To improve the ability of Bacillus velezensis to produce inhibitory substances,the fermentation process was optimized using single-factor experiments,Plackett-Burman test,steepest ascent test,and the Box-Behnken design.The results showed that lactose and sodium nitrate were the optimum carbon and nitrogen sources for the fermentation medium.The Plackett-Burman test showed that the significant factors affecting were the inoculum,sodium nitrate concentration,and fermentation time.The steepest ascent test and response surface test determined the optimum conditions as 10 g/L lactose,6.15 g/L sodium nitrate,3%inoculum,a rotational speed of 220 r/min,34℃,and 30.7 h of fermentation.Under these conditions,the diameter of the inhibition circle was 17.6 mm,which was 55%higher than the diameter before optimization.The biomass increased from 2.42×108 CFU/mL before optimization to 6.71×108 CFU/mL.The findings of this study are beneficial to the further development and utilization of B.velezensis as a potential probiotic and to improve the ability of the strain to resist food spoilage microorganisms.
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