Oxidation of monoterpenes in Protium heptaphyllum oleoresins

Protium heptaphyllum (Burseraceae) oleoresins are rich in volatile monoterpenes, exhibiting a chemical composition that can be strongly altered with time. The present work aimed to discuss the temporal change of the volatile composition of these oleoresins, and search for related supporting evidence. Samples of P. heptaphyllum oleoresin were collected separately for fresh (n = 10) and aged (n = 8) oleoresins, with the essential oils obtained by hydrodistillation analyzed by GC-FID and GC-MS. Fresh oleoresins were characterized by a high content of terpinolene (28.2-69.7%), whereas aged ones contained large amounts of p-cymene (18.7-43.0%) and p-cymen-8-ol (8.2-31.8%). Multivariate analyses were performed based on the yield and major essential oil components to clearly demonstrate the existence of two subsets (fresh and aged oleoresins). In addition, an analysis of the partial genome sequencing of the species was carried out, producing the largest amount of data for the genus Protium. Subsequently, were searched for nucleotide sequences responsible for the enzymes involved in the biosynthesis of monoterpenes. Two hypotheses were formulated to understand the oxidation process during aging of the oleoresins: (i) a natural chemical oxidation of terpenes and (ii) an oxidation catalyzed by enzymes produced by microorganisms associated with the plant. The results suggested that terpinolene was most likely oxidized to p-cymene, which, in turn, was oxidized into p-cymen-8-ol during natural aging of the exudate due to abiotic factors.