Chemometric analysis of the seasonal variation in the essential oil composition and antioxidant activity of a new geraniol chemotype of Lippia alba (Mill.) N.E.Br. ex Britton & P. Wilson from the Brazilian Amazon

Abstract

Lippia alba (Mill.) N.E.Br. ex Britton & P. Wilson is an aromatic shrub native and not endemic to Brazil, popularly known as lemon balm, and widely used throughout Brazil in folk medicine. This study aimed to evaluate the influence of climatic parameters on the yield, radical-scavenging, and chemical composition of the L. alba essential oil. The specimen was collected monthly from August/2021 to May/2022. Essential oils (EOs) were obtained by hydrodistillation, and GC-MS analyzed their chemical composition. Chemometric analyses were performed to verify the climatic influences on the yields, chemical composition, and radical-scavenging apacity on L. alba EOs. The radical-scavenging capacity was performed by the DPPH radical-scavenging method. The lowest oil yield was obtained in October (0.6%) and the highest in March (2.2%). The average yields in the dry season (August–February, 1.1 ± 0.3%) did not show a statistical difference with the rainy season (April–May, 1.7 ± 0.5%). On the other hand, there was a strong and significant correlation between oil yields and humidity (r = 0.79), precipitation (r = 0.77) and insolation (r = −0.76). Oxygenated monoterpenoids (44.4–66.8%), followed by oxygenated sesquiterpenoids (11.1–26.4%) were predominant in the EOs. The major constituents in the EO were geraniol (21.0–46.9%, average 37.5 ± 8.0%) and elemol (9.0–22.2%). The average amounts of geraniol in the dry season (37.9 ± 5.8%) did not show statistical difference with the rainy season (36.5 ± 13.7%). Furthermore, there was no significant correlation between geraniol and elemol amounts with climatic parameters. The PCA analysis showed a separation between the samples from the dry and rainy seasons, and classified them into three groups: groups I and III (rainy season) and group II (dry season). Geraniol standard content showed a moderate correlation (r = 0.52) with antioxidant capacity. However, L. alba EOs showed low antioxidant capacity against DPPH radicals (<8.6%, 148.5 mg. ET/g). The constant chemical composition of the studied specimens, along with low environmental influence, suggests that seasonal changes do not alter the phytotherapeutic effects.