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 an α-glucan containing (α1→3) linked D-glucose units. The invention also provides a branched α-glucan comprising alternating (α1→4) and (α1→3) glucosidic linkages and having (α1→3,4) branching points, a food composition, and the use of an α-glucanotransferase enzyme for reducing the digestible carbohydrates of a starch containing food material. Further aspects of the invention are a bacteria, an enzyme and an expression vector.
1. A method of producing an α-glucan containing (α1-3) linked D-glucose units, the method comprising contacting a polysaccharide or oligosaccharide substrate comprising at its non-reducing end at least two (α1-4) linked D-glucose units with an α-glucanotransferase enzyme capable of cleaving (α1-4) glucosidic linkages and making new (α1-3) glucosidic linkages to form a glucose polymer having linear segments of (α1-4) linked D-glucose units interspersed with (α1 >3) glucosidic linkages, without forming consecutive (α1-3) glucosidic linkages, wherein the α-glucanotransferase comprises an amino acid sequence having at least 90% identity to SEQ ID NO:1.
2. The method according to claim 1 wherein the α-glucanotransferase comprises an amino acid sequence having at least 92% identity to SEQ ID NO:1.
3. The method according to claim 1 wherein the α-glucanotransferase is a Lactobacillus fermentum GTFB enzyme.
4. The method according to claim 1 wherein the substrate has a degree of polymerization of at least five.
5. The method according to claim 1 wherein the substrate is selected from the group consisting of starch, starch derivatives, malto-oligosaccharides, gluco-oligosaccharides, amylose, amylopectin, maltodextrins, (α1-4) glucans and combinations thereof.
6. The method according to claim 1 wherein the substrate is comprised within cereal flour.
7. The method according to claim 1 wherein the α-glucanotransferase comprises an amino acid sequence having at least 95% identity to SEQ ID NO:1.
8. The method according to claim 1 wherein the α-glucanotransferase comprises an amino acid sequence having at least 96% identity to SEQ ID NO:1.
9. The method according to claim 1 wherein the α-glucanotransferase comprises an amino acid sequence having at least 97% identity to SEQ ID NO:1.
10. The method according to claim 1 wherein the α-glucanotransferase comprises an amino acid sequence having at least 98% identity to SEQ ID NO:1.
11. The method according to claim 1 wherein the α-glucanotransferase comprises an amino acid sequence having at least 99% identity to SEQ ID NO:1.