Study on the reuse process of hydrolysate from γ-polyglutamic acid fermentation residues

•Waste biomass hydrolysate could replace tryptone for γ-PGA production.•The addition of waste biomass hydrolysate reduced the amount of glutamate in the medium.•The process could offset the disposal cost of waste biomass.•The waste biomass could be recycled for 2 times. In order to study the feasibility of using γ-polyglutamic acid (γ-PGA) waste biomass hydrolysate as nitrogen source of culture medium, waste biomass was treated with nitric acid to obtain hydrolysate. Through the orthogonal optimization experiment, the optimal conditions of biomass hydrolysis were obtained as follows: 2% nitric acid, solid-liquid ratio 4:10, 110 °C, and 24 h. Under the optimal conditions, the degree of hydrolysis reached 77.08 ± 0.48%. The fermentation medium was further optimized: biomass hydrolysate 60 mL, glucose 38 g/L, L-glutamate 25 g/L. In the optimal medium, γ-PGA yield was 30.69 ± 0.42 g/L, which was 4.49% higher than that in tryptone medium (29.37 ± 0.43 g/L). The results showed that the waste biomass hydrolysate could be used as tryptone for γ-PGA production. Moreover, the addition of waste biomass hydrolysate reduced the amount of glutamate in the medium. In addition, the waste biomass could be recycled for 2 times. This study provided a new idea for the cleaner production technology of γ-PGA.