J Agric Food Chem. 2022 Apr 18. doi: 10.1021/acs.jafc.1c06912. Online ahead of print.
Following recent legalization, the production of hemp (Cannabis sativa L.) for high-value plant compounds became a major crop in many countries across the world. In this study, we profiled popular plant compounds being extracted for emerging markets, terpenes and cannabinoids, developed in two different planting systems of a single, high-cannabidiol (CBD), low-Δ9-tetrahydrocannabinol (Δ9-THC), dioecious hemp cultivar ‘Culver’ in central Oregon, U.S.A. One system is the current conventional system of an open, all-female, clonal transplant (OFCT) production system. This is compared to a dioecious, densely seeded (DDS) production system. Overall, the essential oil (EO, chiefly terpenes) and cannabinoid profiles of plants harvested from the two systems were comparable. In comparison to the DDS plots, the EO obtained from colas of the OFCT plots had higher concentrations of α-pinene, myrcene, limonene, β-bisabolene, γ-cadinene, caryophyllene oxide, guaiol, 10-epi-γ-eudesmol, β-eudesmol, bulnesol, epi-α-bisabolol, α-humulene, and CBD, although lower concentrations of 1,8-cineole, (E)-caryophyllene, γ-elemene, α-selinene, selina-4(15),7(11)-diene, selina-3,7(11)-diene, and germacrene B. Of the various plant parts (female leaves and chaff, male flowers) tested in the DDS plots, the highest EO yield was obtained from the chaff. The main EO constituents of female leaves were (E)-caryophyllene (14-21%), caryophyllene oxide (13-16%), α-humulene (5-6%), humulene epoxide II (3.5-3.8%), epi-α-bisabolol (2.7-5.5%), CBD, and α-eudesmol (1.1-2.6%). The principal EO constituents of female chaff from the DDS system were (E)-caryophyllene (∼21%), α-humulene (6.6%), β-selinene (4.5%), α-selinene (3.6%), selina-3,7(11)-diene (9.8%), selina-4(15),7(11)-diene (6.3%), caryophyllene oxide (5.2%), and cannabichromene (3.1%). The major EO constituents of the male flowers were CBD (19.3%), caryophyllene oxide (11%), α-humulene (4.1%), epi-α-bisabolol (3.9%), selina-3,7(11)-diene (3.4%), and β-selinene (3.4%). Cannabinoids were not detected in the EO distilled for 30 min, but they were present in the EO from 240 min of distillation. The EO content of female leaves and male flowers was relatively low, whereas the EO content of the female chaff from the DDS system was significantly greater. Breaking with conventional knowledge, the EO of male flowers may accumulate up to 19% CBD. Distillation of plants from both production systems converted CBD-A to CBD, CBDV-A to CBDV, CBG-A to CBG, and THC-A to THC as a result of the thermal decarboxylation of acidic cannabinoids but otherwise did not affect the total cannabinoid content. Most of the cannabinoids remained in the distilled biomass after the extraction of terpenes (EO). Therefore, the distilled, terpene-free biomass represents a high-value product that could be further extracted for cannabinoids or used as a component in various products.