Professor
Masahiro Ito
Graduate School of Life Sciences, Bio-resilience research project (BRRP), Bio Nano Electronics Research Center, Toyo University, Asaka, Saitama 351-8510 Japan
Title: Alkaliphilic Strain A5 Facilitates Mass Reduction and Amino Acid Release from Soy Sauce Moromi-kasu
Masahiro Ito1,2,3 and Shunki Ota1,2
1 Graduate School of Life Sciences, Toyo University, Asaka, Saitama 351-8510 Japan
2 Bio-resilience research project (BRRP), Toyo University, Asaka, Saitama 351-8510 Japan
3 Bio Nano Electronics Research Center, Toyo University, Kawagoe, Saitama 350-8585 Japan
Soy sauce moromi-kasu is a high-salt, high-moisture by-product generated during the pressing stage of soy sauce fermentation. Although partially reused as feed or fertilizer, a large portion remains unutilized because of its poor physical properties and high transport cost. Establishing an efficient biorefinery process for moromi-kasu is therefore important for advancing circular resource use in the soy sauce industry. This study aimed to evaluate alkaliphilic bacteria and their enzyme-rich culture supernatants as tools for mass reduction and free amino acid (FAA) recovery from moromi-kasu.
Using an alkaline moromi-kasu medium (pH 10), 21 alkaliphilic strains were isolated from soil. Their degradation capacity was assessed qualitatively and quantitatively. Among all isolates, strain A5 showed the strongest activity, reducing moromi-kasu to 20% residual mass after 6 days. Enzyme assays revealed that A5 produced high and stable protease activity, together with increasing amylase activity, explaining its superior degradation ability. 16S rRNA gene analysis indicated that A5 is closely related to Shouchella miscanthi.
To establish a cell-free process, culture supernatants were tested as biocatalysts. Supplementation of fresh medium with 5% (v/v) A5 supernatant resulted in a 36% residual mass and sharply increased FAA release, reaching 209 mM on day 1, approximately double that of the control. Because the added supernatant itself contained only low amino acid levels, the increase reflected enzymatic hydrolysis of the moromi-kasu proteins. Histamine content remained low throughout the process, supporting its suitability for food- or feed-related applications.
These results demonstrate that alkaliphilic strain A5 and its extracellular enzyme system enable efficient biomass reduction and amino acid liberation from soy sauce moromi-kasu. The cell-free supernatant approach is scalable, avoids handling live microbes, and represents a promising biorefinery strategy for valorizing underutilized high-salt fermentation residues in support of circular bioeconomy goals(1). (1) Ota S and Ito M, (2025), Environmental Technology and Innovation, DOI:10.1016/j.eti.2025.104615
Biography of the presenting author
Masahiro Ito completed his undergraduate studies in Chemistry at Rikkyo University and earned his Ph.D. in Chemical Engineering from the Tokyo Institute of Technology in 1994. From 1994 to 1997, he worked as a postdoctoral fellow in the Department of Biochemistry at the Mount Sinai School of Medicine in New York. In 1997, he joined the Faculty of Life Sciences at Toyo University as a full-time lecturer. He has received several awards, including the 2002 International Conference on Extremophiles Young Poster Award, the 2005 Japan Society for Extremophiles Encouragement Award, and the 2011 JSPS Prize for Outstanding Young Scientists. From 2008 to 2010, he served as a Program Officer at MEXT. In 2020, he became Program Director of the Bio-Resilience Research Project, promoting the social implementation of extremophile science toward achieving the SDGs. The project was selected as a Toyo University Priority Research Program for FY2021 and again for FY2024, launching its second phase, “Realizing a Circular Society with Extremophiles, Enriching Living Environments! TOYO SDGs Global 2024–2030–2037.” He is an Associate Editor for Frontiers in Microbiology, an Editorial Board Member for Applied and Environmental Microbiology and Engineering Microbiology, and an Advisory Board Member for the Journal of Biochemistry. Since 2023, he has also served as an expert member of Japan’s Food Safety Commission. His research focuses on fundamental and applied microbiology of extremophiles, particularly alkaliphilic and halophilic microorganisms.
Presenting author details
Full name: Masahiro Ito
Contact number:+81-48-468-6835
Email: masahiro.ito@toyo.jp
ResearcherID: H-1960-2013
WebsiteCategory: (Oral presentation)