The evaluation of total phenolic, flavonoid, and antioxidant activities of black soybean tempeh and purple sweet potato as antidiabetic candidate

Diabetes mellitus (DM) is a disease that causes blood glucose to increase above normal (hyperglycemia), which results in an increased level of free radicals. Antioxidants can fight the effects of free radicals. The combination of purple sweet potato (PSP) and black soybean tempeh (BST) is expected to increase antioxidant levels. This study aims to determine antioxidants levels, phenolics, and flavonoids from PSP and BST extract as antidiabetic candidates. Extraction was carried out by the maceration method using ethanol. The antioxidant activity test was carried out using the DPPH method, phenolic determination using the Folin-Ciocalteau (F-C) addition method, and the determination of flavonoid levels using quercetin as a standard. The spectrophotometer determined the IC50 of antioxidants, phenol, and flavonoid at 517, 740, and 510 nm, respectively. The highest antioxidant activity test results were obtained from the combination of BST and PSP (1 : 3), the IC50 value was 50.6 µg/mL, and the total phenol was 45.21 mgGAE/g extract. The most considerable total flavonoid level was found in the combination of BST and PSP ratio (3 : 1), 358.805 mgQE/g of extract. Our result suggested that the combination of BST and PSP has high antioxidant content and can be used as an alternative to antidiabetics.