Alpha-glucan mixture, its preparation and uses

1. An α-glucan mixture, which is obtainable by a process comprising the steps of gelatinizing waxy starch and liquefying the resulting gelatinized waxy starch by allowing an amylase to act on it, having the following characteristics (1) to (3):

(1) having the weight average molecular weight (Mw) in a range of 150 kDa to 3,000 kDa;

(2) having the value of dividing weight average molecular weight (Mw) with number average molecular weight (Mn), Mw/Mn, of 35.1 or lower; and

(3) forming a hydrolyzate with isomaltose content of less than 22% by weight, on a dry solid basis of the hydrolyzate, when digested by isomaltodextranase (EC 3.2.1.94).

2. The α-glucan mixture of claim 1 , which contains a-glucan having an isomaltose structure at the non-reducing end.

3. The α-glucan mixture of claim 2 , wherein said α-glucan mixture forms isomaltose in an amount of over 3% by weight but less than 22% by weight, on a dry solid basis of the hydrolyzate, when digested by isomaltodextranase (EC 3.2.1.94).

4. The α-glucan mixture of claim 3 , wherein said waxy starch is waxy corn starch.

5. The α-glucan mixture of claim 3 , which further has the following characteristic:

a film obtained by steps of molding the α-glucan mixture without plasticizer and drying, with a thickness of 40 to 50 mu.m, exhibits a rupture strength of piercing of 2.0 N/mm 2 or higher when analyzed on a piercing test for rupture strength using an adaptor with a sectional area of 1 mm 2 .

6. The α-glucan mixture of claim 3 , which can be made into a homogeneous solution when dissolved into water by admixing with deionized water to give a solid concentration of 20% by weight and stirring at 30° C. for 15 min.

7. An edible film, which is obtainable by steps of molding the α-glucan mixture of claim 3 , without adding any plasticizer and drying and exhibits a rupture strength of piercing of 2.0 N/mm 2 or higher when analyzed on a piercing test for rupture strength using an adaptor with a sectional area of 1 mm 2 .

8. The α-glucan mixture of claim 2 , wherein said waxy starch is waxy corn starch.

9. The α-glucan mixture of claim 2 , which further has the following characteristic:

a film obtained by steps of molding the α-glucan mixture without plasticizer and drying, with a thickness of 40 to 50 mu.m, exhibits a rupture strength of piercing of 2.0 N/mm 2 or higher when analyzed on a piercing test for rupture strength using an adaptor with a sectional area of 1 mm 2 .

10. The α-glucan mixture of claim 2 , which can be made into a homogeneous solution when dissolved into water by admixing with deionized water to give a solid concentration of 20% by weight and stirring at 30° C. for 15 min.

11. An edible film, which is obtainable by steps of molding the α-glucan mixture of claim 2 , without adding any plasticizer and drying and exhibits a rupture strength of piercing of 2.0 N/mm 2 or higher when analyzed on a piercing test for rupture strength using an adaptor with a sectional area of 1 mm 2 .

12. The α-glucan mixture of claim 1 , wherein said waxy starch is waxy corn starch.

13. The α-glucan mixture of claim 1 , which further has the following characteristic:

a film obtained by steps of molding the a-glucan mixture without plasticizer and drying, with a thickness of 40 to 50 mu.m, exhibits a rupture strength of piercing of 2.0 N/mm 2 or higher when analyzed on a piercing test for rupture strength using an adaptor with a sectional area of 1 mm 2 .

14. The α-glucan mixture of claim 1 , which can be made into a homogeneous solution when dissolved into water by admixing with deionized water to give a solid concentration of 20% by weight and stirring at 30° C. for 15 min.

15. A process for producing the α-glucan mixture of claim 1 , comprising the steps of:

gelatinizing waxy starch by heating a waxy starch suspension with a solid concentration of 20% by weight; and

forming α-glucan mixture having the weight average molecular weight (Mw) in a range of 150 kDa to 3,000 kDa by allowing an amylase to act on the resulting gelatinized waxy starch.

16. The process of claim 15 , further comprising a step of allowing an α-glucosyltransferase, which acts on starch hydrolyzate and catalyzes α-1,6 transglucosylation reaction to the non-reducing end of the starch hydrolyzate, to act on the formed α-glucan mixture.

17. The process of claim 16 , wherein said α-glucosyltransferase is derived from a microorganism of the genus Bacillus or Arthrobacter and has the following characteristics (A) to (F):

(A) Action

Acting on maltose and/or α-1,4 glucan having a glucose polymerization degree of 3 or higher, catalyzing mainly α-1,4 transglucosylation reaction and α-1,6 transglucosylation reaction, and transferring glucose to the C-4 or C-6 hydroxyl group of the glucose residue at the non-reducing end;

(B) Molecular weight

90,000±10,000 daltons on SDS-polyacrylamide gel electrophoresis;

(C) Optimum temperature

About 50° C. when reacted at pH 6.0 for 30 min;

(D) Optimum pH

About pH 6.0 when reacted at 40° C. for 30 min;

(E) Thermal stability

Stable up to the temperature of 40° C. when incubated at pH 6.0 for 60 min;

and

(F) pH stability

Stable in the range of pH 4.0 to 8.0 when incubated at 4° C. for 24 hours.

18. An edible film, which is obtainable by the steps of molding the α-glucan mixture of claim 1 , without adding any plasticizer and drying and exhibits a rupture strength of piercing of 2.0 N/mm 2 or higher when analyzed on a piercing test for rupture strength using an adaptor with a sectional area of 1 mm 2 .