| Yeast extract is rich in peptides,amino acids,taste nucleotides,B vitamins and trace elements.It has many advantages such as pure natural,nutritious and mellow taste,and is widely used in the food field.However,its freshness is not outstanding enough(the glutamate content is insufficient).In this paper,at the level of 30 L fermenter(15 L of base material),the two-stage fermentation strategy of exponential growth and growth limiting was used to meet the growth and glutamate anabolism requirements of Saccharomyces cerevisiae under high-density fermentation conditions.The results are as follows:1.In order to overcome the adverse effects of Saccharomyces cerevisiae fermentation glucose overflow ethanol production on glutamate synthesis,the index fed-feeding strategy was used for 2-7 h fermentation,and molasses containing 45%sucrose was added at a concentration of 0.08 h-1(total sugar content 80%).After 8 h of fermentation,the dry weight of the cells was 41.55 g/L,and the intracellular glutamate content reached a peak of 4.42%.There was no ethanol overflow during the feeding period.The?set is lower or higher than 0.08 h-1,and the glutamic acid content is significantly reduced.2.Based on the index feeding strategy,in order to reduce the cell growth requirement for glutamate in the“nitrogen transfer library”,“growth restriction”fermentation was carried out at 7-18 h with ethanol as a carbon source to further accumulate glutamate in the cells.The optimal ethanol uniform flow addition strategy is:7-9 h flow rate 50 mL/h,9-18 h flow rate 40 mL/h.After 13 h of fermentation,the dry weight of the cells was 44.04 g/L,and the intracellular glutamate content reached a peak of 5.02%,which was 13.5%higher than the peak concentration of intracellular glutamate in the"growth stage".The average growth rate of yeast dry weight is only0.71 g/(L·h),which achieves“synthesis stage”growth inhibition and glutamate synthesis accumulation.3.Based on the"synthesis stage"ethanol flow addition strategy,the effects of an equimolar sodium lactate addition strategy on cell growth and glutamate anabolism were studied.Intracellular glutamate reached its peak at 9 h(cell dry weight 39.78 g/L),and the content was 6.57%,which was 48.5%and 30.9%higher than the peak of the index feed and ethanol feed,respectively.4.The transcriptional differences of glutamate anabolism-related genes at 10 h of fermentation were studied and found to:When adding lactate,IDH2,KGD1,SDH1,MDH1,ICL1,MLS1,SNF1(encoding energy-sensing protein),PUT2(coding arginine for glutamate gene),GDH3,PYC2 lg(TPM+1)value Increased by 11.6%,27.2%,16.4%,11.3%,35%,34.5%,71.1%,18.7%,12.5%,54.8%.The lg(TPM+1)value of the gene GCN4 and the amino acid foreign protein gene AQR1,which regulate amino acid synthesis,decreased by 25.6%and 35.2%.Description:The carbon flux of TCA and glyoxylate increased when lactate was used as carbon source.At the same time,the up-regulation of SNF1 repressed the transcription of GCN4 and enhanced the expression of GDH3.In addition,PUT2 up-regulation indicates an increase in arginine transglutamate efficiency;AQR1 transcription down-regulation indicates a decrease in the efficiency of glutamate transport to extracellular.The combination of these factors contributes to the synthesis and accumulation of intracellular glutamate. |
PDF Full Text Request