Study On The Fermentation Technology Of Polyglutamic Acid Based On Sugarcane Molasses

γ-polyglutamic acid（γ-PGA）has been widely used in agriculture,food,cosmetics and medicine due to its nontoxicity,high water retention and biodegradability and many other properties.At present,the production ofγ-PGA is mainly limited by the production cost and the yield ofγ-PGA.Molasses is a by-product of the sugar industry with high sugar content,amino acids and trace elements required by microorganisms.Compared with glucose and sucrose,it has huge cost advantage.In this paper,sugarcane molasses was used as the carbon source to fermentγ-PGA,and the effects of different factors in the molasses medium on the yield ofγ-PGA were investigated through strain screening,single factor experiments and response surface optimization experiments.The scale-up experiments of different fermenter scales from 5L to 200L to 50m³ were carried out.Finally,the effect of FeSO₄·7H₂O onγ-PGA synthesis was analyzed by GC-MS and transcriptome.The main experimental results are as follows:（1）A strain CGMCC NO.23967 suitable for fermentingγ-PGA in molasses medium was screened out.（2）The effects of different compositions of molasses fermentation medium on the yield ofγ-PGA were investigated by single factor experiment,and it was found that peptone,K₂SO₄,（NH₄）₂SO₄,Ca SO₄·2H₂O and Mg SO₄·7H₂O had no significant effect on the yield ofγ-PGA.FeSO₄·7H₂O had a significant effect on the yield ofγ-PGA（3）The optimal fermentation medium was determined using the response surface methodology.The composition of the optimal fermentation medium was:molasses soluble solids 8.68%,yeast extract concentration 4.23 g/L,FeSO₄·7H₂O concentration 0.78 g/L,monosodium glutamate concentration 80 g/L,and the predicted yield ofγ-PGA was as high as 67.17 g/L.（4）Under the optimal fermentation medium conditions,the effects of different ventilation rates and stirring speeds on the yield ofγ-PGA were investigated by using a 5L fermenter.The highest yield of PGA was 76.8g/L.The 200L fermenter was used for verification,and the yield ofγ-PGA at the end of fermentation was 71.958g/L.（5）The effect of FeSO₄·7H₂O on the fermentation and synthesis ofγ-PGA by Bacillus licheniformis CGMCC NO.23967 was investigated by GC-MS and transcriptomic cross-validation.Through GC-MS analysis,it was found that the accumulation of intracellular metabolites glutamate,proline,fructose and succinate was significantly higher than that of the blank group;the up-regulated differential genes obtained by transcriptome analysis mainly promoted the glycolysis pathway and TCA The cycle provides sufficient energy and precursor materials for the synthesis ofγ-PGA.The above results provide a basis for strain improvement and process optimization.（6）Under the optimal fermentation medium and fermentation process conditions,an industrial scale-up production experiment was carried out in a 50-ton fermenter.The final yield at the end of fermentation was 76 g/L,and the yield ofγ-PGA was 0.63 g/（L·h）.