Low-diacetyl yeast

Abstract

The present invention relates to yeast strains of the species Saccharomyces pastorianus that have the useful property of producing low levels of diacetyl during fermentation. Methods for producing malt- and / or grain-based beverages using these strains, as well as the beverages produced thereby, are also provided.

Claims

1. Within that genome, a. One or two functional genes encoding ILV2, each encoding ScILV2 of SEQ ID NO: 32 or SeILV2 of SEQ ID NO: 38, or a functional homolog sharing at least 90% sequence identity therewith, wherein the functional homolog of ILV2, together with ILV6, catalyzes the conversion of pyruvate to α-acetolactate; b. Functional genes 5-6 encoding ILV3, each encoding ScILV3 of SEQ ID NO: 35 or SeILV3 of SEQ ID NO: 41, or a functional homolog sharing at least 90% sequence identity therewith, wherein the functional homolog of ILV3 catalyzes the conversion of 2,3-hydroxyisovaleric acid to 2-ketoisolaterate, and c. Functional genes 4-5 encoding ILV5, each encoding ILV5 encoding ScILV5 of SEQ ID NO: 34 or SeILV5 of SEQ ID NO: 40, or a functional homolog sharing at least 90% sequence identity therewith, wherein the functional homolog of ILV5 catalyzes the conversion of α-acetolactate to 2,3-hydroxyisovaleric acid. A yeast strain that codes for [something].

2. The yeast strain according to claim 1, wherein the genes encoding ILV2, ILV3, and / or ILV5 are expressed from their natural promoters.

3. The yeast strain according to claim 1 or 2, wherein the genes encoding ILV2, ILV3, and / or ILV5, and / or one or more genes encoding ILV6, BAT1, and / or BAT2, are expressed from their natural promoters.

4. The aforementioned yeast strain does not contain heterologous DNA, and / or The yeast strain according to any one of claims 1 to 3, wherein the yeast strain has not undergone a genetic modification process.

5. The yeast strain according to any one of claims 1 to 4, wherein the yeast strain has up to four functional genes encoding ILV6, each gene encoding ScILV6 of SEQ ID NO: 33 or SeILV6 of SEQ ID NO: 39, or a functional homolog that shares at least 90% sequence identity therewith, and the functional homolog of ILV6, together with ILV2, catalyzes the conversion of pyruvate to α-acetolactate.

6. The yeast strain according to any one of claims 1 to 5, wherein the yeast strain has at least three functional genes encoding BAT1, each gene encoding ScBAT1 of SEQ ID NO: 36 or SeBAT1 of SEQ ID NO: 42, or a functional homolog that shares at least 90% sequence identity therewith, and the functional homolog of BAT1 catalyzes the conversion of 2-ketoisolaterate to L-valine in mitochondria.

7. The yeast strain according to any one of claims 1 to 6, wherein the yeast strain has at least four functional genes encoding BAT2, each gene encoding BAT2 encoding ScBAT2 of SEQ ID NO: 37 or SeBAT2 of SEQ ID NO: 43, or a functional homolog that shares at least 90% sequence identity therewith, and the functional homolog of BAT2 catalyzes the conversion of 2-ketoisolaterate to L-valine in the cytoplasm.

8. The yeast strain according to any one of claims 1 to 7, wherein the total number of functional genes in the yeast strain encoding ILV2 and ILV6 is lower than the total number of functional genes encoding ILV5 and ILV3.

9. The yeast strain according to any one of claims 1 to 8, wherein the functional gene ratio of ILV5 and ILV3 to ILV2 in the yeast strain is at least 1.

10. The yeast strain according to any one of claims 1 to 9, wherein the functional gene ratio of ILV5 and ILV3 to ILV2 and ILV6 in the yeast strain is at least 1.

11. The yeast strain has one or more mutations or deletions in the ILV2 gene, and / or The yeast strain possesses one or more frameshift mutations in the ILV2 gene, and / or The yeast strain according to any one of claims 1 to 10, wherein the yeast strain possesses a mutation that results in reduced or absent expression of one or more ILV2 genes.

12. The yeast strain according to any one of claims 1 to 11, wherein the yeast strain can produce a fermentation test solution by incubation in a test solution, the test solution is a malt and / or cereal extract having an appearance extract content of at least 10° Prato, the fermentation test solution contains a maximum of 60 ppb of diacetyl at the earliest point when the appearance extract content of the test solution has not decreased by more than 0.50° Prato in the preceding 24 hours, and the fermentation occurs at a maximum temperature of 18°C.

13. The yeast strain according to claim 12, wherein when the yeast strain is incubated in the test solution, it can produce at least 4.0 mL / L ethanol / °Plate.

14. The yeast strain according to any one of claims 1 to 13, wherein the yeast strain can be grown on a culture medium having melibiose as the sole carbon source.

15. The yeast strain according to any one of claims 12 to 14, wherein the fermentation test solution contains a maximum of 60 ppb of diacetyl.

16. The yeast strain according to any one of claims 12 to 14, wherein the fermentation test solution contains a maximum of 50 ppb of diacetyl.

17. The yeast strain according to any one of claims 12 to 16, wherein the fermentation test solution contains at least 25 mg / L of propanol.

18. The yeast strain according to any one of claims 12 to 17, wherein the fermentation test solution contains a maximum of 8 mg / L of isobutanol.

19. The yeast strain according to any one of claims 12 to 18, wherein the fermentation test solution contains at least a propanol:isobutanol ratio of 2.

5.

20. The yeast strain according to any one of claims 12 to 18, wherein the fermentation test solution contains at least a propanol:isobutanol ratio of 3.

0.

21. A method for producing a fermented aqueous extract, i) A step of providing an aqueous extract of malt and / or cereals; ii) A step of providing a yeast strain of the species Saccharomyces pastorianus, wherein the yeast strain is a yeast strain described in any one of claims 1 to 20; and iii) A step of fermenting the aqueous extract provided in step i) with the yeast strain of step ii), thereby obtaining a fermented aqueous extract. A method that includes this.

22. A method for producing a beverage, i. A step of preparing the fermented aqueous extract according to claim 21, and ii. Process of processing the fermented aqueous extract to make a beverage. Methods that include...

23. The method according to claim 22, wherein the processing step includes one or more of the following: i. filtration, ii. Carbonation, iii. Maturation, or iv. Bottled.

24. A beverage prepared by the method of claim 22 or 23, wherein the beverage contains at least 25 mg / L of propanol and / or up to 8 mg / L of isobutanol, and the beverage has a propanol:isobutanol ratio of at least 3.

0.

25. The beverage according to claim 24, wherein the beverage is beer.

Images