Tasty bread is healthy bread?improved bread quality by fermentation with Limosilactobacillus reuteri expressing a reuteransucrase and an α-4,6-glucanotransferase

Abstract

Reuteransucrase GtfA and 4,6-α-glucanotransferase GtfB are glycoside hydrolase family 70 enzymes that convert sucrose and starch, respectively, to indigestible α-glucans with potential applications in baking. The aim of this study was to investigate whether the use of lactobacilli expressing GtfA and GtfB reduces the digestibility of starch. An initial experiment investigated the role of GtfB using the GtfB negative Lactiplantibacillus plantarum TMW1.460 and the GtfB positive Limosilactobacillus reuteri TMW1.656ΔgtfA to produce white wheat sourdough bread with addition of 10 % and 30 % sourdough. The use of the GtfB expressing Lm. reuteri TMW1.656ΔgtfA in recipes with 10 % sourdough did not increase the bread volume or the dietary fibre content but reduced the in vitro starch digestibility. Subsequently, Lm. reuteri TMW1.656 was compared to single and double knock out mutants lacking GtfA and/or GtfB to produce white wheat sourdough bread with addition of 30 % sourdough. GtfA and GtfB showed a synergistic effect, increasing bread volume by 8.8 % (P < 0.05) and reducing in vitro starch digestibility by 5.2 % (P < 0.05). GtfB increased the total dietary fibre content of sourdough bread by 16.9 % relative to the mutants lacking GtfB (P < 0.05). The characterization of starch in bread revealed that GtfB modified amylopectin toward higher resistance to hydrolysis. In conclusion, lactobacilli expressing GtfA and GtfB are improve both the sensory and the nutritional bread quality.