Efficient production of γ-polyglutamic acid from corn starch liquefied with endogenous malt enzymes using Bacillus...

γ-Polyglutamic acid (γ-PGA) is a versatile biopolymer with a wide range of applications. However, its large-scale production remains limited by high costs and low process efficiency. Wheat malt, rich in endogenous amylases and widely used in beer brewing, has seen limited applications in starch hydrolysis for microbial fermentation. This study developed a cost-effective process for γ-PGA production using corn starch liquefied by malt-derived enzymes as the carbon source. Liquefaction was conducted at 65 °C and pH 6.5 with a solid-to-liquid ratio of 1:6 and a malt-to-starch ratio of 1:7 for 5 h, yielding a solution with a dextrose equivalent (DE) of 21.2% and total sugars of 153 mg/mL (4.45 mg/mL glucose, 28.09 mg/mL maltose, 38.96 mg/mL oligosaccharides, and 81.5 mg/mL dextrins). Fermentation with Bacillus subtilis SCP010-1 in 250 mL shake flasks initially produced 32.5 g/L γ-PGA. Optimization of fermentation conditions (72 h, 4% inoculum, 50 g/L sodium glutamate, and 90 g/L liquefied solution) increased the yield to 41.2 g/L, closely matching the 41.3 g/L predicted by response surface methodology. Scale-up in a 5 L fermenter achieved a maximum yield of 88.2 g/L. Economic analysis indicated that using liquefied starch decreased production costs to USD 512, representing reductions of 52.2 and 47.8% compared with sucrose and glucose, respectively. This strategy significantly improves γ-PGA yield and cost efficiency, offering a practical and scalable solution for industrial production.

The online version contains supplementary material available at 10.1007/s13205-025-04592-z.