Optimization of protease production by Bacillus cereus HMRSC30 for simultaneous extraction of chitin from shrimp shell with value-added recovered products

Abstract

Chitin extraction from shrimp shell powder (SSP) using protease-producing microbes is an attractive approach for valorizing shrimp shell waste because it is simple and environmentally friendly. In this study, the protease production and chitin extraction from SSP by Bacillus cereus HMRSC30 were simultaneously optimized using statistical approaches. As a result, fermentation in medium composed of 30 g/L SSP, 0.2 g/L MgSO₄ · 7H₂O, 3 g/L (NH₄)₂SO₄, 0.5 g/L K₂HPO₄, and 1.5 g/L KH₂PO₄ (pH 6.5) for 7 days maximized protease production (197.75 ± 0.33 U/mL) to approximately 1.64-fold compared to unoptimized condition (126.8 ± 0.047 U/mL). This level of enzyme production was enough to achieve 97.42 ± 0.28% deproteinization (DP) but low demineralization (DM) of 53.76 ± 0.21%. The high DM of 90% could be easily accomplished with the post-treatment using 0.4 M HCl and acetic acid. In addition, the study evaluated the possible roadmap to maximize the value of generated products and obtain additional profits from this microbial process. The observation showed the possibility of serving crude chitin as a bio-adsorbent with the highest removal capacity against Coomassie brilliant blue (97.99%), followed by methylene blue (74.42%). The recovered protease exhibited the function to remove egg yolk stain, indicating its potential for use as a detergent in de-staining. The results corroborated the benefits of microbial fermentation by B. cereus HMRSC30 as green process for comprehensive utilization of shrimp shell waste as well as minimizing waste generation along the established process.

Keywords: De-staining; Deproteinization; Dye adsorbent; Microbial process; Post-demineralization; Valorizing shrimp waste.