| Abstract |
Purpose This study explored diverse substrates/co-substrates to optimize protease production by Bacillus sp. CL18, and examined bioactivities in optimized medium. Methods Protease production was assessed using a one-variable-at-a-time approach. Twelve substrates (10 g/L) were initially tested, and the best one was evaluated at 10-50 g/L. Subsequently, 12 co-substrates were added, and then the best one was investigated (1-20 g/L). Proteolytic activity was measured in culture supernatants at days (d) 0-6, using azocasein. In vitro bioactivity assays involved radical-scavenging and Fe2+- chelating abilities, and the inhibition of dipeptidyl peptidase-IV (DPP-IV) and angiotensin- I converting enzyme (ACE). Results Ground fish scales (FS; 10 g/L) yielded increased protease production (360 U/mL; d4), which was 8-92% higher than other substrates. With FS, higher protease yield (496 U/mL; d4) was observed at 30 g/L ( FS30). Among the co-substrates (1 g/L) added to FS30, milled feathers (MF) were the best one ( 670 U/mL; d4). Finally, highest protease production (780 U/ mL; d4) was detected with 5 g/L MF (MF5). After optimization (FS30 + MF5), production was 216% of that with 10 g/L FS. Regarding antioxidant activities, radical-scavenging and Fe2+-chelating capacities in FS30 + MF5 increased from 31.7 to 3.0% (d0) to 77.2 and 55.3% (d4), respectively. In vitro DPP-IV-inhibiting (antidiabetic) and ACE-inhibiting (antihypertensive) activities reached 65.0-73.0% ( d1-4) and 71.2% (d4), as compared to 8.3% and 28.7% (d0), respectively. Conclusion A low-cost waste- based medium was developed for protease production. Co-production of bioactive hydrolysates further contributes to the valorization of fish scales and feathers, representing a promising bioprocess from a circular economy perspective. [GRAPHICS] . |
