[2S04e] 18. Biorefinery and Bioproduction - Part 3

5:15 PM - 5:30 PM JST(8:15 AM - 8:30 AM UTC)

[2BRBP-15] Bioconversion of Soy Sauce Moromi-kasu Using an Alkaliphilic Bacterium with a Robust Extracellular Enzyme System

○Masahiro Ito¹, Shunki Ota¹ (1. Toyo University (Japan))

Keywords:

Soy sauce moromi-kasu,Alkaliphiles,Bioconversion,Food fermentation by-products,Circular bioeconomy

Soy sauce moromi-kasu is a solid fermentation residue generated during the pressing stage of soy sauce production. Large quantities of this by-product are produced annually, and although it still contains substantial amounts of proteins and carbohydrates, its effective utilization remains limited because of its high salt content and complex solid structure. Conventional microbial processes often fail to efficiently degrade this material due to osmotic stress and inhibitory salt concentrations. Developing biological processes capable of converting such high-salt fermentation residues into valuable products is therefore an important challenge for sustainable food biotechnology and resource recycling.In this study, we investigated the potential of an alkaliphilic bacterium, strain A5, for the bioconversion of soy sauce moromi-kasu. The strain was isolated using an alkaline medium containing moromi-kasu as a selective substrate. Alkaliphilic microorganisms are known to possess enzyme systems that function efficiently under high pH and saline conditions, making them promising candidates for the utilization of high-salt fermentation by-products.Strain A5 exhibited strong extracellular enzyme activity under alkaline conditions and maintained stable activity even in the presence of elevated salt concentrations. Enzyme analysis revealed that extracellular protease activity was the dominant catalytic component of the enzyme system, while amylase activity increased during cultivation. These enzymes collectively contributed to the degradation of proteins and carbohydrates contained in moromi-kasu.The enzyme system efficiently hydrolyzed proteins present in moromi-kasu and promoted the rapid accumulation of free amino acids in the culture medium. Significant amino-acid release was observed during the early phase of the reaction, indicating efficient degradation of residual proteins in the fermentation residue. The alkaline conditions also contributed to suppressing the growth of contaminating microorganisms, allowing stable enzymatic conversion of the substrate.These findings demonstrate that alkaliphilic microorganisms possess enzyme systems well suited for the conversion of high-salt fermentation by-products such as soy sauce moromi-kasu. The study highlights the potential of alkaliphilic bacteria as biocatalysts for the sustainable valorization of food fermentation residues. Such systems may contribute to the development of circular bio-based processes in the food industry by transforming fermentation waste into valuable biochemical resources⁽¹⁾. (1) Ota S and Ito M, (2025), Environmental Technology and Innovation, 40, 104615 https://doi.org/10.1016/j.eti.2025.104615