| L-lysine belongs to aspartic acid group amino acids,its chemical name is 2,6-diaminohexanoic acid or ?,?-diaminohexanoic acid.It is an important raw material and additive for feed,food and medicine,with a large market demand.L-lysine is mainly obtained by microbial fermentation,but the low conversion rate of sugar and acid,low yield and serious corrosion of fermentation equipment are the main factors causing the high cost of products.Therefore,in order to improve L-lysine sugar acid conversion rate and yield,reduce equipment corrosion,the first thing to solve is to optimize the fermentation formula,select efficient fermentation promoter instead of green choline,reduce the concentration of chloride ion in fermentation broth.At the same time,it can solve the bottleneck problem of taking away bacteria and nutrients during L-lysine fed batch fermentation.The specific research contents are as follows.1.Betaine phosphate is used as a new type of fermentation promoter to replace choline chloride in the existing process formula.The phosphate ions in Betaine phosphate can be directly utilized by bacteria.Betaine phosphate can participate in methylation metabolism,regulate cell osmotic pressure and reduce cell fragmentation.The results showed that the replacement of choline chloride with Betaine phosphate could significantly increase the growth rate and shorten the maturity cycle of the third grade seeds.The results showed that there was a positive correlation between the OD value of lysine fermentation and the amount of Betaine phosphate in the substrate.When the amount of Betaine phosphate in the fermentation formula was 0.5 g/L,the conversion rate and acid production were the best.The optimum conditions of using Betaine phosphate in total nitrogen were as follows:the mass concentration of Betaine phosphate was 8 g/L,the adding time was 5?7 h,and the volume ratio of sugar to nitrogen was 20?28.The results of this study have guiding significance for reducing the production cost of lysine and reducing the corrosion of chloride ion to equipment.2.Based on the traditional fed batch fermentation process of lysine,the centrifuge cell separation and recovery technology was used to avoid the loss of cell caused by the traditional process of intermediate feeding,so as to improve the single batch sugar acid conversion rate and single batch yield.The results showed that the optimal process conditions were as follows:the volume ratio of concentrated liquid to clear liquid of centrifuge was 1:3.5,the period of intermediate feeding was 23?37h,the operation volume of fermentation tank was 395m3,the volume ratio of fed total nitrogen to clear liquid of centrifuge was 1:7.5,the conversion rate of sugar and acid was 73.00%,and the single batch yield was 176.149t.In order to reduce the cost of lysine fermentation,improve the fermentation intensity and productivity,a new path was explored.3.On the basis of the recycling technology of centrifuges,according to the existing equipment and fully considering the investment cost,the 1+1 and 2+1 group tank fermentation technology was developed.The technology avoids the loss of bacteria and inorganic salts caused by the traditional process of intermediate feeding,so as to improve the single batch fermentation sugar acid conversion rate and single batch yield.Under the operation mode of one main fermentor and one intermediate material tank,the single batch conversion rate was 73.22%and the yield was 180.33t.In order to reduce the cost of lysine fermentation,a new path is opened up to meet the choice of various production technology modes according to different market conditions. |
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