Volatile oil components of popowia pisocarpa and antioxidant activity

Popowia is a genus of flowering plants in the family Annonaceae. There are about 50 species, widely distributed in tropical Africa, Madagascar, South India, Indonesia, China, Malaysia, and Australia [1]. Popowia pisocarpa (Blume) Endl. ex Walp., known locally in Malaysia as _anggar-kuan_ or _buah manggi_, is mainly distributed in Thailand, Peninsular Malaysia, Sumatra, Java, Borneo, Philippines, Celebes, Moluccas, and New Guinea. It is a shrub or tree up to 12 m tall and grows in undisturbed forests at an altitude of up to 1,250 meter. The flowers are fragrant and are used as a perfume [2]. Phytochemical analysis discovered the isolation of alkaloids [3] and flavonoids [4, 5]. However, a literature search did not reveal any reports on the essential oil composition of P. pisocarpa. The leaves of P. pisocarpa were collected from Langgun Island, Langkawi, in August 2023, and identified by a botanist, Shamsul Khamis. The voucher specimen (PL-01/23) was deposited at the Herbarium of UPSI. The essential oil was obtained by hydrodistillation (4 h) of the fresh leaves (200 g) using a Clevenger-type apparatus. The oil was dried over anhydrous magnesium sulfate and stored at 4_6_C. The oil yield was 0.16% based on the fresh weight. The chemical composition of the isolated oil was analyzed by GC and GC-MS under conditions analogous to those published before [6]. For identification of essential oil components, co-injection with the standards were used, together with correspondence of retention indices and mass spectra with respect to those occurring in the literature [7]. The free radical scavenging activity was measured by the DPPH method with minor modifications. The sample concentration providing 50% inhibition (IC50) was calculated by plotting inhibition percentages against concentrations of the sample. All tests were carried out in triplicate and butylated hydroxytoluene was used as standard [8]. The chemical components identified in the essential oil are shown in Table 1. In total, 35 chemical components, accounting for 91.5% of the total composition, were successfully characterized. The sesquiterpene hydrocarbons were the most dominant components and accounted for 47.6% of the total composition. The most abundant components were _-eudesmol (15.9%), _-eudesmol (15.6%), _-selinene (12.2%), _-bourbonene (7.2%), _-gurjunene (6.5%), and valencene (5.5%). In addition, the essential oil demonstrated moderate activity (IC50 158.2 mg/mL) compared with BHT (IC50 43.5 _g/mL). This could be due to the low abundance of oxygenated sesquiterpenes in the essential oil [9]. A review of the existing literature on the essential oils of the genus Popowia revealed the presence of only one study reporting on the stem bark and leaves of Popowia beddomeana collected from the Western Ghats of Kerala, India. They were successfully identified sesquiterpenes and cycloalkanes as the main components, whereas the bark oil was found to inhibit the growth of 15 bacterial strains and six fungal strains by the disk diffusion method at varying levels [10].