Method for Improving the Transparency of Starch Liquefaction

Abstract

The present disclosure disclosed is method for improving the transparency of starch liquefaction, and belongs to the field of biologically modified starch. The method changes the molecular structure of the starch liquefaction product by adding a 1,4--glucan branching enzyme from Rhodothermus obamensis, so the molecular structure has a smaller branched chain and a higher branching degree, thereby achieving the purpose of improving transparency and stability. The method comprises the steps of dissolving a starch liquefaction product in water according to a certain concentration to prepare an aqueous solution of the starch liquefaction product, and adding a 1,4--glucan branching enzyme to react at a certain temperature for a period of time, so as to improve the transparency of the starch liquefaction product during storage. The method provides a new idea for improving the stability of starch liquefaction products, and has great potential and application prospects.

Claims

1. A method for improving transparency of a starch liquefaction product, comprising: adding a 1,4--glucan branching enzyme to the starch liquefaction product; and treating the starch liquefaction product with the 1,4--glucan branching enzyme, wherein the 1,4--glucan branching enzyme is derived from Rhodothermus obamensis, and the starch liquefaction product is a mixture of short chain small molecule dextrin, oligosaccharides and monosaccharide molecules obtained by hydrolyzing starch with an amylolytic enzyme.

2. The method according to claim 1, wherein the method further comprises: dissolving the starch liquefaction product in water according to a certain concentration for preparing an aqueous solution of the starch liquefaction product, wherein the 1,4--glucan branching enzyme is added for reacting at a certain temperature for a period of time, and enzyme deactivation is carried out by boiling; and wherein the reaction temperature is 50-70 C., and the reaction time is 4-24 h.

3. The method according to claim 2, wherein a concentration of the aqueous solution of the starch liquefaction product is 1-40% (w/v).

4. The method according to claim 2, wherein a DE value of the starch liquefaction product is 20 or less.

5. The method according to claim 4, wherein the DE value of the starch liquefaction product is greater than or equal to 2 and less than 20.

6. The method according to claim 1, wherein the starch is selected from a group consisting of ordinary corn starch, potato starch, tapioca starch, sweet potato starch, rice starch and wheat starch.

7. The method according to claim 2, wherein a pH value of the aqueous solution of the starch liquefaction product is 5.5-7.5.

8. The method according to claim 2, wherein the 1,4--glucan branching enzyme is added in an amount of 30-500 U/g to the starch liquefaction product on a dry basis.

9. The method according to claim 1, wherein a sequence of a gene encoding the 1,4--glucan branching enzyme is set forth in GenBank: AB060080.1.

10. The method according to claim 2, wherein the starch liquefaction product having a DE value of 4 is dissolved in water to prepare a 5% (w/v) aqueous solution of the starch liquefaction product, a pH value is adjusted to 6.5, the 1,4--glucan branching enzyme is added in an amount of 30 U/g on a dry basis, the treatment is carried out at 60 C. for 8 h, and the enzyme deactivation is carried out by boiling.

11. The method according to claim 2, wherein the starch liquefaction product having a DE value of 7 is dissolved in water to prepare a 5% (w/v) aqueous solution of the starch liquefaction product, a pH value is adjusted to 7.5, the 1,4--glucan branching enzyme is added in an amount of 100 U/g on a dry basis, the treatment is carried out at 50 C. for 12 h, and the enzyme deactivation is carried out by boiling.

12. The method according to claim 2, wherein the starch liquefaction product having a DE value of 11 is dissolved in water to prepare a 20% (w/v) aqueous solution of the starch liquefaction product, a pH value is adjusted to 7.0, the 1,4--glucan branching enzyme is added in an amount of 200 U/g on a dry basis, the treatment is carried out at 55 C. for 24 h, and the enzyme deactivation is carried out by boiling.

