Production of glucose from starch using alpha-amylases from
An α-amylase from Bacillus subtilis (AmyE) produces significant amounts of glucose from various carbohydrate substrates, including vegetable starch, maltoheptaose, and maltotriose. Among other things, this advantageous property allows AmyE or variants thereof to be used in a saccharification reaction having a reduced or eliminated requirement for glucoamylase. The reduction or elimination of the glucoamylase requirement significantly improves the efficiency of the production of ethanol or high fructose corn syrup, for example.
1. A method of using a Bacillus subtilis α-amylase (AmyE) to produce glucose from an oligosaccharide or starch substrate solution, comprising:
(i) contacting AmyE with the oligosaccharide or polysaccharide substrate; and
(ii) converting the substrate solution to a solution comprising glucose, wherein the AmyE consists of the amino acid sequence of SEQ ID NO: 1, wherein said α-amylase (AmyE) is not the α-amylase (AmyE) having the amino acid sequence of SEQ ID NO: 1.
2. The method of claim 1 , wherein the oligosaccharide solution comprises predominantly maltoheptaose (DP7) or higher oligosaccharides.
3. The method of claim 1 , wherein the starch solution is uncooked corn starch.
4. The method of claim 1 , wherein the pH of the substrate solution during said converting is pH 5.6 to pH 5.8.
5. The method of claim 1 , where said converting does not comprise contacting the substrate solution with a glucoamylase.
6. The method of claim 1 , wherein step (i) further comprises contacting the starch substrate with a glucoamylase or pullulanase.
7. The method of claim 6 , wherein the glucoamylase is added to a concentration of less than 0.5 GAU/g ds (glucoamylase activity units per gram of dry solids).
8. The method of claim 7 , wherein the glucoamylase is added to a concentration of less than 0.02 GAU/g ds.
9. The method of claim 1 , wherein the solution comprising glucose contains at least 0.2 g/L glucose.
10. The method of claim 9 , wherein the solution comprising glucose contains at least 0.4 g/L glucose.
11. The method of claim 10 , wherein the solution comprising glucose contains at least 1.4 g/L glucose.
12. The method of claim 1 , wherein the AmyE comprises the amino acid sequence set forth in SEQ ID NO: 1.
13. The method of claim 1 , further comprising (iii) fermenting the solution comprising glucose to produce ethanol.
14. The method of claim 13 , wherein the ethanol concentration is at least 6% v/v ethanol.
15. The method of claim 14 , wherein the ethanol concentration is at least 14% v/v ethanol.
16. The method of claim 1 , further comprising (iii) contacting the solution comprising glucose with a glucose isomerase to produce high fructose corn syrup.