate data analysis techniques (principal component and hierarchical cluster analyses) were applied on the GCxGC-ToF-MS data to investigate trends and clustering patterns within propolis samples. The results demonstrated that headspace volatiles of propolis varied between locations. The volatile profiles were dominated by monoterpenes such as alpha-pinene (1.2-46.5%), beta-pinene (2.0-21.8%), dihydrosabinene (trace-17.8%), limonene (trace-11.6%), p-cymene (0.15.3%), 1,8-cineole (0.1-11.0%), 2,7-dimethyl-3-octen-5-yne (trace-11.7%), E-beta-ocimene (trace-17.8%), octanal (trace-12.9%), styrene (trace-13.5%) and alpha-thujene (trace-11.0%). Principal component analysis revealed chemical variation within propolis from the various locations. The heatmap of the averages revealed dehydrosabinene, isopropentyltoluene, p-cymene, acetophenone and alpha-thujene as chemical markers for the Northern Cape propolis, while lambda-terpinene, propanoic acid, furfural, 2-methoxy benzyl alcohol and hexanoic acid methylester were filtered out as markers for Gauteng propolis. The propolis samples originating from the Western Cape Province were dominated by prenal, cinnamaldehyde styrene, 1,8-cineole, decanal, prenyl acetate and butanoic acid. Using GCxGC-ToF-MS in combination with chemometrics, it was possible to profile headspace volatile constituents of propolis and further identify marker compounds that differentiate propolis from various provinces in South Africa. (C) 2019 Sociedade Brasileira de Farmacognosia. Published by Elsevier Editora Ltda.