1State Key Laboratory of Crop Genetics and Germplasm Enhancement, National Center for Soybean Improvement, Nanjing Agricultural University, Nanjing, 210095, PR, China.
2College of Agronomy, Xinjiang Agricultural University, Wulumuqi, 830052, PR, China.
3Center for Introducing Varieties of Animal and Plant, Shanghai Agricultural Academy, Shanghai, 201106, PR, China.
*Corresponding author: (seedtc@njau.edu.cn or Iq-ncsi@njau.edu.cn).
Citric acid is very useful in dairy, medicine or pharmaceutical and biochemical industries. Soybean residue, a byproduct from the protein extraction process in soybean processing industries, is abundant in the world, but mostly discarded. In this article, soybean residue was used to produce citric acid by the solid-state fermentation with Aspergillus niger, and the effects of four factors, including pH value and moisture content of soybean residue, fermentation temperature and time on the production were investigated by Response Surface Methodology (RSM). The citric acid content was analyzed by HPLC. The results showed that all of the four single factors and their interactions could significantly affect citric acid production. The establishing quadratic polynomial regression mathematic model was validated to have goodness of fit and prediction (R ≈ 1.0000). The optimum process parameters obtained by the model were that pH value and moisture content of soybean residue, and temperature and time of fermentation were 6.00, 83.00%, 35.00°C, 92.87 h, respectively. Under these given conditions, maximum critic acid production was 130.63 mg/g. Therefore, the soybean residue will be a good material resource for citric acid production and RSM could be used to optimize the processing conditions.
Soybean residue, citrio acid production, solid-state fermentation, Aspergillus niger, response surface methodology
