Bioconversion of Sushi By-Products through Fermentation with Aspergillus terreus and Bacillus subtilis

The reutilization of food waste supports circular economy goals by transforming organic by-products into valuable bio-based compounds. This study investigated the fermentation of the organic fraction from sushi manufacturing by-products (OFS), which comprises rice, crustacean remnants, avocado peels, cucumber scraps, and algae by-products. Aspergillus terreus DSMZ 23081 and Bacillus subtilis ATCC 1177 were selected for their organic acid biosynthesis and enzymatic hydrolysis abilities. Five batches were tested: (A) A. terreus, (B) B. subtilis, (C) non-inoculated control, (D) pre-fermentation with B. subtilis followed by A. terreus, and (E) pre-fermentation with B. subtilis, autoclaved, then inoculated with A. terreus. B. subtilis effectively hydrolyzed OFS, increasing glucose and ethanol production (75.97 ± 0.21 mg/gDW) in 72 hours. Pre-hydrolysis enhanced substrate availability and improved fermentation. Co-fermentation increased succinic and itaconic acid yields; batch D produced 31.77 ± 0.78 mg/g succinic acid, and batch E yielded 5.23 ± 0.11 mg/g itaconic acid by day 7. HPLC confirmed glucose and maltose consumption, with metabolite production influenced by fermentation strategy. A pH of 6 boosted organic acid production. Overall, OFS proved to be a nutrient-rich substrate, and B. subtilis pre-treatment improved microbial interaction, demonstrating a promising pathway for organic acid production from food residues.