High insoluble fibre content increases in vitro starch digestibility in partially baked breads

Wheat breads prepared from frozen partially baked breads were characterized by their content of rapidly digestible starch (RDS) and slowly digestible starch (SDS) by the in vitro starch digestibility method developed by Englyst. Breads with different contents and types of fibre and breads prepared with different fermentation processes were studied. Bread with inulin and with a double fermentation had the lowest RDS content of 58.8 ± 1.7 and 60.0 ± 1.9 (% dry matter), respectively. Wheat bran bread, seeded bread, triple fermentation white bread and baguette-type bread showed values of RDS between 63.1 ± 1.7 and 65.7 ± 1.7 with no significant differences between them (p < 0.05). The fraction of SDS was higher in wheat breads than in breads with added fibre. The highest values of the starch digestive rate index (SDRI) were obtained by the three types of breads with added fibre, which ranged from 91.8 ± 3.5 to 95.8 ± 3.5 versus 80.2 ± 3.5 to 87.5 ± 3.5 for white wheat breads. A significant (p < 0.01) positive linear correlation between the insoluble fibre content and SDRI was obtained (R² = 0.96). Insoluble fibre dilutes and disrupts gluten network and probably weakens the interaction between gluten and starch, which protects starch from digestive enzymes action. Scanning electronic microscopy microstructure of bread crumbs corroborated this statement.