13. The method according to claim 2, wherein the starch liquefaction product having a DE value of 15 is dissolved in water to prepare a 35% (w/v) aqueous solution of the starch liquefaction product, a pH value is adjusted to 7.0, the 1,4--glucan branching enzyme is added in an amount of 500 U/g on a dry basis, the treatment is carried out at 65 C. for 24 h, and the enzyme deactivation is carried out by boiling.

14. The method according to claim 1, wherein the amylolytic enzyme is medium temperature or high temperature resistant -amylase.

15. A starch liquefaction product prepared by using the method according to claim 1.

Description

BRIEF DESCRIPTION OF FIGURES

[0018] FIG. 1 is a graph showing the effect of modification for 4 h of the 1,4--glucan branching enzyme from Rhodothermus obamensis on the transparency of a 5% (w/v) starch liquefaction product having the DE value of 4, with water transparency as 100%.

[0019] FIG. 2 is a graph showing the effect of modification for 8 h of the 1,4--glucan branching enzyme from Rhodothermus obamensis on the transparency of a 5% (w/v) starch liquefaction product having the DE value of 4, with water transparency as 100%.

[0020] FIG. 3 is a graph showing the effect of the 1,4--glucan branching enzyme from Rhodothermus obamensis on the transparency of a 5% (w/v) starch liquefaction product having the DE value of 7, with water transparency as 100%.

[0021] FIG. 4 is a graph showing the effect of the 1,4--glucan branching enzyme from Rhodothermus obamensis on the transparency of a 10% (w/v) starch liquefaction product having the DE value of 7, with water transparency as 100%.

[0022] FIG. 5 is a graph showing the effect of the 1,4--glucan branching enzyme from Rhodothermus obamensis on the transparency of a 20% (w/v) starch liquefaction product having the DE value of 11, with water transparency as 100%.

[0023] FIG. 6 is a graph showing the effect of the 1,4--glucan branching enzyme from Rhodothermus obamensis on the transparency of a 30% (w/v) starch liquefaction product having the DE value of 11, with water transparency as 100%.

[0024] FIG. 7 is a graph showing the effect of the 1,4--glucan branching enzyme from Rhodothermus obamensis on the transparency of a 35% (w/v) starch liquefaction product having the DE value of 15, with water transparency as 100%.

[0025] FIG. 8 is a graph showing the effect of the 1,4--glucan branching enzyme from Rhodothermus obamensis on the transparency of a 40% (w/v) starch liquefaction product having the DE value of 15, with water transparency as 100%.

[0026] FIG. 9 is a graph showing the effect of the 1,4--glucan branching enzyme from Geobacillus thermoglucosidans on the transparency of a 30% (w/v) starch liquefaction product having the DE value of 4, with water transparency as 100%.

[0027] FIG. 10 is a graph showing the effect of the 1,4--glucan branching enzyme from Geobacillus thermoglucosidans on the transparency of a 30% (w/v) starch liquefaction product having the DE value of 7, with water transparency as 100%.

[0028] FIG. 11 is a graph showing the effect of the 1,4--glucan branching enzyme from Geobacillus thermoglucosidans on the transparency of a 30% (w/v) starch liquefaction product having the DE value of 11, with water transparency as 100%.

[0029] FIG. 12 is a graph showing the effect of the 1,4--glucan branching enzyme from Geobacillus thermoglucosidans on the transparency of a 30% (w/v) starch liquefaction product having the DE value of 15, with water transparency as 100%.

[0030] FIG. 13 is a graph showing the effect of the 1,4--glucan branching enzyme from rice on the transparency of a 6% (w/v) starch liquefaction product having the DE value of 7, with water transparency as 100%.

[0031] FIG. 14 is a graph showing the effect of the 1,4--glucan branching enzyme from rice on the transparency of a 6% (w/v) starch liquefaction product having the DE value of 15, with water transparency as 100%.

DETAILED DESCRIPTION

[0032] Transparency is represented by transmittance measured at 620 nm by using a spectrophotometer. The spectrophotometer is capable of exhibiting the transmittance of a measured sample with respect to water having a transmittance of 100%.

