Comparison of poly-γ-glutamic acid production between sterilized and non-sterilized solid-state fermentation using agricultural waste as substrates

Solid-state fermentation (SSF), using corn stalk and soybean meal as solid substrates, was carried out for the first time to produce poly-gamma-glutamic acid (gamma-PGA) by Bacillus amyloliquefaciens JX-6. Comparison for the yield of gamma-PGA, characteristics of solid substrates, and changes of bacterial communities between sterilized and non-sterilized conditions was performed with an aim to find a cleaner and more efficient approach for producing gamma-PGA. Changes to solid substrates occurred during fermentation, and nonsterilized SSF had a more significant effect on fermentation substrates. Analysis of bacterial communities showed that JX-6 had an excellent ability to produce gamma-PGA. Sterilized SSF resulted in higher yield of gamma-PGA, while non-sterilized SSF possessed a faster fermentation process. The latter could be more suitable and environmental-friendly for large-scale gamma-PGA fermentation because of the advantages of time and cost savings. It is noted that the production of gamma-PGA in this study was the highest in the literatures, indicating a successful bioconversion of agricultural waste into value-added products. (C) 2020 Elsevier Ltd. All rights reserved.