a DPPH radical-scavenging activity and b ABTS radical-scavenging activity of Cheonggukjang prepared using different concentrations of B. subtilis (KCTC 13241). Different colours show the different concentrations (1, 0.75, 0.5, and 0.25 mg/mL) in the samples. All values are the average of three separate experiments. The letters a, b, c, and d indicate significant differences (p ≤ 0.05)