EXAMPLE 1

[0033] The production and the preparation of the 1,4--glucan branching enzyme from Rhodothermus obamensis comprise the following three steps:

[0034] (1) Seed culture: according to an inoculum size of 0.2% (v/v), 100 L of a glycerol strain Escherichia coli/pET-20b(+)/gbe (Escherichia coli containing a vector pET-20b(+)/gbe carrying a gene encoding a 1,4--glucan branching enzyme from Rhodothermus obamensis) preserved at 80 C. is inoculated in a 250 mL Erlenmeyer flask containing 50 mL of LB medium (containing 5 g/L yeast extract, 10 g/L tryptone and 10 g/L NaCl, and pH of 7.0), and cultured for 8-10 h (at 200 r/min) on a 37 C. shaker. Before inoculation, ampicillin with the final concentration of 100 g/mL is added to the LB medium.

[0035] (2) Fermentation culture: the activated seed solution is transferred into a 250 mL Erlenmeyer flask containing 50 mL of TB medium (containing 24 g/L yeast extract, 12 g/L tryptone, 5 g/L glycerol, 17 mM KH.sub.2PO.sub.4 and 72 mM K.sub.2HPO.sub.4, and pH of 7.0) according to an inoculum size of 2% (v/v), and cultured on a 37 C. shaker at 200 r/min. When the thalli are cultured until the OD.sub.600 is 0.5-0.6, IPTG with the final concentration of 0.05 mM is added, and the culture is continued for 48 h. Before inoculation, ampicillin with the final concentration of 100 g/mL is added to the TB medium. After fermentation, the fermentation medium is centrifuged at 4 C., 10,000g for 15 min, and the supernatant is collected to obtain a crude enzyme solution.

[0036] (3) Purification: the obtained crude enzyme solution is purified by nickel column one-step affinity chromatography to obtain a pure enzyme solution of the 1,4--glucan branching enzyme from Rhodothermus obamensis with a specific activity of 6,650.7 U/mg.

EXAMPLE 2

[0037] The production and the preparation of the 1,4--glucan branching enzyme from Geobacillus thermoglucosidans comprise the following three steps:

[0038] (1) Seed culture: according to an inoculum size of 0.2% (v/v), 100 L of a glycerol strain Escherichia coli/pET-20b(+)/gbe (Escherichia coli containing an expression vector pET-20b(+)/gbe carrying a gene encoding a 1,4--glucan branching enzyme from Geobacillus thermoglucosidans) preserved at 80 C. is inoculated in a 250 mL Erlenmeyer flask containing 50 mL of LB medium (containing 5 g/L yeast extract, 10 g/L tryptone and 10 g/L NaCl, pH of 7.0), and cultured for 8-10 h (at 200 r/min) on a 37 C. shaker. Before inoculation, ampicillin with the final concentration of 100 g/mL is added to the LB medium.

[0039] (2) Fermentation culture: the activated seed solution is transferred into a 250 mL Erlenmeyer flask containing 50 mL of TB medium (containing 24 g/L yeast extract, 12 g/L tryptone, 5 g/L glycerol, 17 mM KH.sub.2PO.sub.4 and 72 mM of K.sub.2HPO.sub.4, and pH of 7.0) according to an inoculum size of 2% (v/v), and oscillated and cultured on a 30 C. shaker at 200 r/min for 48 h. Before inoculation, ampicillin with the final concentration of 100 g/mL is added to the TB medium. After fermentation, the fermentation medium is centrifuged at 4 C., 10,000g for 15 min, and the supernatant is collected to obtain a crude enzyme solution.

[0040] (3) Purification: the obtained crude enzyme solution is purified by nickel column one-step affinity chromatography to obtain a pure enzyme solution of the 1,4--glucan branching enzyme from Geobacillus thermoglucosidans with a specific activity of 2,005.1 U/mg.

