Bacterial Branching Enzymes as Agents for Modifying Glucan Structure in Industrial Processing

Starch is used as a cheap, renewable, chemically-reactive matrix in many industrial processes. During processing, access to chemically-reactive groups on starch is essential and largely depends on their exposure, which is in part, a function of the branching frequency within starch. The amylose component of starch increases retrogradation (gelling property) of the cooked polymer at lower temperatures, forcing industries to use high temperatures throughout processing. The ability to manipulate glucan branching in starch and other polyglucans and remove amylose, offers many industrial end users (e.g. paints/inks, coatings, adhesives sectors) with superior performance bio-products. Branching enzymes (BEs) introduce α-1,6 branch points in starch and thus increase the number of reactive non-reducing chemical groups making post-harvest starch more chemically-reactive, facilitating its solubility and reducing retrogradation. Starch-derived polyglucans tend to gel rapidly, particularly in the presence of linear amylose chains, which hinders industrial processing and reduces polyglucan usability. BEs are promising industrial tools for increasing branch frequency and producing starches with improved physicochemical properties, and for reducing glucan chain length (by removing amylose) and alleviating retrogradation, and thus improving the solubility properties of post-harvest starch. Presented here is a detailed biochemical and functional characterization of recombinant glycogen branching enzymes from Thermus thermophilus and Deinococcus radiodurans (DrGBE). Additionally, the presented work shows a proof of concept and demonstrates a novel application of DrGBE to modify a commercial starch-based polyglucan to reduce gelling, improve stability and solubility, and produce a visco-stable product.