Process for propagating a yeast capable to ferment glucose and xylose
It is disclosed a process for propagating a yeast capable to ferment glucose and xylose of a lignocellulosic feedstock hydrolyzate, said process comprising propagating the yeast over at least two propagation cycles. The first propagation cycle comprises the steps of: contacting the yeast at a starting yeast density with a first cultivation medium comprising a first portion of the lignocellulosic feedstock hydrolyzate; and allowing the yeast to propagate to create a first populated broth comprising water and a first propagated yeast, wherein at least 50% of the glucose and less than 20% of the xylose in the first cultivation medium are consumed in the first propagation cycle. The second cycle comprises the steps of: separating the first populated broth in at least a first removed portion and a first residual portion, wherein both the first residual portion and the first removed portion comprise some of the first propagated yeast; contacting the first residual portion with a second cultivation medium comprising a second portion of the lignocellulosic feedstock hydrolyzate; and allowing the yeast to propagate to create a second populated broth comprising water and a second propagated yeast, wherein at least 50% of the glucose and less than 20% of the xylose in the second cultivation medium are consumed in the second propagation cycle.
1. A process for propagating a yeast capable of fermenting glucose and xylose of a lignocellulosic feedstock hydrolyzate, said process comprising:
propagating the yeast over at least a first propagation cycle and a second propagation cycle,
the first propagation cycle (P n , where n=1) comprising the steps of:
a. contacting the yeast at a starting yeast density with a first cultivation medium comprising a first portion of the lignocellulosic feedstock hydrolyzate,
b. allowing the yeast to propagate to create a first populated broth comprising water and a first propagated yeast, wherein less than 20% of the xylose and at least 50% of the glucose in the first cultivation medium are consumed in the first propagation cycle, the second propagation cycle (P 2 , n=2) comprising the steps of:
a. separating the first populated broth into at least a first removed portion and a first residual portion, wherein both the first residual portion and the first removed portion comprise some of the first propagated yeast,
b. contacting the first residual portion with a second cultivation medium comprising a second portion of the lignocellulosic feedstock hydrolyzate, and
c. allowing the yeast to propagate to create a second populated broth comprising water and a second propagated yeast, wherein less than 20% of the xylose and at least 50% of the glucose in the second cultivation medium are consumed in the second propagation cycle;
wherein propagation time of the first propagation cycle is in the range of 14 to 30 hours using the starting yeast density in the first propagation cycle between 1×10 6 and 1×10 8 yeast cells per milligram of the first cultivation medium on a wet basis.
2. The process of claim 1 further comprising subsequent propagation cycles P n , where n is an integer greater than 2 and is one (1) greater than the cycle number of an immediately previous cycle (n−1), each propagation cycle P n comprising the steps of:
a. separating the P n−1 populated broth in at least a P n−1 removed portion and a P n−1 residual portion, wherein both the P n−1 residual portion and the P n−1 removed portion comprise some of the P n−1 propagated yeast,
b. contacting the residual portion of the populated broth of at least one of the previous propagation cycles and a P n cultivation medium comprising a P n portion of the lignocellulosic feedstock hydrolyzate, and
c. allowing the yeast to propagate to create a P n populated broth, wherein less than 20% of the xylose and at least 50% of the glucose in the P n cultivation medium are consumed in the P n propagation cycle.
3. The process of claim 1 , wherein the step of allowing the yeast to propagate in the propagation cycles P n is conducted in batch mode, wherein n is an integer equal to or greater than 1.
4. The process of claim 1 , wherein the cultivation media further comprise a nitrogen source.
5. The process of claim 1 , wherein the lignocellulosic feedstock hydrolyzate contains biological contaminants, and the density of biological contaminants in the starting P n cultivation medium is in a range selected from the group consisting of from 10 0 CFU/ml to 10 6 CFU/ml, from 10 1 CFU/ml to 10 5 CFU/ml, and 10 2 CFU/ml to 10 3 CFU/ml of starting P n cultivation medium, wherein n is an integer equal to or greater than 1.
6. The process of claim 1 , wherein the lignocellulosic feedstock hydrolyzate is a slurry comprising water insoluble pretreated lignocellulosic feedstock.
7. The process of claim 1 , wherein all the propagation cycles are conducted in a single propagation vessel.
8. The process of claim 1 , further comprising the steps of:
a. introducing one or more P n removed portions and a fermenting medium comprising a further portion of the lignocellulosic feedstock hydrolyzate in at least a fermentation vessel, and
b. allowing the yeast to ferment glucose and xylose to create a fermentation broth, comprising a fermentation product,
wherein n is an integer equal to or greater than 1.
9. The process of claim 2 , further comprising the steps of:
a. introducing one or more P n removed portions and a fermenting medium comprising a further portion of the lignocellulosic feedstock hydrolyzate in at least a fermentation vessel, and
b. allowing the yeast to ferment glucose and xylose to create a fermentation broth, comprising a fermentation product,
wherein n is an integer equal to or greater than 1.
10. The process of claim 1 , wherein in the amount of P n−1 removed portion and the amount of the P n portion of the lignocellulosic feedstock hydrolyzate are selected to have a starting yeast density in the P n propagation cycle between 1×10 6 and 1×10 8 yeast cells per milligram of the P n cultivation medium on a wet basis, wherein n is an integer greater than 1.
11. The process of claim 1 , wherein the final yeast density in the P n propagation cycle is in the range of 1×10 7 to 1×10 9 yeast cells per milligram of the P n populated broth on a wet basis, wherein n is an integer equal to or greater than 1.
12. The process of claim 4 , wherein no vitamins and/or trace elements are added to the process.
13. The process of claim 5 , wherein the lignocellulosic feedstock hydrolyzate is not subjected to any sterilization.
14. The process of claim 5 , wherein no anti-bacterial agents are added to the process.
15. The process of claim 6 , wherein the dry matter of the P n cultivation medium is less than 30% and greater than a percent value selected from the group consisting of 5%, 10%, 15%, and 20%, wherein n is an integer equal to or greater than 1.
16. The process of claim 7 , wherein the propagation vessel is not subjected to any sterilization and/or cleaning between and/or during propagation cycles.
17. The process of claim 10 , wherein the starting yeast density in the P n propagation cycle, where n is an integer greater than 1, is greater than the starting yeast density in the first propagation cycle.
18. The process of claim 1 , wherein the propagation time of the P n propagation cycle is less than a percent value selected from the group consisting of 70%, 50%, and 40% of the first propagation time, wherein n is an integer greater than 1.