Silkworm Pupae Coupled with Glucose Control pH Mediates GABA Hyperproduction by Lactobacillus hilgardii

Abstract

γ-Aminobutyric acid (GABA) is a ubiquitous nonprotein amino acid that has multiple physiological functions and has received significant attention in the pharmaceutical and food industries. Although there are many GABA-producing bacteria, the high cost of strain cultivation limits its food additive and pharmaceutical raw material application. In our study, Lactobacillus hilgardii GZ2, a novel GABA-producing strain, was investigated. We attempted to replace nitrogen sources with silkworm pupae, the waste resource of the silk reeling industry, in GYP complex medium. The GABA titer reached 33.2 g/L by using 10 g/L silkworm pupae meal instead of tryptone. Meanwhile, the pH of fermentation was automatically controlled by adjusting the addition of glucose and monosodium glutamate. Finally, the highest GABA yield and productivity were 229.3 g/L and 3.2 g/L/h in L. hilgardii when silkworm pupae meal was replaced with tryptone combined with glucose and monosodium glutamate feeding. By utilizing the waste resource to reduce the cost of the nitrogen source and automatically controlling the pH in L. hilgardii, a hyper titer and productivity of GABA was generated for applications in the food and pharmaceutical industries.