Teor, composição química, atividade antioxidante do óleo essencial de Tetradenia riparia e efeito alelopático em plantas espontâneas

Abstract

Medicinal plants have been used over the years as alternative medicine due to their natural sources of biologically active compounds. Myrrh (Tetradenia riparia), which belongs to the Lamiaceae family, is an important medicinal plant that produces essential oil with various uses in medicine, cosmetics and pharmaceuticals. In the first chapter, the aim of this work was to determine the time and month of harvest that results in the highest essential oil content of myrrh, as well as its chemical composition and antioxidant activity using the DPPH, ABTS and FRAP methods. For this, a completely randomized design was used, arranged in a 3x4 factorial scheme, with three months (May, June and July) and four collection times (8:00 am, 11:00 am, 2:00 pm and 5:00 pm), with three repetitions, during the years 2021-2022. The second chapter evaluated the allelopathic potential of T. riparia essential oil (EO) on the weeds Ipomoea purpurea (morning glory), Euphorbia heterophylla (milkweed) and Raphanus sativus (fodder radish). The experimental design used was a randomized block design with a 4x3 factorial scheme, with four concentrations of essential oil (0.25, 0.50, 0.75 and 1%) and three target weeds, with a control at zero concentration and four replications. The variables analyzed were: Germination Percentage (GP), Germination Speed Index (GSI), Seedling Length (SL) and Dry Mass (DM). The EO content (0.65%) was highest at 17:00 on June 2022. The data obtained on the chemical composition of the EOTr (essential oil of Tetradenia riparia) collected in May 2021, showed that the compounds had greater variation at 08:00, as most of its compounds were integrated by fatty acids; for the hours of 11:00; 14:00 and 17:00 there was an increase in sesquiterpene hydrocarbons with α-Copaene, β-Caryophyllene and α-Cadinol as the majority compounds. For the month of June 2021, there was no difference in the chemical composition at the different times studied and the majority compounds were fenchone, α-Cadinol and β-caryophyllene (with no significant difference between them). The antioxidant activity of myrrh essential oil was highest using the ABTS method at the harvest time of 14:00 hours (1052.73 µM/mg). For milkweed, the 0.5 and 1% concentrations reduced germination, SGI and dry mass by 100%, while fodder radish and morning glory increased germination. The SGI showed no significant difference for morning glory and fodder radish, while there was a difference in seedling length for the three species studied. There was no difference in dry mass between milkweed and morning glory. It was found that harvesting myrrh at 8:00 am and in May resulted in the highest essential oil content, which is the recommended month for this activity. The chemical composition of the essential oil varied between the months and times of harvest, with terpenes and fatty acids being the main components. The high antioxidant activity of myrrh essential oil shows that this plant could be a natural source of different compounds for the food, cosmetics and pharmaceutical industries. Myrrh essential oil has high allelopathic activity on milkweed seeds, being able to inhibit their germination by up to 100%.