High-efficient production of citric acid by Aspergillus niger from high concentration of substrate based on the staged-addition glucoamylase strategy.

Citric acid (CA), an important platform-compound, has attracted much attention because of its broad applications and huge market demand. To solve high residual sugar at the fermentation end, we put forwarded strategy of pre-saccharification and then fermentation. Results showed that the residual total sugar decreased by 10.4% and the productivity increased by 4.0% and initially high glucose inhibited cell growth. Furthermore, commercial glucoamylase with high low-pH stability was proposed to staged-add in the fermentation process, which timely compensated enzyme loss, ensuring the glucose supply rate. The fermentation productivity was evidently enhanced by 13.3% with residual total sugar decreasing by 31.3%, simplifying the subsequent product separation and extraction process. Our results confirmed that staged-addition glucoamylase strategy was feasible to effective production of CA.