Abstract
Objective: Sterculia quadrifida R. Br. of Sterculiaceae family is locally known as “Faloak” in East Nusa Tenggara Province, Indonesia. S. quadrifida is used in folk medicine to treat hepatitis, rheumatism, and to recover stamina. The aim of this study was to determine the total flavonoids, total phenolic content (TPC), and antioxidant activity of extracts from different plant parts of S. quadrifida.
 Methods: The sampled parts of S. quadrifida were non-stripped stem bark, new regrown stem bark, old regrown stem bark, root bark, branch bark, and leaves. Stem bark was classified into three categories, namely, bark that has never been peeled (non-stripped stem bark), old regrown stem bark (estimated to be >6 months after debarking), and new regrown stem bark (estimated to be <6 months after debarking). Total flavonoid content (TFC) was determined by colorimetric aluminum chloride method and TPC was measured using Folin–Ciocalteu’s reagent. Antioxidant activity was determined with 2,2-diphenyl-1-picrylhydrazyl (DPPH).
 Results: The concentrations of flavonoids in S. quadrifida extracts from different plant parts varied from 0.58±0.13 to 1.25±0.10 mg QE/g. The TPC in the extracts of different plant parts ranged between 8.61±0.09 and 10.43±0.08 mg GAE/g. Branch bark has the highest total flavonoid and phenolic content. The extract of new regrown stem bark exhibited potent antioxidant activity with inhibitory concentration (IC50) values of 2.51±0.03 μg/ml.
 Conclusion: This study demonstrated for the first time that extracts from different plant parts of S. quadrifida exhibited strong antioxidant activity. However, the total phenolic and flavonoid contents in S. quadrifida only indicated a weak correlation with its antioxidant activity.
Highlights
Indigenous knowledge of medicinal plants provides the basis for the discovery of new drugs
This study demonstrated for the first time that extracts from different plant parts of S. quadrifida exhibited strong antioxidant activity
The total phenolic and flavonoid contents in S. quadrifida only indicated a weak correlation with its antioxidant activity
Summary
Indigenous knowledge of medicinal plants provides the basis for the discovery of new drugs. Br. is one of the most commonly used medicinal plants in East Nusa Tenggara Province, Indonesia. S. quadrifida bark is used to cure hepatitis, kidney disease, rheumatism, lower back pain, anemia, and stamina recovery [1]. This species belongs to the family Sterculiaceae which generally grows at an altitude of 1–1000 m asl. In the Province of East Nusa Tenggara, S. quadrifida can be found on the islands of Timor, Sumba, Alor, Pantar, Rote, and Flores [2,3]. Aboriginal people in Australia use S. quadrifida leaves to treat stings and consume its young tree roots and seeds [6]
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