From agro-waste to high-value bioproducts: an optimization example of solid-state fermentation with Saccharomyces...

Agro-industrial-residues, such as potato peel waste (PPW), constitute a substantial portion of the waste stream and offer significant opportunities for valorization within circular bioeconomy frameworks. In this study, a laboratory-scale solid-state fermentation (SSF) process for biosurfactant production using fresh or dried PPW as renewable substrates was optimized with Saccharomyces cerevisiae BY4742. A Box-Behnken design was implemented to optimize peel amount, initial pH, and incubation time, targeting enhanced surface tension reduction. Under optimized conditions (10 g fresh PPW, pH 5.25, 5^th day), the biosurfactant reduced surface tension to 30.12 ± 0.32 mN/m and demonstrated a high emulsification index (51.35 ± 0.49%), low critical micelle concentration (1.1 ± 0.09 mg/mL), strong oil spreading activity (6.3 ± 0.05 cm), and positive drop collapse results. Partial structural characterization by FTIR,¹H-NMR and TGA/DTG was consistent with a heterogeneous surface-active biopolymeric fraction, supporting its robust functional properties. The obtained biosurfactant maintained remarkable stability across wide ranges of pH, temperature, and salinity, while achieving an oil removal efficiency of 91.37 ± 0.89%, indicating its strong potential for bioremediation applications. Notably, the SSF platform enabled the simultaneous production of a surface-active fraction and extracellular amylase activity, highlighting the potential of PPW-based SSF as a resource-efficient approach for producing value-added bioproducts.