EXAMPLE 3

[0041] The starch liquefaction product having the DE value of 4 is dissolved in water to prepare a 5% (w/v) aqueous solution of the starch liquefaction product, the pH is adjusted to 6.5, the 1,4--glucan branching enzyme from Rhodothermus obamensis is added in the amount of 30 U/g on a dry basis, treatment is carried out at 60 C. for 4 h, and enzyme deactivation is carried out by boiling. The obtained product is stored in the environment of 4 C., and is measured for transparency at intervals. The results of transparency measurement are shown in FIG. 1, and the control represents an unmodified starch liquefaction product with the same concentration.

[0042] The results in FIG. 1 show that the transparency of the starch liquefaction product modified by the 1,4--glucan branching enzyme for 4 h and stored at 4 C. for 30 d is always 50% or more, and the transparency can reach 50.0% after the product is stored for 30 d. The unmodified starch liquefaction product is completely turbid after stored at 4 C. for 12 d.

EXAMPLE 4

[0043] The starch liquefaction product having the DE value of 4 is dissolved in water to prepare a 5% (w/v) aqueous solution of the starch liquefaction product, the pH is adjusted to 6.5, the 1,4--glucan branching enzyme from Rhodothermus obamensis is added in the amount of 30 U/g on a dry basis, treatment is carried out at 60 C. for 8 h, and enzyme deactivation is carried out by boiling. The obtained product is stored in the environment of 4 C., and is measured for transparency at intervals. The results of transparency measurement are shown in FIG. 2, and the control represents an unmodified starch liquefaction product with the same concentration.

[0044] The results in FIG. 2 show that the transparency of the starch liquefaction product modified by the 1,4--glucan branching enzyme for 8 h and stored at 4 C. for 30 d is always 90% or more, and the transparency can reach 91.0% after the product is stored at 4 C. for 30 d. The unmodified starch liquefaction product with the concentration of 5% (w/v) and the DE value of 4 is completely turbid after stored at 4 C. for 12 d.

EXAMPLE 5

[0045] The starch liquefaction product having the DE value of 7 is dissolved in water to prepare a 5% (w/v) aqueous solution of the starch liquefaction product, the pH is adjusted to 7.5, the 1,4--glucan branching enzyme from Rhodothermus obamensis is added in the amount of 100 U/g on a dry basis, treatment is carried out at 50 C. for 12 h, and enzyme deactivation is carried out by boiling. The obtained product is stored in the environment of 4 C., and is measured for transparency at intervals. The results of transparency measurement are shown in FIG. 3, and the control represents an unmodified starch liquefaction product with the same concentration.

[0046] The results in FIG. 3 show that the transparency of the starch liquefaction product modified by the 1,4--glucan branching enzyme for 12 h and stored at 4 C. for 30 d is always 90% or more, and the transparency can reach 93.2% after the product is stored at 4 C. for 30 d. The unmodified starch liquefaction product with the concentration of 5% (w/v) and the DE value of 7 is completely turbid after stored at 4 C. for 20 d.

EXAMPLE 6

[0047] The starch liquefaction product having the DE value of 7 is dissolved in water to prepare a 10% (w/v) aqueous solution of the starch liquefaction product, the pH is adjusted to 6.0, the 1,4--glucan branching enzyme from Rhodothermus obamensis is added in the amount of 200 U/g on a dry basis, treatment is carried out at 65 C. for 12 h, and enzyme deactivation is carried out by boiling. The obtained product is stored in the environment of 4 C., and is measured for transparency at intervals. The results of transparency measurement are shown in FIG. 4, and the control represents an unmodified starch liquefaction product with the same concentration.

[0048] The results in FIG. 4 show that the transparency of the starch liquefaction product modified by the 1,4--glucan branching enzyme for 12 h and stored at 4 C. for 30 d is always 90% or more, and the transparency can reach 90.8% after the product is stored at 4 C. for 30 d. The unmodified starch liquefaction product with the concentration of 10% (w/v) and the DE value of 7 is completely turbid after stored at 4 C. for 7 d.

