Coupling fermentation of glutamic acid and γ-polyglutamic acid and preparation of poly(amino acid) superabsorbent polymers

Abstract γ-polyglutamic acid (γ-PGA) is a biomarker that can be directly obtained by microbial fermentation, poly (amino acid) superabsorbent polymers (SAPs) were prepared with purified γPGA as raw material and ethylene glycol diglycidyl ether (EGDGE) as cross-linking agent. However, γ-PGA fermentation broth has a high viscosity, requires complex extraction and separation processes, and entails high energy consumption, resulting in the high cost of poly (amino acid) SAPs. Therefore, the coupling fermentation processes of glutamate polyglutamic acid, using glutamate fermentation broth instead of pure glutamate powder for fermentation, and treating the fermentation broth with centrifugation, UV irradiation, and high temperature, respectively were studied. The γ-PGA-co-PASP SAPs were prepared with fermentation broth instead of some part being water by combining the process of preparing polyaspartic acid (PASP) SAPs with polysuccinimide (PSI). The results showed that the yield of γ-PGA after centrifugation decreased by 5%, but it did not affect the synthesis of hydrogels. The addition of γ-PGA fermentation broth had a significant effect on the performance of γ-PGA-co-PASP SAPs. When the liquid-solid ratio of PSI: PGA was 2:1, the water absorption of super-absorbent resin was 40.4% which was higher than that of pure PASP, and the heat resistance and viscoelasticity were significantly improved. This work not only avoids the separation of complex γ-PGA fermentation broth, reduces the cost, but can improve the performance of super-absorbent resin, which has application potential.