Abstract: 【Objective】 To systematically optimize the fermentation and preservation processes of Bacillus velezensis LU4 with high-efficiency cellulase degradation activity. 【Methods】 Single-factor experiments and response surface analysis method were used to jointly optimize enzyme-producing conditions and determine the optimal fermentation parameters of the strain. To address the problem of contamination during storage of liquid microbial agents,a preservative screening experiment was conducted to evaluate the effects of five preservatives（sodium diacetate,methyl paraben,dehydroacetic acid,sodium benzoate,and potassium sorbate）on viable bacterial counts and spore content in the fermentation broth. 【Results】 The optimal fermentation parameters obtained by response surface analysis method were fermentation time of 23 h,fermentation temperature of 23 ℃,inoculum size of strain LU4 of 3%,and initial pH value of 5. Under these conditions,the activity of carboxymethyl cellulase （CMCase） reached 74.268 U/mL,which was significantly higher than that before optimization. Potassium sorbate was the most suitable preservative. Its optimal application conditions were culture media pH value of 6 and an addition amount of 0.1%. After storage of the fermentation broth at 30 ℃ and 170 r/min for 30 d,the viable bacterial count was 4.83×10¹⁰ CFU/mL and the spore content was 4.20×10⁹ CFU/mL. This treatment could effectively control contamination by contaminating bacteria and had the least effect on strain growth. 【Conclusion】 The optimal fermentation parameters of B. velezensis LU4 are fermentation time 23 h,fermentation temperature 23 ℃,inoculum size 3%,and initial pH value 5,under which CMCase activity reached the highest level. When the pH value is adjusted to 6,and 0.1% potassium sorbate was added,contamination by miscellaneous contaminating bacteria can be effectively controlled,and the inhibitory effect on the growth of strain LU4 is the least.

Key words: Bacillus velezensis, Fermentation process optimization, Preservative, Potassium sorbate, Spore content