Production optimization of poly-γ-glutamic acid by <em>Bacillus amyloliquefaciens</em> under solid-state fermentation using soy hull as substrate

Abstract

Poly-γ-glutamic acid (PGA) is a biodegradable polymer with wide applications in the field of medicine, cosmetics, food and agriculture. The aim of the present work was to develop a microbial method to produce PGA under solid-state fermentation. Soy hull was used as the solid media in fermentation by Bacillus amyloliquefaciens. Central composite rotary designs (CCRD) was used to optimize the production of PGA and also studied the pattern of mutual interactions between the variables. The values of P < 0.05 indicated that the model terms were significant with the PGA yield of 111.2 mg/gds at initial moisture 75%, incubation time 60 h and inoculum size 4.7 ml. Characterization of the purified PGA was done by gel permeation chromatography and fourier transformed infrared (FT-IR) spectroscopy. The choice of soy hull as substrate and the process parameters optimization by response surface methodology (RSM) were found to be significant in PGA production. Due to low-cost nature of the process, this study shows the possibility for establishing large scale production of PGA in cost-effective manner.