Drying temperature changes trichome integrity, chemical content and composition of the essential oil of pepper-rosmarin

EnglishMedicinal plants are generally commercialized dried. However, temperatures used in their drying processes may interfere with the content and chemical composition of their essential oils. The Lippia origanoides possesses thymol in the essential oil that is stored in glandular trichomes. Thymol is a major component of economic importance in the chemical and pharmaceutical industry. The objective of this study was to evaluate the effect of the drying temperatures of L. origanoides leaves regarding trichome integrity, content, and chemical composition of the essential oil. The experimental design was completely randomized with four treatments defined by oven drying temperatures (40, 50, 60, and 70oC) and four replications. Essential oil was extracted by hydro distillation and the essential oil contents were determined (%). Chemical composition of the oil was analyzed by gas chromatography coupled to mass spectrometry. Scanning electron microscopy was carried out to determine trichome integrity. Drying the L. origanoides leaves in a forced ventilation oven at 40°C minimized the loss of extracted essential oil content (17.5g kg-1) and relative thymol percentage. Leaves dried at the temperatures of 60 and 70oC exhibited a higher percentage of ruptured trichomes and reduced essential oil content to 13.7g kg-1 and 11.8g kg-1, respectively. Key words: Lippia origanoides; medicinal plant; secretory structures; drying; thymol portuguesAs plantas medicinais sao geralmente comercializadas secas, no entanto, as temperaturas utilizadas nos processos de secagem podem interferir no teor e composicao quimica dos oleos essenciais destas plantas. A Lippia origanoides possui timol em seu oleo essencial, que se encontra armazenado em tricomas glandulares. O timol e um componente majoritario de importância economica na industria quimica e farmaceutica. O objetivo do trabalho foi estudar o efeito das temperaturas de secagem de folhas de L. origanoides na integridade dos tricomas, teor e composicao quimica do oleo essencial. O delineamento experimental foi inteiramente casualizado, com quatro tratamentos definidos por temperaturas de secagem em estufa (40oC, 50oC, 60oC e 70oC) e quatro repeticoes. Foram realizadas extracoes por hidrodestilacao e determinacao dos teores dos oleos essenciais (%), analise de composicao quimica do oleo por cromatografia gasosa acoplada a espectrometria de massas e microscopia eletronica de varredura para determinacao da integridade dos tricomas. A secagem das folhas de L. origanoides em estufa de ventilacao forcada a 40oC minimizou a perda do teor de oleo essencial extraido (17,5g kg-1) e porcentagem relativa de timol. Folhas secas em temperatura de 60 e 70oC exibiram maior porcentagem de tricomas rompidos e reducao do teor de oleo essencial para 13,7g kg-1 e 11,8g kg-1, respectivamente. Palavras-chave: Lippia origanoides; planta medicinal; estruturas secretoras; secagem; timol