Effect of harvesting time variations on the yield and profile composition of essential oils of eucalyptus globulus and psidium guajava medicinal plants from Uganda.

Abstract

The essential oil and phytochemical contents of medicinal plants can be affected byseveral factors. For example, in certain plants, harvesting time has been observed to affect the content and chemical composition of the essential oil and phytochemicals obtained from the plant. The objective of this study was to evaluate the effect of harvesting time on the content and chemical composition of the essential oil and phytochemicals from Eucalyptus globulus and Psidium guajava L. leaves. Leaves were collected at three different times of the day and the content and chemical composition of their essential oil and phytochemicals were determined. Harvesting time did not qualitatively affect the chemical composition of the phytochemicals for both Eucalyptus globulus and Psidium guajava L.leaves.For both plants, the phytochemicals determined present in their leaves regardless of harvesting time differences of the day were; saponins, tannins, alkaloids, reducing compounds, anthocyanosides, anthracenosides, flavonosides, coumarins and steroid glycosides. However, harvesting time variation did affect yields and chemical compositions of their essential oils. Leaves collected at 7:00am had higher essential oil contents of (2.0%) for E.globulus and (0.8%) for P.guajava in volume per 100g dry mass of leaf material respectively. Evening hours (6:00-7:00 pm) harvested leaves also posted higher essential oil yields; (1.6%) for E.globulus and (0.6%) for P.guajava essential oils respectively than afternoon hours (1:00-2:00pm) which gave the lowest essential oil yields for both plants with (1.4%) for E.globulus and (0.4%) for P.guajava plants respectively.Statistical analysis of essential oils composition determined by GC-MS spectrophotometer gave36 compounds each for E.globulusand P. guajavaleaves harvested in the morning (6:00-7:00am),35 constituent compounds for E.globulus and34 for P. guajava respectively in the afternoon (1:00- 2:00pm), 43and35 compounds for E. globulus and P. guajavarespectively were determined in the evening hours (6:00-7:00pm). Concentration of certain compounds in the oils,such as 1,8-Cineole, Viridiflorol and 2-Carneole for E. globulus and beta-Bisabolol, Beta-Selinene, trans-Sesquisabinene hydrate, Caryophyllene oxide andα-humulene for P. guajava did significantlyvary at different harvesting times of the day. The main constituentsof the essential oil forE.globulusleaves were (E)-Pinocarveol (12.87%), 2, 2, 4, 4-Tatramethyl-6-(2-methylbutano... (12.52%) and Viridiflorol (12.33%)whereas for P. guajava;beta-Bisabolol (19.77%), Beta-Selinene (18.24%) and Betaxiii Selinene (14.27%) were dominant. Chemical analysis showed that sesquiterpene compounds represented the highest concentration for P.guajava and monoterpenes for E.globulus.