Introduction: Soy sauce cake (SSC), a protein-rich by-product of soy sauce production, represents a largely underutilized resource, despite its significant potential for sustainable food valorization. Harnessing halophilic bacteria capable of degrading salty food waste offers a promising biotechnological route for upcycling SSC into functional ingredients.
Methods: A halophilic protease-producing bacterium, strain LC4, was isolated from mangrove sediments of Matang Mangrove Forest Reserve, Perak, Malaysia. Taxonomy analysis was conducted with phylogenetic, whole-genome analysis and in silico analyses (ANIb and dDDH) to accurately identify strain LC4. In addition, protease-encoding genes were mined from the whole-genome data of strain LC4 with InterProScan. Crude protease extracts were characterized for activity across various conditions and tested for stability. Strain LC4 was then applied in submerged fermentation of SSC, with protein hydrolysis and peptide production measured over time.
Results: Phylogenetic and whole-genome analyses identified strain LC4 as a novel species within the Mesobacillus genus, with ANIb (<95%) and dDDH (<70%) values. Genome mining revealed 25 extracellular protease-encoding genes, comprising serine and metalloproteases. The identified proteases displayed halophilic and thermotolerant characteristics, with optimal performance at 40–60°C, pH 8, and 4–8% (w/v) NaCl. Enzymes maintained stability in the presence of Ca2+and Al3+ ions, highlighting their industrial potential. Strain LC4 was subsequently applied for SSC biodegradation. Submerged fermentation of SSC resulted in significant protein hydrolysis (5.16 mg/g dry SSC) within 24 h and peptide production (0.63 mg/g dry SSC) after 72 h. The results demonstrate the potential of strain LC4 to convert protein-rich high-salt food waste into functional peptides.
Conclusion: Mesobacillus sp. strain LC4 offers a sustainable approach to upcycling SSC into bioactive peptides. The integration of genomic analysis and wet-lab validation highlights its potential as an efficient biocatalyst, contributing to circular economy efforts and advancing food waste bioprocessing for nutraceutical applications.
