Fructilactobacillus sanfranciscensis-Propionibacterium freudenreichii Compound Sourdough: An Operational Addition...

Clean-label demands are shifting bread preservation from chemical additives to biological approaches. Our prior work showed that a co-fermented F. sanfranciscensis (LAB)-Propionibacterium freudenreichii (PAB) sourdough improves shelf life and quality at low inclusion level; however, longer distribution may require higher additions whose impacts are not well defined. Accordingly, we tested 5%-50% inclusion level to map dose-response relationships linking organic acids, fermentation quotient (FQ), and pH to processing performance, loaf structure, texture, storage-related staling, and antifungal outcomes. Organic acids increased monotonically with inclusion level (e.g., lactic increased by 95% and propionic by 69% at 50% relative to 5%); FQ rose from 2.5 (5%) to 3.6 (50%), whereas pH declined from 4.6 (5%) to 3.0 (50%). Loaf structure exhibited a clear optimum at 20%: Specific volume was 17% higher than at 5%, the height-to-diameter ratio was 13% higher, and baking loss was lowest at ≤20% but increased at higher levels. During refrigerated storage at 4°C, 10%-20% inclusion level best preserved moisture, slowed staling (smaller hardness increase), and yielded a lower Day-7 retrogradation enthalpy (ΔH 2.6 vs. 3.2 J g^-1 at 50%). Antifungal protection strengthened with inclusion level: at a 150 CFU g^-1 threshold, visible mold appeared on Day 5 (5%), Day 7 (10%-15%), Day 9 (20%), Day 11 (25%-30%), Day 13 (35%-45%), and Day 15 (50%). Overall, an inclusion level near 20% provides a practical operating window that balances preservation with processability and key instrumental quality attributes, whereas higher doses extend mold control further but may require mitigation (e.g., acid-tolerant yeast and buffering) to limit quality losses associated with excessive acidification.