In Situ Effects of 4,6-α- and 4,3-α-Glucanotransferases During Sourdough Fermentation: Assessing Microbial Community Dynamics, Bread Glycemic Index, Staling, and Texture

Although some lactic acid bacteria species harbor genes encoding α-glucanotransferases (4,6-α-GTase and 4,3-α-GTase), the technological and functional implications of these enzymes within sourdough ecosystems remain poorly understood. This study investigated the effects associated with α-GTase-positive and α-GTase-negative strains of Limosilactobacillus reuteri and L. fermentum on sourdough microbiota, bread quality, and starch digestibility. Starter culture inoculation steered the assembly of the sourdough microbiota, resulting in stable acidification and altered microbial community structures. High-throughput sequencing analysis showed that starter culture addition generally increased taxonomic richness, while Shannon and Simpson diversity indices varied according to strain genotype and inoculation level. Sourdoughs fermented with α-GTase-positive strains exhibited higher viscosity while maintaining shear-thinning behavior, which was putatively linked to in situ enzymatic synthesis. Additionally, inoculation with these strains improved bread specific volume, suggesting a possible structural modification of the starch matrix or the overlapping effects of fermentation metabolites. During storage, the 4,3-α-GTase-positive L. fermentum PFC282 strain delayed the increase in bread hardness, reflecting a possible mitigation of amylopectin retrogradation and indicating a potential anti-staling effect. In addition, the 4,6-α-GTase-positive L. reuteri PFC338 strain produced breads with lower estimated glycemic index values, suggesting a lower susceptibility to enzymatic starch hydrolysis likely due to the hypothesized alterations in structural linkages. Overall, the findings highlight the potential of α-GTase-positive sourdough starter cultures to modulate the technological and nutritional properties of bread.