Yeast mutant and yeast extract

Abstract

A natural yeast extract which is rich in glutamic acid and therefore has an impact at first taste. Further, provided is a yeast extract which is also rich in 5′-guanylic acid or 5′-inosinic acid and therefore has strong umami. Further, provided is a yeast mutant capable of accumulating a large amount of glutamic acid, glutamine and ribonucleic acid for obtaining such a yeast extract. A yeast mutant to which resistance to organic acids and analogues thereof has been imparted by inducing spontaneous mutation, accumulates a significant amount, i.e., 10% by weight or more of the total of free glutamic acid and glutamine in the cell, and further accumulates 5% by weight or more of a ribonucleic acid. The yeast extract produced by using this strain contains 20% by weight or more of L-glutamic acid, and further contains 3% by weight or more of 5′-IG.

1 . A yeast extract produced from a yeast mutant  Candida utilis , the yeast extract containing L-glutamic acid in an amount of 20% by weight or more converted into an amount of a sodium salt thereof;
 wherein:
 free glutamic acid and glutamine are accumulated in the yeast mutant  Candida utilis  in a total amount of 10% or more based on a total dry cell weight; and 
 the yeast mutant  Candida utilis  is tolerant to ethyl bromopyruvate. 
   
     
     
         2 . The yeast extract according to  claim 1 , wherein the yeast extract further contains 5′-guanylic acid and 5′-inosinic acid or 5′-adenylic acid in a total amount of 3% by weight or more. 
     
     
         3 . The yeast extract according to  claim 1 , wherein ribonucleic acid (RNA) is accumulated in the yeast mutant  Candida utilis  in an amount of 5% or more based on the total dry cell weight. 
     
     
         4 . The yeast extract according to  claim 1 , wherein the yeast mutant is tolerant to ethyl bromopyruvate and 2-oxoglutaric acid. 
     
     
         5 . A method for obtaining a yeast mutant that accumulates free glutamic acid and glutamine in a total amount of 10% or more based on a total dry cell weight, the method comprising:
 subjecting a strain of yeast to a mutagenizing treatment to obtain mutagenizing-treated yeast cells;   culturing the mutagenizing-treated yeast cells on a selective medium containing one or more of ethyl bromopyruvate and 2-oxoglutaric acid on which the strain of yeast cannot grow; and   isolating the mutagenizing-treated yeast cells that grow on the selective medium.   
     
     
         6 . The method according to  claim 5 , wherein ribonucleic acid (RNA) accumulates in the yeast mutant in an amount of 5% or more based on the total dry cell weight.