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

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