Optimization of fermentation conditions for Monascus water-soluble red pigment from soy sauce residues by response surface methodology

Aiming at the resource utilization of soy sauce residue and the demand for low-cost production of water-soluble Monascus red pigment, the research on the optimization of liquid fermentation conditions of soy sauce residue by Monascus were carried out. In this study, Monascus sp. CJ 01-01 with strong salt tolerance was screened as the fermentation strain, using soy sauce residues as the fermentation substrate and water-soluble Monascus red pigment color value as the evaluation index, and the fermentation conditions of water-soluble Monascus red pigment from soy sauce residues were optimized by single factor and response surface experiments. The results showed that the optimal fermentation conditions was as follows: soy sauce residues 60 g/L, ammonium acetate 0.35 g/L, glucose 34.05 g/L, ferrous sulfate 0.2 g/L, initial pH 8, and fermentation time 7 d. Under these optimal conditions, the color value of water-soluble Monascus red pigment from soy sauce residue was (108.5±2.1) U/ml, which was 3.8 times that of before the optimization. In conclusion, soy sauce residues as a substrate for the production of water-soluble Monascus red pigment had a greater potential, providing a valuable reference for the resource utilization of soy sauce residue.