A cold-active 1,4-α-glucan branching enzyme from Bifidobacterium longum reduces the retrogradation and enhances the slow digestibility of wheat starch

To develop a 1,4-alpha-glucan branching enzyme (BE) without homology to known allergens, the glgB gene from Bifidobacterium longum was overexpressed under the control of BLMA promoter in Escherichia coli. B. longum BE (BlBE) had a molecular weight of 86.1 kDa and a specific activity of more than 18.5 U/mg protein at 25-35 degrees C and pH 5.5-7.0, and exhibited 30% of the maximum activity at 10 degrees C. The cold-active BlBE preferred to transfer maltohexaose and introduced DP 4-36 branches into amylose. BlBE also increased the proportion of DP 2-10 branches in amylopectin and decreased its Mw from 1.39 x10(6) to 1.16 x10(5) g/mol. As the BlBE concentration increased from 0.0 to 0.5 U/mg substrate, the retrogradation enthalpy of BlBE-modified wheat starch decreased from 4.50 to 1.83 J/g (p < 0.05) at day 14 and the slowly digestible starch content increased from 2.10% to 17.39% (p < 0.05).