Study Of Effects Of Potassium Ion And Wheat Gluten Protein Hydrolysates On Yeast Tolerance And Fermentation Performance

Very-high-gravity(VHG)fermentation technology is widely used in bioethanol production industry due to its high efficiency,energy saving and low pollution.However,VHG fermentation technology has certain negative effects on yeast cells,such as reducing physiological activity and affecting fermentation performance,which lead to fermentation stuck and low ethanol production.Therefore,it is of great significance to find cost-effective supplementary nutrients and apply them to bioethanol production.Studies have found that metal ions participate in a variety of biochemical processes.They control the catalytic effect by keeping the substrate directly bound to the active site or indirectly using the structure of the enzyme in a specific conformation.The addition of metal cations can effectively improve the tolerance of yeast.Wheat gluten protein hydrolysates can also effectively promote the growth and metabolism of yeast and help yeast resist from the adverse effects of various stresses.However,the combined addition of metal ions and protein hydrolysates has rarely been reported at home and abroad,and the mechanisms of improvement of yeast tolerance by addition are unclear.Therefore,in this paper,yeast was used as the research object to study the mechanism of potassium ion and protein hydrolysate in improving yeast tolerance.Based on this,the optimal co-addition of potassium chloride and protein hydrolysate in the bioethanol fermentation process was explored.The added amount laid the foundation for the development of a convenient,cost-effective,and efficient method for increasing bioethanol production.The main research contents and results are as follows:(1)The response mechanisms of yeast under different degrees of ethanol stress and osmotic stress were studied.The results showed that with the increase of sucrose and ethanol concentrations,the degree of stress deepened,and the physiological and biochemical characteristics of cells such as cell wall integrity,cell membrane permeability,reactive oxygen species,and ATP content changed with stress altered.According to the growth,activity and physiological characteristics of cells,50%(w/v)sucrose and 10%(v/v)ethanol were selected as the stress conditions in subsequent experiments.(2)The effect mechanisms of potassium chloride on tolerance of yeast to ethanol and hyperosmotic stress were studied.The results showed that the addition of KCl had a significant effect on yeast,which could increase the growth,activity and tolerance of yeast cells.During the VHG fermentation process,0.5%(w/v)KCl showed the best promotion effect,which not only promoted the growth of yeast cells,but also reduced membrane permeability and increased membrane stability and mitochondrial functionality to improve the tolerance of yeast to osmosis and ethanol stress.The ethanol production was increased by 3.8% compared with the non-added group.(3)The mechanism of improving the bioethanol fermentation by the combined addition of KCl and WGH was studied,and the optimal amount was determined.The results showed that the co-addition of KCl and WGH improved the growth activity,glucose consumption and ethanol production of yeast under VHG conditions,and was superior to the promotion effect of KCl or WGH alone.When 0.5%(w/v)KCl and 0.3%(w/v)WGH were added together,the improvement effect was the best,where ethanol production increased to 16.77%(v/v).(4)Metabolomics analysis was used to examine the effect of KCl and WGH on cells' metabolism.KCl and WGH mainly affected the metabolism of amino acids and organic acids,but the effects of the addition of the two alone and the co-addition of the two on yeast intracellular metabolism were different.WGH increased the content of trehalose and amino acids,and helps yeast resist oxidative stress;KCl increased the content of Ala,and glycerol and trehalose,which can help yeast resist ethanol and osmotic stress,but little to oxidative stress;the co-addition of the two makes trehalose,glycerol,and amino acids more abundant in the cells,helps yeast resist stresses,and at the same time get more glucose into the ethanol metabolic pathway rather than lactic acid metabolic pathway.