Use of starch-modifying enzymes for enhanced bread quality and reduced in vitro starch hydrolysis

Bread quality can be improved by starch-modifying enzymes, but these differ in their biochemical properties and effects on bread quality. This study investigated the effect of starch-modifying enzymes including the 4,6-α-glucanotransferase GtfB, the reuteransucrase GtfA, and the glucan-branching enzymes GlgB and Branchzyme on bread quality. GtfB, GlgB, and Branchzyme were evaluated individually; GtfA was evaluated in combination with GtfB and Branchzyme. Addition of GtfB, GlgB, and Branchzyme at their optimal dosages increased bread volume by 12.5%, 13.0%, and 2.8%, respectively. GtfB and Branchzyme reduced the crumb hardness after six days of storage, and reduced the in vitro starch digestibility of bread ( P <0.05), whereas GlgB exhibited the opposite trend. GtfA further increased bread volume by 14.0% when combined with GtfB. However, the additional inclusion of Branchzyme reduced this beneficial effect. Substrate characterisation showed that amylose, amylopectin, and maltodextrin served as donor and acceptor substrates for GtfB, whereas GtfB was not active with dextran and reuteran as donor substrate. In a simplified bread model, GtfB activity was increased when maltodextrin and gelatinised wheat starch were added, as shown by increased oligosaccharide peaks and higher isomaltose release after dextranase hydrolysis. However, increased donor substrate availability in bread did not further improve bread volume or crumb firmness when the enzyme dosage was already optimised. Thus, an optimal balance between enzyme dosage, substrate availability and starch modification in the dough is required for optimised bread quality. Results inform on the optimisation of bread quality by enzyme addition or sourdough fermentation.