The Knema L. is the third largest genus among the Asian Myristicaceae, comprising approximately 60 Southeast Asian species. The seeds of some Knema species are used in traditional medicine to treat cancer, sores, pimples, and skin diseases. Previous chemical constituent studies of Knema species are associated with variously crucial pharmacological values, such as anticancer, antioxidant, antimicrobial, antidiabetes, anti-inflammatory, neuroprotection, and hepatoprotection activities. Recently, essential oil and various extracts of plants have provoked interest in studies of its potential natural resources.
In Vietnam, Knema genus comprises 14 species, Knema tonkinensis (Warb.) WJ de Wilde was one of the first species discovered in 1979 by Wilde and distributed in Yunan (China), Laos, and Vietnam. To date, there is no information on the chemical composition of the essential oil of K. tonkinensis. Therefore, this study is the first report on the chemical composition of the essential oil from the leaves and twigs of K. tonkinensis in Vietnam. April 2022, the leaves and twigs of Knema tonkinensis species were collected from a single tree at Xuan Nha Nature Reserve, Son La Province which has geographic characteristics of 20 38′ 08.96′′ N and 104 43′ 22.45′′ E with an altitude of 397 m above sea level. A voucher specimen was authenticated and deposited at the Herbarium of the Vietnam National Museum of Nature with the code BVH07. The essential oil was hydrodistilled for 4 h using a Clevenger apparatus as described in Vietnamese Pharmacopoeia V. The obtained essential oil was dried over anhydrous sodium sulfate Na2 SO 4 to remove any trace of water and stored in sealed glass vials at 4 C until further analysis. The yields of hydrodistillation essential oils were from 0.5% of leaves and 0.02% of twigs, respectively as calculated on a fresh weight basis. The two essential oils were yellowish in color.
A total of eighty-six compounds were identified from two essential oil samples analyzed with 64 compounds from leaf oil and seventy-six compounds from twig oil, comprising 98.1–99.7% of the total components. Monoterpenes and sesquiterpenes were the main classes of compounds presented in all oils. The major constituents of the oils from leaves and twigs were similar. Accordingly, β-pinene (24.0%), α-pinene (23.9%), bicyclogermacrene (11.0%), caryophyllene (8.0%), and copaene (4.5%) were found in the leaves, and β-pinene (19.7%), α-pinene (15.4%), trans-β-ocimene (10.1%), β-copaen-4α-ol (5.2%), bicyclogermacrene (5.1%), caryophyllene (5.1%), and 7-epi-γ-eudesmol (4.1%) were found in the twigs.
Our results showed that essential oil from the leaves of K. tonkinensis has a remarkably strong antimicrobial activity against all of the four tested bacteria and one yeast in a 10% concentration of the essential oil. The ability to inhibit the four strains – E. faecalis, S. aureus, E. coli, K. pneumoniae – and yeast at a 10% essential oil concentration was 94.7%, 94.7%, 88.9%, 79.7%, and 95.1%, respectively. Meanwhile, the effects of the essential oil from only the twigs against the microbial negative was E. coli and K. pneumoniae with 97.4% and 3.9% respectively.
Figure 1. Knema tonkinensis (Warb.) W.J.de Wilde
Source: Bùi Văn Hướng. Bùi Văn Hướng. Nguyễn Hải Đăng. Đỗ Văn Hài. Lưu Đàm Ngọc Anh. Bùi Văn Thanh. Trương Bá Vương (2023). CHEMICAL COMPOSITION AND ANTIMICROBIAL ACTIVITY OF ESSENTIAL OIL FROM THE LEAVES AND TWIGS OF Knema tonkinensis. CHEMISTRY OF NATURAL COMPOUNDS, 1(6): 1-5.
News: Bui Van Huong, The Vietnam National Museum of Nature, VAST