Structure–Function Relationships in Industrial Bread Enriched with Insoluble Dietary Fiber

The growing demand for functional foods has led to the exploration of alternative fiber sources for bread enrichment. This study examined how highly–insoluble citrus fiber (Vitacel CF 312®), known for its nutritional benefits to consumers, such as reducing the intestinal absorption of fatty acids and glucose, modifies the structure–function relationships of industrial bread doughs focusing on their rheological and microstructural behavior. Dough formulations were prepared varying fiber content (1–6% w/w) and hydration level (50–84% w/w), and their viscoelastic behavior was assessed under shear and uniaxial extension. Epifluorescence microscopy revealed a progressive disruption of gluten network continuity in the case of recipes with similar hydration and reduced starch granule swelling due to competitive water uptake by fiber. These structural changes were directly linked to increased dough consistency and toughness, while enhanced hydration mitigated these effects through partial recovery of gluten–starch interactions. Among all formulations, doughs containing 4.5% fiber at elevated hydration exhibited microstructural and rheological properties closest to the commercial benchmark. Even if lower fiber fractions can perform similarly under optimized hydration conditions, the sample with 4.5% fiber was considered as the best choice, among the tested samples, because it yields the highest fiber apport, offering a superior nutritional profile, with minimal compromise to technological performance. • IDF fortifies white bread with limited, but perceivable, quality compromise • Insoluble fiber raises dough consistency; increasing hydration reduces it • Fiber addition acts on starch granules swelling and gluten matrix development • 4.5% fiber + 73% water yields dough properties close to a reference for white bread