Study On Optimization And Scale-up Of Baker's Yeast Fermentation Process And New Semi-continuous Fermentation Process

Yeasts,as important microbes in the nature,are widely used in food,energy and pharmaceutical fields.Due to close relationship with our daily lives,the researches on physiological characteristics of the yeasts for high production efficiency,can not only meet people's requirements,also bring huge economic benefits.Baker's yeast is one of the Saccharomyces genus,and it is popular in dough fermentation.Baker's yeast can catabolize the carbohydrate substances in the dough,and then produce carbon dioxide through the respiration,so that the dough becomes fluffy.Currently,some major problems,such as low yield of yeast cells,lack of cell activity and poor resistance to adverse environment,still remain to be solved.In this paper,we focused on the key points on improving cell yield and activity in the baker's yeast fermentation process through the regulation of nutrition feeding and process dissolved oxygen(DO)control strategies.The main conclusions were indicated as follows:1.Generally,ethanol is easily to be synthesized in the baker's yeast fermentation process under improper control condition.In the industrial production,potassium dichromate titration method was used to monitor the ethanol concentration hourly,which was a time-and labor-consuming process.Here,respiratory quotient(RQ)was introduced to on-line reflect the change of ethanol content in the broth,and it was concluded that almost no ethanol would be present when RQ value was between 1.0 to 1.2.2.The cell growth would be inhibited under N and P limitations,and subsequently,trigged to the trehalose accumulation in the yeast cell.It was found that the current feeding strategy for N and P in the early phase of the fermentation process was insufficient for quick cell growth,thus,the improved N and P feeding strategy could promote the trehalose production in advance,and consequently shorten the whole fermentation cycle significantly from 15h to 13h.3.The limitation of carbon source in the early phase of fermentation would not lead to the accumulation of trehalose.Whereas,in the late phase of fermentation,it was interesting that DO limitation by reducing the agitation and flow rate,could increase cell yield efficiently,ascribing to the decrease of the respiratory metabolism.Moreover,the stress caused by DO limitation would further improve to the accumulation of trehalose.4.On the basis of above results,it was considered that the whole fermentation process could be divided into two phases,the cell growth phase and the trehalose accumulation phase.In the first phase,high DO tension and sufficient N and P sources benefited the cell growth.While in the second phase,the trehalose could be substantially synthesized under DO limiting condition as well as with adequate molasses addition,but no ethanol accumulation in the broth.Finally,a novel semi-continuous fermentation process was developed.And the average productivity achieved 3.7g/(L·h),which was 60.8%higher than the original process.Hopefully,this work would provide a new idea for efficient production of highly active yeast.