Abstract. Antioxidants in chemical terms are electron donors and antioxidants are biologically compounds that can overcome the negative effects of oxidants in the body such as damage to vital cells of the body. The balance between oxidants and antioxidants is very important. Antioxidant from natural sources are safer than synthetic antioxidants. Soybeans are functional food source that contains essential amino acids, vitamin e, saponins and are rich in antioxidants such as flavonoids, isoflavones and anthocyanins. The aim of this research is to investigate antioxidant potential of ethanolic extract of black soybean (EEBS) and its compound daidzein. The phytochemical screening assay evaluated by modified Farnsworth methods and to find out phenolic and flavonoid content, total phenols and flavonoids were tested. DPPH (2,2-diphenyl 1-pichylhydazy), ABTS (2,2’-Azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) reducing activity, FRAP (ferric reducing antioxidant power) activity and H2O2 scavenging activity assay were used to measure antioxidant activity. The analysis of phytochemical of EEBS exhibit the presence of saponins, alkaloids, tannins, steroids and triterpenoids and terpenoids. Total phenol and flavonoid assay showed the presence of phenols and flavonoids. Four assay of antioxidant activity showed that EEBS at highest concentration exhibit higher activity (%), and from three assays EEBS has higher antioxidant activity (expressed as IC50) than daidzein. Overall, three of the four antioxidant tests performed can be concluded that EEBS has better antioxidants activity than daidzein. Further research is needed regarding black soybean as a promising antioxidant resource. 

… The yield of EEBS was 2.63 g stored at 20oC [3,19-23,24]. EEBS was used for next experiment. Daidzein (Chengdu Biopurify Phytochemical Ltd, BP0445) were used as standard compound. 2.2. Phytochemical Assay 2.2.1. Flavonoids …