Addressing temperature gradient challenge in scaling up solid-state fermentation: A strategy using thermophilic strains for biosurfactant production

Solid-state fermentation (SSF) is a promising approach for sustainable bioproduction production, particularly when using organic waste as a substrate. However, temperature gradients inherent to large-scale SSF often reduce process efficiency. This study developed a strategy for designing of a lipopeptide biosurfactant production process , scaling SSF in packed-bed bioreactors by thermophilic strains using winterisation oil cake (WOC) and sugarcane molasses (MOL) as nutrient sources. Fermentations at lab-scale (0.5 L) and pilot-scale (50 L) demonstrated a robust and reproducible process despite temperature changes from microbial activity. Among the strains tested, Bacillus subtilis CBI-7S1 was the highest producer, with optimal substrates amounts of 24 g of WOC and 12 g of MOL, producing 24.9 mg of crude lipopeptides per gram of dry matter (DM) at 0.5 L scale. These conditions were reproduced at pilot scale, with concentrations from 12 to 24 mg g −1 DM. Moisture content strongly influenced biosurfactant production, while oxygen consumption was a reliable monitoring parameter. Surface tension was evaluated under different pH, temperature, and salinity, and mass spectrometry identified surfactin, iturin, and fengycin congeners. These findings provide insights into overcoming temperature gradients during scale-up and show that thermophilic strains enable biosurfactant production under SSF at pilot scale. This approach enhances SSF technological maturity, supporting its broader use in sustainable production of targeted metabolites across diverse bioprocesses. • Thermophilic Bacillus strains overcome temperature gradients in SSF scale-up. • SSF scaled from lab-scale to pilot-scale using 50 L reactor. • Agro-industrial residues used as low-cost substrates in thermophilic SSF. • Oxygen uptake and moisture content are key indicators for SSF performance. • Strategy enhances SSF’s industrial viability under circular bioeconomy models.