Abstract: [Objective] To address the industrial challenges of high production costs and low biomass in feed-grade Saccharomyces cerevisiae. [Methods] The indigenous low-activity strain SCL6 was selected as the research subject, and fermentation process optimization was conducted based on YPD medium. A two-stage optimization strategy was implemented. First, key medium components （carbon source, nitrogen source, inorganic salts） were screened through single-factor experiments, and the key factors affecting the fermentation process were screened by Plackett-Burman test. Subsequently, a Box-Behnken central composite design combined with response surface methodology （RSM） was employed to construct a mathematical model for multi-factor interactions. Parameter optimization and model validation were performed using Design-Expert software. Biomass was quantified via OD₆₀₀ measurements coupled with wet weight determination. Key influential factors were identified via analysis of variance （ANOVA）. Finally, the optimized process was conducted in a 3 L fermenter with dynamic feeding and parameter control. [Results] ①Factor significance analysis：carbon source type, cultivation temperature and initial pH exhibited highly significant （P<0.01） impacts on biomass accumulation, identifying them as primary limiting factors. Nitrogen composition, inorganic salt concentration and inoculum size showed no significant （P>0.05） effects. ②Optimized parameters：maltose （50.46 g/L） as carbon source, corn steep liquor （20 g/L） as complex nitrogen source, trace elements （MgSO₄·7H₂O 4 g/L, ZnSO₄ 0.1 g/L, KH₂PO₄ 2 g/L）, initial pH 6.10, and dynamic temperature control （29.52 ℃）. ③Process validation：in 3 L fermenters, SCL6 achieved an OD_{600 nm} of 106.8, cell wet weight of 150.2 g/L, representing 2.33-fold and 5.34-fold improvements over optimized flask culture （OD_{600 nm}=46.6） and original flask culture （OD_{600 nm}=20）, respectively. The viable cell count reached 2.1×10⁹ CFU/mL, complying with GB/T 22547—2008 feed additive standards. ④Economic evaluation：the optimized process reduced production costs by 35.8% per ton of culture, including 29.9% savings in carbon source expenditure and 42.5% reduction in energy consumption, effectively resolving inefficiencies in glucose utilization and excessive energy demand for temperature control in conventional processes. [Conclusion] The two-stage fermentation optimization process based on the response surface methodology established in this study has significantly improved the industrial cultivation efficiency of the indigenous Saccharomyces cerevisiae SCL6. By accurately identifying the key limiting factors and establishing a dynamic regulation model, an exponential increase in the biomass of the yeast cells and a significant reduction in the production cost have been achieved.

Key words: Saccharomyces cerevisiae, biomass, response surface methodology, feed additive, cultivation conditions, process optimization