Abstract: To provide effective use from a yeast extract residue, an excess of which is produced as a byproduct of yeast extract, or reduction in amount of the yeast extract residue. Also to obtain various useful substances. A cell wall lytic enzyme having no protease is allowed to act on a yeast extract residue, after which a heat treatment is performed at 70 to 80° C. for 10 to 20 minutes, thereby enabling separation into a fraction of primarily cell walls and a fraction of primarily protein. A yeast protein having a protein content of 60% or more is obtained from the fraction of primarily protein and, by subjecting the yeast protein to enzymatic degradation, a seasoning having a high amount of total nitrogen is obtained.

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.

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.

Abstract: The present invention provides a natural yeast extract having a high-impact first taste by containing glutamic acid in a large amount. Further, the present invention provides a yeast extract having strong umami by containing 5?-guanylic acid or 5?-inosinic acid in a large amount. In addition, the present invention provides a yeast mutant accumulating glutamic acid, glutamine, and ribonucleic acid in a large amount for obtaining the yeast extract. A yeast mutant inducing a natural mutation to which organic acid-tolerance or organic acid analogue-tolerance is imparted accumulates free glutamic acid and glutamine in such a significant amount as a total amount of 10% by weight or more in a cell, and further accumulates ribonucleic acid in an amount of 5% by weight or more. A yeast extract produced using the above yeast mutant contains L-glutamic acid in an amount of 20% by weight or more, and further contains 5?-IG in an amount of 3% by weight or more.

Abstract: To provide effective use from a yeast extract residue, an excess of which is produced as a byproduct of yeast extract, or reduction in amount of the yeast extract residue. Also to obtain various useful substances. A cell wall lytic enzyme having no protease is allowed to act on a yeast extract residue, after which a heat treatment is performed at 70 to 80° C. for 10 to 20 minutes, thereby enabling separation into a fraction of primarily cell walls and a fraction of primarily protein. A yeast protein having a protein content of 60% or more is obtained from the fraction of primarily protein and, by subjecting the yeast protein to enzymatic degradation, a seasoning having a high amount of total nitrogen is obtained.

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.