Screening for high-purity L-lactic acid-producing thermotolerant Bacillus capable of utilizing sucrose and starch in an energy-efficient production process

Vichai Leelavatcharamas

Department of Biotechnology, Faculty of Technology, Khon Kaen University, Khon Kaen, Thailand

Ayyapruk Moungprayoon

Department of Biotechnology, Faculty of Technology, Khon Kaen University, Khon Kaen, Thailand

Kenji Sakai

Graduate School of Bioresource and Bioenvironmental Sciences, Kyushu University, Japan

Saowanit Tongpim

Department of Microbiology, Faculty of Science, Khon Kaen University, Khon Kaen, Thailand

DOI: https://doi.org/10.14456/apst.2025.54

Keywords: Bacillus coagulans Energy-saving bioprocess optically pure lactic acid Sucrose utilizing Bacillus

Abstract

This study aimed to isolate and characterize thermotolerant Bacillus strains capable of utilizing sucrose and starch for efficient production of optically pure L-lactic acid. High-purity L-lactic acid is a valuable bio-based chemical with applications in bioplastics and other industries. Thailand’s abundant sucrose and tapioca starch byproducts present an opportunity to produce L-lactic acid from low-cost feedstocks using thermotolerant bacteria like Bacillus coagulans. Twenty-eight thermotolerant Bacillus isolates were screened for their capability to grow on glucose, sucrose, and cassava starch at 50 °C. Four strains (NF17, N24A2t, NF11, N47B2) could utilize all three carbon sources. These were further evaluated for growth, acid production profile, and L-lactic acid yield. Strain NF11, identified as B. coagulans, produced the highest L-lactic acid titter, 108 g/L from molasses, with a yield of 1.12 g/g at 50 °C under aerobic conditions. The effects of aeration, initial sugar concentration and sterilization method on L-lactic acid production were investigated using the NF11 strain. Moderate aeration at 100 rpm improved sugar utilization and lactic acid productivity over that of static conditions. An initial 100 g/L total sugar concentration from molasses was optimal. Remarkably, NF11 could produce high L-lactic acid titers without conventional heat sterilization, using only chemical sterilization with potassium metabisulfite or no pretreatment at all. This energy-efficient bioprocess employing a thermotolerant B. coagulans strain enables valorization of sugary byproducts like molasses into optically pure L-lactic acid, a valuable bio-based chemical feedstock. Eliminating energy-intensive pasteurization/sterilization offers significant cost advantages for large-scale L-lactic acid biorefineries.

How to Cite

Leelavatcharamas, V., Moungprayoon, A., Sakai, K. ., & Tongpim, S. . (2025). Screening for high-purity L-lactic acid-producing thermotolerant Bacillus capable of utilizing sucrose and starch in an energy-efficient production process. Asia-Pacific Journal of Science and Technology, 30(04), APST–30. https://doi.org/10.14456/apst.2025.54

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