Biopreservation technology of sourdough co-fermented with Fructilactobacillus sanfranciscensis and Propionibacterium freudenreichii: Effects and mechanisms for enhancing bread quality and extending shelf life.

This study presents a biopreservation method using sourdough co-fermented with Fructilactobacillus sanfranciscensis and Propionibacterium freudenreichii, optimizing conditions to 220 hydration and 24 h fermentation. The composite sourdough bread quality was evaluated through physicochemical, storage, sensory, and microbial tests, with mechanisms analyzed based on microstructure, rheology, and dough structure. Results showed that: first, the composite sourdough enhanced bread physicochemical properties, increasing volume, height-to-diameter ratio, elasticity, and resilience, while reducing baking loss, hardness, chewiness, and adhesiveness. Second, it improved bread storage performance by increasing moisture content, reducing moisture loss, hardness, aging rate and retrogradation enthalpy. Third, it improved bread color by enhancing Maillard reaction browning, reducing ΔE, and maintaining color stability during storage, while improving sensory attributes such as mouthfeel, texture and flavor. Fourth, the composite sourdough inhibited mold and bacterial growth, extending shelf life to the ninth day. Mechanistic analysis revealed that at the micro level, it increased colony counts of Fructilactobacillus sanfranciscensis and Propionibacterium freudenreichii, enhanced organic acid content (lactic acid, propionic acid, succinic acid), and lowered pH to inhibit harmful microbes. At the macro level, it optimized fermentation rheology by improving expansion height, gas retention, and reducing collapse, while improving dynamic rheology, lowering G' and G", and increasing tanδ, enhancing viscoelasticity and softness. Additionally, it improved dough structure by enhancing free thiol groups, amino groups, and free amino acids, optimizing secondary structure. This study shows that the composite strain improves bread quality and shelf life by optimizing sourdough microbial properties, rheology, and dough structure, providing a promising biopreservation method.