Abstract:

In order to find the most suitable strain for the production of antioxidant peptides and plasmin from millet bran,
initial screening of 27 Bacillus subtilis stains for the ratio of transparent circle diameter to bacterial colony diameter (HC
value) was performed on casein agar plates and further screening of the selected strains based on total proteinase activity,
peptide content and total antioxidant capacity (T-AOC) of fermentation supernatants was conducted using the basal medium
containing millet bran. This study also investigated the optimal fermentation time for antioxidant activities of fermentation
supernatants using the selected optimal strain. Results showed that NattoD-3 was found to be the optimal strain for the
fermentation of millet bran, yielding a protease activity of 90.22 IU/mL. The optimal fermentation time was 72 h, and the
resulting T-AOC, DPPH radical scavenging activity, reducing power and Fe2+ chelating ability of millet bran fermentation
supernatant were 38.04 U/mL, 75.37%, 0.18 and 44.34%, respectively. The peptide content in the fermentation supernatant
reached 4.28 mg/mL with plasmin activity of 522.64 IU/mL.

Key words: Bacillus subtilis, fermentation, millet bran, antioxidant peptide