Abstract: A yeast which harbors a mutant glutathione synthetase having one or both of mutations selected from the group consisting of a mutation to replace a threonine residue at the position 47 with an isoleucine residue and a mutation to replace a glycine residue at the 387-position with an aspartic acid residue and produces ?-glutamylcysteine. The yeast is cultured under suitable conditions, the resultant culture or fractionation product thereof or the resultant culture or fractionation product thereof that had been heat-treated is mixed with food or beverage materials and processed into foods or beverage to produce ?-glutamylcysteine- or cysteine-containing foods or beverage.

Abstract: The present invention relates to a method for producing a cysteine-rich food material by maintaining a food material containing ?-glutamylcysteine at a ratio of at least 1 wt % to the solid content thereof at a temperature ranging from 50 to 120° C. and at a pH ranging from 1 to 7. This process is conducted in the absence of a sugar and in the presence of water. The present invention also relates to a method for producing a cysteine-rich food material by reacting the food material with a ?-glutamyl peptide hydrolase at a pH ranging from 3 to 9 and at a temperature ranging from 15 to 70° C. in the present of water. Further, the present invention relates to a method for producing a flavor-enhancing material for use in food, food products obtained by these processes, and yeast cells or extracts for use in food products.

Abstract: A yeast which harbors a mutant glutathione synthetase having one or both of mutations selected from the group consisting of a mutation to replace a threonine residue at the position 47 with an isoleucine residue and a mutation to replace a glycine residue at the 387-position with an aspartic acid residue and produces ?-glutamylcysteine. The yeast is cultured under suitable conditions, the resultant culture or fractionation product thereof or the resultant culture or fractionation product thereof that had been heat-treated is mixed with food or beverage materials and processed into foods or beverage to produce ?-glutamylcysteine- or cysteine-containing foods or beverage.

Abstract: The present invention relates to a method for producing a cysteine-rich food material by maintaining a food material containing &ggr;-glutamylcysteine at a ratio of at least 1 wt % to the solid content thereof at a temperature ranging from 50 to 120° C. and at a pH ranging from 1 to 7. This process is conducted in the absence of a sugar and in the presence of water. The present invention also relates to a method for producing a cysteine-rich food material by reacting the food material with a &ggr;-glutamyl peptide hydrolase at a pH ranging from 3 to 9 and at a temperature ranging from 15 to 70° C. in the present of water. Further, the present invention relates to a method for producing a flavor-enhancing material for use in food, food products obtained by these processes, and yeast cells or extracts for use in food products.

Abstract: A method of screening a yeast strain having a reduced glutathione activity and &ggr;-glutamylcysteine productivity comprising the steps of:

Abstract: Yeast extract is produced by using a strain of Saccharomyces cerevisiae, which can contain 1% by weight or more of &ggr;-glutamylcysteine and contains 0.004-0.1% by weight of glutathione during its logarithmic growth phase, when the strain is cultured in a medium in which a glutathione synthetase deficient strain shows a slower growth rate than a wild strain of Saccharomyces cerevisiae, for example, a strain of Saccharomyces cerevisiae, wherein glutathione synthetase encoded by a glutathione synthetase gene on a chromosome has deletion of a C-terminus region from the 370th arginine residue. There are provided yeast that can be used for production at industrial level and shows a high &ggr;-glutamylcysteine accumulation amount, and yeast extract produced by using the yeast.