Biological activities and determination of stilbenoids from extracts of Gnetum gnemon L. (maninjau)

Gnetum gnemon or known as maninjau (Malaysia) , which belongs to genus of Gnetum, order of Gnetales and family of Gnetaceae is a dioecious, evergreen tree that are widely cultivated in Southeast Asia. The seeds are usually cooked as crackers and well known among Indonesian while leaves, shoots and fibres are used as ‘ulam’ and ropes. Although some studies has done on Gnetacae family but studies specifically on Gnetum gnemon are very limited since the researchers only concentrate on isolation of the compound and limited to certain solvents. Analyses on biological activities of G. gnemon were done to determine the total phenolic,antioxidant, antimicrobial and anti-tyrosinase of the plant. The determination of stilbenoids using high-performance liquid chromatography (HPLC) was done since most of the family of this plant contained high amount of stilbenoids and this plant may have the potential to contain the same compounds. Four parts of Gnetum gnemon were used in this study, which were leaf, bark, twig, and seed of the plant. All parts were extracted in methanol, ethanol, hexane, chloroform and hot water using reflux technique. The total phenolic content of the plant extracts were determine by using Folin-Ciocalteu method. The results demonstrated that the bark from hot water extract showed the highest total phenolic which was 10.71 ± 0.008 mg GAE/ FDW, while the lowest was seed from chloroform extract which was 2.15 ± 0.006 mg GAE/ FDW. The antioxidant activity of the plant extracts were determined by using DPPH and FRAP assays. The DPPH results showed that all plant extracts demonstrated weak free radical scavenging activity tested at final concentration of 300 μg/ml. In contrast, the methanolic twig extract showed strong reducing power activity (FRAP) with 83.55± 1.05 %, while the hot water seed extract showed the least activity with 41.86 ± 4.22 % tested at final concentration of 300 μg/ml. There were no correlation between total phenolics and both antioxidant assays tested based on the results obtained. Anti-tyrosinase activity of the plant extracts were determined by using mushroom tyrosinase enzymatic assay. The results showed that hot water bark extract demonstrated moderate anti-tyrosinase activity with 57.78 ± 2.13 %, while other plant extracts demonstrated weak anti-tyrosinase activity tested at final concentration of 200 μg/ml. In addition, four Gram-positive bacteria (Bacillus subtilis, Micrococcus luteus, Enterococcus avium and Staphylococcus aureus) and four Gram-negative bacteria (Escherichia coli, Klebsiella pneumoniae, Pseudomomas aeruginosa and Shigella sonnei) were tested for antimicrobial activity of the plant extracts. The results showed that ethanolic twig extract demonstrated the highest antimicrobial inhibition among all samples tested which were 4.33 mm upon antimicrobial activity upon Gram-positive bacteria (Staphylococcus aureus) at concentration of 20 mg/ml . On the other hand, the antifungal activities of the plant extracts were evaluated upon Aspergillus terreus,Penicillum notatum, Mucor, Ganoderma lucidum and Tricoderma harzianum.The results showed that the hot water extract of seed showed moderate anti-fungal activity which were 1.60 mm upon G. lucidium. Resveratrol, piceatannol and ptereostilbene were used as the stilbenoids standard in this study. The HPLC results showed that piceatannol was the highest in the methanolic seed extract (2.62 mg), while the resveratrol was the lowest in hexanoic bark extracts (0.03 mg). Overall, from the result obtained, the stilbenoids compounds in the samples extract did not contribute to the antioxidant activity. However, they show a potential activity upon antimicrobial and anti-tyrosinase activities since the result are quite promising. Further reserach is needed to identify the active compound from this plant and their phyto-pharmaceutical studies.

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