Avaliação sazonal e atividade antibacteriana do óleo essencial das folhas de Eugenia calycina (pitanga-do-cerrado)

Abstract

Eugenia calycina is a plant species found in the Cerrado, popularly known as "pitanga do cerrado". Studies showed the presence of oxygenated and non-oxygenated sesquiterpenes in the essential oil of the leaves, which showed good activity against bacteria present in the oral cavity. It is known that the composition of essential oils is subject to variations caused by climatic conditions and vegetative stages. Due to these variations, it is important to determine the best time of year for leaf collection. The objective of this work was to evaluate the influence of seasonal variations on the chemical composition of the essential oil of fresh E. calycina leaves, as well as their antibacterial activity against bacteria of the oral cavity. This study identified and compared compounds of the essential oil extracted from fresh leaves collected every two months, the first collection was in January and the last one was in November 2018. The essential oil was extracted by hydrodistillation and its chemical composition was determined by analysis using gas chromatographic coupled to mass spectrometry (GC-MS). It was observed that the chemical composition of the essential oil varied throughout the year, qualitatively and quantitatively. In sample 1 (collection and extraction performed in January) the major constituent of the essential oil was bicyclogermacrene (22.13%), while in samples 2, 3, 4 and 6 (collections and extractions performed in March, May, July and November, respectively) the major constituent was spatulenol (54.61, 15.60, 16.50, 24.04%). Sample 5 (collection and extraction performed in September) presented trans-caryophyllene as the major constituent (20.22%). Essential oil showed a homogeneous yield throughout the year, approximately 0.35%. We highlight the sample 4 that showed 0.18% yield, showing as the worst period for collection. Antibacterial activity against oral cavity bacteria (aerobic and anaerobic) was performed by microdilution in microplate broth, the result being expressed as minimum inhibitory concentration (MIC). Antibacterial activity showed that it is not influenced by rainfall index, since all samples showed moderate antimicrobial activity against aerobic bacteria (MIC between 200 to 400 μg mL -1) and for anaerobic bacteria, all samples showed low antibacterial activity (MIC equal to or greater than 400 μg mL-1).