Optimization of High-density Fermentation Medium for Streptococcus Thermophilus S-3
Streptococcus thermophilus can generally be used in the production of fermented foods.Based on this,the paper optimized the traditional LM17 medium by improving the types and contents of carbon sources,nitrogen sources,and inorganic salts,and achieved high-density growth of Streptococcus thermophilus S-3 to meet industrial fermentation requirements.By comparing carbon sources such as lactose,galactose,glucose,sucrose,and fructose,the optimal carbon source was determined to be lactose;Yeast extract powder was used as a fixed nitrogen source and was compounded with beef extract powder,soy peptone,and yeast extract powder.It was found that the combination of yeast extract powder and beef extract powder was the optimal choice.This study constructed a genome-wide metabolic network model of Streptococcus thermophilus S-3 to predict the effect of urea replacing β-glycerol-3-phosphate disodium.The validation results showed that urea could significantly improve the growth rate of Streptococcus thermophilus S-3.The substances in the final improved culture medium included 10 g/L lactose,10 g/L yeast extract,15 g/L beef extract,3 g/L food grade urea,and 1.1 g/L MgSO4·7H2O.To study the optimal formulation ratio,single factor optimization and orthogonal experiments were conducted on each factor.The experimental results showed that the fermentation effect was optimal when lactose was 15 g/L;beef extract was 15 g/L;yeast extract was 11 g/L;urea was 4 g/L,and MgSO4·7H2O was 1 g/L.The OD600 after amplification cultivation increased from 4 to 5.
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