EXAMPLE 7

[0049] The starch liquefaction product having the DE value of 11 is dissolved in water to prepare a 20% (w/v) aqueous solution of the starch liquefaction product, the pH is adjusted to 7.0, the 1,4--glucan branching enzyme from Rhodothermus obamensis is added in the amount of 200 U/g on a dry basis, treatment is carried out at 55 C. for 24 h, and enzyme deactivation is carried out by boiling. The obtained product is stored in the environment of 4 C., and is measured for transparency at intervals. The results of transparency measurement are shown in FIG. 5, and the control represents an unmodified starch liquefaction product with the same concentration.

[0050] The results in FIG. 5 show that the transparency of the starch liquefaction product modified by the 1,4--glucan branching enzyme and stored at 4 C. for 30 d is always about 100%, and the transparency can reach 99.1% after the product is stored at 4 C. for 30 d. The unmodified starch liquefaction product with the concentration of 20% (w/v) and the DE value of 11 is completely turbid after stored at 4 C. for 10 d.

EXAMPLE 8

[0051] The starch liquefaction product having the DE value of 11 is dissolved in water to prepare a 30% (w/v) aqueous solution of the starch liquefaction product, the pH is adjusted to 5.5, the 1,4--glucan branching enzyme from Rhodothermus obamensis is added in the amount of 300 U/g on a dry basis, treatment is carried out at 70 C. for 24 h, and enzyme deactivation is carried out by boiling. The obtained product is stored in the environment of 4 C., and is measured for transparency at intervals. The results of transparency measurement are shown in FIG. 6, and the control represents an unmodified starch liquefaction product with the same concentration.

[0052] The results in FIG. 6 show that the transparency of the starch liquefaction product modified by the 1,4--glucan branching enzyme and stored at 4 C. for 30 d is always about 100%, and the transparency can reach 99.0% after the product is stored at 4 C. for 30 d. The unmodified starch liquefaction product with the concentration of 30% (w/v) and the DE value of 11 is completely turbid after stored at 4 C. for 5 d.

EXAMPLE 9

[0053] The starch liquefaction product having the DE value of 15 is dissolved in water to prepare a 35% (w/v) aqueous solution of the starch liquefaction product, the pH is adjusted to 7.0, the 1,4--glucan branching enzyme from Rhodothermus obamensis is added in the amount of 500 U/g on a dry basis, treatment is carried out at 65 C. for 24 h, and enzyme deactivation is carried out by boiling. The obtained product is stored in the environment of 4 C., and is measured for transparency at intervals. The results of transparency measurement are shown in FIG. 7, and the control represents an unmodified starch liquefaction product with the same concentration.

[0054] The results in FIG. 7 show that the transparency of the starch liquefaction product modified by the 1,4--glucan branching enzyme and stored at 4 C. for 30 d is always about 100%, and the transparency can reach 99.3% after the product is stored at 4 C. for 30 d. The unmodified starch liquefaction product with the concentration of 35% (w/v) and the DE value of 15 is completely turbid after stored at 4 C. 8 d.

EXAMPLE 10

[0055] The starch liquefaction product having the DE value of 15 is dissolved in water to prepare a 40% (w/v) aqueous solution of the starch liquefaction product, the pH is adjusted to 7.0, the 1,4--glucan branching enzyme from Rhodothermus obamensis is added in the amount of 500 U/g on a dry basis, treatment is carried out at 65 C. for 24 h, and enzyme deactivation is carried out by boiling. The obtained product is stored in the environment of 4 C., and is measured for transparency at intervals. The results of transparency measurement are shown in FIG. 8, and the control represents an unmodified starch liquefaction product with the same concentration.

