BIODIVERSITAS ISSN: 1412-033X Volume 23, Number 8, August 2022 E-ISSN: 2085-4722 Pages: 4209-4215 DOI: 10.13057/biodiv/d230844 Endophytic actinobacteria of Eleutherine palmifolia as antioxidant producer AFINA PUTRI SHABIRA ♥ , ARIS TJAHJOLEKSONO, YULIN LESTARI Department of Biology, Faculty of Mathematics and Natural Sciences, Institut Pertanian Bogor. Jl. Raya Dramaga, Bogor 16680, West Java, Indonesia. Tel./Fax.: +62-251-8622833,  email: afina.putrishabira@gmail.com Manuscript received: 18 June 2022. Revision accepted: 31 July 2022. Abstract. Shabira AP, Tjahjoleksono A, Lestari Y. 2022. Endophytic actinobacteria of Eleutherine palmifolia as antioxidant producer. Biodiversitas 23: 4209-4215. Endophytic actinobacteria can generate bioactive compounds similar to those produced by the host plant. The Eleutherine palmifolia (L.) Merr is an example of a widely utilized host plant in the Dayak community. Flavonoids, which have antioxidant effects, are among the bioactive compounds found in E. palmifolia. The antioxidant activity of bioactive compounds produced by endophytic actinobacteria of E. palmifolia remains unidentified. The aim of this study was to examine the antioxidant activity of bioactive compounds produced by endophytic actinobacteria of E. palmifolia. Antioxidant activity from isolates actinobacteria was determined quantitatively using the DPPH and ABTS methods. Identification of the types of bioactive compound in the samples was identified using TLC assay and bioautography test. Analysis of flavonoid levels was performed using colorimetric aluminum chloride (AlCl3). The result showed that the extraction of six isolates of endophytic actinobacteria with ethyl acetate solvent had different yields. The extract of endophytic actinobacteria EPB 6 isolate produced the highest (0.013%) yield. The extract of endophytic actinobacteria EPB 3 isolate had the best antioxidant activity, with 53.85 mg/mL (DPPH) and 42.43 mg/mL (ABTS). The extract of endophytic actinobacteria EPB 3 isolate and E. palmifolia had the same blue spots in TLC analysis, indicating the presence of bioactive compounds flavonol and flavones groups. The bioautography test of EPB 3 isolate endophytic actinobacteria extract produced yellow color, indicating qualitatively antioxidant activity. The total flavonoid content of the EPB 3 isolate extract was also higher (25.30 QE/mg) than the other five isolates, while it was 46.03 QE/mg in E. palmifolia extract. It is clear from the present study that the endophytic actinobacteria extract can produce antioxidants. Keywords: Antioxidant, endophytic actinobacteria, Eleutherine palmifolia, flavonoid Abbreviations: ABTS: 2,2-azinobis-3-ethyl benzothiazoline-6-sulphonic acid, DPPH: 2,2-diphenyl-1-picrylhydrazyl, IC50: Half- maximal inhibitory concentration, TLC: Thin-layer chromatography, QE: Quercetin equivalen INTRODUCTION Actinobacteria are gram-positive bacteria that vary in shape and size, have 70% guanine-cytosine in their genome, and are wide spread due to their ability to survive in diverse environments, including the soil, rhizosphere, and internal parts of plant tissues (Singh and Dubey 2015). Endophytic actinobacteria live as colonies in plant tissues and protect the host plant from diseases. Endophytic actinobacteria are also harmless to the host plant. Endophytic actinobacteria can produce bioactive chemicals similar to those produced by their hosts. These bioactive chemicals are known to have various properties (including antioxidant activity, antibiotics, and immunosuppressants), making them suitable for human consumption (Tan and Zou 2001; Millker et al. 2012; Singh and Dubey 2018). The antioxidant can counteract free radicals from the environment to prevent disorders in the human body, like reduced respiratory function, premature ageing, blood vessel obstruction, tumors, and breast cancer. The number of free radicals that enter the human body is not proportional to the number of available antioxidants, allowing it to cause excess free radicals (Ganie et al. 2013; Ahmadinejad et al. 2017). DPPH and ABTS are two commonly used techniques to measure antioxidant activity. The DPPH method can describe the body's defensive mechanism against free radicals, whereas ABTS approach is typically used to test the antioxidant activity of food ingredients. In DPPH method, antioxidant uses an electron transfer mechanism to give hydrogen to stabilize DPPH radicals, while in ABTS approach, it uses protons to stabilize ABTS radicals (Re et al. 1999; Prakash et al. 2001). Antioxidant activity indicates a value of 50% inhibitory capacity (IC50). The lower the IC50 value of bioactive compound, the better its antioxidant activity. Artificial and natural antioxidants are the two types of antioxidants that help counteract free radicals. Natural antioxidants have fewer side effects than artificial antioxidants. Plants that produce flavonoids are examples of natural antioxidants including anthocyanins, flavonols, and isoflavones (Panche et al. 2016). Flavonoids are renowned for their antioxidant properties and biochemical effects on human health issues. The aluminum chloride colorimetric method is commonly used to determine the quantity of flavonoids in a bioactive compound. This approach works by forming bonds between flavonoids in the tested substances with AlCl3 to produce color (Zuraida et al. 2017).