Seasonality’s Effects on the Chemical Composition and Antiradical Capacity of the Floral Essential Oil of Acmella oleracea (L.) R.K. Jansen Cultivated in the Brazilian Amazon

For the first time, this work reports the seasonal influence on the chemical composition and antiradical capacity of Acmella oleracea floral essential oil, produced from a perennial herb of great nutritional and pharmacological importance in the Amazon region. The species was cultivated and the plantation was monitored from May to September 2022 between the rainy and dry seasons. The essential oils were obtained by hydrodistillation, analyzed by gas chromatography coupled with a mass spectrometer, and subjected to the free radical inhibition assay using the DPPH method. The highest oil yield (1.61%) occurred in May (rainy season), and the lowest (0.68%) occurred in September (dry season). Despite the difference in the oil yield between the rainy and dry seasons, no significant correlation with weather conditions (p > 0.05) occurred. During the collection period, the class of sesquiterpene hydrocarbons was predominant (16.35–46.01%). The main constituents of A. oleracea were E-caryophyllene (13.57–25.74%), caryophyllene oxide (0.88–31.72%), 1-pentadecene (5.42–16.58%), germacrene D (0.14–15.17%), and myrcene (1.08–11.99%), and a low concentration of its main bioactive spilanthol (0.66–5.2%) was also observed. The antiradical capacity was considered low, with inhibition of 7.96 to 7.53% of free radicals and a Trolox equivalence of 68.4 to 64.7 mg·ET/g. Although there were some changes in the levels of chemical components in A. oleracea essential oils, the species can be considered an alternative source of pharmacologically active compounds such as E-caryophyllene and caryophyllene oxide, in addition to presenting amounts of other bioactive molecules.