[0056] The results in FIG. 8 show that the transparency of the starch liquefaction product modified by the 1,4--glucan branching enzyme and stored at 4 C. for 30 d is always 80% or more, and the transparency can reach 83.0% after the product is stored at 4 C. for 30 d. The unmodified starch liquefaction product with the concentration of 40% (w/v) and the DE value of 15 is completely turbid after stored at 4 C. for 4 d.

[0057] Comparing the results of the present example with the results of Example 9, it can be seen that when the concentration of the starch liquefaction product is 40%, the modification effect of the 1,4--glucan branching enzyme on the product is lowered, so the concentration of the starch liquefaction product shall be not higher than 35%.

COMPARATIVE EXAMPLE 1

[0058] The starch liquefaction product having the DE value of 4 is dissolved in water to prepare a 30% (w/v) aqueous solution of the starch liquefaction product, the pH is adjusted to 6.5, the 1,4--glucan branching enzyme from Geobacillus thermoglucosidans is added in the amount of 0.12 U/g on a dry basis, treatment is carried out at 45 C. for 4 h, and enzyme deactivation is carried out by boiling. The obtained product is stored in the environment of 4 C., and is measured for transparency at intervals. The results of transparency measurement are shown in FIG. 9, and the control represents an unmodified starch liquefaction product with the same concentration.

[0059] The results in FIG. 9 show that the 1,4--glucan branching enzyme from Geobacillus thermoglucosidans has a poor modification effect on the starch liquefaction product having the DE value of 4. The unmodified starch liquefaction product having the DE value of 4 is completely turbid after stored at 4 C. for 16 h, the completely turbid time of the modified starch liquefaction product is prolonged from 16 h to 18 h only, and the effect is poor.

COMPARATIVE EXAMPLE 2

[0060] The starch liquefaction product having the DE value of 7 is dissolved in water to prepare a 30% (w/v) aqueous solution of the starch liquefaction product, the pH is adjusted to 6.5, the 1,4--glucan branching enzyme from Geobacillus thermoglucosidans is added in the amount of 0.12 U/g on a dry basis, treatment is carried out at 45 C. for 4 h, and enzyme deactivation is carried out by boiling. The obtained product is stored in the environment of 4 C., and is measured for transparency at intervals. The results of transparency measurement are shown in FIG. 10, and the control represents an unmodified starch liquefaction product with the same concentration.

[0061] The results in FIG. 10 show that the 1,4--glucan branching enzyme from Geobacillus thermoglucosidans has a poor modification effect on the starch liquefaction product having the DE value of 7. The unmodified starch liquefaction product having the DE value of 7 is completely turbid after stored at 4 C. for 26 h, the completely turbid time of the modified starch liquefaction product is prolonged from 26 h to 32 h only, and the effect is poor.

COMPARATIVE EXAMPLE 3

[0062] The starch liquefaction product having the DE value of 11 is dissolved in water to prepare a 30% (w/v) aqueous solution of the starch liquefaction product, the pH is adjusted to 6.5, the 1,4--glucan branching enzyme from Geobacillus thermoglucosidans is added in the amount of 0.12 U/g on a dry basis, treatment is carried out at 45 C. for 4 h, and enzyme deactivation is carried out by boiling. The obtained product is stored in the environment of 4 C., and is measured for transparency at intervals. The results of transparency measurement are shown in FIG. 11, and the control represents an unmodified starch liquefaction product with the same concentration.

[0063] The results in FIG. 11 show that the 1,4--glucan branching enzyme from Geobacillus thermoglucosidans has a poor modification effect on the starch liquefaction product having the DE value of 11. The unmodified starch liquefaction product having the DE value of 11 is completely turbid after stored at 4 C. for 5 d, and the completely turbid time of the modified starch liquefaction product is prolonged from 5 d to 7 d only. While when the 1,4--glucan branching enzyme from Rhodothermus obamensis of the present disclosure is used for carrying out modification, the transparency of the modified starch liquefaction product can still reach 99.0% after the product is stored at 4 C. for 30 d.

