Abstract
We optimized culture conditions using Bacillus sp. FBL-2 as a poly-(γ-glutamic acid) (PGA) producing strain isolated from cheonggukjang. All experiments were performed under aerobic conditions using a laboratory scale 2.5 L fermentor. We investigated the effects of fermentation parameters (temperature, pH, agitation, and aeration) and medium components (glutamic acid, citric acid, and yeast extract) on poly-(γ-glutamic acid) production, viscosity, and dry cell mass. A non-optimized fermentation method (1.5 vvm, 350 rpm, and 37 °C) yielded PGA, viscosity, and dry cell mass at levels of 100.7 g/L, 483.2 cP, and 3.4 g/L, respectively. L-glutamic acid, citric acid, and yeast extract supplementation enhanced poly-(γ-glutamic acid) production to 175.9 g/L. Additionally, the production of poly-(γ-glutamic acid) from rice bran and wheat bran was assessed using response surface methodology (central composite rotatable design). Agricultural byproducts (rice bran and wheat bran) and H2SO4 were selected as factors, and experiments were performed by combining various component concentrations to determine optimal component concentrations. Our experimentally-derived optimal parameters included 38.6 g/L of rice bran, 0.42% of H2SO4, 28.0 g/L of wheat bran, and 0.32% of H2SO4. Under optimum conditions, rice bran medium facilitated poly-(γ-glutamic acid) production of up to 22.64 g/L, and the use of wheat bran medium yielded up to 14.6 g/L. Based on a validity test using the optimized culture conditions, poly-(γ-glutamic acid) was produced at 47.6 g/L and 36.4 g/L from these respective mediums, and both results were higher than statistically predicted. This study suggests that rice bran can be used as a potential alternative substrate for poly-(γ-glutamic acid) production.
Highlights
Poly-(γ-glutamic acid) (PGA) is a natural polyaminoic acid and biocompatible compound that is naturally synthesized by members of the genus Bacillus during food fermentation
This study suggests that rice bran can be used as a potential alternative substrate for poly-(γ-glutamic acid) production
Poly-(γ-glutamic acid), the produced by microorganisms, obtained at 32 homopolypeptide
Summary
Poly-(γ-glutamic acid) (PGA) is a natural polyaminoic acid and biocompatible compound that is naturally synthesized by members of the genus Bacillus during food fermentation. This compound was first discovered by Ivanovics during a study of the film produced by Bacillus anthracis. Poly-γ-glutamate is produced as a non-cellular product that is completely biodegradable and soluble in water. Biomolecules 2019, 9, 754; doi:10.3390/biom9120754 www.mdpi.com/journal/biomolecules and a 0.2% ninhydrin acetic acid solution was identified. This solution was dried for 10 min at 110 °C to identify visible hydrolysis products [17]
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