Method of producing lactic acid by continuous fermentation

Abstract

A method of producing lactic acid by continuous fermentation includes filtering a culture of polyploidy prototrophic yeast having a capacity to produce lactic acid by introduction of a lactate dehydrogenase gene through a porous membrane having an average pore size of not less than 0.01 μm and less than 1 μm; and recovering the lactic acid from filtrate while the unfiltered liquid is retained in or returned to the culture and a fermentation feedstock is added to the culture.

1 . A method of producing lactic acid by continuous fermentation comprising:
 filtering a culture of polyploidy prototrophic yeast having a capacity to produce lactic acid by introduction of a lactate dehydrogenase gene through a porous membrane having an average pore size of not less than 0.01 μm and less than 1 μm; and   recovering the lactic acid from filtrate while the unfiltered liquid is retained in or returned to the culture and a fermentation feedstock is added to the culture.   
     
     
         2 . The method according to  claim 1 , wherein said filtration is carried out with a transmembrane pressure difference of said porour membrane within a range of 0.1 kPa to less than 20 kPa. 
     
     
         3 . The method according to  claim 1 , wherein said polyplid yeast is diploid. 
     
     
         4 . The method according to  claim 1 , wherein the yield of lactic acid to saccharides in said continuous fermentation is not less than 70%. 
     
     
         5 . The method according to  claim 1 , wherein the concentration of accumulated lactic acid in the culture subjected to said continuous fermentation is not less than 40 g/L. 
     
     
         6 . The method according to  claim 1 , wherein the rate of production of lactic acid during said continuous fermentation is not less than 7.5 g/L/h. 
     
     
         7 . The method according to  claim 5 , wherein said continuous fermentation is continued for not less than 400 hours. 
     
     
         8 . The method according to  claim 1 , wherein said polyplid prototrophic yeast belongs to  Saccharomyces.    
     
     
         9 . The method according to  claim 1 , wherein said polyplid prototrophic yeast is  Saccharomyces cerevisiae.