Potential Antioxidant Activity of Tropical Brown Macroalgae Turbinaria Ethanol Extract from Kabung Island West Kalimantan

: Naturally, the human body has tolerance to free radical attacks. However, the natural antioxidant ability will decrease when exposure to free radicals from within and outside the body occurs intensively. Antioxidants play potential preventive role to protect the body from damage associated with oxidative stress by free radicals. One of the potential marine resources used as an antioxidant is macroalgae. Turbinaria is widely distributed in tropical waters of Indonesia, including West Kalimantan. This genus produces secondary metabolites with several biological activities. This genus abundantly grows in Kabung Island. However, it has not been used by the local community, even tends to be considered as a weed that disturbs others marine biota. This study aimed to evaluate the potential antioxidant activity of tropical brown macroalgae Turbinaria ethanol extract from Kabung Island, West Kalimantan. antioxidant activity was evaluated using the DPPH (1,1-diphenyl-2-picrylhydrazyl) free radical scavenger method with UV-vis spectrophotometer. The result showed that the ethanolic extract had a high of potential antioxidant activity which IC 50 was 87.31 mg/L and it was classified into strong antioxidant potential.

Naturally, the human body has tolerance to free radical attacks. However, the natural antioxidant ability will decrease when exposure to free radicals from within and outside the body occurs intensively. This condition eventually causes some damage to the body, disrupt cellular metabolism, and alter the major target as lipids, proteins, and DNA (Young and Woodside, 2001). Free radical attacks are closely related to the body's physiological processes, especially degenerative diseases (diabetes mellitus, cancer and atherosclerosis), and aging (Bhaigyabati et al., 2011). Antioxidants play potential preventive role to protect the body from damage associated with oxidative stress by free radicals (Ozsoy et al., 2008). These substances can also inhibit the oxidation of lipids and other biomolecules by blocking the initiation step and scavenging various free radicals in order to detoxify the organism (Kumaran and Karunakaran, 2006).
Turbinaria belongs to the group of Phaeophyceae due to the pigment of fucoxanthin (Husni and Budhiyanti, 2021). Today, the study on the genus Turbinaria is currently increasing. This genus abundantly grows in Kabung Island. However, it has not been used by the local community, even tends to be considered as a weed that disturbs others marine biota. For this reason, this study aimed to evaluate the potential antioxidant activity of tropical brown macroalgae Turbinaria ethanol extract from Kabung Island, West Kalimantan.

Samples collection and identification
Sample of Turbinaria was taken from Kabung Island, West Kalimantan, Indonesia. Sample identification and extraction were carried out in the Laboratory of Marine Science, Faculty of Mathematics and Natural Sciences, Universitas Tanjungpura. The test of antioxidant activity was conducted in the Laboratory of PT. Sucofindo, Pontianak.

Samples preparation
Sample of Turbinaria was cleaned, then dried at room temperature approximately for five days to reduce water content. Extraction was carried out by maceration method using ethanol solvent. Samples were roughly chopped and grinded to be fine powder. A total of 250 g of sample powder was macerated using ethanol in a ratio of 1:5 (w/v), then shaken at 150 rpm for 1 x 24 hours. The ethanol extract was hereinafter concentrated using a rotary evaporator for further analysis.

Antioxidant Activity Test
The determination of antioxidant activity was realized according to the method of Banerjee et al. (2005). Sample solution was prepared in several concentrations of 50, 100, 150, 200, and 250 ppm. The next step was preparation of 0.1 mM DPPH (1,1-diphenyl-2-picrylhydrazyl) reagent by dissolving 0,002 g of DPPH in 50 mL of 95% ethanol. As much as 3 mL of sample solution of each concentration was added with 1 mL of DPPH solution. Furthermore, samples and DPPH were mixed using vortex for 1 minute and incubated at room temperature for 30 minutes. The measurement of absorbance was conducted using a Spectrophotometer U-1240 Shimadzu UV-vis at a wavelength of 517 nm, and ethanol was used as blank solution. Antioxidant standard solution using ascorbic acid. The percentage of inhibition was calculated by the following formula: where, A0 is control absorbance (DPPH 0.1 mM) and A1 is sample absorbance (sample + DPPH 0.1 mM).

Identification of Macroalgae
Thallus of Turbinaria is brown in colour, has many branches, and serrated at the edges. The stipe tapers downwards and widens upwards, forming a crown-like portion. According to Guiry and Guiry (2018) Macroalgae are widely distributed in Indonesian waters with suitable physio-chemical parameters condition (Kadi, 2006). Currently, the study on brown algae, especially the genus Turbinaria has been conducted from biodiversity, bioprospecting, and the use of bioactive compound in various industrial fields. In West Kalimantan, this genus found in Kabung Island and Lemukutan Island with the abundances of 1.92 ind/m 2 .
The test of antioxidant activity was based on the ability of antioxidant compounds in Turbinaria extract to capture free radicals released by DPPH compounds, with reactions as described below (Figure 2). The concentration of antioxidant compounds in the sample was measured through the absorbance of the sample solution added with DPPH free radicals. Decreasing color intensity of DPPH from dark purple to light yellow is proportional to the content of antioxidant compounds in the samples. The determination of antioxidant activity was done by IC50, value describes the concentration of antioxidant needed to inhibit 50% of DPPH radicals (Chakraborty and Joseph, 2016). This value was obtained using linear regression as the relationship between the concentration of the test extract and the percentage of free radical inhibition (Zou et al., 2004). The result of ethanolic extract of Turbinaria showed a potential antioxidant activity which IC50 was 87.31 mg/L, and it was classified into strong antioxidant potential. According to Molyneux (2004), the value of IC50 <50 mg/L was classified as a very strong antioxidant, ranging from 50-100 mg/L was classified as a strong antioxidant, and IC50 >100 mg/L was classified as a weak antioxidant.

Conclusion
It could be concluded that ethanolic extract of Turbinaria showed a potential antioxidant activity which IC50 was 87.31 mg/L, and it was classified as strong antioxidant potential.

Acknowledgement
Authors would like to address our sincere gratitude to Rusdi Palureng for laboratory analysis of PT Sucofindo Pontianak, West Kalimantan in this research.