Branched α-glucan, α-glucosyltransferase which forms the glucan, their preparation and uses
The present invention has objects to provide a glucan useful as water-soluble dietary fiber, its preparation and uses. The present invention solves the above objects by providing a branched α-glucan, which is constructed by glucose molecules and characterized by methylation analysis as follows: (1) Ratio of 2,3,6-trimethyl-1,4,5-triacetyl-glucitol to 2,3,4-trimethyl-1,5,6-triacetyl-glucitol is in the range of 1:0.6 to 1:4; (2) Total content of 2,3,6-trimethyl-1,4,5-triacetyl-glucitol and 2,3,4-trimethyl-1,5,6-triacetyl-glucitol is 60% or higher in the partially methylated glucitol acetates; (3) Content of 2,4,6-trimethyl-1,3,5-triacetyl-glucitol is 0.5% or higher but less than 10% in the partially methylated glucitol acetates; and (4) Content of 2,4-dimethyl-1,3,5,6-tetraacetyl-glucitol is 0.5% or higher in the partially methylated glucitol acetates; a novel α-glucosyltransferase which forms the branched α-glucan, processes for producing them, and their uses.
1. A process for producing a saccharide composition comprising branched α-glucan, comprising the steps of:
allowing an α-glucosyltransferase and cyclomaltodextrin glucanotransferase to act on maltose and/or α-1,4 glucan having a glucose polymerization degree of 3 or higher; and
collecting the formed saccharide composition comprising branched α-glucan;
said saccharide composition is characterized in that it forms isomaltose in an amount of 25% (w/w) or higher but 50% (w/w) or lower, on a dry solid basis, when the saccharide composition is digested by isomaltodextranase (EC 3.2.1.94).
2. The process of claim 1 , wherein said saccharide composition has the following characteristics upon methylation analysis:
(1) Ratio of 2,3,6-trimethyl-1,4,5-triacetyl-glucitol to 2,3,4-trimethyl-1,5,6-triacetyl-glucitol, which indicates the ratio of glucose residues with α-1,4 linkages to glucose residues with α-1,6 linkages, is in the range of 1:0.6 to 1:4; and
(2) Total content of 2,3,6-trimethyl-1,4,5-triacetyl-glucitol and 2,3,4-trimethyl-1,5,6-triacetyl-glucitol, which indicates that the total content of glucose residues with α-1,4 linkages and glucose residues with α-1,6 linkages, is 60% or higher in the partially methylated glucitol acetates.
3. The process of claim 2 , wherein said saccharide composition has the following characteristics upon methylation analysis:
(3) Content of 2,4,6-trimethyl-1,3,5-triacetyl-glucitol, which indicates that the content of glucose residues with α-1,3 linkage, is 0.5% or higher but less than 10% in the partially methylated glucitol acetates; and
(4) Content of 2,4-dimethyl-1,3,5,6-tetraacetyl-glucitol, which indicates that the content of glucose residues with both α-1,3 and α-1,6 linkages, is 0.5% or higher in the partially methylated glucitol acetates.
4. The process of claim 1 , wherein said saccharide composition is characterized in that the content of water-soluble dietary fiber of the saccharide composition, obtained by applying a high performance liquid chromatography method is 40% (w/w) or higher.
5. The process of claim 1 , wherein said α-glucosyltransferase is an enzyme having the activity of forming a saccharide composition comprising branched α-glucan from a substrate of maltose or α-1,4 glucan having a glucose polymerization degree of 3 or higher;
wherein said saccharide composition having the following characteristics upon methylation analysis:
(1) Ratio of 2,3,6-trimethyl-1,4,5-triacetyl-glucitol to 2,3,4-trimethyl-1,5,6-triacetyl-glucitol, which indicates the ratio of glucose residues with α-1,4 linkages to glucose residues with α-1,6 linkages, is in the range of 1:0.6 to 1:4;
(2) Total content of 2,3,6-trimethyl-1,4,5-triacetyl-glucitol and 2,3,4-trimethyl-1,5,6-triacetyl-glucitol, which indicates that the total content of glucose residues with α-1,4 linkages and glucose residues with α-1,6 linkages, is 60% or higher in the partially methylated glucitol acetates;
(3) Content of 2,4,6-trimethyl-1,3,5-triacetyl-glucitol, which indicates that the content of glucose residues with α-1,3 linkage, is 0.5% or higher but less than 10% in the partially methylated glucitol acetates; and
(4) Content of 2,4-dimethyl-1,3,5,6-tetraacetyl-glucitol, which indicates that the content of glucose residues with both α-1,3 and α-1,6 linkages, is 0.5% or higher in the partially methylated glucitol acetates.
6. The process of claim 1 , wherein said α-glucosyltransferase has the following physicochemical properties:
(1) Molecular weight
90,000±10,000 daltons on SDS-polyacrylamide gel electrophoresis;
(2) Optimum temperature
50 to 55° C. when reacted at pH 6.0 for 30 min;
(3) Optimum pH
pH 5.0 to 6.3 when reacted at 40° C. for 30 min;
(4) Thermal stability
Stable up to the temperature of 40° C. when incubated at pH 6.0 for 60 min; and
(5) pH Stability
Stable at least in the range of pH 4.0 to 8.0 when incubated at 4° C. for 24 hours.
7. The process of claim 4 , wherein the high performance liquid chromatography method is Enzyme-HPLC.