COMPARATIVE EXAMPLE 4

[0064] The starch liquefaction product having the DE value of 15 is dissolved in water to prepare a 30% (w/v) aqueous solution of the starch liquefaction product, the pH is adjusted to 6.5, the 1,4--glucan branching enzyme from Geobacillus thermoglucosidans is added in the amount of 0.12 U/g on a dry basis, treatment is carried out at 45 C. for 4 h, and enzyme deactivation is carried out by boiling. The obtained product is stored in the environment of 4 C., and is measured for transparency at intervals. The results of transparency measurement are shown in FIG. 12, and the control represents an unmodified starch liquefaction product with the same concentration.

[0065] The reaction results show that the 1,4--glucan branching enzyme from Geobacillus thermoglucosidans has a poor modification effect on the starch liquefaction product having the DE value of 15. The unmodified starch liquefaction product having the DE value of 15 is completely turbid after stored at 4 C. for 10 d, the completely turbid time of the modified starch liquefaction product is prolonged from 10 d to 14 d only, and the effect is poor.

COMPARATIVE EXAMPLE 5

[0066] The starch liquefaction product having the DE value of 7 is dissolved in water to prepare a 6% (w/v) aqueous solution of the starch liquefaction product, the pH is adjusted to 6.5, the 1,4--glucan branching enzyme from rice is added in the amount of 4 U/g on a dry basis, treatment is carried out at 45 C. for 3 h, and enzyme deactivation is carried out by boiling. The obtained product is stored in the environment of 4 C., and is measured for transparency at intervals. The results of transparency measurement are shown in FIG. 13, and the control represents an unmodified starch liquefaction product with the same concentration.

[0067] The results in FIG. 13 show that the 1,4--glucan branching enzyme from rice has a poor modification effect on the starch liquefaction product having the DE value of 7. The unmodified starch liquefaction product having the DE value of 7 is completely turbid after stored at 4 C. for 18 d, the completely turbid time of the modified starch liquefaction product is prolonged from 18 d to 20 d, and the effect is poor.

COMPARATIVE EXAMPLE 6

[0068] The starch liquefaction product having the DE value of 15 is dissolved in water to prepare a 6% (w/v) aqueous solution of the starch liquefaction product, the pH is adjusted to 7.5, the 1,4--glucan branching enzyme from rice is added in the amount of 6 U/g on a dry basis, treatment is carried out at 60 C. for 5 h, and enzyme deactivation is carried out by boiling. The obtained product is stored in the environment of 4 C., and is measured for transparency at intervals. The results of transparency measurement are shown in FIG. 14, and the control represents an unmodified starch liquefaction product with the same concentration.

[0069] The results in FIG. 14 show that the 1,4--glucan branching enzyme from rice has a poor modification effect on the starch liquefaction product having the DE value of 15. The transparency of the unmodified starch liquefaction product having the DE value of 15 is 85.1% after the product is stored at 4 C. for 30 d, the transparency of the modified starch liquefaction product is 92.3% after stored at 4 C. for 30 d, and the effect is poor.

COMPARATIVE EXAMPLE 7

[0070] A certain amount of corn starch is dissolved in water to prepare 6% (w/v) starch milk. The starch milk is gelatinized in a boiling water bath for 30 min, then cooled to room temperature, and subjected to heat preservation at 60 C. in a water bath shaker for 15 min at a speed of 160 r/min, and the pH is adjusted to 7.0. 2 U/g 1,4--glucan branching enzyme from Rhodothermus obamensis on a starch dry basis is added, treatment is carried out at 60 C. for 4 h, and enzyme deactivation is carried out by boiling. The modified corn starch is obtained by freeze drying, grinding and sieving, and re-prepared into 6% (w/v) starch milk, and the transparency is measured. The control is unmodified starch milk with the same concentration. The transparency of the modified corn starch milk is increased by 78.3% compared to the control.