Sourdough Bioactives from Fermentation to Human Physiology: Biosynthesis, Bioavailability, Mechanisms and Clinical Evidence

Sourdough is a metabolically active cereal ecosystem in which lactic acid bacteria, yeasts and endogenous flour enzymes transform carbohydrates, proteins and phytochemicals. These reactions can increase organic acids, release phenolic compounds, generate peptides, form exopolysaccharides and, in strain- tand substrate-dependent systems, enrich γ-aminobutyric acid and selected vitamins. However, the detection of a compound in fermented dough does not establish physiological benefit: This narrative review organizes the evidence from precursor and microbial pathway to processing stability, gastrointestinal fate, mechanical and clinical effect. Appraisal was narrative, not a systematic review; evidence strength reflected design limitations, consistency, directness, precision and plausibility. Strong evidence supports acidification, phytate degradation, phenolic release and technological functions of exopolysaccharides. Mechanistic evidence for antioxidant, antihypertensive, immunomodulatory and microbiota-mediated effects is plausible but is dominated by chemical assays, cell models and studies of purified compounds. Human trials mainly examine postprandial glycaemia, gastrointestinal responses and satiety; their results are heterogeneous and do not establish that sourdough fermentation alone prevents chronic disease. Flour composition, strain identity, fermentation time, temperature, hydration and baking interact, making the final bread not the fermented dough the relevant exposure. Future work should employ chemically characterized breads, matched comparators, simulated digestion linked to targeted metabolomics, dose–response designs and adequately powered randomized trials. Sourdough is best viewed as a controllable biotransformation platform whose health value depends on the product-specific survival and bioavailability of its metabolites rather than on fermentation as a generic label