Branched alpha glucans
The present invention relates to the field of poly- and oligosaccharides and their dietary effects. In particular it relates to a method of producing a branched α-glucan. Further aspects of the invention are a branched α-glucan comprising linear segments of (α1→4) linked D-glucose units interspersed with (α1→6) glucosidic linkages and having (α1∴4,6) branching points; a food composition; and the use of an α-glucanotransferase enzyme for reducing the digestible carbohydrates of a starch containing food material.
1. A method of producing an α-glucan with a ratio of branching of at least 8%, the method comprising:
contacting a polysaccharide or oligosaccharide substrate with an α-glucanotransferase enzyme to form a glucose polymer,
wherein the polysaccharide or oligosaccharide substrate comprises, at its non-reducing end, at least two (α1→4) linked D-glucose units,
wherein the α-glucanotransferase enzyme is capable of cleaving (α1→4) glucosidic linkages and making new (α1→6) glucosidic linkages without forming consecutive (α1→6) glucosidic linkages,
wherein the glucose polymer comprises linear segments of (α1→4) linked D-glucose units interspersed with (α1→6) glucosidic linkages and having (α1→4,6) branching points,
wherein the α-glucanotransferase comprises an amino acid sequence selected from the group consisting of SEQ ID NOS. 1 and 19.
2. The method of claim 1 , wherein the α-glucanotransferase is a GtfB enzyme from a bacterium selected from the group consisting of L. reuteri CNCM1-2451, and L. reuteri CNCM 1-2452.
3. The method of claim 1 , wherein the substrate has a degree of polymerization of at least four.
4. The method of claim 1 , wherein the substrate is selected from the group consisting of starch, starch derivatives, malto-oligosaccharides, amylose, amylopectin, maltodextrins, (α1→4) glucans and combinations thereof.
5. The method of claim 1 , wherein the polysaccharide or oligosaccharide substrate is contacted with the α-glucanotransferase enzyme at a temperature between 30° C. and 75° C. and a pH of between 4.0 and 9.0.